NASDAQ: RGNX

•
Surabgene lomparvovec (sura-vec, ABBV-RGX-314), which we are developing in collaboration with AbbVie to treat large patient populations impacted by wet age-related macular degeneration (wet AMD) and diabetic retinopathy (DR).

2

Table of Contents

•
RGX-202, which we are developing to treat Duchenne muscular dystrophy (Duchenne), one of the most common fatal genetic disorders affecting children.

•
RGX-121 (clemidsogene lanparvovec) and RGX-111, which we are developing and plan to commercialize with Nippon Shinyaku to treat Mucopolysaccharidosis type II (MPS II) and Mucopolysaccharidosis type I (MPS I), both of which are progressive, neurodegenerative lysosomal storage disorders.

Our internal pipeline is shown below.

Since our founding, we have built a team of experts in research and development, preclinical and clinical development, scalable manufacturing and commercialization, enabling us to have integrated, end-to-end capabilities. We believe AAV therapeutics represent a simplified and efficient potential new class of innovative medicines. Our experience and expertise distinguish us from other gene therapy companies and will help ensure value generation and our continued growth.

AAV Therapeutics

Historically, the primary challenge for gene therapy has been the safe and effective delivery of genes into cells. To address this challenge, scientists designed and developed a variety of gene vectors to facilitate gene delivery into cells.

Our gene therapies are designed to deliver working genes to cells using AAV vectors as the delivery “vehicles.” We chose AAV vectors, modified viruses that cannot increase their numbers or reproduce themselves, based on several factors including their demonstrated efficiency in gene delivery to date and promising safety profiles for gene therapy.

Since our inception, we have built and advanced multiple promising gene therapies into late-stage clinical development. All of our gene therapies were built on our NAV Technology Platform. Together, with our in-house, U.S.-based manufacturing and end-to-end capabilities, we are excited about the prospect of bringing these assets to commercial stage and continuing to leverage our NAV Technology Platform to generate additional promising gene therapies.

Our NAV Technology Platform

In 2009, we acquired exclusive rights to our NAV Technology Platform. Our NAV Technology Platform includes over 100 NAV Vectors, as well as vectors that are at least 95% identical to any NAV Vector, that provide the foundation for the development of new AAV therapeutics. We have observed that several of our NAV Vectors demonstrate preferential tropisms for a range of tissues, as well as efficient transgene delivery and expression that may produce a therapeutic effect. Our NAV Technology Platform has enabled the development of a number of gene therapies being investigated in clinical trials and two that are FDA-approved.

3

Table of Contents

For many years, by sublicensing NAV Vectors from our NAV Technology Platform to other biopharmaceutical companies with disease-specific expertise, which we refer to as our NAV Technology Licensees, we received capital to advance our own research and capabilities. Our NAV Technology Platform is being applied to a number of programs over a broad range of therapeutic areas and disease indications by our NAV Technology Licensees. These partnered programs include Novartis’ Zolgensma® and Itvisma® gene therapies for the treatment of spinal muscular atrophy (SMA), a debilitating and potentially deadly disease. Zolgensma was approved by the U.S. Food and Drug Administration (FDA) in 2019 for the treatment of SMA in patients under the age of two years old, and Itvisma was approved by the FDA in November 2025 for the treatment of SMA in patients two years and older. Together, Zolgensma and Itvisma have been used to treat thousands of patients suffering from SMA. Our partnering strategy provides us the flexibility to sublicense development of treatments designed to address significant unmet medical needs, while remaining focused on our own pipeline of gene therapies.

We believe we have extensive human safety experience to support the development of our investigational AAV therapeutics based on data from thousands of patients dosed with AAV therapeutics derived from our NAV Technology Platform in two FDA approved products and numerous clinical stage programs. To date, we have observed that AAV therapeutics derived from our NAV Technology Platform have been generally well tolerated.

Our AAV Platform

Discovery and Development

We have a team of scientists and engineers dedicated to expanding the understanding and applications of AAV vectors, applying the differentiated capabilities of the NAV Technology Platform and exploring the potential to generate new, innovative AAV therapeutics. We endeavor to rapidly discover and develop a pipeline of investigational AAV therapeutics with the potential, through a single administration, to alter the course of disease significantly and deliver improved patient outcomes with long-lasting effects. We believe that we have created a reproducible process and modular platform for the discovery and development of innovative AAV therapeutics.

Our scientists are researching and evaluating NAV Vectors to identify and characterize new features that may be more clinically effective by improving tissue tropism and specificity, de-targeting the liver, increasing transduction efficiency and requiring a lower dose.

We are also discovering and engineering novel capsids by leveraging the natural diversity of our NAV Vectors and our detailed knowledge of AAV structure and function. Leveraging an AI-powered engineering platform, we are generating new capsids with the potential to improve efficacy at lower doses.

We are designing new NAV Vectors with new features that may enhance tissue and cell type specificity, increase potency and potentially improve the safety profile of AAV therapeutics. Through our internal efforts and collaborations, we are also designing novel vectors to which we add high affinity targeting domains with the goal of enabling them to deliver genes more precisely to specific tissues and cells.

With AAV therapeutics, the transgene is eventually transported to the cell nucleus where it is transcribed into RNA. The production of RNA in the cell is controlled by transcriptional elements called enhancers and promoters that are linked to the gene. We have designed optimized enhancer and promoter combinations with the goal of enabling sustained gene expression in particular cell types and potentially increasing the durability of therapeutic effect.

We can design our AAV therapeutics to deliver transgenes encoding a spectrum of therapeutic modalities. Our current pipeline of investigational AAV therapeutics uses NAV Vectors to deliver transgenes encoding therapeutic antibodies, or able to compensate for a missing or non-functional gene.

We also conduct research studying the potential of NAV Vectors to deliver small RNAs, such as microRNA (miRNA) or antisense sequences, which could alter the structure or silence an RNA transcript. We have created a platform for designing efficient small RNA scaffolds to address targets of interest while avoiding off-target effects and cellular toxicity. In addition, NAV Vectors have been designed to enable in vivo gene editing, which involves the alteration of a gene via targeted insertion or deletion of DNA base pairs.

4

Table of Contents

In addition to our research evaluating NAV Vectors, we also work on identifying potential indications for the development of new AAV therapeutics, guided by our expertise and experience in bringing AAV therapeutics to the clinical stage. Our early evaluation of targets includes scientific rationale and cross-functional analysis of technical feasibility. In our exploratory research, we work internally and through collaborations with external researchers to identify and optimize AAV therapeutics based on AAV vector targeting, transgene optimization and evaluation of effective delivery devices. We then execute proof-of-concept research that informs the next steps in our pipeline strategy. While much of our research into potential AAV therapeutics extends from our clinical expertise in eye diseases, AAV-mediated antibody delivery, neurodegenerative diseases and neuromuscular diseases, we are also able to research potential opportunities to advance AAV therapeutics for new disease areas.

Our platform capabilities include a team of scientists that develop analytical assays and approaches to support our preclinical and clinical-stage pipeline. The ability to determine dose levels, biodistribution, and target engagement requires an understanding of complex variables that are related to properties of both the NAV Vector and the gene, and dependent on the delivery device. We believe that our analytical capabilities are at the forefront of AAV Therapeutic development.

AAV Therapeutic Manufacturing

We have invested in innovative manufacturing process development and analytical capabilities and use a suspension cell culture-based manufacturing process. We have deep in-house knowledge of biologics and gene therapy manufacturing, which has enabled us to scale manufacturing of our AAV therapeutics while ensuring product quality for patients and improving cost-of-goods. We have developed systems which we believe will provide robust manufacturing and global supply of AAV therapeutics to meet quality requirements and anticipated research, clinical and future commercial demand. Our Good Manufacturing Practices (cGMP) production facility, the REGENXBIO Manufacturing Innovation Center (RMIC), is located in our corporate headquarters in Rockville, Maryland. The RMIC was designed to support clinical and future commercial production of AAV therapeutics and has been in operation since mid-2022. In 2025, the FDA completed a pre-license inspection (PLI) and bioresearch monitoring (BIMO) inspection as part of the RGX-121 Biologics License Application (BLA) with no observations.

We have developed a proprietary, high-yielding manufacturing process platform for NAV vector production (NAVXpress®) that can be applied across multiple AAV therapeutics. This manufacturing process platform approach improves development efficiency and shortens timelines by leveraging data across multiple programs. The suspension-based manufacturing platform has demonstrated robust scalability from bench-scale to 500 liter and 1,000-liter cGMP batches with consistent yield and product purity demonstrated via comparability studies. At the RMIC facility, we have demonstrated the ability to scale the manufacturing process up to 2,000 liters.

We believe NAVXpress enables consistent, rapid, and reliable manufacturing across programs, addressing key challenges in advancing gene therapies to market and at scale. The NAVXpress manufacturing process is fully characterized, and we have completed full-scale process validation across three of our late-stage programs to support the RGX-121 BLA and future BLA submissions.

We have designed custom starting materials for use in the NAVXpress platform, including plasmids and cell lines, that increase the efficiency and productivity of NAV vectors. We have demonstrated that these cell lines, named NAVXcell®, enable high-yielding production processes while allowing for efficient purification.

We have developed product formulations specific to our different delivery devices and routes of administration. We aim to ensure that our formulations are designed and assessed to ensure product stability can be maintained for numerous years and that our AAV therapeutics can be exposed to a variety of handling and delivery procedures.

We have endeavored to design our platform manufacturing process, formulations and devices to enable efficient transition from research to clinical trials to commercial readiness, while minimizing changes during product development. To support our platform, we have developed a comprehensive set of analytical methods to assess quality and characterize the product. We continue to expand and enhance internal analytical lab capabilities with the aim of improving quality and control and supporting accelerated development of AAV therapeutics.

The close collaboration of our research and manufacturing teams allows us to evaluate the manufacturability of AAV therapeutics early in the discovery process and move quickly from candidate selection to the manufacturing of clinical-grade material. We believe this allows us to accelerate the process of developing AAV therapeutics.

5

Table of Contents

AAV Therapeutic Delivery Devices

We believe that a critical component of AAV Therapeutic development is to deliver treatments safely, effectively and efficiently to the right part of the body. We leverage the differentiated characteristics of NAV Vectors to target different tissues and cells. To further enhance the profile of AAV therapeutics, we have developed a platform of different devices to assist in the delivery of AAV therapeutics using multiple routes of administration to tissues and cells.

We have developed significant expertise in designing delivery device systems for use with AAV therapeutics and have also developed and in-licensed relevant intellectual property, including know-how, related to delivery devices. Our research and development activities have involved several delivery device advancements for AAV therapeutics. We focus research on designing features and implementing delivery device solutions that we believe have the potential to improve the effect, patient safety and caregiver usability of AAV therapeutics.

We leverage and support the advancement of innovative devices to deliver our investigational gene therapies using multiple routes of administration, including to the central nervous system and subretinal and suprachoroidal regions of the eye. As part of our delivery device expertise, we have created teams of experts to support and train physicians to deliver AAV therapeutics in operating room and physician office settings.

In recent years, a tremendous amount of progress has been made in the development of gene therapies, and we believe we are a leader in these advancements.

Our Investigational AAV Therapeutics

We are currently focusing our internal development pipeline in three areas: retinal diseases, neuromuscular diseases and neurodegenerative diseases.

Sura-vec (ABBV-RGX‑314) for the Treatment of Wet AMD and DR

We are developing surabgene lomparvovec (sura-vec, ABBV-RGX‑314) in collaboration with AbbVie as a potential one-time treatment for wet AMD and DR. These diseases are characterized by loss of vision due to excess fluid accumulation from new blood vessel formation and treated with anti-vascular endothelial growth factor (anti-VEGF) therapies.

Wet AMD is the leading cause of vision loss in people over 60, affecting more than two million patients in the United States, Europe and Japan. The risk for developing wet AMD increases with age and we anticipate that the incidence of new cases will continue to increase significantly with the growth of an aging population. In patients with wet AMD, fluid accumulation can result in physical changes in the structure of the retina and adverse changes in vision. As this process progresses, blindness can result from atrophy and scar formation.

