NASDAQ: XLO

The design of each of our masked molecules is illustrated further below. Generally, the key design components for each molecule include one or more of the following: functional domains; masking domains; linker sequences; and protease cleavage sites.

Each of our masked molecules contains at least one protease cleavage site, which is cleaved by tumor-specific proteases resulting in the release of the masking domain, allowing the unmasked molecule to bind to the target protein. In the case of our masked T cell engager molecules, our modular architecture enables us to mask the CD3 targeting domain, one or more tumor-associated antigen, or TAA, binding domains and/or the co-stimulatory signaling domain. The mask is designed to release when the protease cleavage site is cleaved in the tumor microenvironment, allowing the unmasked molecule to bind to the T cell and TAA to facilitate an immune synapse. For any of our masked T cell engager molecules that incorporate a co-stimulatory signaling domain, the additional co-stimulatory domain is designed to further enhance potency and durability of the T cell response. We refer to our masked T cell engager format without a co-stimulatory domain as our advanced tumor-activated cell engager, or ATACR, format, and we refer to our masked T cell engager format incorporating a co-stimulatory domain as our selective effector-enhanced cell engager, or SEECR, format.

Ultimately, each of our masked molecules is designed to minimize interaction with healthy tissues and cells outside the tumor microenvironment until the mask is released by tumor-specific proteases that cleave the protease cleavage site in the tumor microenvironment. Depending on the particular molecule design, our molecules may also incorporate conditional half-life modulation, which is designed to result in a long half-life while masked and a relatively short half-life post-activation in the tumor microenvironment. Our design approach across all of our masked molecules also seeks to ensure stable molecules with well-understood properties and a reproducible manufacturing approach.

Importantly, we believe that our clinically-validated masking technology and capabilities provide the following key advantages:

masking that is affinity-optimized and takes advantage of multiple intra-molecular interactions, minimizing the risk of activity outside of the tumor microenvironment and therefore minimizing the risk of toxicity;

protease cleavage sites optimized for efficient cleavage by multiple families of MMPs and other tumor-specific proteases present in the tumor microenvironment to ensure broad applicability across a wide range of solid tumor types;

the ability to engineer the active molecule such that unmasking in the tumor microenvironment promotes a potent, localized anti-tumor immune response;

early consideration and incorporation of manufacturing and development aspects into the design of molecules to facilitate production of high-quality drug product for clinical use; and

half-life optimized molecules with prolonged half-life in the masked, or inactive, state to support administration to patients on a schedule consistent with other biologic agents and the ability to incorporate conditional half-life modulation into our molecules, which allows for either a short half-life or an extended half-life post activation in the tumor microenvironment consistent with the specific desired property and mechanism of action of the molecule.

Our Strategy

Our vision is to transform the lives of patients with cancer by harnessing the power of highly potent, masked I-O therapies that deliver deep and durable clinical responses without the severe side effects associated with systemically active I-O agents. Leveraging our clinically-validated masking technology and capabilities, we aim to discover, develop and, ultimately, commercialize masked I-O therapies that overcome the known limitations of systemically active I-O agents. Key elements of our strategy include:

Submit an investigational new drug, or IND, application for XTX501, our bispecific PD-1 / masked IL-2, in the middle of 2026, and subject to clearance of the IND by the U.S. Food and Drug Administration, or FDA, initiate a Phase 1 trial for XTX501 in the second half of 2026 and report initial Phase 1 data in the second half of 2027. We plan to initially evaluate XTX501 in patients with metastatic non-small cell lung cancer, or NSCLC, before expanding development to other solid tumor types, including tumors that are insensitive to PD-1 therapy. We believe XTX501 also has the potential to be a foundational “backbone” therapy for combination treatment with other agents.

Rapidly advance our wholly-owned program for a multi-specific, masked T cell engager targeting PSMA and STEAP1 with co-stimulatory signaling built into the molecule (SEECR format) into IND-enabling studies and submit an IND application for this program in 2027.

Rapidly advance our wholly-owned program for a masked T cell engager targeting CLDN18.2 (ATACR format) into IND-enabling studies and submit an IND application in 2027. Our modular architecture for T cell engagers also enables flexibility to evaluate designs that incorporate masking of the CLDN18.2 binding domain and/or add a co-stimulatory domain (SEECR format) in parallel with advancing the current molecule design.

Continue to advance our AbbVie collaboration toward key program milestones for both the masked antibody-based program and masked T cell engager program.

Continue to advance efarindodekin alfa, our masked IL-12, through our ongoing Phase 2 clinical trial in patients with advanced solid tumors to enable delivery of an option data package to Gilead in the first half of 2027.

Leverage the broad applicability of our clinically-validated masking technology and capabilities, including our deep expertise in biology and protein engineering, to continue to accelerate and expand our pipeline through strategic collaborations and partnerships.

Our Pipeline

Leveraging our clinically-validated masking technology and capabilities, we are advancing a pipeline of differentiated masked I-O therapies for validated targets.

1. Subject to clearance of the IND by the FDA.

2. Exclusive global option to license with Gilead.

3. Multi-program collaboration with AbbVie, including a licensed masked antibody program and option to license masked T cell engager program.

XTX501 (bispecific PD-1 / masked IL-2)

XTX501 is a potential best-in-class bispecific PD-1 / masked IL-2 antibody fusion protein designed to selectively stimulate PD-1 positive, antigen-experienced T cells and enhance their function. XTX501 incorporates masking and is designed to overcome IL-2 receptor-mediated clearance, peripheral activity and tolerability issues associated with non-masked IL-2 agents. In clinical trials, a third-party PD-1 / non-masked IL-2 bispecific antibody fusion protein has demonstrated promising clinical efficacy and survival benefits in several solid tumor types, including in patients with immunotherapy-resistant NSCLC, and “cold” tumors historically resistant to immunotherapy such as acral melanoma, mucosal melanoma and microsatellite stable, or MSS, colorectal cancer, or CRC. By masking the IL-2 component, XTX501 has the potential for meaningfully differentiated overall anti-tumor activity and an improved overall safety profile. In preclinical studies, XTX501 has demonstrated robust monotherapy activity (including in settings insensitive to PD-1), antibody-like pharmacokinetics, or PK, and tumor-selective pharmacodynamics, or PD, consistent with its intended mechanism of action.

We are currently advancing XTX501 through IND enabling studies and plan to submit an IND application for XTX501 in the middle of 2026. Subject to clearance of the IND by the FDA, we plan to initiate a Phase 1 trial for XTX501 in the second half of 2026 and report initial Phase 1 data in the second half of 2027. We plan to initially evaluate XTX501 in patients with metastatic NSCLC before expanding development to other solid tumor types, including tumors that are insensitive to PD-1 therapy. We believe XTX501 also has the potential to be a foundational “backbone” therapy for combination treatment with other agents.

Masked T Cell Engager Programs

T cell engagers are designed to redirect immune effector cells against cancer cells by simultaneously binding to a specific TAA expressed on the cancer cells and the T cell receptor complex on T cells, resulting in T cell-mediated killing of tumor cells. To date, T cell engagers have demonstrated significant promise as cancer immunotherapies in a variety of advanced solid tumors, but their potential has been limited by systemic toxicity, including cytokine release syndrome and on-target, off-tumor toxicity.

Leveraging our proprietary, clinically-validated masking technology, we are advancing two wholly-owned programs for masked T cell engagers, as well as an additional program in collaboration with AbbVie. Our masked T cell engagers include molecules with one or more TAA binding domain(s) and a CD3 targeting domain, which are designed to release a potent, short half-life T cell engager upon tumor-selective activation (ATACR format), and molecules that include a co-stimulatory domain designed to further enhance potency and durability of the T cell response (SEECR format). Depending on the desired properties that we are seeking to achieve for a particular molecule and particular TAA(s) that we are targeting, our modular architecture for our masked T cell engagers enables us with optionality to:

include multiple TAA binding domains;

add a co-stimulatory domain;

mask the CD3 targeting domain, TAA binding domain(s) and/or the co-stimulatory signaling domain.

In preclinical studies, our masked T cell engager molecules have demonstrated potent anti-tumor activity with evidence of reduced systemic toxicity and the potential to significantly expand the therapeutic window. In addition, the incorporation of a co-stimulatory signaling domain further enhanced anti-tumor activity compared to T cell engager molecules that lacked co-stimulation in both in vitro and in vivo studies.

Our wholly-owned masked T cell engager programs consist of the following:

PSMA+STEAP1 with co-stimulation (SEECR format): We are advancing a multi-specific masked T cell engager program targeting PSMA and STEAP1 with built in co-stimulatory signaling (SEECR format). We anticipate nominating a development candidate in the second quarter of 2026. PSMA and STEAP1 are expressed in most prostate cancer tumors, and targeting both of these TAAs has the potential to address tumor heterogeneity while minimizing the potential for resistance due to antigen escape.

CLDN18.2 (ATACR format): We are advancing a masked T cell engager program targeting CLDN18.2 (ATACR format). Our modular design architecture for T cell engagers also enables flexibility to evaluate designs that incorporate masking of the CLDN18.2 binding domain and/or add a co-stimulatory domain (SEECR format) in parallel with advancing the current molecule design. CLDN18.2 is expressed in gastrointestinal cancers (including gastric, pancreatic and esophageal) and lung cancer.

We plan to advance these programs into IND-enabling studies and submit IND applications for each of these programs in 2027.

In addition, in February 2025, our wholly owned subsidiary, Xilio Development, Inc., or Xilio Development, entered into a collaboration, license and option agreement with AbbVie leveraging our proprietary tumor-activation technology and platform to discover and develop novel tumor-activated immunotherapies, including up to three programs for masked T cell engagers and a program for a masked antibody-based immunotherapy. For more information, please see “—License and Collaboration Agreements—Collaboration, License and Option Agreement with AbbVie” below.

Efarindodekin alfa (masked IL-12)

IL‑12 is a potent, pro-inflammatory cytokine that is produced by antigen-presenting cells and has highly compelling biology for cancer immunotherapy, but also significant limitations due to toxicity in its native, systemically active form. Efarindodekin alfa is an investigational, masked IL-12 designed to potently stimulate anti-tumor immunity and reprogram the tumor microenvironment of poorly immunogenic “cold” tumors towards an inflamed or “hot” state. We are currently evaluating efarindodekin alfa as a monotherapy in an ongoing Phase 2 clinical trial in patients with advanced solid tumors.

In March 2024, our wholly owned subsidiary Xilio Development entered into an exclusive license agreement with Gilead related to efarindodekin alfa and our IL-12 program. We expect to deliver an option data package to Gilead in the first half of 2027. For more information, please see “—License and Collaboration Agreements—Exclusive License Agreement with Gilead” below.

Phase 1 Data Presented in November 2025 for Efarindodekin Alfa

In November 2025, we announced data from our Phase 1 clinical trial evaluating efarindodekin alfa as a monotherapy in patients with advanced solid tumors at the Society for Immunotherapy of Cancer 40th Annual Meeting.

As of a data cutoff date of September 2, 2025, 62 patients with advanced solid tumors had been treated with efarindodekin alfa in Phase 1 monotherapy dose escalation. The median age was 66 years (ranging from 43 to 83 years), and patients were heavily pre-treated, with 89% having previously received two or more prior lines of anti-cancer therapy and 81% having received prior immunotherapy.

In Phase 1, efarindodekin alfa has been administered at doses more than 100-fold greater than the maximum tolerated dose of recombinant human IL-12. At dose levels up to the recommended Phase 2 dose, efarindodekin alfa has been generally well-tolerated, and treatment-related adverse events, or AEs, were primarily Grade 1 or 2.

Efarindodekin alfa also demonstrated encouraging anti-tumor activity, including two partial responses, or PRs, in patients with advanced solid tumors consisting of a confirmed PR in a patient with HPV-negative head and neck squamous cell carcinoma (33% decrease in target lesions), with meaningful changes in PD biomarkers, and an unconfirmed PR in a patient with uveal melanoma (55% decrease in target lesions).

Treatment with efarindodekin alfa induced sustained, dose-dependent interferon gamma, or IFNɣ, signaling without evidence of tachyphylaxis throughout treatment cycles and transformed the tumor microenvironment towards an inflamed state with increased T cell infiltration and differentiation to effector memory.

PD data for efarindodekin alfa were consistent with IL-12 biology and demonstrated that efarindodekin alfa induced robust immune cell infiltration and PD-1, PD-L1 upregulation in patient tumors.

Vilastobart (masked, Fc-enhanced anti-CTLA-4)

Vilastobart is an investigational tumor-activated, Fc-enhanced, high affinity binding anti-CTLA-4 monoclonal antibody designed to block CTLA-4 and deplete regulatory T cells when activated in the tumor microenvironment. CTLA‑4 is an immune checkpoint that is well-established as a potent immunotherapy capable of regulating T cell priming with complementary biology to PD-1, including with the first FDA approval for ipilimumab in 2011. However, systemic toxicity has limited the potential of non-masked CTLA-4 as a monotherapy and combination therapy.

Vilastobart is designed to have a dual mechanism of action that promotes T cell responses against lower quality neoantigens:

CTLA-4 blockade and co-stimulation lower the threshold for priming naïve T cells against lower quality neoantigens; and

depletion of regulatory T cells reduces immune suppressive signaling during priming and drives potent, polyclonal CD8 T cell expansion including for weaker antigens.

In 2023, we entered into a co-funded clinical trial collaboration with F. Hoffmann-La Roche Ltd, or Roche, to evaluate vilastobart in combination with atezolizumab (Tecentriq®) in a multi-center, open-label Phase 1/2 clinical trial. In our Phase 2 clinical trial, we have demonstrated promising clinical efficacy and a generally well-tolerated safety profile for vilastobart in combination with atezolizumab in heavily pre-treated patients with MSS metastatic CRC without liver metastases. We believe these clinical data support the best-in-class potential for vilastobart for use in combination therapies, and we are actively seeking a partner to maximize the value of vilastobart.

Competition

We believe our novel and proprietary platform technology and masking approach represent a meaningful competitive advantage in seeking to develop novel and highly effective treatments for cancer. However, the biotechnology and biopharmaceutical industries are characterized by rapid evolution of technologies and sharp competition and emphasis on intellectual property. Any product candidates that we successfully develop and commercialize will have to compete with existing therapies and new therapies that may become available in the future. While we believe that our technology, development experience and scientific knowledge provide us with competitive advantages, we face potential competition from many different sources, including major pharmaceutical, specialty pharmaceutical and biotechnology companies, academic institutions, governmental agencies and public and private research institutions.

Some of our competitors, either independently or with strategic partners, have substantially greater financial, technical and human resources than we do. In addition, our competitors may be more successful than we are in research and development, manufacturing, preclinical testing, conducting clinical trials, obtaining regulatory approval for treatments and achieving widespread market acceptance. Merger and acquisition activity in the biotechnology and biopharmaceutical industries may result in resources being concentrated among

a smaller number of our competitors. These companies also compete with us in recruiting and retaining qualified scientific and management personnel, establishing clinical trial sites and patient registration for clinical trials and acquiring technologies complementary to, or necessary for, our programs. Smaller or early-stage companies may also prove to be significant competitors, particularly through collaborative arrangements with large and established companies.

In addition to competitors specifically targeting PD-1/IL-2, PSMA or STEAP1, CLDN18.2, IL-12 and anti-CTLA-4, we also face competition more broadly across the oncology market. The most common methods of treating patients with cancer are surgery, radiation and drug therapy, including chemotherapy, hormone therapy, biologic therapy, such as monoclonal and bispecific antibodies, immunotherapy, cell-based therapy and targeted therapy, or a combination of any such treatments. Beyond these treatments, we may also be subject to competition from additional modalities, including oncolytic viruses and cancer vaccines.