DR is a complication of diabetes and is the leading cause of blindness in adults between 24 and 75 years of age worldwide. It is a progressive retinopathy, and the spectrum of DR severity ranges from non-proliferative diabetic retinopathy (NPDR) to proliferative diabetic retinopathy (PDR). As DR progresses, a large proportion of patients develop vision-threatening complications, including diabetic macular edema (DME) and neovascularization that can lead to blindness. An estimated 27 million patients are affected with DR across the U.S., Europe and Japan, and of those, there are more than 23 million DR patients without center-involved DME. DR is the leading cause of vision loss in working-age adults and the incidence is expected to continue to grow significantly with the prevalence of diabetes.

Frequent anti-VEGF injections in the eye have been shown to reduce the risk of blindness in randomized controlled clinical trials and are approved for the treatment of wet AMD and DR. The current standard-of-care anti-VEGF treatments require patients to receive injections in the eye every four to 16 weeks for the duration of the disease. Real world evidence shows that patients with wet AMD are severely undertreated, and DR patients with early non-proliferative disease are often not treated due to the unsustainable treatment burden of administering frequent injections required with currently approved anti-VEGF therapies. As a result, the majority of wet AMD patients experience significant vision loss over time and most patients with early non-proliferative DR progress to more severe forms of the proliferative disease, developing common vision-threatening complications such as center-involved DME and proliferative DR.

6

Table of Contents

Sura-vec is being developed as a novel, one-time treatment that includes the NAV AAV8 vector containing a gene for a monoclonal antibody fragment designed to inhibit VEGF activity, modifying the pathway for formation of new leaky blood vessels and retinal fluid accumulation. After delivery of sura-vec, we believe retinal cells will continue to produce the anti-VEGF protein. Two separate routes of administration of sura-vec to the eye are being evaluated: a subretinal delivery procedure as well as a targeted, in-office administration to the suprachoroidal space. We have licensed certain exclusive rights to the SCS Microinjector® from Clearside Biomedical, Inc. (Clearside) to deliver gene therapy treatments to the suprachoroidal space of the eye.

Sura-vec is currently being evaluated in multiple clinical trials, including two pivotal trials (ATMOSPHERE and ASCENT), one Phase II bridging study, one long-term follow-up study and a fellow eye sub-study in patients with wet AMD, all utilizing subretinal delivery. Additionally, two Phase II clinical trials in patients with wet AMD (AAVIATE) and DR (ALTITUDE) are ongoing along with two corresponding long-term follow-up studies, all utilizing in-office suprachoroidal delivery. Within the Phase II study in DR, we are also evaluating ABBV-RGX-314 in diabetic macular edema (DME). Additionally, we are planning a Phase IIb/III program in DR and expect to dose the first patient in a two-part Phase IIb/III study (NAAVIGATE) in the second quarter of 2026.

Clinical Development of Sura-vec Subretinal Delivery for the Treatment of Wet AMD

We have two ongoing pivotal trials, ATMOSPHERE® and ASCENT®, for the treatment of wet AMD using sura-vec (ABBV-RGX-314) delivered subretinally.

ATMOSPHERE and ASCENT are multi-center, randomized, active-controlled pivotal trials to evaluate the efficacy and safety of a single-administration of sura-vec versus standard of care in patients with wet AMD. Enrollment in both trials completed in October 2025. To support future commercialization of sura-vec, the cGMP material produced by our NAVXpress platform process has been incorporated in the ongoing pivotal trials, ATMOSPHERE and ASCENT, for the treatment of wet AMD using sura-vec delivered subretinally.

These trials are expected to support global regulatory submissions, including with the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA). Over 1,200 participants enrolled in ATMOSPHERE and ASCENT combined. We expect topline data from these trials to be shared in the fourth quarter of 2026.

In October 2022, we announced data from the Phase I/IIa long-term follow-up study of sura-vec for the treatment of wet AMD using subretinal delivery (n=37). Results show that sura-vec demonstrated to be generally well-tolerated (nine SAEs were reported in four patients, none of which were considered related to sura-vec) and patients treated with sura-vec demonstrated a durable treatment effect up to four years in Cohort 3 and up to three years in Cohort 4. Stable to improved visual acuity was observed, with a mean BCVA of +12 letters from baseline at four years for Cohort 3 patients and -5 letters from baseline at three years for Cohort 4 patients following sura-vec administration.

Two-year findings from this study were published in The Lancet in March 2024, in a paper titled "Gene therapy for neovascular age-related macular degeneration by subretinal delivery of RGX-314: a phase 1/2a dose-escalation study".

In July 2025, we presented final one-year data at the American Society of Retinal Specialists annual meeting from the Phase II pharmacodynamic study designed to evaluate the same dose levels being used in the two pivotal trials. Results support the dose levels demonstrated similar clinical profiles. As of October 21, 2024, sura-vec manufactured using REGENXBIO's NAVXpress platform process was well tolerated at both dose levels with no drug-related serious adverse events (SAEs). At one year, at both dose levels, participants receiving sura-vec demonstrated stable to improved best corrected visual acuity and central retinal thickness, as well as meaningful reductions in anti-VEGF burden in participants with high treatment burden, with the majority remaining injection-free.

In June 2025, we reported one-year results from the Phase II fellow eye sub-study Clinical Trials at the Summit. The sub-study evaluated subretinal delivery of sura-vec in patients who received sura-vec in the Phase I/IIa or bridging studies and elected to receive treatment in their second eye. As of May 26, 2025, sura-vec was well tolerated in the treated second eye with no drug-related serious adverse events and no cases of intraocular inflammation observed. At 12 months post-administration, patients saw a 93% reduction in anti-VEGF treatment burden and sustained vision and anatomy. We believe these data demonstrate the potential of sura-vec to preserve vision long-term for patients with wet AMD as a one-time treatment for both eyes. Bilateral disease impacts a significant number of patients with wet AMD.

7

Table of Contents

Clinical Development of Sura-vec Suprachoroidal Delivery for the Treatment of Wet AMD

We are also evaluating the efficacy, safety and tolerability of suprachoroidal delivery of sura-vec through AAVIATE®, a multi-center, open label, randomized, controlled, dose-escalation Phase II trial of sura-vec for the treatment of wet AMD.

In January 2024, we announced data from the AAVIATE trial demonstrating that patients treated with sura-vec continue to demonstrate stable BCVA and CRT at six months. In addition, a meaningful reduction in anti-VEGF treatment burden was observed following administration of sura-vec. The highest reduction was seen in dose level 3, demonstrating an 80% reduction in annualized injection rate with 50% of patients remaining injection-free.

As of July 29, 2024, sura-vec at dose level 3 with short course prophylactic steroid eye drops continued to be well tolerated with no drug-related serious adverse events (SAEs) and no cases of intraocular inflammation, endophthalmitis, vasculitis, retinal artery occlusion, choroidal effusion, or hypotony. Mild episcleritis occurred in three patients, all resolved and completed treatment with topical steroids. There were no cases of elevated intraocular pressure. Based on this favorable safety profile, the Phase II AAVIATE trial also enrolled a cohort to evaluate sura-vec at dose level 4 (1.5x10e12 GC/eye). Patients in this cohort also received short course prophylactic steroid eye drops.

Clinical Development of Sura-vec Suprachoroidal Delivery for the Treatment of DR

We are evaluating the efficacy, safety and tolerability of suprachoroidal delivery of sura-vec for the treatment of DR. In August 2025, we announced 2-year results from ALTITUDE®, a multi-center, open label, randomized, controlled, dose-escalation Phase II trial evaluating patients with non-proliferative DR (NPDR) who received a single, in-office injection of sura-vec.

As of June 9, 2025, sura-vec was well tolerated at dose levels 1, 2 and 3, with no drug-related SAEs. No intraocular inflammation was observed through two years at dose level 3 (1.0x10e12 GC/eye) (n=15) with short-course topical prophylactic steroids. Additionally, NPDR patients that received sura-vec demonstrated durable, long-term efficacy. Sura-vec demonstrated a dose-dependent increased rate of meaningful improvement as measured by the Early Treatment Diabetic Retinopathy Study-Diabetic Retinopathy Severity Scale, with 50% of dose level 3 patients achieving at least a two-step improvement without the need for any supplemental treatment. We also reported that dose level 3 patients achieved an over 70% reduction in the risk of vision threatening events compared to historical control.

Based on these results, we announced we will initiate a pivotal Phase IIb/III trial evaluating sura-vec in subjects with NPDR without center-involved DME, and a corresponding amendment to our eyecare collaboration with AbbVie. We are activating clinical sites for a Phase IIb/III double-masked sham injection controlled trial. We expect to dose the first patient in the second quarter of 2026.

The Phase II ALTITUDE trial also includes a cohort of patients with center-involved DME. Enrollment completed in this cohort in June 2025. DME is a vision-threatening complication of DR. Patients will receive a one-time, in-office injection of sura-vec dose level 4 (1.5x10e12 GC/eye) with short course prophylactic steroid eye drops.

RGX-202 for the Treatment of Duchenne

We believe that RGX-202 has the potential to serve as a second-to-market, differentiated gene therapy treatment for Duchenne.

RGX-202 is our investigational AAV Therapeutic for the treatment of Duchenne, a rare disease caused by mutations in the gene responsible for making dystrophin, a protein of central importance for muscle cell structure and function. Without dystrophin, muscles throughout the body degenerate and become weak, eventually leading to loss of movement and independence, required support for breathing, cardiomyopathy and premature death. There is presently no cure for Duchenne, and there is a significant unmet need for disease modifying treatment options. Duchenne is one of the most common fatal genetic disorders affecting children, primarily boys. Duchenne is estimated to occur in approximately one in every 3,500-5,000 live male births and has an estimated prevalence of more than 30,000 cases in the U.S., Europe and Japan.

8

Table of Contents

RGX-202 is designed to deliver a transgene for a novel microdystrophin that includes the functional elements of the C-Terminal (CT) domain found in naturally occurring dystrophin. Presence of the CT domain has been shown in preclinical studies to recruit several key proteins to the muscle cell membrane, leading to improved muscle resistance to contraction-induced muscle damage in dystrophic mice. Additional design features may potentially improve gene expression, increase translational efficiency and reduce immunogenicity. RGX-202 is designed to support the delivery and targeted expression of the transgene throughout skeletal and heart muscle using the NAV AAV8 vector, and a well-characterized muscle-specific promoter (Spc5-12).

We have received orphan drug product, Fast Track designation and rare pediatric disease designation from the FDA for RGX‑202.

Clinical Development of RGX-202

AFFINITY DUCHENNE® is a multicenter, open-label Phase I/II/III trial evaluating two dose levels (1x1014 GC/kg and 2x1014 GC/kg) of RGX-202 in ambulatory patients aged one and older. The pivotal phase of the trial, evaluating dose level 2, is fully enrolled (n=30) and expected to support a BLA submission using the accelerated approval pathway in 2026.

In November 2024, we reported positive interim safety and efficacy data from the Phase I/II portion of the trial. This included a favorable safety profile at both dose levels among the first eleven patients, with no adverse events (AEs) or series adverse events (SAEs) reported, positive RGX-202 microdystrophin expression results for the first nine patients, with all patients exceeding 10% expression, and positive functional outcomes from the first five Phase I/II participants. Functional results included 12-month data from three dose level 1 patients aged 4-10 and nine-month data from two dose level 2 (pivotal dose) patients aged 8 and 12. In all five participants, across both dose levels, RGX-202 demonstrated evidence of positively impacting disease trajectory, with patients demonstrating stable or improved function on NSAA and timed function tests including time to stand, 10 meter walk/run and time to climb. Results were measured against external natural history controls matched for age and baseline function.