Our commercial opportunity could be substantially limited if our competitors develop and commercialize products that are more effective, safer, less toxic, more convenient, or less expensive than products we may develop. In geographies that are critical to our commercial success, competitors may also obtain regulatory approvals before us, resulting in our competitors building a strong market position in advance of the entry of our products. In addition, our ability to compete may be affected in many cases by insurers or other third-party payers seeking to encourage the use of other drugs. The key competitive factors affecting the success of any products we may develop are likely to be their efficacy, safety, convenience, price and availability of reimbursement.

Bispecific PD-1/masked IL-2 Program

With respect to XTX501, currently there are no bispecific PD-1 targeted IL-2 therapies approved for the treatment of cancer. However, we are aware of several companies that have bispecific PD-1 targeted IL-2 programs in development, including but not limited to Anaveon AG, Bright Peak Therapeutics, Inc., Innovent Biologics, Inc., Medicenna Therapeutics Corp., Regeneron Pharmaceuticals, Inc., Roche, and Teva Pharmaceutical Industries, Ltd.

Masked T Cell Engager Programs

With respect to our masked T cell engager programs, currently there are no T cell engager therapies targeting PSMA, STEAP1 or CLDN18.2 approved for the treatment of cancer. However, we are aware of other companies that have masked T cell engager programs in development for PSMA, including but not limited to Janux Therapeutics, Inc. and Vir Biotechnology, Inc., and at least one other company, Werewolf Therapeutics, Inc., that has a masked T cell engager program in development for STEAP1. To our knowledge, there are no companies currently developing a masked T cell engager program targeting both PSMA and STEAP1 or a masked T cell engager program for CLDN18.2. However, we are aware of several companies developing non-masked T cell engager programs for CLDN18.2, including but not limited to Amgen Inc., Astellas Pharma Inc., AstraZeneca PLC, Innovent Biologics, Inc., Transcenta Holding Ltd. and Zai Lab Limited, for PSMA, including but not limited to AbCellera Biologics Inc., Regeneron Pharmaceuticals Inc. and Xencor, Inc., and for STEAP1, including but not limited to Amgen Inc. and Xencor Inc.

IL-12 Program

With respect to efarindodekin alfa, currently there are no IL-12 therapies approved for the treatment of cancer. However, we are aware of several companies that have IL-12 programs in development, including but not limited to ImmunityBio, Inc., PDS Biotechnology Corporation, Philogen S.p.A., Shanghai KangaBio Co., Ltd., Werewolf Therapeutics, Inc., Xencor Inc. and Zymeworks Inc.

Anti-CTLA-4 Program

Vilastobart, if approved, may face competition from other anti-CTLA-4 based therapies. For example, Yervoy (ipilimumab), an anti-CTLA-4, is approved to treat melanoma, renal cell carcinoma and certain cancers of the large intestine, and Imjudo (tremelimumab) is approved as a combination therapy to treat unresectable hepatocellular carcinoma. In addition, we are aware of several companies that have anti-CTLA-4 programs in development, including but not limited to Adagene, Inc., Agenus Inc., AstraZeneca plc, BioAtla, Inc., Chugai Pharmaceutical Co. Ltd., MacroGenics, Inc., OncoC4, Inc. and Solstice Oncology.

Intellectual Property

We strive to protect our proprietary technology, inventions, improvements, and platforms, including composition of matter for product candidates, methods of use and processes for their manufacture that we believe are important to our business, including by obtaining, maintaining, defending and enforcing patent and other intellectual property rights for the foregoing in the United States and in certain foreign jurisdictions. We also rely on trade secrets and confidentiality agreements to protect our confidential information and know-how and other aspects of our business that are not amenable to, or that we do not consider appropriate for, patent protection.

Our success depends in part on our ability to:

obtain, maintain, enforce and defend patent and other intellectual property rights for our commercially important technology, inventions and improvements;

preserve the confidentiality of our trade secrets and other confidential information;

obtain and maintain licenses to use and exploit intellectual property owned or controlled by third parties;

operate without infringing, misappropriating or otherwise violating any valid and enforceable patents and other intellectual property rights of third parties; and

defend against challenges and assertions by third parties challenging the validity or enforceability of our intellectual property rights, or our rights in our intellectual property, or asserting that the operation of our business infringes, misappropriates or otherwise violates their intellectual property rights.

Patent portfolio

As of February 28, 2026, we own, co-own or exclusively license 18 patent application families related to our business, including four pending Patent Cooperation Treaty, or PCT, patent applications, 15 pending U.S. non-provisional applications, 11 issued U.S. patents, 61 issued patents in Armenia, Australia, Azerbaijan, Belarus, China, Eurasia, Europe, France, Germany, Hong Kong, India, Indonesia, Italy Israel, Japan, Kazakhstan, Kyrgyzstan, Malaysia, Mexico, New Zealand, Philippines, Singapore, South Korea, Russia, Saudi Arabia, South Africa, Spain, the United Kingdom, Taiwan, Tajikistan, and Turkmenistan and 164 pending foreign applications in Australia, Brazil, Canada, China, Eurasia, Europe, Hong Kong, Indonesia, Israel, India, Japan, South Korea, Mexico, Malaysia, New Zealand, the Philippines, Saudi Arabia, Singapore, South Africa and Taiwan. In addition, we own four U.S. provisional patent applications within the priority year. Our owned, co-owned or exclusively in-licensed patent applications cover various aspects of our programs and technology, including composition of matter and method of use as further described below. Any U.S. or foreign patents issued from national stage filings of our owned, co-owned, or exclusively in-licensed PCT patent applications and any U.S. patents issued from non-provisional applications we may file in connection with our provisional patent applications will have a statutory expiration date ranging between 2037 and 2046, without taking into account any possible patent term adjustments or extensions and assuming payment of all appropriate maintenance, renewal, annuity and other governmental fees.

Xilio’s Platform for Masked I-O Molecules

Our proprietary engineering platform technology enables novel, masked I-O molecules designed to selectively activate within the tumor microenvironment to achieve durable efficacy without the severe side effects associated with systemically active I-O agents. By masking components of I-O therapies, our platform technology can be used to decouple therapeutic effects from toxicity for treating different cancers. As of February 28, 2026, we own four patent families covering the platform in the cytokine space: a first patent family, including one pending U.S. patent application and corresponding foreign applications in Australia, Brazil, Canada, China, Eurasia, Europe, Hong Kong, Indonesia, Israel, Japan, India, South Korea, Mexico, Malaysia, New Zealand, the Philippines, Saudi Arabia, Singapore and South Africa; and three additional patent families covering our multi-functional, including bispecific, platform technology in the cytokine space, including three pending U.S. patent applications, one pending PCT application, and 30 pending foreign applications in Australia, Brazil, Canada, China, Europe, Hong Kong, Israel, India, Japan, South Korea, Mexico, Malaysia, New Zealand, Philippines, Singapore, South Africa, and Taiwan. We own three patent families covering our immune cell engagers platform technology, two of which are at provisional stage within the priority year and one pending PCT application. We exclusively license two patent families relating to the platform technology and our cytokine and antibody programs. These owned and exclusively licensed patent families will have a statutory expiration date ranging between 2038 and 2046, without taking into account any possible patent term adjustments or extensions and assuming payment of all appropriate maintenance, renewal, annuity and other governmental fees.

In addition, we own two patent families covering various linker designs that are used or can be used in our technology, including one issued U.S. patent, two pending U.S. applications, one issued patent in Europe, which is validated in France, Germany, Spain, Italy and the United Kingdom, and ten foreign applications in Canada, Europe, Hong Kong, Japan, South Korea, Singapore and Taiwan.

XTX501 (masked PD-1/IL-2 bispecific)

As of February 28, 2026, we own three families relating to XTX501, a bispecific PD-1 / masked IL-2, covering the construct design, key elements and full-length sequences with composition of matter and methods of use claims. These patent families include four pending U.S. applications, two pending PCT applications, and 11 foreign applications in Australia, Brazil, Canada, China, Europe, Hong

Kong, Indonesia, Israel, India, Japan, South Korea, Mexico, Malaysia, New Zealand, Philippines, Singapore, South Africa and Taiwan. These owned patent families will have a statutory expiration date ranging between 2043 and 2045, without taking into account any possible patent term adjustments or extensions and assuming payment of all appropriate maintenance, renewal, annuity and other governmental fees.

Masked T Cell Engager Programs

As of February 28, 2026, we own three patent families covering our masked T cell engager programs and platform technology, including one patent family covering various bispecific molecules designed using our ATACR format, the second patent family covering various tri-specific molecules using our SEECR format, and the third family covering variant costimulatory molecules. These three patent families include one pending PCT application, two pending U.S. provisional applications within the priority year, and one pending application in Taiwan.

These patent families will have statutory expiration dates in 2045 and 2046, without taking into account any possible patent term adjustments or extensions and assuming payment of all appropriate maintenance, renewal, and annuity and other governmental fees.

Efarindodekin Alfa (masked IL‑12)

As of February 28, 2026, we own four patent families directed to different masked IL‑12 constructs and sequences, including efarindodekin alfa, with composition of matter and methods of use claims. These patent families include two issued U.S. patents, two pending U.S. non-provisional applications, two U.S. provisional applications, two issued patents in Japan and Taiwan and 46 foreign applications in Australia, Brazil, Canada, China, Eurasia, Europe, Hong Kong, Indonesia, Israel, India, Japan, South Korea, Mexico, Malaysia, New Zealand, Philippines, Saudi Arabia, Singapore, South Africa and Taiwan. These patent families will have a statutory expiration date in 2039 and 2047, without taking into account any possible patent term adjustments or extensions and assuming payment of all appropriate maintenance, renewal, annuity and other governmental fees.

Vilastobart (masked, Fc-enhanced anti-CTLA-4)

As of February 28, 2026, we own, co-own or exclusively in-license three patent families relating to masked anti-CTLA‑4 antibody constructs and sequences, including vilastobart, with composition of matter and methods of use claims. A first patent family is exclusively in-licensed from WuXi Biologics (Shanghai) Co., Ltd. and directed to anti-CTLA‑4 antibodies. This family includes three issued U.S. patents and one pending U.S. application covering certain complementarity-determining regions and variable region sequences of anti-CTLA-4 antibodies, including vilastobart. Twenty-seven foreign applications are issued in Armenia, Australia, Azerbaijan, Belarus, China, Eurasia, Indonesia, Israel, Japan, Kazakhstan, Kyrgyzstan, Malaysia, Mexico, New Zealand, Philippines, Russia, South Korea, Saudi Arabia, Singapore, Taiwan, Tajikistan, and Turkmenistan. Nine foreign applications are pending in Brazil, Canada, China, European Patent Office, Hong Kong, India, Mexico, Philippines and South Africa. A second patent family is owned and directed to anti-CTLA‑4 antibodies with modifications that improve antibody-dependent cellular cytotoxicity and includes one issued U.S. patent and one pending U.S. application. One foreign patent is issued in Mexico. Twenty foreign applications are pending in Australia, Brazil, Canada, China, Eurasia, Europe, Hong Kong, India, Indonesia, Israel, Japan, South Korea, Malaysia, New Zealand, Philippines, Saudi Arabia, Singapore, and South Africa. A third patent family is co-owned and directed to masked anti-CTLA‑4 antibodies, which includes one issued U.S. patent and one pending U.S. application. Six foreign patents are issued in Japan, China, Eurasia, Hong Kong, Indonesia and Mexico. Twenty-one foreign applications are pending in Australia, Brazil, Canada, China, Europe, Hong Kong, India, Israel, Japan, South Korea, Malaysia, New Zealand, Philippines, Saudi Arabia, Singapore, South Africa and Taiwan. These owned, co-owned and licensed patent families will have a statutory expiration date ranging between 2037 and 2039, without taking into account any possible patent term adjustments or extensions and assuming payment of all appropriate maintenance, renewal, annuity and other governmental fees.

Trademark portfolio

As of February 28, 2026, we own two federal trademark registrations for XILIO and XILIO THERAPEUTICS (Class 42) in the United States and a pending federal trademark application for XILIO (Class 5) in the United States that has been approved and published for opposition.

Patent prosecution

A PCT patent application is not eligible to become an issued patent until, among other things, we file one or more national stage patent applications within 30 months, 31 months or 32 months of the PCT application’s priority date, depending on the jurisdiction, in the countries in which we seek patent protection. If we do not timely file any national stage patent applications, we may lose our priority date with respect to our PCT patent application and any potential patent protection on the inventions disclosed in such PCT patent

application. Moreover, a provisional patent application is not eligible to become an issued patent. A provisional patent application may serve as a priority filing for a non-provisional patent application, we file within 12 months of such provisional patent application. If we do not timely file non-provisional patent applications, we may lose our priority date with respect to our existing provisional patent applications and any potential patent protection on the inventions disclosed in our provisional patent applications.

While we intend to timely file additional provisional patent applications and national stage and non-provisional patent applications relating to our PCT patent applications, we cannot predict whether any of our patent applications will result in the issuance of patents. If we do not successfully obtain patent protection, or if the scope of the patent protection we or our licensors obtain with respect to our product candidates, platform or technology is not sufficiently broad, we will be unable to prevent others from using our technology or from developing or commercializing technology and products similar or identical to ours or other similar competing products and technologies. Our ability to stop third parties from making, using, selling, offering to sell, importing or otherwise commercializing any of our technology, inventions and improvements, either directly or indirectly will depend in part on our success in obtaining, maintaining, defending and enforcing patent claims that cover our technology, inventions and improvements.

The patent positions of companies like ours are generally uncertain and involve complex legal and factual questions. The protection afforded by a patent varies on a product-by-product basis, from jurisdiction-to-jurisdiction, and depends upon many factors, including the type of patent, the scope of its coverage, the availability of patent term adjustments and regulatory-related patent term extensions, the availability of legal remedies in a particular jurisdiction and the validity and enforceability of the patent. Moreover, patent laws and related enforcement in various jurisdictions outside of the United States are uncertain and may not protect our rights to the same extent as the laws of the United States. Changes in the patent laws and rules, whether by legislation, judicial decisions or regulatory interpretation, in the United States and other jurisdictions may diminish our ability to protect our inventions and obtain, maintain, defend and enforce our patent rights, and could therefore affect the value of our business.

The area of patent and other intellectual property rights in biotechnology is evolving and has many risks and uncertainties, and third parties may have blocking patents and other intellectual property that could be used to prevent us from commercializing our platforms and product candidates and practicing our proprietary technology. Our patent rights may be challenged, narrowed, circumvented, invalidated or ruled unenforceable, which could limit our ability to stop third parties from marketing and commercializing related platforms or product candidates or limit the term of patents that cover our platforms and product candidates. In addition, the rights granted under any issued patents may not provide us with protection or competitive advantages against third parties with similar technology, and third parties may independently develop similar technologies. Moreover, because of the extensive time required for development, testing and regulatory review of a potential product, it is possible that before any of our product candidates can be commercialized, any related patent may expire or remain in force for only a short period following commercialization, thereby reducing any competitive advantage provided by the patent. For this and other risks related to our proprietary technology, inventions, improvements, platforms and product candidates and intellectual property rights related to the foregoing, please see the section entitled “Risk Factors—Risks Related to our Intellectual Property.”