Through January 2026, subsequent interim data from the Phase I/II study was presented and was generally consistent with the positive initial findings. Results reported in June 2025 demonstrated a continued favorable safety profile with no SAEs or adverse events of special interest (AESI) reported (n = 13), positive safety data including consistent, robust microdystrophin expression and transduction across all treated ages (n = 12) and positive interim functional results from all dose level 2 recipients at 9 and 12 months (all dose level 2 participants exceeded external natural history controls on all functional measures). Additional positive data evaluating individual patient North Star Ambulatory Assessment (NSAA) using the established cTAP disease progression model results at 12 months were presented in October 2025 (at the 2025 International Congress of the World Muscle Society) and at 18 months in January 2026 (via a company announcement). As of January 5, 2026, RGX-202 was well tolerated in the Phase I/II trial, with no SAEs or AESIs.

The pivotal portion of AFFINITY DUCHENNE is ongoing and we expect to report topline data from the ongoing pivotal study of AFFINITY DUCHENNE in early second quarter of 2026. To support potential accelerated approval, the primary endpoint of the pivotal trial is the proportion of participants whose RGX-202 microdystrophin expression is ≥ 10% at Week 12. Secondary endpoints include change from baseline on timed function tests including time to stand, 10 meter walk/run and time to climb in participants ages 4 and older. Participants aged 1 to < 4 years will be evaluated using the Peabody Developmental Motor Scale-Third Edition and stride velocity 95th centile. Patients will be assessed on the North Star Ambulatory Assessment (NSAA) as an exploratory endpoint. We expect to request a pre-BLA meeting with the FDA based on this data in mid-2026. Additional regulatory interactions with the FDA and European Medical Association (EMA) are planned for the first half of 2026. We are recruiting patients (n=30) in the confirmatory portion of the AFFINITY DUCHENNE trial of RGX-202.

Additionally, preclinical results comparing a microdystrophin gene therapy construct that included the C-terminal (CT) domain, which is included in the RGX-202 construct, to a microdystrophin construct without the CT domain which were published in Molecular Therapy Methods and Clinical Development in July 2025. The results showed that the microdystrophin with the CT domain improved functional benefit compared to the microdystrophin without, supporting the potential of RGX-202 to drive functional improvements in patients with Duchenne Muscular Dystrophy.

RGX-202 is manufactured using our proprietary, high-yielding NAVXpress platform process. This suspension-based manufacturing process has demonstrated scalability up to 2,000 liters with consistent yield and product purity. The RMIC has the capacity and yields to produce up to 2,500 doses of RGX-202 per year to support future commercialization. We began manufacturing

9

Table of Contents

the first batches of RGX-202 intended for commercial supply at the RMIC and completed the Process Performance Qualification (PPQ) campaign in the fourth quarter of 2025.

Additionally, we are recruiting patients in the AFFINITY BEYOND® trial, an observational screening study. The primary objective of AFFINITY BEYOND is to evaluate the prevalence of AAV8 antibodies in patients with Duchenne up to 12 years of age. Information collected in this study may be used to identify potential participants for the AFFINITY DUCHENNE trial and potential future trials of RGX-202.

RGX‑121 for the Treatment of MPS II

RGX‑121 (clemidsogene lanparvovec) is our investigational AAV Therapeutic for the treatment of MPS II, which we are developing in collaboration with Nippon Shinyaku in the U.S. and certain countries in Asia. MPS II, also known as Hunter syndrome, is a rare disease caused by mutations in the gene responsible for making iduronate-2-sulfatase (IDS), which encodes the I2S enzyme. The I2S enzyme is responsible for the breakdown of the polysaccharides heparan sulfate (HS) and dermatan sulfate in lysosomes, structures that dispose of waste products inside cells. These polysaccharides, called glycosaminoglycans (GAGs), accumulate in tissues of MPS II patients, resulting in diverse clinical signs and symptoms. HS is a key biomarker of I2S enzyme activity and high amounts of HS accumulate in the central nervous system (CNS) of neuronopathic MPS II patients, which has been shown to correlate with neurocognitive manifestations of the disease. In severe forms of the disease, early developmental milestones may be met during the first year after birth, but developmental delay is readily apparent by 18 to 24 months. Developmental progression begins to plateau between three and five years of age, with regression reported to begin around six and a half years. By the time of death, most patients with CNS involvement are severely mentally handicapped and require constant care. MPS II is estimated to occur in approximately 1 in 100,000 to 1 in 170,000 births worldwide. Based on global population, this equates to approximately 500 to 1,000 MPS II patients born each year worldwide.

Enzyme replacement therapy (ERT), the current standard of care for patients with MPS II, does not treat CNS manifestations of the disease because the enzyme cannot cross the blood-brain barrier. We believe that specific treatment to address the neurological manifestations of MPS II and prevent or stabilize cognitive decline remains a significant unmet medical need.

RGX‑121 is designed to use the NAV AAV9 vector to deliver the human IDS gene to cells in the CNS. Delivery of the gene therapy and expression of the enzyme that is deficient within cells in the CNS could provide a permanent source of secreted I2S enzyme on the CNS side of the blood-brain barrier, allowing for long-term cross-correction of cells throughout the CNS. We believe this strategy could provide rapid I2S enzyme delivery to the brain, potentially preventing the progression of cognitive deficits that otherwise occur in MPS II patients.

We have received orphan drug product designation, rare pediatric disease designation, regenerative medicine advanced therapy (RMAT) and Fast Track designation from the FDA, as well as orphan designation and advanced therapy medicinal products (ATMP) classification from the EMA for RGX‑121.

Clinical Development of RGX‑121 for the Treatment of MPS II

CAMPSIITE® is a Phase I/II/III multicenter, open-label trial enrolling boys with MPS II, aged 4 months up to 5 years of age.

In February 2024, we reported that the pivotal phase of the CAMPSIITE trial achieved its primary endpoint, proportion of patients with cerebrospinal fluid (CSF) D2S6 below maximum attenuated level at W16. Accurate and sensitive measurements of CSF GAGs, such as HS D2S6, have the potential to be considered a surrogate endpoint that is reasonably likely to predict clinical benefit in MPS II disease under the accelerated approval pathway, as buildup of GAGs in the CSF of MPS II patients correlates with clinical manifestations including neurodevelopmental deficits. MPS II patients treated with RGX-121 achieved decreased CSF levels of D2S6 below maximum attenuated disease levels at 16 weeks (p value of 0.00016). Patients receiving RGX-121 demonstrated an 86% median reduction in D2S6, approaching normal levels. Initial pivotal results were consistent with data from the dose-finding phase of CAMPSIITE, in which the majority of patients were shown to be exceeding expectations in neurodevelopmental function compared to natural history data up to four years.

In June 2024, we announced the completion of a successful pre-BLA meeting for RGX-121, where we finalized details of our BLA with FDA. In that announcement, we shared that the FDA continued to be aligned with our plan to use CSF levels of HS D2S6 as a surrogate endpoint reasonably likely to predict clinical benefit to support accelerated approval of RGX-121.

10

Table of Contents

In September 2024, we reported long term data showing that patients receiving RGX-121 at the pivotal dose level demonstrated an 85% median reduction of CSF levels of HS D2S6 approaching normal levels and sustained for up to two years. In the dose-finding part of the trial, investigators chose to discontinue standard-of-care intravenous enzyme replacement therapy (ERT) or to remain ERT-naïve for a majority of patients. At the pivotal dose level (dose level 3), 80% of patients were ERT-free at last time point, up to more than 18 months post-dosing. At dose level 2, 71% of patients were ERT-free at last time point, up to almost three years.

In January 2025, we announced a strategic partnership with Nippon Shinyaku to develop and commercialize RGX-121 and RGX-111 in the United States and certain countries in Asia. For more information, refer to "Nippon Shinyaku Partnership for MPS Diseases" below.

In March 2025, we submitted a BLA for RGX-121 seeking accelerated approval to the FDA, which we believe is likely to be eligible for priority review. In August 2025, the FDA completed a pre-license inspection and bioresearch monitoring information inspection for the RGX-121 BLA with no observations. Also in August 2025, we announced the FDA had extended its review timeline of the RGX-121 BLA following the Company's submission of longer-term clinical data for all patients in the pivotal study of RGX-121 (n=13) in response to an FDA information request, resulting in an extension of the Prescription Drug User Fee Act (PDUFA) date from November 9, 2025 to February 8, 2026. These positive 12-month clinical data, which were consistent with biomarker and neurodevelopmental data previously submitted on the same patients in the BLA, were presented during the International Congress of Inborn Errors of Metabolism (ICIEM) in September 2025.

In January 2026, we announced that the FDA placed the RGX-121 program on clinical hold in relation to a serious adverse event in a patient treated in the Phase I/II trial of RGX-111. The FDA cited the similarities in products, study populations, and shared risk between the clinical studies. For more information, refer to the “Clinical Development of RGX-111 for the Treatment of MPS I” below.

In February 2026, we announced that the FDA issued a Complete Response Letter (CRL) for the RGX-121 BLA. The FDA stated in the CRL that it had agreed to the study protocol in principle and outlined several reasons for not approving the gene therapy, including uncertainty regarding the study eligibility criteria to adequately define a population with neuronopathic disease (vs. attenuated disease), the comparability of the natural history external control to the study population, and the appropriateness of CSF HS D2S6 as a surrogate endpoint reasonably likely to predict clinical benefit. The CRL lists several potential paths forward, including a new study, treating additional patients and conducting longer-term follow up, and using an untreated control arm. Throughout active discussions during the BLA process, we believed we had addressed the points raised in the CRL through the submission of additional data and responses to numerous information requests. The FDA did not agree the data set provided substantial evidence of effectiveness to support approval of RGX-121 for the treatment of MPS II. We plan to request a Type A meeting with the FDA.

As of March 2026, we plan to work with the FDA to address the clinical holds and CRL, and discuss potential paths forward for the program. Potential approval of the BLA for RGX-121 could result in receipt of a Rare Pediatric Disease Priority Review Voucher, assuming the statutory criteria are met. If approved, RGX-121 is expected to be the first approved gene therapy and one-time treatment for MPS II.

RGX‑111 for the Treatment of MPS I

RGX-111 is our investigational AAV Therapeutic for the treatment of MPS I, a rare disease caused by deficiency of IDUA, an enzyme required for the breakdown of polysaccharides in lysosomes. Like RGX-121, this program is included our strategic partnership with Nippon Shinyaku to develop and commercialize RGX-121 and RGX-111 in the United States and certain countries in Asia.

Similar to MPS II, many MPS I patients develop symptoms related to GAG accumulation in the CNS, which can include excessive accumulation of fluid in the brain, spinal cord compression and cognitive impairment. MPS I patients span a broad spectrum of disease severity and extent of CNS involvement. The severe form of MPS I is also referred to as Hurler syndrome. Hurler patients have two mutations in the IDUA gene, resulting in no active enzyme. These patients typically present with symptoms before two years of age and universally exhibit severe cognitive decline after an initial period of normal development. MPS I is estimated to occur in approximately 1 in 100,000 births worldwide. Based on global population, this equates to more than 1,000 MPS I patients born each year worldwide. The current standard of care for patients with an attenuated form of MPS I is a recombinant form of human IDUA, given as a weekly ERT infusion. This has demonstrated improvement in hepatosplenomegaly, growth, mobility and respiratory function. However, as the enzyme cannot cross the blood-brain barrier, ERT does not treat the CNS manifestations of MPS I. Patients are also often treated with hematopoietic stem cell transplantation (HSCT). Although this approach has demonstrated improvements in survival, growth, cardiac and respiratory function, mobility and intellect, it is also associated with clinically relevant morbidity and an

11

Table of Contents

estimated 10% to 20% mortality. Accordingly, the procedure is reserved for patients with severe disease before two years of age because the risk-benefit ratio is thought to be more favorable in younger patients who have not yet experienced advanced cognitive decline. Another critical limitation of HSCT is that cognitive decline continues for up to a year after transplant before stabilizing, leaving permanent cognitive deficits.

Overall, we believe the limitations of HSCT and ERT leave a significant unmet need for a method to safely achieve long-term IDUA reconstitution in the CNS for MPS I patients experiencing neurological complications. RGX-111 is designed to use the NAV AAV9 vector to deliver the human IDUA gene to the CNS. Delivery of the enzyme that is deficient within cells in the CNS could provide a permanent source of secreted IDUA beyond the blood-brain barrier, allowing for long-term cross-correction of cells throughout the CNS. We believe this strategy could also provide rapid IDUA delivery to the brain, potentially preventing the progression of cognitive deficits that otherwise occurs in MPS I patients. We have received orphan drug product designation, rare pediatric disease designation and fast track designation from the FDA, as well as orphan designation and ATMP classification from the EMA for RGX-111.

Clinical Development of RGX‑111 for the Treatment of MPS I

A Phase I/II study evaluating RGX-111 initiated in 2017 and enrollment for that study completed in 2023. The multi-center, open-label, dose escalation trial evaluated the safety, tolerability and pharmacodynamics of RGX-111 delivered via single injection to the CNS to patients with MPS I. Interim results from the study, reported in February 2023, showed RGX-111 to be well tolerated across two dose levels in the eight patients enrolled in the Phase I/II trial as of January 17, 2023 and in the single-patient IND as of December 12, 2021, with no drug-related SAEs. Biomarker and neurodevelopmental assessments indicated an encouraging CNS profile in patients dosed with RGX-111.

In November 2023, future development of RGX-111 was largely halted as a result of a strategic pipeline prioritization and corporate restructuring. Efforts to continue development of RGX-111 are set to be reinitiated following our announcement in January 2025 of a strategic partnership with Nippon Shinyaku to develop and commercialize RGX-111 in the United States and Asia. For more information, refer to "Nippon Shinyaku Partnership for MPS Diseases" below.

In January 2026, we announced that the FDA placed the RGX-111 program on clinical hold following preliminary analysis of a single case of neoplasm (intraventricular CNS tumor) in a participant treated in the Phase I/II study. The case was identified during a routine brain MRI of an asymptomatic five-year-old participant who received intracisternal RGX-111 four years prior. Preliminary genetic analysis of the resected tumor detected an AAV vector genome integration event associated with overexpression of a proto-oncogene (PLAG1), which is known to be susceptible to chromosomal rearrangements. Final analysis of the resected tumor was conducted by an independent third-party lab, and, as previously reported, detected an AAV vector genome integration event associated with overexpression of a PLAG1. Clonal integration of AAV vector elements into the PLAG1 gene was detected in the tumor tissue. Analyses supported classification as a PLAG1‑family neuroepithelial tumor and are consistent with the hypothesis that AAV vector integration at the PLAG1 site contributed to tumor formation. Of note, this participant had a background of factors that could have contributed to risk of oncogenic transformation. This child underwent unsuccessful stem cell transplant at 4 months of age, with loss of donor chimerism, and he received chemotherapeutics that may have contributed to DNA damage. The report concludes, based on formal neuropsychologic testing and developmental pediatrician assessment, that the patient’s neurocognitive development is above average, which indicates mitigation of MPS I disease, and the patient continues to do well. We anticipate the analysis will be published in a peer-reviewed journal this year.

Collaborations, Licensing and Company Formation

Collaborations, licensing and company formation are a key part of our commitment to enable the ongoing development of gene therapy treatments.

AbbVie Eye Care Collaboration

In September 2021, REGENXBIO and AbbVie announced a global strategic partnership to develop and commercialize surabgene lomparvovec (sura-vec, ABBV-RGX-314), a potential one-time gene therapy for the treatment of wet AMD, DR and other chronic retinal diseases.

Under the terms of our Collaboration and License Agreement with AbbVie (the AbbVie Collaboration and License Agreement), we received an upfront payment of $370 million. Additionally, we are eligible to receive up to $1.38 billion in additional development, regulatory and commercial milestone payments.

12

Table of Contents

In accordance with the AbbVie Collaboration and License Agreement, we and AbbVie will collaborate to develop sura-vec in the United States, and AbbVie will be responsible for the development of sura-vec in specified markets outside the United States. Global development expenses for sura-vec are shared by the parties, with AbbVie being responsible for the majority of total development expenses.

In the United States, we will participate in commercialization of licensed products to the extent set forth in a commercialization plan to be determined in accordance with the AbbVie Collaboration and License Agreement, and the parties will equally share net profits and net losses associated with commercialization of the licensed products in the United States. Outside the United States, AbbVie will be responsible, at its sole cost, for the commercialization of licensed products. We will also be eligible to receive tiered royalties on net sales by AbbVie of licensed products outside the United States at percentages in the mid-teens to low twenties, subject to specified offsets and reductions.

We will lead the manufacturing of sura-vec for clinical development and U.S. commercial supply, and AbbVie will lead manufacturing of sura-vec for commercial supply outside the United States. Manufacturing expenses will be allocated between the parties in accordance with the terms of the AbbVie Collaboration and License Agreement and mutually agreed supply agreements.

In August 2025, REGENXBIO and AbbVie announced an amendment to the AbbVie Collaboration and License Agreement which modified the development plan and milestone payment structure for the sura-vec DR program. Under the amendment, we will conduct the first registration enabling trial for DR suprachoroidal (SCS) treatment as a combined Phase IIb/III trial (NAAVIGATE) which will be performed in two parts (Part 1 and Part 2), and AbbVie will conduct the second registration enabling trial as a separate, standalone Phase III trial. In lieu of the $200.0 million development milestone due to us under the original AbbVie Collaboration and License Agreement upon first patient dosed in the first registration enabling trial for DR SCS treatment, AbbVie will pay us $100.0 million upon first patient dosed in the NAAVIGATE trial and an additional $100.0 million upon first patient dosed in the subsequent Phase III trial. Also pursuant to the amendment, AbbVie will lead a new Phase III randomized controlled study (ACHIEVE) to assess the injection burden, adverse events, change in disease activity, and long-term preservation of visual acuity of sura-vec in adult participants with neovascular AMD. We will be responsible for our development expenses to conduct Part 1 of the NAAVIGATE trial and the parties will share the development expenses related to Part 2 of the NAAVIGATE trial and the subsequent Phase III trial for DR in accordance with the existing terms of the AbbVie Collaboration and License Agreement. AbbVie will be responsible for all development expenses related to the ACHIEVE study.

Nippon Shinyaku Partnership for MPS Diseases

In January 2025, REGENXBIO and Nippon Shinyaku announced a strategic partnership to develop and commercialize RGX-121, a potential one-time gene therapy for the treatment of MPS II, and RGX-111, a potential one-time gene therapy for the treatment of MPS I, in the United States and certain countries in Asia. The Collaboration and License Agreement with Nippon Shinyaku (the Nippon Shinyaku Collaboration and License Agreement) became effective in March 2025.

Under the terms of the Nippon Shinyaku Collaboration and License Agreement, we received an upfront payment of $110 million. Additionally, we are eligible to receive up to $700 million in additional milestone payments, including $40 million in development and regulatory milestone payments and $660 million in sales milestones. We are eligible to receive meaningful double-digit royalties on net sales by Nippon Shinyaku of licensed products, subject to specified offsets and reductions. We retain all rights to, and 100% of any potential proceeds related to the sale of, the Priority Review Voucher for RGX-121 received upon approval.

In accordance with the Nippon Shinyaku Collaboration and License Agreement, we will lead the development of RGX-121 and RGX-111 in the United States and Nippon Shinyaku will be responsible for development in licensed territories outside of the United States. We will lead the manufacturing of the licensed products for clinical development and commercial supply and reserve the right to develop and commercialize in countries outside of the licensed territories. Nippon Shinyaku will be responsible, at its sole cost, for the commercialization of licensed products. Manufacturing expenses will be allocated between the parties in accordance with the terms of the Nippon Shinyaku Collaboration and License Agreement and mutually agreed supply agreements.

In January 2026, we announced that the FDA placed the RGX-121 and RGX-111 programs on clinical hold in relation to a serious adverse event in a patient treated in the Phase I/II trial of RGX-111. In February 2026, we announced that the FDA issued a CRL for the RGX-121 BLA. Refer to “Clinical Development of RGX‑121 for the Treatment of MPS II” and “Clinical Development of RGX‑111 for the Treatment of MPS I” above for further information.

13

Table of Contents

NAV Technology Licensees

In addition to our internal product development efforts, we sublicense our NAV Vectors to other leading biotechnology and pharmaceutical companies. As of December 31, 2025, our NAV Technology Licensees are currently applying our NAV Technology Platform to a number of AAV therapeutics over a broad range of therapeutic areas and disease indications. NAV Vectors have been extensively investigated in clinical trials registered in the National Institutes of Health (NIH) clinical trials database and are being used in two FDA-approved AAV therapeutics in the United States (Novartis’ Zolgensma and Itvisma). To date, thousands of patients have been treated by REGENXBIO and our NAV Technology Licensees using NAV Vectors across clinical trials, managed access and commercial settings.

Our NAV Technology Licensees are shown below.

We have also taken an active role in the formation of several of our NAV Technology Licensees, including being a founding shareholder in Dimension Therapeutics, Inc., Prevail Therapeutics Inc. and Corlieve Therapeutics SAS, all of which were acquired in strategic transactions since their formation. We entered into a license agreement with each of these NAV Technology Licensees upon their formation, for which we received equity in the NAV Technology Licensee in addition to other consideration.

NAV Technology licenses have been an important component of our strategy since REGENXBIO’s formation, creating opportunity for the development of additional therapies for patients and potential for additional value generation from the platform. Equity ownership in certain NAV Technology Licensees has generated significant additional return for REGENXBIO stockholders, and we believe the acquisition of these NAV Technology Licensees in strategic transactions by biopharmaceutical companies is an important validation of the NAV Technology Platform.

Novartis License for Zolgensma and Itvisma

In March 2014, we entered into an agreement with AveXis, Inc. (AveXis, now Novartis Gene Therapies) for an exclusive, worldwide commercial license, with rights to sublicense, to the NAV AAV9 vector for the treatment of SMA. In 2018, we amended the license to include additional intellectual property owned or in-licensed by us including a patent family covering intrathecal treatment of SMA that expires in 2037, and including rights to the NAV Technology Platform beyond NAV AAV9, as well as additional AAV vectors we may discover or license for a certain period of time, for the treatment of SMA. Under the license agreement, as amended, we were entitled to receive over $270 million in fees, development and commercial milestones. In addition, we are entitled to receive mid-single to low double-digit royalties on net sales of Zolgensma, Itvisma or any other product developed for the treatment of SMA using the NAV AAV9 vector. For any product developed for the treatment of SMA using a licensed vector other than NAV AAV9, we are entitled to receive a low double-digit royalty on net sales.

Novartis acquired AveXis for $8.7 billion in April 2018, and Zolgensma was subsequently approved by the FDA in May 2019 for the treatment of SMA in patients under the age of two years old. In November 2025, Itvisma was approved by the FDA for the treatment of SMA in patients two years and older. As of December 31, 2025, Zolgensma is approved in most major countries and Itvisma is approved in the U.S. and United Arab Emirates, with thousands of patients treated with these products globally through clinical trials, early access programs and in the commercial setting. Novartis reported combined, worldwide sales of Zolgensma and Itvisma of $1.23 billion in 2025.

In December 2020, we sold a portion of our royalty rights from the net sales of Zolgensma and Itvisma to entities managed by Healthcare Royalty Management, LLC (collectively and with other affiliated entities, HCR) for a gross purchase price of $200 million. In May 2025, we entered into a limited recourse loan agreement with HCR for up to $250 million in gross proceeds, of which $150 million was funded at closing. Principal and interest under the loan agreement are payable to HCR using Zolgensma and Itvisma royalties, along with certain consideration received under other license and collaboration agreements.

14

Table of Contents

Platform License Agreements and Other Licenses

Platform Licenses

We have exclusively licensed many of our rights in our NAV Technology Platform from the University of Pennsylvania (Penn) and GlaxoSmithKline LLC (GSK), which together we refer to as our Platform Licenses. We currently use our NAV Technology Platform to develop treatments in the areas of retinal, neuromuscular and neurodegenerative diseases. We also sublicense our NAV Technology Platform to third parties in order to develop and bring to market AAV therapeutics for a range of severe diseases with significant unmet medical needs outside of our core disease indications and therapeutic areas.