Patent term extensions

The term of individual patents depends upon the laws of the jurisdictions in which they are obtained. In most jurisdictions in which we file, the patent term is 20 years from the earliest date of filing of the first non-provisional patent application to which the patent claims priority. However, the term of U.S. patents may be extended or adjusted for delays incurred due to compliance with FDA requirements or by delays encountered during prosecution that are caused by the U.S. Patent and Trademark Office, or the USPTO. For example, in the United States, a patent claiming a new biologic product, its method of use or its method of manufacture may be eligible for a limited patent term extension under the Drug Price Competition and Patent Term Restoration Act of 1984, or the Hatch-Waxman Act, for up to five years beyond the normal expiration date of the patent. Patent term restoration cannot be used to extend the remaining term of a patent past a total of 14 years from the product’s approval date in the United States. Only one patent applicable to an approved product is eligible for the extension, and the application for the extension must be submitted prior to the expiration of the patent for which extension is sought. A patent that covers multiple products for which approval is sought can only be extended in connection with one of the approvals. For more information on patent term extensions, see “Business—Government Regulation and Product Approval—Patent Term Restoration and Extension.” In the future, if and when any product candidates we may develop receive FDA approval, we expect to apply for patent term extensions on issued patents covering those product candidates. Moreover, we intend to seek patent term adjustments and extensions for any of our issued patents in any jurisdiction where such adjustments and extensions are available. However, there is no guarantee that the applicable authorities, including the USPTO and FDA, will agree with our assessment of whether such adjustments and extensions should be granted, and even if granted, the length of such adjustments and extensions.

Trade secrets

In addition to patent protection, we also rely on trade secrets, know-how, unpatented technology and other proprietary information to strengthen our competitive position. We take steps to protect and preserve our trade secrets and other confidential and proprietary

information and prevent the unauthorized disclosure of the foregoing, including by entering into non-disclosure and invention assignment agreements with parties who have access to our trade secrets or other confidential and proprietary information, such as employees, consultants, outside scientific collaborators, contract research and manufacturing organizations, sponsored researchers and other advisors, at the commencement of their employment, consulting or other relationships with us. In addition, we take other appropriate precautions, such as maintaining physical security of our premises and physical and electronic security of our information technology systems, to guard against any misappropriation or unauthorized disclosure of our trade secrets and other confidential and proprietary information by third parties.

Despite these efforts, third parties may independently develop substantially equivalent proprietary information and techniques or otherwise gain access to our trade secrets or other confidential or proprietary information. In addition, we cannot provide any assurances that all of the foregoing non-disclosure and invention assignment agreements have been duly executed, and any of the counterparties to such agreements may breach them and disclose our trade secrets and other confidential and proprietary information. Although we have confidence in the measures we take to protect and preserve our trade secrets and other confidential and proprietary information, they may be inadequate, our agreements or security measures may be breached, and we may not have adequate remedies for such breaches. Moreover, to the extent that our employees, contractors, consultants, collaborators and advisors use intellectual property owned by others in their work for us, disputes may arise as to our rights in any know-how or inventions arising out of such work. For more information, please see the section entitled “Risk Factors—Risks Related to our Intellectual Property.”

License, Collaboration and Option Agreements

Collaboration, License and Option Agreement with AbbVie

In February 2025, our wholly-owned subsidiary Xilio Development entered into a collaboration, license and option agreement with AbbVie for up to four programs leveraging our proprietary masking technology and platform, consisting of (i) an exclusive option for (a) an initial program to discover, develop and commercialize masked T cell engager molecules for an agreed upon initial target and backup target, or the initial option program, and (b) subject to the terms of the agreement, up to two additional programs to discover, develop, and commercialize masked T cell engager molecules for an initial target and backup target determined at the time of program initiation, each of which we refer to as an additional option program, and (ii) an exclusive license for a program to develop and commercialize a masked antibody-based immunotherapy, which we refer to as the collaboration program.

Under the agreement, Xilio Development granted AbbVie an option to obtain an exclusive global license to exploit products discovered and developed under the initial option program. During the three-year period following the effective date of the agreement, AbbVie has the right to initiate up to two additional option programs by (a) selecting an initial target and backup target for each such additional option program (excluding the target known as PSMA and any other target for which Xilio Development has completed specified activities prior to lead selection) and (b) paying Xilio Development an additional program nomination fee for each additional option program. In addition, on an option program-by-option program basis, prior to the initiation of specified activities related to lead optimization and selection for the initial target for such option program, AbbVie has a one-time right to substitute the initial target with the backup target agreed upon by the parties at the time of option program initiation, subject to the payment by AbbVie of a one-time substitution fee with respect to such substituted target and the other terms of the agreement. For the initial option program, AbbVie’s option right is exercisable beginning on the effective date of the agreement, and for each additional option program, AbbVie’s option right is exercisable following delivery of written notice of nomination of such additional option program. For each option program, prior to option exercise, Xilio Development will be responsible for conducting preclinical discovery and development up to the completion of IND-enabling studies, subject to AbbVie paying Xilio Development option extension fees upon completion of specified stages of preclinical discovery and development. Unless AbbVie elects to extend preclinical development through the next stage and pays the applicable option extension fee, AbbVie’s option right terminates within a specified time period following completion of each stage of preclinical development. Upon exercising its option for an option program, AbbVie will be responsible for any remaining preclinical development, if applicable, and all clinical development, regulatory and commercialization activities with respect to licensed products under the applicable option program.

In connection with the collaboration program, Xilio Development granted AbbVie an exclusive global license to exploit products discovered and developed under the collaboration program. Xilio Development is responsible for conducting all preclinical development through lead generation, and AbbVie is responsible for all further development and commercialization activities for any licensed products generated under the collaboration program.

As of December 31, 2025, we have received $52.0 million in total upfront payments from AbbVie, consisting of a cash payment of $42.0 million and an equity investment of $10.0 million in our common stock at a purchase price of $32.20 per share. In the first quarter of 2026, we received a $5.0 million development milestone related to the collaboration program. We are eligible to receive up to approximately $2.1 billion in additional contingent payments from AbbVie, consisting of (i) up to $305.0 million in aggregate program nomination fees, preclinical development option extension fees and option fees for the option programs and (ii) up to $1.8 billion in

aggregate development, regulatory and sales-based milestones for all option programs and the collaboration program. In addition, we are eligible to receive tiered royalties ranging in the mid to high single digits on annual global net product sales.

Subject to the terms, conditions and specified exceptions set forth in the agreement, until the agreement is terminated or expires with respect to an option program or the collaboration program, Xilio Development has agreed to work exclusively with AbbVie with respect to the target for (i) each option program and (ii) the collaboration program. In addition, Xilio Development has agreed to work exclusively with AbbVie with respect to the backup target for each option program until the expiration of the applicable target substitution period.

Unless earlier terminated in accordance with its terms, the agreement will expire upon expiration of the last royalty term for the last licensed product. AbbVie may terminate the agreement for convenience upon specified time periods. On an option program-by-option program basis, if AbbVie elects not to pay the applicable option extension fee following completion of each stage of preclinical development, or if AbbVie elects not to exercise its option right and pay the option exercise fee for the applicable option program, then the agreement will automatically terminate with respect to such option program. Subject to the terms and specified exceptions set forth in the agreement, either party may terminate the agreement for the other party’s uncured material breach or insolvency.

In connection with the execution of the agreement, on February 10, 2025, we entered into a stock purchase agreement with AbbVie Inc. pursuant to which we issued and sold 310,559 shares of common stock to AbbVie Inc. in a private placement at a purchase price of $32.20 per share for an aggregate purchase price of $10.0 million. The private placement closed on February 11, 2025. The stock purchase agreement contains customary terms and conditions, including closing conditions, mutual representations, warranties and covenants for each of us and AbbVie Inc. In addition, pursuant to the terms of an investor rights agreement entered into by and between us and AbbVie Inc. in connection with the stock purchase agreement, AbbVie Inc. agreed to certain transfer and standstill restrictions. In addition, AbbVie Inc. is entitled to certain registration rights with respect to the shares issued pursuant to the stock purchase agreement following termination of the transfer restrictions. We and AbbVie Inc. each granted the other party customary indemnification rights in connection with the registration of the shares issued pursuant to the stock purchase agreement.

Exclusive License Agreement with Gilead

In March 2024, Xilio Development entered into an exclusive license agreement with Gilead pursuant to which it granted Gilead an exclusive global license to develop and commercialize our clinical-stage product candidate efarindodekin alfa, a masked IL-12, and specified other molecules directed to IL-12.

Xilio Development is responsible for conducting clinical development for efarindodekin alfa through the initial Phase 2 portion of the ongoing Phase 1/2 clinical trial. Following the delivery by Xilio Development of a specified clinical data package for efarindodekin alfa related to the Phase 1/2 clinical trial, Gilead can elect to transition responsibilities for the development and commercialization of efarindodekin alfa to Gilead, subject to the terms of the license agreement and payment by Gilead of a $75.0 million transition fee.

In connection with the execution of the license agreement, in March 2024, we also entered into a stock purchase agreement with Gilead. Under the stock purchase agreement, Gilead purchased an aggregate of $25.0 million of our common stock and prefunded warrants (in lieu of shares of common stock) in three private placements during the year ended December 31, 2024, consisting of an aggregate of 650,387 shares of common stock and 712,514 prefunded warrants to purchase common stock. The prefunded warrants are exercisable at any time at an exercise price of $0.0014 per share, subject to Gilead not being deemed a beneficial owner of greater than 19.9% of our common stock upon the exercise of the prefunded warrants.

As of December 31, 2025, we have received $72.5 million in payments under the Gilead agreements, consisting of the $30.0 million upfront cash payment under the license agreement, $25.0 million in gross proceeds from private placements under the stock purchase agreement and a $17.5 million development milestone payment. We are eligible to receive up to $575.0 million in additional contingent payments under the license agreement, which consist of (i) the $75.0 million transition fee and (ii) up to $500.0 million in development, regulatory and sales-based milestones. In addition, we are eligible to receive tiered royalties ranging from high single digits to mid-teens on annual global net product sales.

Unless earlier terminated in accordance with its terms, the license agreement will expire upon expiration of the last royalty term for the last licensed product. Gilead may terminate the license agreement for convenience upon specified time periods. If Gilead elects not to transition responsibilities for development and commercialization of the licensed products and pay the transition fee, then the license agreement will automatically terminate. Either party may terminate the license agreement for the other party’s uncured material breach or insolvency. Subject to the terms of the license agreement, effective upon termination of the license agreement, the licenses to Gilead terminate and Xilio Development is entitled to continue to exploit the licensed products.

During the term of the license agreement, Xilio Development and its affiliates have agreed not to directly or indirectly conduct specified development, manufacturing or commercialization activities with respect to any molecule that contains, comprises or incorporates IL-12, except for the performance of Xilio Development’s activities under and in accordance with the license agreement.

In-License Agreements

We are a party to license agreements under which we license patents, patent applications and other intellectual property from third parties. These licenses impose various diligence and financial payment obligations on us. We expect to continue to enter into these types of license agreements in the future. We consider the following license agreements to be material to our business.

Amended and Restated Exclusive License Agreement with City of Hope

In August 2016, Xilio Development entered into an amended and restated exclusive license agreement with City of Hope pursuant to which City of Hope granted us an exclusive worldwide license to specified patent rights related to our anti-CTLA‑4 monoclonal antibody program.

For the first three licensed products or licensed services to achieve specified development and regulatory milestones, we are obligated to pay City of Hope up to $10.3 million in the aggregate per licensed product or licensed service. To date, we have made an aggregate of $0.8 million in specified development and regulatory milestone payments to City of Hope related to our anti-CTLA-4 monoclonal antibody program. Subject to specified conditions, we are obligated to pay City of Hope tiered royalties in the low single digits on aggregate annual net sales of licensed products or licensed services on a country-by-country basis until the expiration of the last-to-expire patent or patent application licensed from City of Hope covering the applicable licensed product or licensed service in such country. We are also obligated to pay City of Hope a portion of any consideration we receive for the grant of sublicenses under the agreement in an amount equal to a low double-digit percentage of such consideration, subject to specified conditions under that agreement at the time that we grant any such sublicense. In addition, we paid $0.5 million to City of Hope in connection with the closing of our initial public offering.

The agreement continues on a country-by-country basis until the expiration of the last to expire licensed patent right in such country. We have the right to terminate the agreement for convenience at any time on 30 days’ prior written notice to City of Hope. Either party has the right to terminate the agreement if the other party materially breaches the agreement and fails to cure such breach within specified cure periods. City of Hope may terminate the agreement if we or any of our affiliates or sublicensees bring specified patent challenges with respect to the licensed patents against City of Hope or if we assist others in bringing a patent challenge against City of Hope. However, instead of terminating as a result of a patent challenge, City of Hope may elect to increase our payment obligations by a specified percentage amount retroactive to the commencement of such patent challenge.

CTLA‑4 Monoclonal Antibody License Agreement with WuXi Biologics

In September 2016, we entered into a license agreement with WuXi Biologics (Hong Kong) Limited, or WuXi Biologics, as amended in December 2017, pursuant to which WuXi Biologics granted us an exclusive worldwide license, including the rights to grant sublicenses through multiple tiers, to specified monoclonal antibodies and patent rights and know-how controlled by WuXi Biologics, including certain patent rights related to our anti-CTLA‑4 mAb program.

For each product that incorporates a licensed antibody that has been modified using the rights licensed under the agreement, we are obligated to pay WuXi Biologics up to approximately $25.8 million in the aggregate for specified development and regulatory milestones. To date, we have made an aggregate of $5.8 million in specified development and regulatory milestones payments to WuXi Biologics related to our anti-CTLA-4 monoclonal antibody program. In addition, subject to specified conditions, we are obligated to pay WuXi Biologics tiered royalties in the low to mid-single digits on aggregate annual worldwide net sales of licensed products during the applicable royalty term and subject to early expiration or adjustment in specified circumstances. Our obligation to make royalty payments extends with respect to a licensed product in a country until the later of the expiration of the last-to-expire patent or patent application licensed from WuXi Biologics covering the applicable licensed product in such country or for a specified time period following the first commercial sale of such licensed product. Subject to specified conditions under the agreement, we also have certain obligations to contract with WuXi Biologics for specified services related to the development or manufacture of licensed products.

Unless terminated earlier in accordance with its terms, the agreement will continue until the expiration of the last to expire royalty term for a licensed product. We have the right to terminate the agreement for convenience at any time upon at least 90 days’ prior written notice to WuXi Biologics. Either party may terminate the agreement for the other party’s uncured material breach. Other than following our termination for convenience or termination by WuXi Biologics for our material breach, upon the expiration of the applicable royalty term for a licensed product in a country, we will receive a paid-up and royalty free license to exploit such licensed product in such country.

Manufacturing

We currently contract with a third-party contract development and manufacturing organization, or CDMO, to manufacture our product candidates for preclinical studies and our ongoing clinical trials, and we intend to continue to do so with one or more third parties for future preclinical studies and clinical trials. We do not own or operate manufacturing facilities for the production of our product candidates, and we currently do not have plans to build our own clinical or commercial scale manufacturing capabilities. To date, our CDMO has met our production requirements. Our CDMO is under contract to provide clinical material meeting FDA current good manufacturing practice, or cGMP, requirements and in sufficient quantities to meet anticipated clinical-trial demands. To meet our projected needs for commercial manufacturing, our current third-party manufacturer will need to increase its scale of production, or we will need to secure one or more alternate suppliers. We believe that there are alternate manufacturers that could satisfy our anticipated clinical and commercial requirements, although we cannot be certain that identifying and establishing relationships with such manufacturers, if necessary, would not result in significant delay or material additional costs.

Although we expect to rely on one or more third-party contract manufacturers for the production of our current and future product candidates, we have personnel with extensive technical, manufacturing, analytical and quality experience in biotherapeutic protein manufacturing to oversee our contract manufacturer relationships. In collaboration with our third-party manufacturer, we have manufactured cGMP clinical supply for our clinical trials for our clinical-stage product candidates, vilastobart (anti-CTLA-4) and efardindodekin alfa (IL-12) and cGMP manufacturing for XTX501 (PD-1/IL-2) clinical supply is in process. As we scale clinical and develop commercial manufacturing capability for each of our product candidates, we intend to develop the network of contract manufacturing sites operated by our CDMO to include EU- or U.S.-based sites.

Government Regulation and Product Approval

Government authorities in the United States, at the federal, state and local level, and in other countries and foreign jurisdictions, including the European Union, or EU, extensively regulate, among other things, the research, development, testing, manufacture, quality control, approval, packaging, storage, recordkeeping, labeling, advertising, promotion, distribution, marketing, sales, pricing, reimbursement, post-approval monitoring and reporting, and import and export of pharmaceutical products. The processes for obtaining regulatory approvals in the United States and in foreign countries and jurisdictions, along with subsequent compliance with applicable statutes and regulations and other regulatory authorities, require the expenditure of substantial time and financial resources and may have a significant impact on our business.

Review and Approval of Drugs and Biologics in the United States

In the United States, the FDA approves and regulates drugs under the Federal Food, Drug, and Cosmetic Act, or FDCA, and related regulations. Biological products, or biologics, are licensed for marketing under the Public Health Service Act, or PHSA, and subject to regulation under the FDCA and related regulations. A company, institution, or organization that takes responsibility for the initiation and management of a clinical development program for such products is generally referred to as a sponsor. A sponsor seeking approval to market and distribute a new drug or biological product in the United States must typically secure the following:

completion of preclinical laboratory tests in compliance with the FDA’s good laboratory practice, or GLP, regulations and standards;

design of a clinical protocol and submission to the FDA of an investigational new drug application, or IND, which must take effect before human clinical trials may begin;

approval by an independent institutional review board, or IRB, representing each clinical site before each clinical trial may be initiated;

performance of adequate and well-controlled human clinical trials in accordance with good clinical practices, or GCPs, to establish the safety and efficacy of the proposed drug product, and with respect to biologics, the purity, potency and safety of such drug product, for each proposed indication;

submission to the FDA of a biologics license application, or BLA, for a biological product requesting marketing for one or more proposed indications;

review of the request for approval by an FDA advisory committee, where appropriate or if applicable;

completion of one or more FDA inspections of the manufacturing facility or facilities at which the product, or components thereof, are produced to assess compliance with cGMP to assure the product’s identity, strength, quality and purity;

completion of FDA audits of clinical trial sites to assure compliance with GCPs and the integrity of the clinical data;

payment of user application and program fees pursuant to the Prescription Drug User Fee Act, or PDUFA;

securing FDA approval of the BLA, authorizing marketing of the product in the United States for one or more indications; and

compliance with any post-approval requirements, including the potential requirement to implement a Risk Evaluation and Mitigation Strategy, or REMS, and the potential requirement to conduct post-approval studies.

Preclinical Studies

Before a sponsor begins testing a compound with potential therapeutic value in humans, the product candidate enters the preclinical testing stage. Preclinical studies include laboratory evaluation of the purity and stability of the manufactured substance or active pharmaceutical ingredient and the formulated product, as well as in vitro and animal studies to assess the safety and activity of the product candidate for initial testing in humans and to establish a rationale for therapeutic use. These studies are typically referred to as IND-enabling studies. The conduct of preclinical studies is subject to federal regulations and requirements, including GLP regulations and standards and the U.S. Department of Agriculture’s Animal Welfare Act, if applicable. Some long-term preclinical testing, such as animal tests of reproductive AEs and carcinogenicity, and long-term toxicity studies, may continue after the IND is submitted.

In December 2022, Congress eliminated provisions in both the FDCA and the PHSA that required animal testing in support of a BLA. While animal testing may still be conducted, the FDA was authorized to rely on alternative non-clinical tests, including cell-based assays, micro-physiological systems, or bio-printed or computer models. In April 2025, the FDA released a roadmap to replace animal testing in preclinical safety studies with scientifically validated new approach methodologies.

The IND and IRB Processes

An IND is a request for FDA authorization to administer an investigational product candidate to humans. Such authorization must be secured prior to interstate shipment and administration of any new drug or biologic that is not the subject of an approved BLA. In support of a request for an IND, sponsors must submit a protocol for each clinical trial and any subsequent protocol amendments must be submitted to the FDA as part of the IND. In addition, the results of the preclinical tests, together with manufacturing information, analytical data, any available clinical data or literature and plans for clinical trials, among other things, are submitted to the FDA as part of an IND. The FDA requires a 30‑day waiting period after the filing of each IND before clinical trials may begin. This waiting period is designed to allow the FDA to review the IND to determine whether human research subjects and patients will be exposed to unreasonable health risks or whether there are any issues surrounding chemistry, manufacturing and controls, or CMC, for the proposed product. At any time during this 30‑day period, or thereafter, the FDA may raise concerns or questions about the conduct of the trials as outlined in the IND and impose a clinical hold or partial clinical hold. In this case, the IND sponsor and the FDA must resolve any outstanding concerns before clinical trials can begin. The FDA’s primary objectives in reviewing an IND are to assure the safety and rights of patients and to help assure that the quality of the investigation will be adequate to permit an evaluation of the drug’s effectiveness and safety and of the biological product’s safety, purity and potency.

Following commencement of a clinical trial under an IND, the FDA may also place a clinical hold or partial clinical hold on that trial. Clinical holds are imposed by the FDA whenever there is concern for patient safety and may be a result of new data, findings or developments in clinical, nonclinical, and/or CMC. A clinical hold is an order issued by the FDA to the sponsor to delay a proposed clinical investigation or to suspend an ongoing investigation. A partial clinical hold is a delay or suspension of only part of the clinical work requested under the IND. For example, a specific protocol or part of a protocol is not allowed to proceed, while other protocols may do so. No more than 30 days after imposition of a clinical hold or partial clinical hold, the FDA will provide the sponsor a written explanation of the basis for the hold. Following issuance of a clinical hold or partial clinical hold, an investigation may only resume after the FDA has notified the sponsor that the investigation may proceed. The FDA will base that determination on information provided by the sponsor correcting the deficiencies previously cited or otherwise satisfying the FDA that the investigation can proceed.

A sponsor may choose, but is not required, to conduct a foreign clinical study under an IND. When a foreign clinical study is conducted under an IND, all IND requirements must be met unless waived. When a foreign clinical study is not conducted under an IND, the sponsor must ensure that the study complies with certain regulatory requirements of the FDA in order to use the study as support for an IND or application for marketing approval in the United States. Specifically, the studies must be conducted in accordance with GCP, including undergoing review and receiving approval by an independent ethics committee, or IEC, and seeking and receiving informed

consent from subjects. The FDA’s regulations are intended to help ensure the protection of human subjects enrolled in non-IND foreign clinical studies, as well as the quality and integrity of the resulting data. They further help ensure that non-IND foreign studies are conducted in a manner comparable to that required for IND studies.

In addition to the foregoing IND requirements, an IRB representing each institution participating in the clinical trial must review and approve the plan for any clinical trial before it commences at that institution, and the IRB must conduct continuing review and reapprove the trial at least annually. The IRB must review and approve, among other things, the trial protocol and informed consent information to be provided to trial subjects. An IRB must operate in compliance with FDA regulations. An IRB can suspend or terminate approval of a clinical trial at its institution, or an institution it represents, if the clinical trial is not being conducted in accordance with the IRB’s requirements or if the product candidate has been associated with unexpected serious harm to patients.

Additionally, some trials are overseen by an independent group of qualified experts organized by the trial sponsor, known as a data monitoring committee, or DMC. This group provides authorization for whether a trial may move forward at designated check points based on access that only the group maintains to available data from the trial. Suspension or termination of development during any phase of clinical trials can occur if it is determined that the participants or patients are being exposed to an unacceptable health risk or for other reasons, including evolving business objectives and/or competitive climate.

Human Clinical Studies in Support of a BLA

Clinical trials involve the administration of the investigational product to human subjects under the supervision of qualified investigators in accordance with GCP requirements, which include, among other things, the requirement that all research subjects provide their informed consent in writing before their participation in any clinical trial. Clinical trials are conducted under written trial protocols detailing, among other things, the inclusion and exclusion criteria, the objectives of the trial, the parameters to be used in monitoring safety and the effectiveness criteria to be evaluated.

The clinical investigation of an investigational drug or biological product is generally divided into four phases. Although the phases are usually conducted sequentially, they may overlap or be combined. The four phases of an investigation are as follows:

Phase 1. Phase 1 studies include the initial introduction of an investigational new drug or biological product into humans. These studies are designed to evaluate the safety, dosage tolerance, metabolism and pharmacologic actions of the investigational drug or biological product in humans, the side effects associated with increasing doses, and if possible, to gain early evidence on effectiveness.

Phase 2. Phase 2 includes the controlled clinical trials conducted to preliminarily or further evaluate the effectiveness of the investigational drug or biological product for a particular indication(s) in patients with the disease or condition under trial, to determine dosage tolerance and optimal dosage, and to identify possible adverse side effects and safety risks associated with the drug or biological product. Phase 2 trials are typically well-controlled, closely monitored, and conducted in a limited patient population.

Phase 3. Phase 3 trials are generally controlled clinical trials conducted in an expanded patient population generally at geographically dispersed clinical trial sites. They are performed after preliminary evidence suggesting effectiveness of the drug or biological product has been obtained, and are intended to further evaluate dosage, clinical effectiveness and safety, to establish the overall benefit-risk relationship of the investigational drug or biological product, and to provide an adequate basis for product approval.

Phase 4. Post-approval studies may be conducted after initial marketing approval. These studies are used to gain additional experience from the treatment of patients in the intended therapeutic indication.

A company’s designation of a clinical trial as being of a particular phase is not necessarily indicative that the study will be sufficient to satisfy the FDA requirements of that phase because this determination cannot be made until the protocol and data have been submitted to and reviewed by the FDA. Moreover, a pivotal trial is a clinical trial that is believed to satisfy FDA requirements for the evaluation of a product candidate’s safety and efficacy such that it can be used, alone or with other pivotal or non-pivotal trials, to support regulatory approval. Generally, pivotal trials are Phase 3 trials, but they may be Phase 1 or Phase 2 trials if the design provides a well-controlled and reliable assessment of clinical benefit, particularly in an area of unmet medical need.

In December 2022, with the passage of Food and Drug Omnibus Reform Act, or FDORA, Congress required sponsors to develop and submit a diversity action plan, or DAP, for each Phase 3 clinical trial or any other “pivotal study” of a new drug or biological product. These plans are meant to encourage the enrollment of more diverse patient populations in late-stage clinical trials of FDA-regulated products. Specifically, plans must include the sponsor’s goals for enrollment, the underlying rationale for those goals, and an explanation of how the sponsor intends to meet them. In addition to these requirements, the legislation directs the FDA to issue new guidance on

diversity action plans. In January 2024, the FDA issued draft guidance setting out its policies for the collection of race and ethnicity data in clinical trials. On January 27, 2025, in response to an executive order regarding diversity, equity and inclusion programs, the FDA removed this draft guidance from its website. Subsequently, in July 2025, pursuant to a court order, the FDA restored the draft DAP guidance to its website with a statement that “information on this page may be modified and/or removed in the future subject to the terms of the court’s order and implemented consistent with applicable law.” In light of these ongoing actions, there is considerable uncertainty surrounding the draft DAP guidance and how the FDA will consider diversity action plans in connection with its review of BLAs.

In March 2022, the FDA released a final guidance entitled “Expansion Cohorts: Use in First-In-Human Clinical Trials to Expedite Development of Oncology Drugs and Biologics,” which outlines how developers can utilize an adaptive trial design commonly referred to as a seamless trial design in early stages of oncology biological product development (i.e., the first-in-human clinical trial) to compress the traditional three phases of trials into one continuous trial called an expansion cohort trial. Information to support the design of individual expansion cohorts are included in IND applications and assessed by FDA. Expansion cohort trials can potentially bring efficiency to biological product development and reduce developmental costs and time.

In September 2025, the FDA issued final guidance with updated recommendations for GCPs aimed at modernizing the design and conduct of clinical trials. The updates are intended to help pave the way for more efficient clinical trials to facilitate the development of medical products. The final guidance is adopted from the International Council for Harmonisation’s recently updated E6(R3) final guideline that was developed to enable the incorporation of rapidly developing technological and methodological innovations into the clinical trial enterprise. In addition, the FDA issued draft guidance outlining recommendations for the implementation of decentralized clinical trials.

In October 2025, the FDA issued final guidance that focuses on patient-focused drug development. The guidance outlines how stakeholders, such as patients, caregivers, researchers and medical product developers, can submit patient experience data in support of the development and approval of drug products. To that end, the guidance provides an overview of clinical outcome assessments, or COAs, in clinical trials, and the role that COAs may play in in evaluating the clinical benefit of a medical product.

Concurrent with clinical trials, companies often complete additional animal studies and must also develop additional information about the chemistry and physical characteristics of the candidate product as well as finalize a process for manufacturing the product in commercial quantities in accordance with cGMP requirements. The manufacturing process must be capable of consistently producing quality batches of the drug candidate and, among other things, must develop methods for testing the identity, strength, quality, purity, and potency of the final drug. Additionally, appropriate packaging must be selected and tested, and stability studies must be conducted to demonstrate that the drug candidate does not undergo unacceptable deterioration over its shelf life.

Sponsors of clinical trials are required to register and disclose certain clinical trial information on a public registry (clinicaltrials.gov) maintained by the U.S. National Institutes of Health, or NIH. In particular, information related to the product, patient population, phase of investigation, study sites and investigators and other aspects of the clinical trial is made public as part of the registration of the clinical trial. The NIH’s Final Rule on registration and reporting requirements for clinical trials became effective in 2017. Although the FDA has historically not enforced these reporting requirements, the FDA has, as of January 31, 2026 issued eight notices of non-compliance. While these notices of non-compliance did not result in civil monetary penalties, the failure to submit clinical trial information to clinicaltrials.gov is a prohibited act under the FDCA with violations subject to potential civil monetary penalties of up to $10,000 for each day the violation continues. Violations may also result in injunctions and/or criminal prosecution or disqualification from federal grants.

Interactions with FDA During the Clinical Development Program

Following the clearance of an IND and the commencement of clinical trials, the sponsor will continue to have interactions with the FDA. An annual report on the progress of the study must be submitted to the FDA and more frequently if serious AEs occur. In addition, IND safety reports must be submitted to the FDA for any of the following: serious and unexpected suspected adverse reactions; findings from other studies or animal or in vitro testing that suggest a significant risk in humans exposed to the product; and any clinically important increase in the occurrence of a serious suspected adverse reaction over that listed in the protocol or investigator brochure. Phase 1, Phase 2 and Phase 3 clinical trials may not be completed successfully within any specified period, or at all. The FDA will typically inspect one or more clinical sites to assure compliance with GCP and the integrity of the clinical data submitted.