The Trustees of the University of Pennsylvania. In February 2009, we entered into an exclusive, worldwide license agreement with Penn for patent and other intellectual property rights relating to a gene therapy technology platform based on AAVs discovered at Penn in the laboratory of James M. Wilson, M.D., Ph.D. This license was amended in September 2014, April 2016, April 2019, September 2020 and March 2022. In February 2009, we also entered into a sponsored research agreement with Penn (the 2009 SRA) under which we funded the nonclinical research of Dr. Wilson relating to AAV gene therapy and obtained an option to acquire an exclusive worldwide license in certain intellectual property created pursuant to such 2009 SRA. We entered into an additional sponsored research agreement (the 2013 SRA) with Penn in November 2013 which was funded entirely by our NAV Technology Licensee, Dimension Therapeutics, Inc. In December 2014, we entered into another SRA with Penn funding related nonclinical research of Dr. Wilson (the 2014 SRA).

Our license agreement with Penn, as amended, provides us with an exclusive, worldwide license under certain patents and patent applications in order to make, have made, use, import, offer for sale and sell products covered by the claims of the licensed patents and patent applications as well as all patentable inventions (to the extent they are or become available for license) that:

•
were discovered by Dr. Wilson or other Penn researchers working under his direct supervision at Penn; and

•
are related to the AAV technology platform discovered by Dr. Wilson at Penn prior to February 2009, pursuant to a sponsored research agreement or subsequent amendment to a sponsored research agreement; or

•
are necessary or useful for the practice of Penn’s patent rights in the treatment of CLN2 disease, a form of Batten disease, and conceived and reduced to practice since October 2015; and

•
are owned and controlled by Penn.

Prior to entering into the license agreement with us, Penn had entered into two license agreements with third parties with respect to certain of the licensed patents and patent applications. Our license from Penn is subject to those preexisting license grants in addition to certain other retained fields. With respect to the first third-party license granted by Penn, our license is non-exclusive with respect to the patents and patent applications licensed to the third party for so long as that preexisting license grant remains in effect and will become exclusive upon the expiration or termination of that existing license agreement. The pre-existing licenses also include a license agreement Penn entered into with GSK in May 2002, granting a license to certain patents and patent applications, of which we subsequently sublicensed certain rights to from GSK in March 2009. For further information regarding our GSK sublicense, please see “Platform License Agreements and Other Licenses—Platform Licenses—GlaxoSmithKline LLC” located elsewhere in this Annual Report on Form 10-K. Our license agreement with Penn provides that should the rights Penn licensed to GSK ever revert to Penn, such rights shall automatically be included in our license agreement with Penn.

The Penn license agreement, as amended, also provides us with certain additional rights, including a non-exclusive, worldwide license to use (i) all data and information that was developed since October 2015 by Dr. Wilson, or other Penn researchers working under his direct supervision at Penn, that is related to Batten disease, owned by Penn, and necessary or useful for the practice of the licensed patent rights in the treatment of CLN2 disease; and (ii) all know-how that:

•
was developed by Dr. Wilson, or other Penn researchers working under his direct supervision at Penn;

•
is related to the AAV technology platform discovered by Dr. Wilson prior to September 2014 or discovered by Dr. Wilson at Penn after September 2014 during the performance of a research program we sponsored;

•
is owned by Penn; and

•
is necessary or useful for the practice of the licensed patent rights.

Under the terms of the Penn license agreement, we issued equity to Penn and are also obligated to pay Penn:

•
up to $20.5 million upon the achievement of various development and sales-based milestones, of which $0.5 million have been paid to date;

•
low- to mid-single digit royalties on net sales of licensed pharmaceutical products sold by us or our affiliates;

15

Table of Contents

•
low-single digit to low-double digit royalty percentages of net sales on licensed products intended for research purposes only;

•
low- to mid-double digit royalty percentage on royalties received from third parties on net sales of licensed pharmaceutical products by such third parties;

•
certain sublicense fees, of which $3.0 million remain outstanding as of December 31, 2025; and

•
reimbursements for ongoing patent prosecution and maintenance expenses.

Our Penn license agreement, as amended, will terminate with respect to licensed products in a field of use other than the treatment of familial hypercholesterolemia (FH) on a product-by-product and country-by-country basis on the date each particular licensed product ceases to be covered by at least one valid claim, issued or pending, under the licensed patent rights. We can terminate this license agreement by giving Penn prior written notice. Penn has the right to terminate:

•
with notice if we are late in paying money due under the license agreement;

•
with notice if we fail to achieve a diligence event on or before the applicable completion date or otherwise breach the license agreement;

•
if we or our affiliates experience insolvency; or

•
if we commence any action against Penn to declare or render any claim of the licensed patent rights invalid or unenforceable.

Under the 2014 SRA, as amended, we funded research at Penn, paid certain intellectual property legal and filing expenses and received the rights to certain research results. The Penn license agreement, as amended, and the 2014 SRA, as amended, provide that all patentable inventions conceived, created, or conceived and reduced to practice pursuant to the 2014 SRA, together with patent rights represented by or issuing from the U.S. patents and patent applications, including provisional patent applications, automatically become exclusively licensed to us and all research results become automatically licensed to us as know-how. Under the 2009 SRA, as amended, in consideration for our funding of research at Penn, we received an option to acquire a worldwide license on commercially reasonable terms to practice all patentable inventions conceived, created, or reduced to practice pursuant to the 2009 SRA, together with patent rights represented by or issuing from the U.S. patents and patent applications, including provisional patent applications.

GlaxoSmithKline LLC. In March 2009, we entered into a license agreement with GSK, which was amended in April 2009, in order to secure the exclusive rights to patents and patent applications covering NAV Technology that GSK had previously licensed from Penn (subject to certain rights retained by GSK and Penn). Under this GSK license agreement, we receive an exclusive, worldwide sublicense under the licensed patent rights to make, have made, use, import, sell and offer for sale products covered by the licensed patent rights anywhere in the world. Our rights under this GSK license agreement are subject to certain rights retained by GSK for the benefit of itself and other third parties, including rights relating to: domain antibodies; RNA interference and antisense drugs; internal research purposes and GSK’s discovery research efforts with non-profit organizations and GSK collaborators; AAV8 for the treatment of hemophilia B; AAV9 for the treatment of Muscular Dystrophy, congestive heart failure suffered by Muscular Dystrophy patients and cardiovascular diseases by delivery of certain genes; and non-commercial research in the areas of Muscular Dystrophy, hemophilia B, congestive heart failure suffered by Muscular Dystrophy patients, and other cardiovascular disease. Under the terms of the license agreement, we issued equity to GSK and are obligated to pay GSK:

•
up to $1.5 million in aggregate milestone payments, all of which have been paid;

•
low- to mid-double digit percentages of any sublicense fees we receive from sublicensees for the licensed intellectual property rights; and

•
reimbursements for certain patent prosecution and maintenance expenses.

In addition, under our GSK license agreement, we are obligated to pay low- to mid-single digit royalty percentages on net sales of licensed products. This payment has been assigned by GSK to Penn such that any royalties we are obligated to pay under the GSK license agreement will be paid to Penn rather than GSK. Under our GSK license agreement, we are required to use commercially reasonable efforts to develop and commercialize licensed products. Our GSK license agreement will terminate upon the expiration, lapse, abandonment or invalidation of the last licensed claim to expire, lapse, become abandoned or unenforceable in all the countries of the world where the licensed patent rights existed. The last to expire patent under the GSK license agreement, absent patent term

16

Table of Contents

extension, was in January 2026. We may terminate this license agreement for any reason upon a specified number of days’ written notice. GSK can terminate this license agreement if:

•
we are late in paying GSK any money due under the agreement and do not pay in full within a specified number of days of GSK’s written demand;

•
we materially breach the agreement and fail to cure within a specified number of days; or

•
we file for bankruptcy.

We have been notified of a dispute with GSK over the amount of sublicense fees paid by us to GSK under the GSK license agreement. We disagree with GSK's interpretation of the GSK license agreement and engaged in non-binding mediation with GSK but the dispute has not yet been resolved. For additional information, please see Note 8, “Commitments and Contingencies—In-Licensed Technology—GlaxoSmithKline” to the accompanying audited consolidated financial statements.

Other Licenses

Regents of the University of Minnesota. In November 2014, we entered into a license agreement with Regents of the University of Minnesota (Minnesota) for the exclusive rights to Minnesota’s undivided interest in intellectual property that Minnesota and we jointly own relating to the delivery of AAV vectors to the CNS. This license was amended in November 2016 and September 2021. Under this Minnesota license agreement, as amended, we receive an exclusive license under the licensed patent rights to make, have made, use, offer to sell or sell, offer to lease or lease, import or otherwise offer to dispose or dispose of products covered by the licensed patent rights in all fields of use in any country or territory in which a licensed patent has been issued and is unexpired or a licensed patent application is pending until November 2019, after which time the field of use would be limited to all fields of use using our NAV Vectors in addition to certain additional indications and areas. Under the terms of the agreement, we are obligated to pay Minnesota upfront fees, annual maintenance fees, royalties on net sales, if any, sublicense fees and fees upon the achievement of various milestones.

Emory University. In August 2018, we entered into a license agreement with Emory University (Emory) for the exclusive rights to Emory’s undivided interest in intellectual property that we and Emory jointly own relating to the delivery of AAV vectors to the CNS. Under this Emory license agreement, we receive an exclusive license under the licensed patent rights to make, have made, use, import, offer to sell or sell licensed products in all fields of use in any country. Under the terms of the agreement, we are obligated to pay Emory an upfront fee, annual maintenance fees under certain circumstances, royalties on net sales, sublicense fees, and fees upon the achievement of various milestones for the first licensed product. This patent estate is sublicensed to Novartis for the treatment of spinal muscular atrophy.

Clearside Biomedical, Inc. In August 2019, we entered into an option and license agreement with Clearside for the option to receive an exclusive, worldwide commercial license, with rights to sublicense, to Clearside’s SCS Microinjector for the delivery of AAV gene therapies for the treatment of wet AMD, DR, and other conditions for which chronic anti-VEGF treatment is currently the standard of care. In October 2019, we exercised the option. This option and license agreement was amended in January and September 2023. Under the terms of the agreement, as amended, we are obligated to pay Clearside an upfront fee, royalties on net sales, and fees upon the achievement of various milestones. As between us and Clearside, we will be responsible for all development, regulatory and commercialization activities for our gene therapy product candidates. Clearside will be responsible for supplying the SCS Microinjector in support of our preclinical studies, clinical studies and commercial use. In November 2025, Clearside announced that it filed a voluntary petition under Chapter 11 of the U.S. Bankruptcy Code in the District of Delaware and that it was seeking authorization to sell all or substantially all of its assets in a court-supervised auction and sale process under Section 363 of the U.S. Bankruptcy Code. Clearside subsequently announced that it entered into an asset purchase agreement with a stalking horse bidder, Health Ocean Pharma (Eye) Limited, for the sale of substantially all of its assets, including its remaining rights with respect to the SCS Microinjector. The sale process is still ongoing and is subject to pending objections by parties in interest, and, therefore, the ultimate outcome of that process is unknown.

Johns Hopkins University. In June 2022, we entered into a license agreement with Johns Hopkins University (JHU) for the exclusive rights to JHU's undivided interest in intellectual property JHU and we jointly own relating to suprachoroidal delivery of anti-VEGF vectors. Under this JHU license agreement, we receive an exclusive license under the licensed patent rights to make, have made, use, import, export, offer to sell and sell licensed products in all fields of use in any country. Under the terms of the agreement, we are obligated to pay JHU an upfront fee, royalties on net sales, minimum annual royalties, sublicense fees and fees upon the achievement of various milestones for the first two licensed products. Additionally, the Company is obligated to pay for certain costs incurred related to the maintenance of the licensed patents.

17

Table of Contents

Intellectual Property

Our patent portfolio includes patents and patent applications that we own, co-own and license from third parties and covers all aspects of our NAV Technology Platform, clinical candidates and programs, formulations, devices, manufacturing and research programs. We believe this patent portfolio enables us to support our development of AAV therapeutics to address significant unmet medical needs.

NAV Technology Platform

As of December 31, 2025, our patent portfolio has included 25 issued U.S. patents and five European patents relating to the AAV7, AAV8, AAV9, AAVrh10 and AAVrh46 vectors and their uses. These patents have terms that will expire as late as 2027, not including patent term extensions.

Our Investigational AAV Therapeutics

As of December 31, 2025, in addition to the patents related to our NAV Technology Platform described above, our patent portfolio included a total of six issued U.S. patents, one issued European patent, one pending International Patent application filed pursuant to the Patent Cooperation Treaty (PCTs) and 23 PCTs that have entered national stage relating to our product candidates, which are described below:

Retinal Diseases

In addition to our patents covering the manufacture of NAV AAV8 vectors used in our retinal disease programs, our patent portfolio includes more recent filings relating to our clinical candidate vectors, clinical protocols, routes of administration to the eye (subretinal and suprachoroidal), formulations and target diseases treated by our gene therapy vectors.

Our patent portfolio relating to sura-vec supports our clinical development and our collaboration with AbbVie for the clinical development of sura-vec. Our patent portfolio covers the use of sura-vec for the treatment of wet AMD through subretinal or suprachoroidal administration and for the treatment of DR through suprachoroidal administration; it also covers formulations and devices used for suprachoroidal administration. Our patent portfolio relating to sura-vec includes one issued U.S. patent that will expire in 2037 and eight PCTs that have entered national stage for which any issued U.S. or European patent would expire in 2037, 2038, 2039, 2040 or 2043, in each case without taking into account any possible patent term adjustment or extension.

Neuromuscular Diseases

In addition to our patents covering the manufacture of the AAV8 vector, our patent portfolio includes more recent filings relating to RGX-202, the NAV AAV8 capsid carrying our microdystrophin construct used to treat Duchenne and the manufacture of RGX-202. Our patent portfolio also covers other AAV vectors carrying our microdystrophin transgene, as well as intravenous and other modes of administration, formulations and bioanalytical assays.

Our patent portfolio relating to RGX-202 includes five pending PCTs that have entered the national stage for which any issued U.S. or European patent would expire in 2040, 2042 or 2043 without taking into account any possible patent term adjustment or extension.

Neurodegenerative Diseases

In addition to our patents covering the manufacture of NAV AAV9 vector used in our neurodegenerative disease program, our RGX-121 patent portfolio includes more recent filings that cover our clinical candidate vector, routes of administration used in our neurodegenerative disease clinical-stage program (intracisternal administration for intrathecal delivery, as well as lumbar puncture and intraventricular administration), formulations and clinical protocols.

Our patent portfolio relating to RGX-121 includes one issued U.S. patent that will expire in 2034, one issued U.S. patent that will expire in 2038, one issued U.S. patent that will expire in 2039, one issued U.S. patent that will expire in 2040, one issued U.S. patent that will expire in 2042, one issued European patent that will expire in 2036, one pending PCT application and ten PCTs that have entered national stage for which any issued U.S. or European patents would expire in 2034, 2036, 2037, 2038, 2039, 2041 or 2042, in each case without taking into account any possible patent term adjustment or extension.

18

Table of Contents

Manufacturing

Our patent portfolio covers aspects of our manufacturing processes which support our ability to perform large scale manufacturing, increase yield and purity of AAV vector products and meet clinical supply requirements.

Our patent portfolio also includes protection for novel validation and potency assays that further support and streamline our manufacturing processes.

Customers

Our revenues for the years ended December 31, 2025 and 2024 consisted solely of license, royalty and service revenues earned under our license and collaboration agreements. Two customers (Novartis Gene Therapies and Nippon Shinyaku) accounted for approximately 99% of our total revenues for the year ended December 31, 2025. One customer (Novartis Gene Therapies) accounted for approximately 98% of our total revenues for the year ended December 31, 2024. We expect future license, royalty and service revenue to continue to be derived from a limited number of licensees and collaboration partners. Future revenues under our license and collaboration arrangements are uncertain due to the contingent nature of the consideration payable under the arrangements, and revenues may fluctuate significantly from period to period.

Competition

We are aware of a number of companies focused on developing and commercializing gene therapies in various disease indications, including 4D Molecular Therapeutics, Inc., Amicus Therapeutics, Inc., Astellas Pharma, BioMarin Pharmaceutical, Inc., Lilly, MeiraGTx Limited, Novartis AG, Passage Bio, Inc., PTC Therapeutics, Inc., Roche, Sanofi, Sarepta Therapeutics, Inc., Solid Biosciences, Inc., Taysha Gene Therapies, Inc., Tenaya Therapeutics, Inc., Ultragenyx Pharmaceutical Inc. and uniQure N.V., as well as a number of companies addressing other methods for modifying genes and regulating gene expression. Additionally, we have sublicensed our NAV Technology Platform for developing gene therapies in various disease indications to our NAV Technology Licensees. Not only must we compete with other companies that are focused on gene therapy products technology and other gene therapy platforms, but any products that we may commercialize will have to compete with existing therapies and new therapies that may become available in the future.

There are other organizations working to improve existing therapies or to develop new therapies for our initially selected disease indications. Depending on how successful these efforts are, it is possible they may increase the barriers to adoption and success for our product candidates, if approved. These efforts include the following:

•
Wet AMD. Marketed competition for wet AMD largely consists of anti-VEGF therapies developed by Roche/Genentech, Inc. (Lucentis, Susvimo, Vabysmo), Regeneron Pharmaceuticals, Inc. (Eylea, Eylea HD) and Novartis (Beovu). Biosimilars for Lucentis (Biogen - Byooviz, Sandoz - Cimerli) and Eylea (Amgen - Pavblu) have launched in the United States. Companies with products in development for the treatment of wet AMD include, but may not be limited to, 4D Molecular Therapeutics, Avirmax Bio, Exegenesis Bio, Eyepoint Pharmaceuticals, Kodiak Sciences, Inc., Lilly, Ocular Therapeutix, and Skyline Therapeutics.

•
DR. Currently marketed anti-VEGF competition for DR with DME include Roche/Genentech (Lucentis, Vabysmo, Susvimo), Regeneron (Eylea, Eylea HD), Novartis (Beovu), and Amgen (Pabvlu). Companies with products in development for the treatment of DR with DME include, but may not be limited to, 4D Molecular Therapeutics, Eyepoint, Kodiak Sciences, Merck, Oculis, and Roche. The principal marketed anti-VEGF competition for DR without DME is Roche/Genentech (Lucentis, Susvimo) and Regeneron (Eylea, Eylea HD). Companies with products in development for the treatment of DR without DME include, but may not be limited to, Kodiak Sciences, Novartis, and Ocular Therapeutix.

•
DMD. The principal marketed competition for the treatment of DMD is a gene therapy marketed by Sarepta/Roche (Elevidys). Currently marketed exon-skipping competition for DMD includes Sarepta (Exondys, Vyondys, Amondys) and Nippon Shinyaku Co., Ltd. (Viltepso). There are three principal competitive gene therapy products in clinical development from Solid Biosciences (SGT-003), Genethon (GNT0004), and Insmed (INS1201). Other companies with gene therapies in early development for DMD include, but may not be limited to, Ultragenyx, Huidagene, and Novartis.

•
MPS II. The principal marketed competition for the treatment of MPS II is a systemic enzyme replacement therapy marketed by Takeda Pharmaceutical Company, Ltd. and Sanofi (Elaprase). Two additional products are marketed in select geographies in Asia by JCR Pharmaceuticals Co., Ltd. (Izcargo) and GC Pharma (Hunterase ICV). Companies with products in development for the treatment of MPS II include, but may not be limited to, Denali Therapeutics Inc., Esteve and Immusoft.

19

Table of Contents

Many of our competitors, either alone or with their strategic partners, have substantially greater financial, technical and human resources than we do. Our competitors may be more successful than us in obtaining approval for treatments and achieving widespread market acceptance. Our competitors’ treatments may be more effective, or more effectively marketed and sold, than any treatment we may commercialize and may render our treatments obsolete or non-competitive before we can recover the expenses of developing and commercializing any of our treatments.

Mergers and acquisitions in the biotechnology and pharmaceutical industries may result in even more resources being concentrated among a smaller number of our competitors. These competitors also compete with us in recruiting and retaining qualified scientific and management personnel and establishing clinical trial sites and patient registration for clinical trials, as well as in 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.

We anticipate that we will face intense and increasing competition as new drugs and treatments enter the market and advanced technologies become available. We expect any treatments that we develop and commercialize to compete on the basis of, among other things, efficacy, safety, convenience of administration and delivery, price, level of biosimilar competition and availability of reimbursement from government and other third-party payors.

Government Regulation

In the United States, biological products, including gene therapy products, are subject to regulation under the Federal Food, Drug, and Cosmetic Act (FD&C Act), and the Public Health Service Act (PHS Act) and other federal, state, local and foreign statutes and regulations. Both the FD&C Act and the PHS Act and their corresponding regulations govern, among other things, the testing, manufacturing, safety, efficacy, labeling, packaging, storage, record keeping, distribution, reporting, advertising and other promotional practices involving biological products. Applications to the FDA are required before conducting clinical testing of biological products, and each clinical study protocol for a gene therapy product is reviewed by the FDA.

Within the FDA, the Center for Biologics Evaluation and Research (CBER) regulates gene therapy products as biological products. The FDA has published guidance documents related to, among other things, gene therapy products in general, their preclinical assessment, observing subjects involved in gene therapy studies for delayed adverse events, potency testing, and chemistry, manufacturing and control information in gene therapy INDs.

Ethical, scientific, social and legal concerns about gene therapy, genetic testing and genetic research could result in additional regulations restricting or prohibiting the processes we may use. Federal and state agencies, congressional committees and foreign governments have expressed interest in further regulating biotechnology. More restrictive regulations or claims that our products are unsafe or pose a hazard could prevent us from commercializing any products. New government requirements may be established that could delay or prevent regulatory approval of our product candidates under development. In addition, while the FDA currently considers all gene therapy products to be biological products, this classification could come under scrutiny in the future, and it is possible that some gene therapies could be regulated as drug products (requiring a new drug application rather than a BLA for marketing).

It is impossible to predict whether legislative changes will be enacted, regulations, policies or guidance changed, or interpretations by agencies or courts changed, or what the impact of such changes, if any, may be.

U.S. Biological Products Development Process

The process required by the FDA before a biological product may be marketed in the United States generally involves the following:

•
completion of nonclinical laboratory tests, including evaluations of product chemistry, formulations, toxicity in animal studies in accordance with good laboratory practice (GLP) and applicable requirements for the humane use of laboratory animals or other applicable regulations;

•
submission to the FDA of an IND, which must become effective before human clinical studies may begin;

•
performance of adequate and well-controlled human clinical studies according to the FDA’s requirements for good clinical practice (GCP) and additional requirements for the protection of human research subjects and their health information, to establish the safety and efficacy of the proposed biological product for its intended use;

20

Table of Contents

•
submission to the FDA of a BLA for marketing approval that includes substantive evidence of safety, purity, and potency from results of nonclinical testing and clinical studies, as well as information on the chemistry, manufacturing and controls to ensure product identity and quality, and proposed labeling;

•
satisfactory completion of an FDA inspection of the manufacturing facility or facilities where the biological product is produced to assess compliance with cGMP, to assure that the facilities, methods and controls are adequate to preserve the biological product’s identity, strength, quality and purity and, if applicable, the FDA’s current good tissue practice (GTP), for the use of human cellular and tissue products;

•
potential FDA inspection of the nonclinical and clinical study sites and the clinical study sponsor that generated the data in support of the BLA; and

•
FDA review and approval, or licensure, of the BLA.