In addition, sponsors are given opportunities to meet with the FDA at certain points in the clinical development program. Specifically, sponsors may meet with the FDA prior to the submission of an IND, or Pre-IND meeting, at the end of Phase 1 clinical trial, or EOP1 meeting, at the end of Phase 2 clinical trial, or EOP2 meeting, and before a BLA is submitted, or Pre-BLA meeting. Meetings at other times may also be requested. There are five types of meetings that occur between sponsors and the FDA. Type A meetings are those that are necessary for an otherwise stalled product development program to proceed or to address an important safety issue. Type B

meetings include Pre-IND and Pre-BLA meetings, as well as end of phase meetings such as EOP2 meetings. A Type C meeting is any meeting other than a Type A or Type B meeting regarding the development and review of a product, including, for example, meetings to facilitate early consultations on the use of a biomarker as a new surrogate endpoint that has never been previously used as the primary basis for product approval in the proposed context of use. A Type D meeting is focused on a narrow set of issues and does not require input from more than three disciplines or divisions. Finally, INTERACT meetings are intended for novel products and development programs that present unique challenges in the early development of an investigational product.

At the conclusion of these meetings, the FDA will typically provide its responses to questions posed by the sponsor regarding the clinical development program. The FDA will not indicate whether a BLA will be approved, but it will provide guidance to the sponsor on various questions, including whether an application should be submitted in the first place on the basis of the studies and data proposed by the sponsor. The agency may also generally express support for the sponsor’s approach in the clinical development program, but also indicate that questions concerning whether the data support approval will be subject to review by the agency following its acceptance for filing of the BLA. The FDA has indicated that its responses, as conveyed in meeting minutes and advice letters, only constitute mere recommendations and/or advice made to a sponsor and, as such, sponsors are not bound by such recommendations and/or advice. Nonetheless, from a practical perspective, a sponsor’s failure to follow the FDA’s recommendations for design of a clinical program may put the program at significant risk of failure. In September 2023, the FDA issued draft guidance outlining the terms of such meetings in more detail.

Expanded Access

Expanded access, sometimes called “compassionate use,” is the use of investigational products outside of clinical trials to treat patients with serious or immediately life-threatening diseases or conditions when there are no comparable or satisfactory alternative treatment options. FDA regulations allow access to investigational products under an IND by the sponsor or the treating physician for treatment purposes on a case-by-case basis for: individual patients (single-patient IND applications for treatment in emergency settings and non-emergency settings); intermediate-size patient populations; and larger populations for use of the investigational product under a treatment protocol or treatment IND application.

There is no requirement for a sponsor to provide expanded access to an investigational product. However, if a sponsor decides to make its investigational product available for expanded access, the FDA reviews requests for expanded access and determines if treatment may proceed. Expanded access may be appropriate when all of the following criteria apply: patient(s) have a serious or immediately life-threatening disease or condition, and there is no comparable or satisfactory alternative therapy to diagnose, monitor or treat the disease or condition; the potential patient benefit justifies the potential risks of the treatment and the potential risks are not unreasonable in the context or condition to be treated; and the expanded use of the investigational drug for the requested treatment will not interfere with initiation, conduct or completion of clinical investigations that could support marketing approval of the product or otherwise compromise the potential development of the product.

Sponsors of one or more investigational products for the treatment of a serious disease(s) or condition(s) must make publicly available their policy for evaluating and responding to requests for expanded access for individual patients. Sponsors are required to make such policies publicly available upon the earlier of initiation of a Phase 2 or Phase 3 trial; or 15 days after the investigational drug or biologic receives designation as a Breakthrough Therapy, fast track product or regenerative medicine advanced therapy.

In addition, on May 30, 2018, the Right to Try Act was signed into law. The law, among other things, provides an additional mechanism for patients with a life-threatening condition who have exhausted approved treatments and are unable to participate in clinical trials to access certain investigational products that have completed a Phase 1 trial, are the subject of an active IND and are undergoing investigation for FDA approval. Unlike the expanded access framework described above, the Right to Try Pathway does not require FDA to review or approve requests for use of the investigational product. There is no obligation for a manufacturer to make its investigational products available to eligible patients under the Right to Try Act.

Pediatric Studies

Under the Pediatric Research Equity Act of 2003, or PREA, an application or supplement thereto must contain data that are adequate to assess the safety and effectiveness of the product for the claimed indications in all relevant pediatric subpopulations, and to support dosing and administration for each pediatric subpopulation for which the product is safe and effective. Sponsors must also submit pediatric study plans prior to the assessment data. Those plans must contain an outline of the proposed pediatric study or studies the sponsor plans to conduct, including study objectives and design, any deferral or waiver requests and other information required by regulation. The sponsor, the FDA, and the FDA’s internal review committee must then review the information submitted, consult with each other and agree upon a final plan. The FDA or the sponsor may request an amendment to the plan at any time. In May 2023, the FDA issued new draft guidance that further describes the pediatric study requirements under PREA.

For investigational products intended to treat a serious or life-threatening disease or condition, the FDA must, upon the request of a sponsor, meet to discuss preparation of the initial pediatric study plan or to discuss deferral or waiver of pediatric assessments. In addition, the FDA will meet early in the development process to discuss pediatric study plans with sponsors, and the FDA must meet with sponsors by no later than the end-of-phase 1 meeting for serious or life-threatening diseases and by no later than 90 days after the FDA’s receipt of the study plan.

The FDA may, on its own initiative or at the request of the sponsor, grant deferrals for submission of some or all pediatric data until after approval of the product for use in adults, or full or partial waivers from the pediatric data requirements. A deferral may be granted for several reasons, including a finding that the product is ready for approval for use in adults before pediatric trials are complete or that additional safety or effectiveness data needs to be collected before the pediatric trials begin. The law now requires the FDA to send a PREA Non-Compliance letter to sponsors who have failed to submit their pediatric assessments required under PREA, have failed to seek or obtain a deferral or deferral extension or have failed to request approval for a required pediatric formulation. Unless otherwise required by regulation, the pediatric data requirements do not apply to products with orphan designation, although FDA has taken steps to limit what it considers abuse of this statutory exemption in PREA by announcing that it does not intend to grant any additional orphan drug designations for rare pediatric subpopulations of what is otherwise a common disease. The FDA maintains a list of diseases that are exempt from PREA requirements due to low prevalence of disease in the pediatric population.

In 2017, with the passage of the FDA Reauthorization Act of 2017, or FDARA, Congress established new requirements to govern certain molecularly targeted cancer indications. Section 505B of the FDCA, as amended by FDARA, requires that any original BLA submitted on or after August 18, 2020, for a new active ingredient, must contain reports on the molecularly targeted pediatric cancer investigation, unless the requirement is waived or deferred, if the drug that is the subject of the application is: (i) intended for the treatment of an adult cancer, and (ii) directed at a molecular target that the Secretary of the U.S. Department of Health and Human Services, or HHS, determines to be substantially relevant to the growth or progression of a pediatric cancer in accordance with FDA guidance. The FDA maintains a list of diseases that are exempt from PREA requirements due to low prevalence of disease in the pediatric population.

Submission and Review of a BLA by the FDA

In order to obtain approval to market a drug or biological product in the United States, a marketing application must be submitted to the FDA that provides data establishing the safety and effectiveness of the proposed drug product for the proposed indication, and the safety, purity and potency of the biological product for its intended indication. The application includes all relevant data available from pertinent preclinical and clinical trials, including negative or ambiguous results as well as positive findings, together with detailed information relating to the product’s chemistry, manufacturing, controls and proposed labeling, among other things. Data can come from company-sponsored clinical trials intended to test the safety and effectiveness of a use of a product, or from a number of alternative sources, including studies initiated by investigators. To support marketing approval, the data submitted must be sufficient in quality and quantity to establish the safety and effectiveness of the investigational drug product and the safety, purity and potency of the biological product to the satisfaction of the FDA.

The application is the vehicle through which sponsors formally propose that the FDA approve a new product for marketing and sale in the United States for one or more indications. Every new product candidate must be the subject of an approved BLA before it may be commercialized in the United States. Under federal law, the submission of most applications is subject to an application user fee. The sponsor of an approved application is also subject to an annual program fee. Certain exceptions and waivers are available for some of these fees, such as an exception from the application fee for products with orphan designation and a waiver for certain small businesses. If an application is withdrawn prior to the FDA acceptance for filing, 75% of these fees may be refunded to the sponsor. If an application is withdrawn after filing, a lower portion of these fees may be refunded in certain circumstances. Currently, the fee required for the submission and review of an application for federal fiscal year 2026 is approximately $4,682,003, and the sponsor of an approved application is also subject to an annual program fee, currently more than $442,213 for federal fiscal year 2026.

The FDA conducts a preliminary review of all applications within 60 days of receipt and must inform the sponsor at that time or before whether an application is sufficiently complete to permit substantive review. The FDA’s regulations state that an application “shall not be considered as filed until all pertinent information and data have been received” by the FDA. In the event that the FDA determines that an application does not satisfy this standard, it will issue a Refuse to File, or RTF, determination to the applicant. Typically, an RTF will be based on administrative incompleteness, such as clear omission of information or sections of required information. In October 2025, the FDA issued internal guidance clarifying that “materially incomplete or inadequately organized” applications that would not permit timely, efficient and complete review will be the subject of an RTF. The internal guidance also provides that the agency will issue an RTF for an application that relies on a single adequate and well-controlled investigation to support approval if prior communications with the FDA determined the need for more than one clinical study and any justification for a single investigation is inadequate.

The FDA has agreed to specified performance goals in the review process of BLAs. Under that agreement, 90% of applications seeking approval of New Molecular Entities, or NMEs, are meant to be reviewed within ten months from the date on which FDA accepts the BLA for filing, and 90% of applications for NMEs that have been designated for “priority review” are meant to be reviewed within six months of the filing date. The review process and the PDUFA goal date may be extended by the FDA for three additional months to consider new information or clarification provided by the sponsor to address an outstanding deficiency identified by the FDA following the original submission.

The FDA seeks to meet these timelines for review of an application but its ability to do so may be affected by a variety of factors, including government budget and funding levels, the ability to hire and retain key personnel and statutory, regulatory and policy changes. Average review times at the agency have fluctuated in recent years as a result. For example, during the past decade, the U.S. government has shut down several times and certain regulatory agencies, including the FDA, have had to furlough critical employees and stop critical activities, including the review of BLAs.

In connection with its review of an application, the FDA typically will inspect the facility or facilities where the product is or will be manufactured. These pre-approval inspections may cover all facilities associated with a BLA submission, including drug component manufacturing (e.g., active pharmaceutical ingredients), finished drug product manufacturing, and control testing laboratories. The FDA will not approve an application unless it determines that the manufacturing processes and facilities are in compliance with cGMP requirements and adequate to assure consistent production of the product within required specifications.

Moreover, the FDA will review a sponsor’s financial relationship with the principal investigators who conducted the clinical trials in support of the BLA. Depending on the level of that compensation and any other financial interest a principal investigator may have in a sponsor, the sponsor may be required to report these relationships to the FDA. The FDA will then evaluate that financial relationship and determine whether it creates a conflict of interest or otherwise affects the interpretation of the trial or the integrity of the data generated at the principal investigator’s clinical trial site. If so, the FDA may exclude data from the clinical trial site in connection with its determination of the approvability of the application for the investigational product.

Additionally, before approving a BLA, the FDA will typically inspect one or more clinical sites to assure compliance with GCP and the integrity of the clinical data submitted to the FDA. With the passage of FDORA, Congress clarified the FDA’s authority to conduct inspections by expressly permitting inspection of facilities involved in the preparation, conduct, or analysis of clinical and non-clinical studies submitted to the FDA as well as other persons holding study records or involved in the study process.

In addition, as a condition of approval, the FDA may require a sponsor to develop a REMS. REMS use risk minimization strategies beyond the professional labeling to ensure that the benefits of the product outweigh the potential risks. To determine whether a REMS is needed, the FDA will consider the size of the population likely to use the product, seriousness of the disease, expected benefit of the product, expected duration of treatment, seriousness of known or potential AEs, and whether the product is a new molecular entity. Under FDARA, the FDA must implement a protocol to expedite review of responses to inspection reports pertaining to certain applications, including applications for products in shortage or those for which approval is dependent on remediation of conditions identified in the inspection report.

The FDA may refer an application for a novel product to an advisory committee or explain why such referral was not made. Typically, an advisory committee is a panel of independent experts, including clinicians and other scientific experts, that reviews, evaluates and provides a recommendation as to whether the application should be approved and under what conditions. The FDA is not bound by the recommendations of an advisory committee, but it considers such recommendations carefully when making decisions.

The FDA’s Decision on a BLA

The FDA reviews an application to determine, among other things, whether the product is safe and whether it is effective for its intended use(s), with the latter determination being made on the basis of substantial evidence. The term “substantial evidence” is defined under the FDCA as “evidence consisting of adequate and well-controlled investigations, including clinical investigations, by experts qualified by scientific training and experience to evaluate the effectiveness of the product involved, on the basis of which it could fairly and responsibly be concluded by such experts that the product will have the effect it purports or is represented to have under the conditions of use prescribed, recommended, or suggested in the labeling or proposed labeling thereof.” The FDA has interpreted this evidentiary standard to require at least two adequate and well-controlled clinical investigations to establish effectiveness of a new product. Under certain circumstances, however, the FDA has indicated that a single trial with certain characteristics and additional information may satisfy this standard. In December 2019, the FDA issued draft guidance further explaining the studies that are needed to establish substantial evidence of effectiveness. Although the FDA has not yet finalized that guidance, it did issue additional draft guidance in September 2023 that outlines considerations for relying on confirmatory evidence in lieu of a second clinical study.

After evaluating the application and all related information, including the advisory committee recommendations, if any, and inspection reports of manufacturing facilities and clinical trial sites, the FDA will issue either an approval letter or a Complete Response Letter, or CRL. To issue an approval letter, the FDA must determine that the drug is effective and that its expected benefits outweigh its potential risks to patients. This “benefit-risk” assessment is informed by the extensive body of evidence about the product’s safety and efficacy in the BLA. This assessment is also informed by other factors, including: the severity of the underlying condition and how well patients’ medical needs are addressed by currently available therapies; uncertainty about how the premarket clinical trial evidence will extrapolate to real-world use of the product in the post-market setting; and whether risk management tools are necessary to manage specific risks.

A CRL indicates that the review cycle of the application is complete, and the application will not be approved in its present form. A CRL generally outlines the deficiencies in the submission and may require substantial additional testing or information in order for the FDA to reconsider the application. The CRL may require additional clinical or other data, additional pivotal Phase 3 clinical trial(s) and/or other significant and time-consuming requirements related to clinical trials, preclinical studies or manufacturing. If a CRL is issued, the sponsor will have one year to respond to the deficiencies identified by the FDA, at which time the FDA can deem the application withdrawn or, in its discretion, grant the sponsor an additional six-month extension to respond. The FDA has committed to reviewing resubmissions in response to an issued CRL in either two or six months depending on the type of information included. Even with the submission of this additional information, however, the FDA ultimately may decide that the application does not satisfy the regulatory criteria for approval. The FDA has taken the position that a CRL is not final agency action making the determination subject to judicial review. For those seeking to challenge a CRL decision, the FDA has indicated that sponsors may request a formal hearing on the CRL or they may file a request for reconsideration or a request for a formal dispute resolution. While CRLs were previously treated by the FDA as confidential and were only disclosed in action packages for approved products, the FDA announced in September 2025 that it will now release CRLs promptly after they are issued to sponsors. Since that announcement, the FDA has posted a number of CRLs on its website.