The clinical study sponsor must submit the results of the preclinical tests, together with manufacturing information, analytical data, any available clinical data or literature and a proposed clinical protocol, to the FDA as part of the IND. Some preclinical testing may continue even after the IND is submitted. The IND automatically becomes effective 30 days after receipt by the FDA, unless the FDA places the clinical study on a clinical hold within that 30-day period. The FDA may also impose a clinical hold on an IND or clinical study after the IND is in effect, including because of concerns that patients would be exposed to an unreasonable and significant risk of because of concerns about the sufficiency of safety information in the IND. In addition, some clinical holds are partial clinical holds, which may limit parts of an investigation (e.g., halting new patient enrollment, additional dosing, or specific study arms). In contrast, a full clinical hold delays or suspends the investigation generally. Once a clinical hold is imposed, the IND sponsor and the FDA must resolve any outstanding concerns before the clinical study can resume or begin. Accordingly, we cannot be sure that submission of an IND will result in the FDA allowing clinical studies to begin, or that, once begun, issues will not arise that would lead to the FDA suspending or terminating such studies.

Clinical studies involve the administration of the biological product candidate to healthy volunteers or patients under the supervision of qualified investigators, generally physicians not employed by the study sponsor or under the study sponsor's control. Clinical studies are conducted under protocols detailing, among other things, the objectives of the clinical study, dosing procedures, subject selection and exclusion criteria, and the parameters to be used to monitor subject safety, often including stopping rules that ensure a clinical study or treatment of a specific patient will be stopped if certain adverse events occur. Each protocol and any significant change to the protocol must be submitted to FDA as an amendment to the IND . Clinical studies must be conducted and monitored in accordance with the FDA’s regulations imposing the GCP requirements, including the requirement that all research subjects provide informed consent. Further, each clinical study must be reviewed and approved by an independent institutional review board (IRB) at or servicing each institution at which the clinical study will be conducted. An IRB is charged with protecting the welfare and rights of study participants and considers such items as whether the risks to individuals participating in the clinical studies are minimized and are reasonable in relation to anticipated benefits. The IRB also approves the form and content of the informed consent that must be signed by each clinical study subject or his or her legal representative and must monitor the clinical study until completed. The IRB can suspend or terminate approval of a clinical study at its institution if the clinical study is not being conducted in accordance with the IRB’s requirements or if the biological product has been associated with unexpected serious harm to patients. Clinical studies generally also must be reviewed by an institutional biosafety committee (IBC), a local institutional committee that reviews and oversees basic and clinical research conducted at that institution. The IBC assesses the safety of the research and identifies any potential risk to public health or the environment. Some studies also employ a Data and Safety Monitoring Board (DSMB) or Data Monitoring Committee (DMC), which operates with independence from the study sponsor and has access to unblinded study data during the course of the study. Most DSMB are empowered by the sponsor to halt a study for ethical or safety reasons such as undue safety risks—and some can also halt a study for other reasons, such as a finding of futility.

Human clinical studies are typically conducted in three sequential phases that may overlap or be combined:

•
Phase I. The biological product is initially introduced into healthy human subjects and tested for safety. However, in the case of some products for rare, severe or life-threatening diseases, the initial human testing is often conducted in patients.

•
Phase II. The biological product is evaluated in a limited patient population to identify possible adverse effects and safety risks, to preliminarily evaluate the efficacy of the product for specific targeted diseases and to determine dosage tolerance, optimal dosage and dosing schedule.

•
Phase III. Clinical studies are undertaken to further evaluate dosage, clinical efficacy, potency, and safety in an expanded patient population at geographically dispersed clinical study sites. These clinical studies are intended to establish the overall risk/benefit ratio of the product and provide an adequate basis for product approval and labeling. Post-approval clinical studies, sometimes referred to as Phase IV clinical studies, may be conducted after initial marketing approval. These clinical studies are used to gain additional experience from the treatment of patients in the intended therapeutic

21

Table of Contents

indication, particularly for long-term safety follow-up. In some cases, Phase IV studies may be required by the FDA as a condition of approval. For some gene therapy products, FDA has required Phase IV safety studies for as long as 15 years, in addition to special long-term monitoring for delayed adverse events.

During all phases of clinical development, regulatory agencies require extensive monitoring and auditing of all clinical activities, clinical data, and clinical study investigators. Annual progress reports detailing the results of the clinical studies must be submitted to the FDA. Written IND safety reports must be promptly submitted to the FDA and the investigators for serious and unexpected adverse events, any findings from other studies, tests in laboratory animals or in vitro testing that suggest a significant risk for human subjects, or any clinically important increase in the rate of a serious suspected adverse reaction over that listed in the protocol or investigator brochure. The sponsor must submit an IND safety report within 15 calendar days after the sponsor determines that the information qualifies for expedited reporting. The sponsor also must notify the FDA of any unexpected fatal or life-threatening suspected adverse reaction within seven calendar days after the sponsor’s initial receipt of the information. Phase I, Phase II and Phase III clinical studies may not be completed successfully within any specified period, if at all.

Human gene therapy products are a relatively new category of therapeutics—with the first gene therapy products approved by FDA in 2017. Because this is a relatively new and expanding area of novel therapeutics, there can be no assurance as to the length of the study period, the number of patients the FDA will require to be enrolled in the studies in order to establish the safety, efficacy, purity and potency of human gene therapy products, our ability to recruit sufficient numbers of study subjects for any trial, or that the data generated in these studies will be acceptable to the FDA to support marketing approval.

Concurrent with clinical studies, companies usually complete additional animal studies and must also develop additional information about the physical characteristics of the biological product as well as finalize a process for manufacturing the product in commercial quantities in accordance with cGMP requirements. To help reduce the risk of the introduction of adventitious agents with use of biological products, the PHS Act emphasizes the importance of manufacturing control for products whose attributes cannot be precisely defined. The manufacturing process must be capable of consistently producing quality batches of the product candidate and, among other things, the sponsor must develop methods for testing the identity, strength, quality, potency and purity of the final biological product. Additionally, appropriate packaging must be selected and tested and stability studies must be conducted to demonstrate that the biological product candidate does not undergo unacceptable deterioration over its shelf life.

U.S. Review and Approval Processes

After the completion of clinical studies of a biological product, FDA approval of a BLA must be obtained before commercial marketing of the biological product. The BLA must include results of product development, laboratory and animal studies, human studies, information on the manufacture and composition of the product, proposed labeling and other relevant information. Under the Prescription Drug User Fee Act (PDUFA), the BLA must be accompanied by a substantial user fee payment unless an exception or waiver applies. In addition, under the Pediatric Research Equity Act (PREA), a BLA or supplement to a BLA must contain data to assess the safety and effectiveness of the biological 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. The FDA may grant deferrals for submission of pediatric data or full or partial waivers of pediatric requirements. Unless otherwise required by regulation, PREA does not apply to any biological product for an indication for which orphan designation has been granted. The testing and approval processes require substantial time and effort and there can be no assurance that the FDA will accept the BLA for filing and, even if filed, that any approval will be granted on a timely basis, if at all.

Within 60 days following submission of the application, the FDA reviews a BLA submitted to determine if it is substantially complete before the agency accepts it for filing. The FDA may refuse to file any BLA that it deems incomplete or not properly reviewable at the time of submission and may request additional information. In this event, the BLA must be resubmitted with the additional information. The resubmitted application also is subject to review before the FDA accepts it for filing. Once the submission is accepted for filing, the FDA begins an in-depth substantive review of the BLA. The FDA reviews the BLA to determine, among other things, whether the proposed product is safe and potent, including whether it is effective, for its intended use, and has an acceptable purity profile, and whether the product is being manufactured in accordance with cGMP to assure and preserve the product’s identity, strength, quality, potency and purity as those factors relate to the safety or effectiveness of the product. The FDA may refer applications for novel biological products or biological products that present difficult questions of safety or efficacy to an advisory committee, typically a panel that includes clinicians and other experts, for review, evaluation and 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. During the biological product approval process, the FDA also will determine whether a Risk Evaluation and Mitigation Strategy (REMS) is necessary to assure the safe use of the biological product upon marketing. If the FDA concludes a REMS is needed, the sponsor of the BLA must submit a proposed REMS; the FDA will not approve the BLA without a REMS, if required.

22

Table of Contents

Before approving a BLA, the FDA will inspect the facilities at which the product is manufactured. The FDA will not approve the product unless it determines that the manufacturing processes and facilities are in compliance with cGMP requirements and adequate to ensure consistent production of the product within required specifications. For a gene therapy product that involves human cells or tissues as part of the manufacturing process, the FDA also will not approve the product if the manufacturing process is not in compliance with GTP. These are FDA regulations that govern the methods used in, and the facilities and controls used for, the manufacture of human cells, tissues, and cellular and tissue based products (HCT/Ps) which are human cells or tissue intended for implantation, transplant, infusion, or transfer into a human recipient. The primary intent of the GTP requirements is to ensure that cell and tissue based products are manufactured in a manner designed to prevent the introduction, transmission and spread of communicable disease. FDA regulations also require tissue establishments to register and list their HCT/Ps with the FDA and, when applicable, to evaluate donors through screening and testing. Additionally, before approving a BLA, the FDA will typically inspect one or more clinical sites to assure that the clinical studies were conducted in compliance with IND study requirements and GCP requirements. To assure cGMP, GTP and GCP compliance, an applicant must incur significant expenditure of time, money and effort in the areas of training, record keeping, production, and quality control.

Notwithstanding the submission of relevant data and information, the FDA may ultimately decide that the BLA does not satisfy its regulatory criteria for approval and deny approval. Data obtained from clinical studies are not always conclusive and the FDA may interpret data differently than we interpret the same data. If the agency decides not to approve the BLA in its present form, the FDA will issue a complete response letter that usually describes all of the specific deficiencies in the BLA identified by the FDA. The deficiencies identified may be minor, for example, requiring labeling changes, or major, for example, requiring additional clinical studies. Additionally, the complete response letter may include recommended actions that the applicant might take to place the application in a condition for approval. If a complete response letter is issued, the applicant may either resubmit the BLA, addressing all of the deficiencies identified in the letter, or withdraw the application.

If a product receives regulatory approval, the approval may be significantly limited to specific diseases and dosages or the indications for use may otherwise be limited, which could restrict the commercial value of the product. Further, the FDA may require that certain contraindications, warnings or precautions be included in the product labeling. The FDA may impose restrictions and conditions on product distribution, prescribing, or dispensing in the form of a REMS, or otherwise limit the scope of any approval. In addition, the FDA may require post marketing clinical studies designed to further assess a biological product’s safety and effectiveness, and testing and surveillance programs to monitor the safety of approved products that have been commercialized.

For new molecular entities, one of the performance goals agreed to by the FDA under PDUFA is to review 90% of standard BLAs within 10 months of the 60-day filing date and 90% of priority BLAs in six months of the 60-day filing date, whereupon a review decision is to be made. The FDA does not always meet its PDUFA goal dates for standard and priority BLAs and its review goals are subject to change from time to time. The review process and the PDUFA goal date may be extended by three months if the FDA requests or the BLA sponsor otherwise provides additional information, or clarification regarding information already provided in the submission, constituting a major amendment to the BLA.

Orphan Drug Designation

Under the Orphan Drug Act, the FDA may grant orphan designation to a drug or biological product intended to treat a rare disease or condition, which is defined under the FD&C Act as a disease or condition that affects fewer than 200,000 individuals in the United States, or more than 200,000 individuals in the United States and for which there is no reasonable expectation that the cost of developing and making a drug or biological product available in the United States for this type of disease or condition will be recovered from sales of the product. Orphan product designation must be requested before submitting a BLA. After the FDA grants orphan product designation, the identity of the therapeutic agent and its potential orphan use are disclosed publicly by the FDA. Orphan product designation does not convey any advantage in or shorten the duration of the regulatory review and approval process.

If a product that has orphan designation subsequently receives the first FDA approval for that product for the disease or condition for which it has such designation, the product is entitled to orphan product exclusivity, which means that the FDA may not approve any other applications to market the same drug or biological product for the same indication for seven years, except in limited circumstances, such as a showing of clinical superiority to the product with orphan exclusivity. Competitors, however, may receive approval of different products for the indication for which the orphan product has exclusivity or obtain approval for the same product but for a different indication for which the orphan product has exclusivity. Orphan product exclusivity also could block the approval of one of our products for seven years if a competitor obtains approval of the same biological product as defined by the FDA or if our product candidate is determined to be contained within the competitor’s product for the same indication or disease. If a drug or biological product designated as an orphan product receives marketing approval for an indication broader than what is designated, it may not be entitled to orphan product exclusivity.