An approval letter, on the other hand, authorizes commercial marketing of the product with specific prescribing information for specific indications described in the FDA-approved labeling. Depending on the specific risk(s) to be addressed, the FDA may require that contraindications, warnings or precautions be included in the product labeling, require that post-approval trials, including Phase 4 clinical trials, be conducted to further assess a product’s safety after approval, require testing and surveillance programs to monitor the product after commercialization or impose other conditions, including distribution and use restrictions or other risk management mechanisms under a REMS which can materially affect the potential market and profitability of the product. The FDA may prevent or limit further marketing of a product based on the results of post-marketing trials or surveillance programs. After approval, some types of changes to the approved product, such as adding new indications, manufacturing changes and additional labeling claims, are subject to further testing requirements and FDA review and approval.

Under the Ensuring Innovation Act, which was signed into law in April 2021, the FDA must publish action packages summarizing its decisions to approve new drugs and biologics within 30 days of approval of such products.

Expedited Review Programs

The FDA is authorized to designate certain products for expedited review if they are intended to address an unmet medical need in the treatment of a serious or life-threatening disease or condition. These programs include fast track designation, Breakthrough Therapy designation and priority review designation. None of these expedited programs changes the standards for approval but they may help expedite the development or approval process governing product candidates.

Specifically, the FDA may designate a product for Fast Track review if it is intended, whether alone or in combination with one or more other products, for the treatment of a serious or life-threatening disease or condition, and it demonstrates the potential to address unmet medical needs for such a disease or condition. For Fast Track products, sponsors may have greater interactions with the FDA and the FDA may initiate review of sections of a Fast Track product’s application before the application is complete. This rolling review may be available if the FDA determines, after preliminary evaluation of clinical data submitted by the sponsor, that a Fast Track product may be effective. The sponsor must also provide, and the FDA must approve, a schedule for the submission of the remaining information and the sponsor must pay applicable user fees. However, the FDA’s time period goal for reviewing a Fast Track application does not begin until the last section of the application is submitted. In addition, the Fast Track designation may be withdrawn by the FDA if the FDA believes that the designation is no longer supported by data emerging in the clinical trial process.

Second, a product may be designated as a Breakthrough Therapy if it is intended, either alone or in combination with one or more other products, to treat a serious or life-threatening disease or condition and preliminary clinical evidence indicates that the product may demonstrate substantial improvement over existing therapies on one or more clinically significant endpoints, such as substantial treatment effects observed early in clinical development. The FDA may take certain actions with respect to Breakthrough Therapies, including holding meetings with the sponsor throughout the development process; providing timely advice to the product sponsor

regarding development and approval; involving more senior staff in the review process; assigning a cross-disciplinary project lead for the review team; and taking other steps to help the sponsor design the clinical trials in an efficient manner.

Third, the FDA may designate a product for priority review if it is a product that treats a serious condition and, if approved, would provide a significant improvement in safety or effectiveness. The FDA determines, on a case-by-case basis, whether the proposed product represents a significant improvement when compared with other available therapies. Significant improvement may be illustrated by evidence of increased effectiveness in the treatment of a condition, elimination or substantial reduction of a treatment-limiting product reaction, documented enhancement of patient compliance that may lead to improvement in serious outcomes, and evidence of safety and effectiveness in a new subpopulation. A priority designation is intended to direct overall attention and resources to the evaluation of such applications, and to shorten the FDA’s goal for taking action on a marketing application from ten months to six months.

Accelerated Approval Pathway

The FDA may grant accelerated approval to a product for a serious or life-threatening condition that provides meaningful therapeutic advantage to patients over existing treatments based upon a determination that the product has an effect on a surrogate endpoint that is reasonably likely to predict clinical benefit. The FDA may also grant accelerated approval for such a condition when the product has an effect on an intermediate clinical endpoint that can be measured earlier than an effect on irreversible morbidity or mortality, or IMM, and that is reasonably likely to predict an effect on irreversible morbidity or mortality or other clinical benefit, taking into account the severity, rarity or prevalence of the condition and the availability or lack of alternative treatments. Products granted accelerated approval must meet the same statutory standards for safety and effectiveness as those granted traditional approval.

For the purposes of accelerated approval, a surrogate endpoint is a marker, such as a laboratory measurement, radiographic image, physical sign or other measure that is thought to predict clinical benefit, but is not itself a measure of clinical benefit. Surrogate endpoints can often be measured more easily or more rapidly than clinical endpoints. An intermediate clinical endpoint is a measurement of a therapeutic effect that is considered reasonably likely to predict the clinical benefit of a drug, such as an effect on IMM. The FDA has limited experience with accelerated approvals based on intermediate clinical endpoints but has indicated that such endpoints generally may support accelerated approval where the therapeutic effect measured by the endpoint is not itself a clinical benefit and basis for traditional approval, if there is a basis for concluding that the therapeutic effect is reasonably likely to predict the ultimate clinical benefit of a product.

The accelerated approval pathway is most often used in settings in which the course of a disease is long, and an extended period of time is required to measure the intended clinical benefit of a product, even if the effect on the surrogate or intermediate clinical endpoint occurs rapidly. Thus, accelerated approval has been used extensively in the development and approval of products for treatment of a variety of cancers in which the goal of therapy is generally to improve survival or decrease morbidity and the duration of the typical disease course requires lengthy and sometimes large trials to demonstrate a clinical or survival benefit. Thus, the benefit of accelerated approval derives from the potential to receive approval based on surrogate endpoints sooner than possible for trials with clinical or survival endpoints, rather than deriving from any explicit shortening of the FDA approval timeline, as is the case with priority review.

The accelerated approval pathway is usually contingent on a sponsor’s agreement to conduct, in a diligent manner, additional post-approval confirmatory studies to verify and describe the product’s clinical benefit. As a result, a product candidate approved on this basis is subject to rigorous post-marketing compliance requirements, including the completion of phase 4 or post-approval trials to confirm the effect on the clinical endpoint. Failure to conduct required post-approval studies, or confirm a clinical benefit during post-marketing studies, would allow the FDA to initiate expedited proceedings to withdraw approval of the product. All promotional materials for product candidates approved under accelerated regulations are subject to prior review by the FDA.

With the passage of FDORA, Congress modified certain provisions governing accelerated approval of drug and biologic products. Specifically, the new legislation authorized the FDA to require a sponsor to have its confirmatory clinical trial underway before accelerated approval is awarded, and to submit progress reports on its post-approval studies to the FDA every six months until the study is completed. Moreover, FDORA established expedited procedures authorizing the FDA to withdraw an accelerated approval if certain conditions are met, including where a required confirmatory trial fails to verify and describe the predicted clinical benefit or where evidence demonstrates the product is not shown to be safe or effective under the conditions of use. The FDA may also use such procedures to withdraw an accelerated approval if a sponsor fails to conduct any required post-approval study of the product with due diligence, including with respect to “conditions specified by the Secretary.” The new procedures include the provision of due notice and an explanation for a proposed withdrawal, and opportunities for a meeting with the FDA Commissioner or the FDA Commissioner’s designee and a written appeal, among other things.

In March 2023, the FDA issued draft guidance that outlines its current thinking and approach to accelerated approval. The agency indicated that the accelerated approval pathway is commonly used for approval of oncology drugs due to the serious and life-threatening nature of cancer. Although single-arm trials have been commonly used to support accelerated approval, a randomized controlled trial is

the preferred approach as it provides a more robust efficacy and safety assessment and allows for direct comparisons to an available therapy. To that end, the FDA outlined considerations for designing, conducting, and analyzing data for trials intended to support accelerated approvals of oncology therapeutics. Subsequently, in December 2024 and January 2025, the FDA issued additional draft guidance relating to accelerated approval. This guidance describe the FDA’s views on what it means to conduct a confirmatory trial with due diligence and how the agency plans to interpret whether such a study needs to be underway at the time of approval. While this guidance is currently only in draft form and will ultimately not be legally binding even when finalized, sponsors typically observe the FDA’s guidance closely to ensure that their investigational products qualify for accelerated approval.

Post-Approval Regulation

Drugs and biologics manufactured or distributed pursuant to FDA approvals are subject to pervasive and continuing regulation by the FDA, including, among other things, requirements relating to recordkeeping, periodic reporting, product sampling and distribution, advertising and promotion and reporting of adverse experiences with the product. After approval, most changes to the approved product, such as adding new indications or other labeling claims, are subject to prior FDA review and approval. There also are continuing annual user fee requirements for any marketed products and the establishments at which such products are manufactured, as well as new application fees for supplemental applications with clinical data.

In addition, manufacturers and other entities involved in the manufacture and distribution of approved products are required to register their establishments with the FDA and state agencies and are subject to periodic unannounced inspections by the FDA and these state agencies for compliance with cGMP requirements. Changes to the manufacturing process are strictly regulated and often require prior FDA approval before being implemented. FDA regulations also require investigation and correction of any deviations from cGMP and impose reporting and documentation requirements upon the sponsor and any third-party manufacturers that the sponsor may decide to use. Accordingly, manufacturers must continue to expend time, money, and effort in the area of production and quality control to maintain cGMP compliance.

Once an approval is granted, the FDA may withdraw the approval if compliance with regulatory requirements and standards is not maintained or if problems occur after the product reaches the market. Later discovery of previously unknown problems with a product, including AEs of unanticipated severity or frequency, or with manufacturing processes, or failure to comply with regulatory requirements, may result in revisions to the approved labeling to add new safety information; imposition of post-market studies or clinical trials to assess new safety risks; or imposition of distribution or other restrictions under a REMS program. Other potential consequences include, among other things:

restrictions on the marketing or manufacturing of the product, suspension of the approval, or complete withdrawal of the product from the market or product recalls;

fines, warning letters or holds on post-approval clinical trials;

refusal of the FDA to approve pending BLAs or supplements to approved BLAs, or suspension or revocation of product license approvals;

product seizure or detention, or refusal to permit the import or export of products; or

injunctions or the imposition of civil or criminal penalties.

The FDA strictly regulates marketing, labeling, advertising and promotion of products that are placed on the market. Products may be promoted only for the approved indications and in accordance with the provisions of the approved label. The FDA and other agencies actively enforce the laws and regulations prohibiting the promotion of off-label uses, and a company that is found to have improperly promoted off-label uses may be subject to significant liability. If a company is found to have promoted off-label uses, it may become subject to adverse public relations and administrative and judicial enforcement by the FDA, the Department of Justice, or the Office of the Inspector General of the Department of Health and Human Services, as well as state authorities. This could subject a company to a range of penalties that could have a significant commercial impact, including civil and criminal fines and agreements that materially restrict the manner in which a company promotes or distributes drug products. In September 2021, the FDA published final regulations that describe the types of evidence the FDA will consider in determining the intended use of a drug or biologic.

It may be permissible, under very specific, narrow conditions, for a manufacturer to engage in nonpromotional, non-misleading communication regarding off-label information, such as distributing scientific or medical journal information. Moreover, with the passage of the Pre-Approval Information Exchange Act in December 2022, sponsors of products that have not been approved may proactively communicate to payors certain information about products in development to help expedite patient access upon product approval. Previously, such communications were permitted under FDA guidance, but the new legislation explicitly provides protection to sponsors who convey certain information about products in development to payors, including unapproved uses of approved products.

In addition, in January 2025, the FDA published final guidance outlining its policies governing the distribution of scientific information to healthcare providers about unapproved uses of approved products. The final guidance calls for such communications to be truthful, non-misleading and scientifically sound and to include all information necessary for healthcare providers to interpret the strengths and weaknesses, validity and utility of the information about the unapproved use of the approved product. If a company engages in such communications as consistent with the guidance’s recommendations, the FDA indicated that it will not treat such communications as evidence of unlawful promotion of a new intended use for the approved product.

In addition, the distribution of prescription pharmaceutical products is subject to a variety of federal and state laws. The Prescription Drug Marketing Act, or PDMA, was the first federal law to set minimum standards for the registration and regulation of drug distributors by the states and to regulate the distribution of drug samples. Both the PDMA and state laws limit the distribution of prescription pharmaceutical product samples and impose requirements to ensure accountability in distribution. In November 2013, the federal Drug Supply Chain Security Act, or DSCSA, became effective in the United States, mandating an industry-wide, electronic, interoperable system to trace prescription drugs through the pharmaceutical distribution supply chain with a ten-year phase-in process. Manufacturers were required by November 2023 to have such systems and processes in place, but in August 2023, the FDA granted certain exemptions from enhanced drug distribution security requirements for eligible trading partners for particular periods of time.

Biosimilars and Regulatory Exclusivity

The 2010 Patient Protection and Affordable Care Act, or ACA, which was signed into law on March 23, 2010, included a subtitle called the Biologics Price Competition and Innovation Act of 2009, or BPCIA. The BPCIA established a regulatory scheme authorizing the FDA to approve biosimilars and interchangeable biosimilars. To date, the FDA has approved a number of biosimilar products and several interchangeable biosimilar products. The FDA has also issued numerous guidance documents outlining its approach to reviewing and licensing biosimilars and interchangeable biosimilars under the PHSA.

Under the BPCIA, a manufacturer may submit an application for licensure of a biologic product that is “biosimilar to” or “interchangeable with” a previously approved biological product or “reference product.” In order for the FDA to license a biosimilar product, it must find that there are no clinically meaningful differences between the reference product and proposed biosimilar product in terms of safety, purity, and potency. For the FDA to license a biosimilar product as interchangeable with a reference product, the agency must find that the biosimilar product can be expected to produce the same clinical results as the reference product, and (for products administered multiple times) that the biologic and the reference biologic may be switched after one has been previously administered without increasing safety risks or risks of diminished efficacy relative to exclusive use of the reference biologic. In December 2022, Congress clarified through FDORA that the FDA may license multiple first interchangeable biosimilar biological products so long as the products are all approved on the first day on which such a product is approved as interchangeable with the reference product.

Under the BPCIA, an application for a biosimilar product may not be submitted to the FDA until four years following the date of approval of the reference product. The FDA may not license a biosimilar product until 12 years from the date on which the reference product was approved. Even if a product is considered to be a reference product eligible for exclusivity, another company could market a competing version of that product if the FDA approves a full BLA for such product containing the sponsor’s own preclinical data and data from adequate and well-controlled clinical trials to demonstrate the safety, purity and potency of their product. The BPCIA also created certain exclusivity periods for biosimilars approved as interchangeable products.

The BPCIA also includes provisions to protect reference products that have patent protection. The biosimilar product sponsor and reference product sponsor may exchange certain patent and product information for the purpose of determining whether there should be a legal patent challenge. Based on the outcome of negotiations surrounding the exchanged information, the reference product sponsor may bring a patent infringement suit and injunction proceedings against the biosimilar product sponsor. The biosimilar applicant may also be able to bring an action for declaratory judgment concerning the patent.

The FDA maintains a publicly-available online database of licensed biological products, which is commonly referred to as the “Purple Book.” The Purple Book lists product names, dates of licensure, and applicable periods of exclusivity. Further, the reference product sponsor must provide patent information and patent expiration dates to the FDA following the exchange of patent information between biosimilar and reference product sponsors. This information is then published in the Purple Book.

There have been recent government proposals to reduce the 12-year reference product exclusivity period, but none have been enacted to date. At the same time, since passage of the BPCIA, many states have passed laws or amendments to laws, which address pharmacy practices involving biosimilar products. Further, the FDA may revise the standards governing approval of biosimilars so as to bring such products to the market more quickly. For example, in October 2025, the FDA issued draft guidance which proposes to eliminate the need for sponsors of biosimilar products to conduct comparative human clinical efficacy studies, allowing them to rely instead on analytical testing to demonstrate product differences from a reference product.

Orphan Drug Designation and Exclusivity

Under the Orphan Drug Act, the FDA may designate a drug product as an “orphan drug” if it is intended to treat a rare disease or condition, generally meaning that it affects fewer than 200,000 individuals in the United States, or more in cases in which there is no reasonable expectation that the cost of developing and making a drug product available in the United States for treatment of the disease or condition will be recovered from sales of the product. A company must request orphan drug designation before submitting a BLA for the product candidate. If the request is granted, the FDA will disclose the identity of the therapeutic agent and its potential use. Orphan drug designation does not shorten the Prescription Drug User Fee Act, or PDUFA, goal dates for the regulatory review and approval process, although it does convey certain advantages such as tax benefits and exemption from the PDUFA application fee.

If a product with orphan designation receives the first FDA approval for the disease or condition for which it has such designation or for a select indication or use within the rare disease or condition for which it was designated, the product generally will receive orphan drug exclusivity. Orphan drug exclusivity means that the FDA may not approve another sponsor’s marketing application for the same drug for the same indication for seven years, except in certain limited circumstances. Orphan exclusivity does not block the approval of a different product for the same rare disease or condition, nor does it block the approval of the same product for different indications. If a drug or biologic designated as an orphan drug ultimately receives marketing approval for an indication broader than what was designated in its orphan drug application, it may not be entitled to exclusivity.

Orphan exclusivity will not bar approval of another product under certain circumstances, including if a company with orphan drug exclusivity is not able to meet market demand and in cases where a subsequent product with the same drug or biologic for the same indication is shown to be clinically superior to the approved product on the basis of greater efficacy or safety, or providing a major contribution to patient care. Under Omnibus legislation signed by President Trump on December 27, 2020, the requirement for a subsequent product to show clinical superiority in order to break the previous product’s orphan drug exclusivity applies to drugs and biologics that received orphan drug designation before enactment of FDARA in 2017 but have not yet been approved or licensed by FDA.

In September 2021, in Catalyst Pharms, Inc. v. Becerra, or Catalyst, the Court of Appeals for the 11th Circuit held that, for the purpose of determining the scope of orphan drug exclusivity, the term “same disease or condition” in the statute means the designated “rare disease or condition” and could not be interpreted by the FDA to mean the “indication or use.” Thus, the court concluded, orphan drug exclusivity applies to the entire designated disease or condition rather than the approved “indication or use.” Although there have been legislative proposals to overrule this decision, they have not been enacted into law. On January 23, 2023, the FDA announced that, in matters beyond the scope of the Catalyst court order, the FDA will continue to apply its existing regulations tying orphan-drug exclusivity to the uses or indications for which the orphan drug is approved. More recently, however, on February 14, 2025, a federal district court in Washington, D.C., fully embraced the reasoning of the Catalyst decision in another decision challenging the scope of orphan drug exclusivity. On April 17, 2025, the FDA appealed this decision to the U.S. Court of Appeals for the D.C. Circuit. The implications of this decision, and its impact on the FDA’s implementation of the Orphan Drug Act, are unclear at this point.

Pediatric Exclusivity

Pediatric exclusivity is another type of non-patent marketing exclusivity in the United States and, if granted, provides for the attachment of an additional six months of existing regulatory exclusivity. For drug products, the six-month exclusivity may be attached to the term of any existing patent or regulatory exclusivity. For biologic products, the six-month period may be attached to any existing regulatory exclusivities but not to any patent terms. This six-month exclusivity may be granted if a BLA sponsor submits pediatric data that fairly respond to a written request from the FDA for such data. The data do not need to show the product to be effective in the pediatric population studied; rather, if the clinical trial is deemed to fairly respond to the FDA’s request, the additional protection is granted. If reports of requested pediatric studies are submitted to and accepted by the FDA within the statutory time limits, whatever statutory or regulatory periods of non-patent exclusivity for drugs and biologics, or patent protection that covers a drug product, are extended by six months. This is not a patent term extension, but it effectively extends the regulatory period during which the FDA cannot approve another application.

Patent Term Restoration and Extension

A patent claiming a new drug product may be eligible for a limited patent term extension under the Hatch-Waxman Act, which permits a patent restoration of up to five years for patent term lost during product development and the FDA regulatory review. The restoration period granted on a patent covering a product is typically one-half the time between the effective date of the IND approval and the submission date of an application, plus the time between the submission date of an application and the ultimate approval date. Patent term restoration cannot be used to extend the remaining term of a patent past a total of 14 years from the product’s approval date. Only one patent applicable to an approved product is eligible for the extension, and the application for the extension must be submitted prior to the expiration of the patent in question. A patent that covers multiple products for which approval is sought can only be extended in

connection with one of the approvals. The USPTO reviews and approves the application for any patent term extension or restoration in consultation with the FDA.

Pharmaceutical Coverage, Pricing and Reimbursement

In the United States and markets in other countries, patients who are prescribed treatments for their conditions and providers performing the prescribed services generally rely on third-party payors to reimburse all or part of the associated healthcare costs. Significant uncertainty exists as to the coverage and reimbursement status of products approved by the FDA and other government authorities. Thus, even if a product candidate is approved, sales of the product will depend, in part, on the extent to which third-party payors, including government health programs in the United States such as Medicare and Medicaid, commercial health insurers and managed care organizations, provide coverage, and establish adequate reimbursement levels for, the product. The process for determining whether a payor will provide coverage for a product may be separate from the process for setting the price or reimbursement rate that the payor will pay for the product once coverage is approved. Third-party payors are increasingly challenging the prices charged, examining the medical necessity, and reviewing the cost-effectiveness of medical products and services and imposing controls to manage costs. Third-party payors may limit coverage to specific products on an approved list, also known as a formulary, which might not include all of the approved products for a particular indication.

It is time consuming and expensive to seek coverage and reimbursement from third-party payors. In order to secure coverage and reimbursement for any product that might be approved for sale, a company may need to conduct expensive pharmacoeconomic studies in order to demonstrate the medical necessity and cost- effectiveness of the product, in addition to the costs required to obtain FDA or other comparable marketing approvals. Nonetheless, product candidates may not be considered medically necessary or cost effective. A decision by a third-party payor not to cover a product candidate could reduce physician utilization once the product is approved and have a material adverse effect on sales, results of operations and financial condition. Additionally, a payor’s decision to provide coverage for a product does not imply that an adequate reimbursement rate will be approved. Further, one payor’s determination to provide coverage for a drug product does not assure that other payors will also provide coverage and reimbursement for the product, and the level of coverage and reimbursement can differ significantly from payor to payor.

Healthcare Law and Regulation

Healthcare providers and third-party payors play a primary role in the recommendation and prescription of pharmaceutical products that are granted marketing approval. Arrangements with providers, consultants, third-party payors and customers are subject to broadly applicable fraud and abuse, anti-kickback, false claims laws, reporting of payments to physicians and teaching physicians, patient privacy laws and regulations, and other healthcare laws and regulations that may constrain our business and/or financial arrangements.

Restrictions under applicable federal and state healthcare laws and regulations include the following:

the U.S. federal Anti-Kickback Statute, which prohibits, among other things, persons and entities from knowingly and willfully soliciting, offering, paying, receiving or providing remuneration, directly or indirectly, in cash or in kind, to induce or reward either the referral of an individual for, or the purchase, order or recommendation of, any good or service, for which payment may be made, in whole or in part, under a federal healthcare program such as Medicare and Medicaid;

the federal civil and criminal false claims laws, including the civil False Claims Act, and civil monetary penalties laws, which prohibit individuals or entities from, among other things, knowingly presenting, or causing to be presented, to the federal government, claims for payment that are false, fictitious or fraudulent or knowingly making, using or causing to made or used a false record or statement to avoid, decrease or conceal an obligation to pay money to the federal government;

the federal civil monetary penalty and false statement laws and regulations relating to pricing and submission of pricing information for government programs, including penalties for knowingly and intentionally overcharging 340b eligible entities and the submission of false or fraudulent pricing information to government entities;

the federal Health Insurance Portability and Accountability Act of 1996, or HIPAA, which created additional federal criminal laws that prohibit, among other things, knowingly and willfully executing, or attempting to execute, a scheme to defraud any healthcare benefit program or making false statements relating to healthcare matters;

HIPAA, as amended by the Health Information Technology for Economic and Clinical Health Act, and their respective implementing regulations, including the Final Omnibus Rule published in January 2013, which impose obligations, including mandatory contractual terms, with respect to safeguarding the privacy, security, and transmission of individually identifiable health information;

the federal false statements statute, which prohibits knowingly and willfully falsifying, concealing or covering up a material fact or making any materially false statement in connection with the delivery of or payment for health care benefits, items or services;

the Foreign Corrupt Practices Act, which prohibits companies and their intermediaries from making, or offering or promising to make, improper payments to non-U.S. officials for the purpose of obtaining or retaining business or otherwise seeking favorable treatment;

the federal transparency requirements known as the federal Physician Payments Sunshine Act, under the Patient Protection and Affordable Care Act, or PPACA, as amended by the Health Care Education Reconciliation Act, which requires certain manufacturers of drugs, devices, biologics and medical supplies to report annually to the Centers for Medicare & Medicaid Services, or CMS, within HHS, information related to payments and other transfers of value made by that entity to physicians, other healthcare providers and teaching hospitals, as well as ownership and investment interests held by physicians and their immediate family members; and

analogous state and foreign laws and regulations, such as state anti‑kickback and false claims laws, which may apply to healthcare items or services that are reimbursed by non‑governmental third‑party payors, including private insurers.

Some state laws require pharmaceutical companies to comply with the pharmaceutical industry’s voluntary compliance guidelines and the relevant compliance guidance promulgated by the federal government in addition to requiring pharmaceutical manufacturers to report information related to payments to physicians and other healthcare providers or marketing expenditures. State and foreign laws also govern the privacy and security of health information in some circumstances, many of which differ from each other in significant ways and often are not preempted by HIPAA, thus complicating compliance efforts.

Similar healthcare laws and regulations exist in the EU and other jurisdictions, including reporting requirements detailing interactions with and payments to healthcare providers and laws governing the privacy and security of personal information

Healthcare Reform in the United States and Potential Changes to Healthcare Laws

A primary trend in the U.S. healthcare industry and elsewhere is cost containment. There have been a number of federal and state proposals during the last few years regarding the pricing of pharmaceutical and biopharmaceutical products, limiting coverage and reimbursement for drugs and other medical products, government control, and other changes to the healthcare system in the United States. By way of example, the United States and state governments continue to propose and pass legislation designed to reduce the cost of healthcare. In March 2010, the United States Congress enacted the PPACA, which, among other things, includes changes to the coverage and payment for products under government health care programs.

In addition, other legislative changes have been proposed and adopted since the PPACA was enacted. In August 2011, the Budget Control Act of 2011, among other things, created measures for spending reductions by Congress. A Joint Select Committee on Deficit Reduction, tasked with recommending a targeted deficit reduction of at least $1.2 trillion for the years 2013 through 2021, was unable to reach required goals, thereby triggering the legislation’s automatic reduction to several government programs. These changes included aggregate reductions to Medicare payments to providers of up to 2% per fiscal year, which went into effect in April 2013 and will remain in effect through 2031 under the Coronavirus Aid, Relief, and Economic Security Act, or the CARES Act.

The American Taxpayer Relief Act of 2012, among other things, reduced Medicare payments to several providers and increased the statute of limitations period for the government to recover overpayments to providers from three to five years. These laws may result in additional reductions in Medicare and other healthcare funding and otherwise affect the prices we may obtain for any drug product candidates for which we may obtain regulatory approval or the frequency with which any such product candidate is prescribed or used.

Since enactment of the PPACA, there have been, and continue to be, numerous legal challenges and Congressional actions to repeal and replace provisions of the law. For example, with enactment of the Tax Cuts and Jobs Act of 2017, or the TCJA, Congress repealed the “individual mandate.” The repeal of this provision, which required most Americans to carry a minimal level of health insurance, became effective in 2019. On June 17, 2021, the U.S. Supreme Court dismissed the most recent judicial challenge to the PPACA brought by several states without specifically ruling on the constitutionality of the PPACA. Litigation and legislation over the PPACA are likely to continue, with unpredictable and uncertain results.

Pharmaceutical Price Initiatives

There has been heightened governmental scrutiny in recent years over the manner in which manufacturers set prices for their marketed products, which has resulted in proposed and enacted federal and state legislation designed to, among other things, bring more transparency to product pricing and reform government program reimbursement methodologies for pharmaceutical and biologic

products. For example, in October 2020, HHS and the FDA published a final rule allowing states and other entities to develop a Section 804 Importation Program, or SIP, to import certain prescription drugs from Canada into the United States. That regulation was challenged in a lawsuit by the Pharmaceutical Research and Manufacturers of America, or PhRMA, but the case was dismissed by a federal district court in February 2023 after the court found that PhRMA did not have standing to sue HHS. A number of states have submitted Section 804 Importation Program proposals to the FDA with the goal of obtaining authority to import drugs from Canada, subject to conditions. On May 21, 2025, the FDA announced that it would offer individual states the opportunity to submit a draft proposal for pre-review and meet with the FDA to obtain its initial feedback prior to formally submitting SIP proposals. The intent of these meetings is to assist states in developing their proposals by further clarifying requirements, enhancing the quality of proposals submitted to the FDA and ultimately shortening the review timeline.

On August 16, 2022, the Inflation Reduction Act of 2022, or the IRA, was signed into law. The new legislation has implications for Medicare Part D, which is a program available to individuals who are entitled to Medicare Part A or enrolled in Medicare Part B, to give them the option of paying a monthly premium for outpatient prescription drug coverage. Among other things, the IRA requires manufacturers of certain drugs to engage in price negotiations with Medicare (beginning in 2026), with prices that can be negotiated subject to a cap; imposes rebates under Medicare Part B and Medicare Part D to penalize price increases that outpace inflation (first due in 2023); and replaces the Part D coverage gap discount program with a new discounting program (beginning in 2025). The IRA permits the Secretary of HHS to implement many of these provisions through guidance, as opposed to regulation, for the initial years.

Specifically, with respect to price negotiations, Congress authorized Medicare to negotiate lower prices for certain costly single-source drug and biologic products that do not have competing generics or biosimilars and are reimbursed under Medicare Part B and Part D. CMS may negotiate prices for ten high-cost drugs paid for by Medicare Part D starting in 2026, followed by 15 Part D drugs in 2027, 15 Part B or Part D drugs in 2028, and 20 Part B or Part D drugs in 2029 and beyond. This provision applies to drug products that have been approved for at least 9 years and biologics that have been licensed for 13 years. Drugs and biologics that have been approved for a single rare disease or condition were originally categorically excluded from price negotiation but, with passage of the One Big Beautiful Bill Act, or OBBBA, on July 3, 2025, Congress extended this exemption to drugs and biologics with multiple orphan drug designations.

Further, the legislation subjects drug manufacturers to civil monetary penalties and a potential excise tax for failing to comply with the legislation by offering a price that is not equal to or less than the negotiated “maximum fair price” under the law or for taking price increases that exceed inflation. The legislation also requires manufacturers to pay rebates for drugs in Medicare Part D whose price increases exceed inflation. The new law also caps Medicare out-of-pocket drug costs at an estimated $4,000 a year in 2024 and, thereafter beginning in 2025, at $2,000 a year.

The first cycle of negotiations for the Medicare Drug Price Negotiation Program commenced in the summer of 2023 with the negotiated prices for ten selected drug products becoming effective on January 1, 2026. The second cycle of negotiations with participating drug companies occurred during 2025, and the negotiated prices for this second set of 15 drugs will become effective on January 1, 2027. On January 27, 2026, CMS published the list of 15 drugs selected for the third cycle of negotiations. These negotiated prices will become effective on January 1, 2028.

On June 6, 2023, Merck & Co. filed a lawsuit against the HHS and CMS asserting that, among other things, the IRA’s Drug Price Negotiation Program for Medicare constitutes an uncompensated taking in violation of the Fifth Amendment of the Constitution. Subsequently, a number of other parties, including the U.S. Chamber of Commerce, Bristol Myers Squibb Company, the Pharmaceutical Research and Manufacturers of America, or PhRMA, Astellas, Novo Nordisk, Janssen Pharmaceuticals, Novartis, AstraZeneca and Boehringer Ingelheim, also filed lawsuits in various courts with similar constitutional claims against the HHS and CMS. HHS has generally won the substantive disputes in these cases or succeeded in getting claims dismissed for lack of standing or on the merits. For example, on May 8, 2025, the U.S. Court of Appeals for the Third Circuit rejected AstraZeneca L.P.’s challenge to the Medicare price negotiation program, finding that the program did not violate the company’s due process rights under the Constitution. Litigation involving these and other provisions of the IRA will continue with unpredictable and uncertain results.

Since adoption of the IRA, the current administration has taken a number of actions to reduce the costs of pharmaceutical products. For example, an April 2025 executive order directed HHS to take steps to reduce the prices of pharmaceutical products, and a May 2025 executive order called on pharmaceutical manufacturers to voluntarily reduce the prices of medicines in the United States. The May 2025 executive order provides that if such actions do not lower the costs of pharmaceuticals, the Secretary of HHS would pursue other actions, including proposing a rulemaking that imposes most favored nation, or MFN, pricing in the United States. Thereafter, on July 31, 2025, 17 pharmaceutical companies were issued letters reiterating the requirements of the May 2025 executive order and demanding that such companies extend MFN pricing to Medicaid patients. Virtually all of these pharmaceutical companies have entered into agreements with the administration to provide for lower prices on certain pharmaceuticals. On February 5, 2026, the administration launched a website that directs individuals to pharmaceutical manufacturer websites that are offering price discounts based on the administration’s pricing agreements with pharmaceutical manufacturers.

Separately, on December 23, 2025, CMS, through its Center for Medicare and Medicaid Innovation, or CMMI, proposed two five-year pilot programs to implement a “reference pricing” regime for drugs paid for under Medicare for 25% of covered beneficiaries. The programs are referred to as the Global Benchmark for Efficient Drug Pricing Model for Medicare Part B drugs, or GLOBE, and the Guarding U.S. Medicare Against Rising Drug Costs for Medicare Part D drugs, or GUARD. Under the proposed pilot programs, a manufacturer would owe rebates to Medicare if prices for its drugs exceeded the prices paid by other economically comparable reference countries, defined in the proposed regulations as Organisation for Economic Co-Operation and Development countries with a gross domestic product, or GDP, of $400 billion and a per capita GDP that is at least 60% of the U.S. per capita GDP (an initial list of 19 reference countries is included in the proposed rule). These pilot programs are proposed to go into effect beginning October 1, 2026.

At the state level, legislatures are increasingly passing legislation and implementing regulations designed to control pharmaceutical and biological product pricing, including price or patient reimbursement constraints, discounts, restrictions on certain product access and marketing cost disclosure and transparency measures, and, in some cases, designed to encourage importation from other countries and bulk purchasing. In addition, regional health care authorities and individual hospitals are increasingly using bidding procedures to determine what pharmaceutical products and which suppliers will be included in their prescription drug and other health care programs. These measures could reduce the ultimate demand for our products, once approved, or put pressure on our product pricing. We expect that additional state and federal healthcare reform measures will be adopted in the future, any of which could limit the amounts that federal and state governments will pay for healthcare products and services, which could result in reduced demand for our product candidates or additional pricing pressures. This may be increasingly true with respect to products approved pursuant to the accelerated approval pathway. State Medicaid programs and other payers are developing strategies and implementing significant coverage barriers, or refusing to cover these products outright, arguing that accelerated approval drugs have insufficient or limited evidence despite meeting the FDA’s standards for accelerated approval.

Data Privacy Regulation

U.S. Privacy Law

There are multiple privacy and data security laws that may impact our business activities in the United States and in other countries where we may conduct trials or do business in the future. These laws are evolving and may increase both our obligations and our regulatory risks in the future. In the health care industry generally, for example, under HIPAA, the U.S. Department of Health and Human Services has issued regulations to protect the privacy and security of protected health information used or disclosed by specific covered entities including certain healthcare providers, health plans and healthcare clearinghouses. HIPAA also imposes certain obligations on the business associates of covered entities that obtain protected health information in the course of providing services to or on behalf of covered entities. HIPAA may apply to us in certain circumstances and may also apply to our business partners in ways that may impact our relationships with them. Our clinical trials are regulated by the Federal Policy for the Protection of Human Subjects, also known as the Common Rule, which also includes specific privacy-related provisions. In addition to federal privacy regulations, there are a number of state laws governing confidentiality and security of health information that may be applicable to our business. In addition to possible federal civil and criminal penalties for HIPAA violations, state attorneys general are authorized to file civil actions for damages or injunctions in federal courts to enforce HIPAA and seek attorney’s fees and costs associated with pursuing federal civil actions. In addition, state attorneys general (along with private plaintiffs) have brought civil actions seeking injunctions and damages resulting from alleged violations of HIPAA’s privacy and security rules. State attorneys general also have authority to enforce state privacy and security laws. Moreover, new laws and regulations governing privacy and security may be adopted in the future as well.

There have been several developments in recent years with respect to U.S. state data privacy laws. In 2018, California passed into law the California Consumer Privacy Act, or the CCPA, which took effect on January 1, 2020 and imposed many requirements on businesses that process the personal information of California residents. Many of the CCPA’s requirements are similar to those found in the General Data Protection Regulation, or the GDPR, including requiring businesses to provide notice to data subjects regarding the information collected about them and how such information is used and shared, and providing data subjects the right to request access to such personal information and, in certain cases, request the erasure of such personal information. The CCPA also affords California residents the right to opt-out of “sales” of their personal information. The CCPA contains significant penalties for companies that violate its requirements. In addition, the California Privacy Rights Act, or the CPRA, went into effect on January 1, 2023 and significantly expanded the CCPA to incorporate additional GDPR-like provisions including requiring that the use, retention, and sharing of personal information of California residents be reasonably necessary and proportionate to the purposes of collection or processing, granting additional protections for sensitive personal information, and requiring greater disclosures related to notice to residents regarding retention of information. The CPRA also created the California Privacy Protection Agency, a new enforcement agency whose sole responsibility is to enforce the CPRA, which will further increase compliance risk.

In addition to California, a number of other states have passed comprehensive privacy laws similar to the CCPA and CPRA. These laws are either in effect or will go into effect sometime before the end of 2026, with other states likely to consider or pass similar laws in the future. Like the CCPA and CPRA, these laws create obligations related to the processing of personal information, as well as special

obligations for the processing of “sensitive” data, which includes health data in some cases. Some of the provisions of these laws may apply to our business activities. Congress has also been debating passing a federal privacy law. There are also states that are specifically regulating health information that may affect our business. For example, the State of Washington passed the My Health My Data Act in 2023 which specifically regulated health information that is not otherwise regulated by the HIPAA rules, and the law also has a private right of action, which further increases the relevant compliance risk. Connecticut and Nevada have also passed similar laws regulating consumer health data, and more states are considering such legislation. These laws may impact our business activities, including our identification of research subjects, relationships with business partners and ultimately the marketing and distribution of our products.

Plaintiffs’ lawyers are also increasingly using privacy-related statutes at both the state and federal level to bring lawsuits against companies for their data-related practices. In particular, there have been a significant number of cases filed against companies for their use of pixels and other web trackers. These cases often allege violations of the California Invasion of Privacy Act and other state laws regulating wiretapping, as well as the federal Video Privacy Protection Act. The rise in these types of lawsuits creates potential risk for our business.

General data protection regulation

Many countries outside of the United States maintain rigorous laws governing the privacy and security of personal information. The collection, use, disclosure, transfer or other processing of personal data, including personal health data, regarding individuals who are located in the European Economic Area, or EEA, and the processing of personal data that takes place in the EEA, is subject to the GDPR, which became effective on May 25, 2018. The GDPR is wide-ranging in scope and imposes numerous requirements on companies that process personal data, and it imposes heightened requirements on companies that process health and other sensitive data, such as requiring in many situations that a company obtain the consent of the individuals to whom the sensitive personal data relate before processing such data. Examples of obligations imposed by the GDPR on companies processing personal data that fall within the scope of the GDPR include providing information to individuals regarding data processing activities, implementing safeguards to protect the security and confidentiality of personal data, appointing a data protection officer, providing notification of data breaches and taking certain measures when engaging third-party processors. The GDPR also imposes strict rules on the transfer of personal data to countries outside the EEA, including the United States, and permits data protection authorities to impose large penalties for violations of the GDPR, including potential fines of up to €20 million or 4% of annual global revenues, whichever is greater. The GDPR also confers a private right of action on data subjects and consumer associations to lodge complaints with supervisory authorities, seek judicial remedies, and obtain compensation for damages resulting from violations of the GDPR. Compliance with the GDPR is a rigorous and time-intensive process that may increase the cost of doing business or require companies to change their business practices to ensure full compliance.

In July 2020, the Court of Justice of the European Union, or the CJEU, invalidated the EU-U.S. Privacy Shield framework, one of the mechanisms used to legitimize the transfer of personal data from the EEA to the United States. The CJEU decision also drew into question the long-term viability of an alternative means of data transfer, the standard contractual clauses, for transfers of personal data from the EEA to the United States. Following the July 2020 Court of Justice of the EU judgment invalidating the so-called EU-U.S. Privacy Shield, the EC adopted an adequacy decision for the EU-U.S. Data Privacy Framework in July 2023. This adequacy decision permits U.S. companies who self-certify under the EU-U.S. Data Privacy Framework to rely on it as a valid data transfer mechanism for data transfers from the EU to the United States. However, some privacy advocacy groups have already suggested that they will be challenging the EU-U.S. Data Privacy Framework, and there is currently one pending litigation against the EU-U.S. Data Privacy Framework before the Court of Justice of the EU (CJEU), C-703/25 P - Latombe v Commission. If these challenges are successful, they may not only impact the EU-U.S. Data Privacy framework, but also further limit the viability of the so-called standard contractual clauses and other data transfer mechanisms.

Following the withdrawal of the United Kingdom from the EU, the U.K. Data Protection Act applies to the processing of personal data that takes place in the United Kingdom and includes parallel obligations to those set forth by GDPR. The United Kingdom government has determined that it considers all EU member states and EEA member states to be adequate for the purposes of data protection, ensuring that data flows from the United Kingdom to the EU/EEA remain unaffected. Further, the EC decided in June 2021 that the level of data protection in the United Kingdom is “essentially adequate” for purposes of data transfer from the EU to the United Kingdom. On December 19, 2025, the EC renewed this decision until December 27, 2031. The United Kingdom and the United States have also agreed to a U.S.-U.K. “Data Bridge,” which functions similarly to the EU-U.S. Data Privacy Framework and provides an additional legal mechanism for companies to transfer personal data from the United Kingdom to the United States.

Beyond GDPR, there are privacy and data security laws in a growing number of countries around the world. While many loosely follow GDPR as a model, other laws contain different or conflicting provisions. These laws will impact our ability to conduct our business activities, including both our clinical trials and any eventual sale and distribution of commercial products.

Review and Approval of Biologics and Drug Products Outside the United States

In addition to regulations in the United States, we are subject to a variety of foreign regulations governing clinical trials and commercial sales and distribution of our products outside of the United States. Whether or not we obtain FDA approval for a product candidate, we must obtain approval by the comparable regulatory authorities of foreign countries or economic areas, such as the EU, before we may commence clinical trials or market products in those countries or areas. In the EU, our product candidates also may be subject to extensive regulatory requirements. As in the United States, medicinal products can be marketed only if a marketing authorization from the competent regulatory agencies has been obtained. Similar to the United States, the various phases of preclinical and clinical research in the EU are subject to significant regulatory controls.

With the exception of the EU and European Economic Area, or EEA, applying the harmonized regulatory rules for medicinal products, the approval process and requirements governing the conduct of clinical trials, product licensing, pricing and reimbursement vary greatly between countries and jurisdictions and can involve additional testing and additional administrative review periods. The time required to obtain approval in other countries and jurisdictions might differ from and be longer than that required to obtain FDA approval. Regulatory approval in one country or jurisdiction does not ensure regulatory approval in another, but a failure or delay in obtaining regulatory approval in one country or jurisdiction may negatively impact the regulatory process in others.

Employees and Human Capital Resources

As of February 28, 2026, we had 76 full-time employees, including 30 employees with M.D., Pharm.D. or Ph.D. degrees. Of these full-time employees, 54 were engaged in research and development activities and 22 were engaged in general and administrative activities. None of our employees is represented by a labor union or covered by a collective bargaining agreement. We consider our relationship with our employees to be good.

Our human capital resources objectives include, as applicable, identifying, recruiting, retaining, incentivizing and developing our existing and additional employees. We are committed to equal opportunity and inclusion across all aspects of our organization, including in our recruitment, advancement and development practices. We conduct annual performance and development reviews for each of our employees to discuss the individual’s strengths and development opportunities, career development goals and performance goals. We also regularly survey employees to assess employee engagement and satisfaction. In addition, each regular full-time employee is provided an allowance and time to attend appropriate job-related trainings and other professional development courses, seminars, meetings, and similar sessions.

The principal purposes of our equity incentive plans are to attract, retain and motivate selected employees, consultants and directors through the granting of stock-based compensation awards. We value our employees and regularly benchmark total rewards we provide, such as short- and long-term compensation, 401(k) contributions, tuition reimbursement, health, welfare and quality of life benefits, paid time off and personal leave, against our industry peers to ensure we remain competitive and attractive to potential new hires.

Corporate Information

We are a Delaware corporation that was incorporated on June 18, 2020 under the name Xilio Therapeutics, Inc. We maintain a website at the following address: www.xiliotx.com. The information contained on, or that can be accessed through, our website is not incorporated by reference into this Annual Report on Form 10-K or in any other report or document we have filed or may file with the Securities and Exchange Commission, or SEC, and any reference to our website address is intended to be an inactive textual reference only.

We make available on or through our website certain reports and amendments to those reports that we file with or furnish to the SEC in accordance with the Securities Exchange Act of 1934, as amended, or the Exchange Act. These include our Annual Reports on Form 10-K, our Quarterly Reports on Form 10-Q and our Current Reports on Form 8-K. We make this information available on our website free of charge as soon as reasonably practicable after we electronically file the information with, or furnish it to, the SEC. In addition, we routinely post on the “Investors & Media” page of our website investor and scientific presentations, SEC filings, press releases, public conference calls and webcasts and other statements about our business and results of operations, some of which may contain information that may be deemed material to investors. Accordingly, investors should monitor these portions of our website, in addition to following our press releases, SEC filings, public conference calls and webcasts, as well as current or future social media channels (including LinkedIn). This list of channels may be updated from time to time on our investor relations website and may include other social media channels than the one described above. The contents of our website or these channels, or any other website that may be

accessed from our website or these channels, shall not be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended.

The SEC maintains a website that contains reports, proxy and information statements, and other information regarding issuers that file electronically with the SEC at the following address: http://www.sec.gov.