23

Table of Contents

Orphan drug products are also eligible for Rare Pediatric Disease Designation if greater than 50% of patients living with the disease are under age 18. A priority review voucher will be given to the sponsor of a product with a Rare Pediatric Disease Designation at the time of product approval that is transferable to another company.

Expedited Development and Review Programs

The FDA has a Fast Track program that is intended to expedite or facilitate the process for development and review of new drugs and biological products, including precision drugs or biological products, that meet certain criteria. Specifically, new drugs and biological products are eligible for Fast Track designation if they are intended to treat a serious or life-threatening condition and demonstrate the potential to address unmet medical needs for the condition. Fast Track designation applies to the combination of the product and the specific indication for which it is being studied. The sponsor of a new drug or biologic may request the FDA to designate the drug or biologic as a Fast Track product at any time during the clinical development of the product.

Any product submitted to the FDA for marketing, including under a Fast Track program, may be eligible for other types of FDA programs intended to expedite development and review, such as Breakthrough Therapy designation, priority review, and accelerated approval. Under the Breakthrough Therapy program, products intended to treat a serious or life-threatening disease or condition may be eligible for additional benefits when preliminary clinical evidence indicates that such product may demonstrate substantial improvement on one or more clinically significant endpoints over available therapies. Products with a Breakthrough Therapy designation are eligible for the benefits of Breakthrough Therapy, and the FDA will seek to ensure the sponsor of a breakthrough therapy product receives timely advice and interactive communications to help the sponsor design and conduct a development program as efficiently as possible. In addition, gene therapies may be eligible for regenerative medicine advanced therapy (RMAT) designation if preliminary clinical evidence indicates that the drug has the potential to address unmet medical needs for a serious or life-threatening disease or condition. Products with an RMAT designation are eligible for the benefits of Breakthrough Therapy in addition to allowing the sponsor the ability to participate in meetings with the FDA to discuss whether accelerated approval would be appropriate based on surrogate or intermediate endpoints reasonably likely to predict long-term clinical benefit.

A product with a Fast Track, Breakthrough Therapy, or RMAT designation may be eligible for “rolling review,” which means the FDA may consider for review sections of the BLA on a rolling basis before the complete application is submitted, if the sponsor provides a schedule for the submission of the sections of the application, the FDA agrees to accept sections of the application and determines that the schedule is acceptable, and the sponsor pays any required user fees upon submission of the first section of the application.

A BLA may be eligible for priority review if the product has the potential to provide safe and effective therapy where no satisfactory alternative therapy exists or a significant improvement in the treatment, diagnosis or prevention of a serious or life-threatening disease or condition compared to marketed products. Specific priority review programs exist for material threat medical countermeasures, rare pediatric diseases and tropical diseases. The FDA will attempt to direct additional resources to the evaluation of an application for a new drug or biological product designated for priority review in an effort to facilitate the review, in accordance with FDA guidance.

Additionally, a product may be eligible for accelerated approval. Drug or biological products studied for their safety and effectiveness in treating serious or life-threatening illnesses may be eligible for accelerated approval, which means that they may be approved on the basis of an effect on a surrogate endpoint that is reasonably likely to predict a clinical benefit, or on the basis of an effect on a clinical endpoint that can be measured earlier than irreversible morbidity or mortality or other clinical benefit, 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. Drugs granted accelerated approval generally provide a meaningful therapeutic advantage to patients over existing treatments. As a condition of approval, the FDA will often require that a sponsor of a drug or biological product receiving accelerated approval perform additional post-approval confirmatory trials to verify and describe the clinical benefit of the medicine. Any such confirmatory trial must be completed with due diligence and FDA may require that the trial be underway prior to approval. In addition, the FDA currently requires as a condition for accelerated approval pre-submission of promotional materials, which could adversely impact the timing of the commercial launch of the product.

The expedited programs, in general, do not change the standards for approval. Rather, these programs are intended to expedite the development and approval process, but they do not necessarily accomplish that intent.

24

Table of Contents

Post-Approval Requirements

Maintaining substantial compliance with applicable federal, state, and local statutes and regulations requires the expenditure of substantial time and financial resources. Rigorous and extensive FDA regulation of biological products continues after approval, particularly with respect to cGMP. Accordingly, we and our CDMOs will be required to comply with applicable requirements in the cGMP regulations, including quality control and quality assurance and maintenance of records and documentation, with respect to the manufacturing and distribution of any of our product candidates that receive regulatory approval. Other post-approval requirements applicable to biological products, include reporting of cGMP deviations that may affect the identity, strength, quality, potency, or purity of a distributed product in a manner that may impact the safety or effectiveness of the product, record-keeping requirements, reporting of adverse effects, reporting updated safety and efficacy information, and complying with electronic record and signature requirements. After a BLA is approved, the product also may be subject to official lot release. As part of the manufacturing process, manufacturers are required to perform certain tests on each lot of the product before it is released for distribution. If the product is subject to official release by the FDA, the manufacturer submits samples of each lot of product to the FDA together with a release protocol showing a summary of the history of manufacture of the lot and the results of all of the manufacturer’s tests performed on the lot. The FDA also may perform certain confirmatory tests on lots of some products, such as viral vaccines, before releasing the lots for distribution by the manufacturer. In addition, the FDA conducts laboratory research related to the regulatory standards on the safety, purity, potency, and effectiveness of biological products. We and our CDMOs will also be required to comply with all relevant FDA requirements and regulations and any applicable international agency regulatory requirements in our continued manufacturing and promotion of our approved products.

We also must comply with the FDA’s advertising and promotion and related medical communication requirements, such as those related to direct-to-consumer advertising, the prohibition on promoting products for uses or in patient populations that are not described in the product’s approved labeling (known as “off-label use”), the requirement to balance promotion information on efficacy with important safety information and limitations on use, industry-sponsored scientific and educational activities, and promotional activities involving the internet. Discovery of previously unknown problems or the failure to comply with the applicable regulatory requirements may result in restrictions on the marketing of a product or withdrawal of the product from the market as well as possible civil or criminal sanctions. Failure to comply with the applicable U.S. requirements at any time during the product development process, approval process or after approval, may subject an applicant or manufacturer to administrative or judicial civil or criminal sanctions and adverse publicity. FDA sanctions could include refusal to approve pending applications, withdrawal of an approval, clinical hold, warning or untitled letters, product recalls, product seizures, total or partial suspension of production or distribution, injunctions, fines, refusals of government contracts, mandated corrective advertising or communications with doctors, debarment, restitution, disgorgement of profits, or civil or criminal penalties. Any agency or judicial enforcement action could have a material adverse effect on us.

Biological product manufacturers and other entities involved in the manufacture and distribution of approved biological products are required to register their establishments with the FDA and certain state agencies, and are subject to periodic unannounced inspections by the FDA and certain state agencies for compliance with cGMP and other laws. Accordingly, manufacturers must continue to expend time, money, and effort in the area of production and quality control to maintain cGMP compliance. Discovery of problems with a product after approval may result in restrictions on a product, manufacturer, or holder of an approved BLA, including withdrawal of the product from the market. In addition, changes to the manufacturing process or facility generally require prior FDA approval before being implemented and other types of changes to the approved product or conditions of approval, such as adding new indications and additional labeling claims, are also subject to further FDA review and approval.

U.S. Patent Term Restoration and Marketing Exclusivity

Depending upon the timing, duration and specifics of the FDA approval of the use of our product candidates, some of our U.S. patents may be eligible for limited patent term extension under the Drug Price Competition and Patent Term Restoration Act of 1984, commonly referred to as the Hatch-Waxman Amendments. The Hatch-Waxman Amendments permit a patent restoration term of up to five years as compensation for patent term lost during product development and the FDA regulatory review process. However, patent term restoration cannot extend the remaining term of a patent beyond a total of 14 years from the product’s approval date. The patent term restoration period is generally one-half the time between the effective date of an IND and the submission date of a BLA plus the time between the submission date of a BLA and the approval of that application. Only one patent applicable to an approved biological product is eligible for the extension and the application for the extension must be submitted prior to the expiration of the patent. The U.S. Patent and Trademark Office, in consultation with the FDA, reviews and approves the application for any patent term extension or restoration. In the future, we may apply for restoration of patent term for one of our currently owned or licensed patents to add patent life beyond its current expiration date, depending on the expected length of the clinical studies and other factors involved in the filing of the relevant BLA.

25

Table of Contents

A biological product can obtain pediatric market exclusivity in the United States. Pediatric exclusivity, if granted in the case of a biologic approved under a BLA, adds six months to existing exclusivity periods. This six-month exclusivity, which runs from the end of other exclusivity protection, may be granted based on the voluntary completion of a pediatric study in accordance with an FDA-issued “Written Request” for such a study.

The Patient Protection and Affordable Care Act (PPACA) signed into law on March 23, 2010, includes a subtitle called the Biologics Price Competition and Innovation Act of 2009, which created an abbreviated approval pathway for biological products shown to be similar to, or interchangeable with, an FDA-licensed reference biological product. This amendment to the PHS Act attempts to minimize duplicative testing. Biosimilarity, which requires that there be no clinically meaningful differences between the biological product and the reference product in terms of safety, purity, and potency, can be shown through analytical studies, animal studies, and a clinical study or studies. Interchangeability requires that a product is biosimilar to the reference product and the product must demonstrate that it can be expected to produce the same clinical results as the reference product and, for products administered multiple times, 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. However, complexities associated with the larger, and often more complex, structure of biological products, as well as the process by which such products are manufactured, pose significant hurdles to interchangeability approval.

A reference biologic is granted 12 years of exclusivity from the time of first licensure of the reference product. The first biologic product submitted under the abbreviated approval pathway that is determined to be interchangeable with the reference product has exclusivity against other biologics submitting under the abbreviated approval pathway for the lesser of (i) one year after the first commercial marketing, (ii) 18 months after approval if there is no legal challenge, (iii) 18 months after the resolution in the applicant’s favor of a lawsuit challenging the biologics’ patents if an application has been submitted, or (iv) 42 months after the application has been approved if a lawsuit is ongoing within the 42-month period.

Additional Regulation

In addition to the foregoing, state and federal laws regarding environmental protection and hazardous substances, including the Occupational Safety and Health Act, the Resource Conservancy and Recovery Act and the Toxic Substances Control Act, affect our business. These and other laws govern our use, handling and disposal of various biological, chemical and radioactive substances used in, and wastes generated by, our operations. If our operations result in contamination of the environment or expose individuals to hazardous substances, we could be liable for damages and governmental fines. We believe that we are in material compliance with applicable environmental laws and that continued compliance therewith will not have a material adverse effect on our business. We cannot predict, however, how changes in these laws may affect our future operations. Equivalent laws have been adopted in other countries that impose similar obligations.

Other U.S. Healthcare Laws and Regulations

Healthcare providers, physicians and third-party payors play a primary role in the recommendation and use of pharmaceutical products that are granted marketing approval. Arrangements with third-party payors, existing or potential customers and referral sources are subject to broadly applicable fraud and abuse and other healthcare laws and regulations, and these laws and regulations may constrain the business or financial arrangements and relationships through which manufacturers market, sell and distribute the products for which they obtain marketing approval. Such restrictions under applicable federal and state healthcare laws and regulations include the following:

•
the federal Anti-Kickback Statute, which prohibits, among other things, persons from knowingly and willfully soliciting, receiving, offering or paying remuneration, directly or indirectly, in cash or kind, in exchange for, or to induce, either the referral of an individual for, or the purchase, order or recommendation of, any good or service for which payment may be made under federal healthcare programs such as the Medicare and Medicaid programs. This statute has been interpreted to apply to arrangements between pharmaceutical manufacturers, on the one hand, and prescribers, patients, purchasers and formulary managers on the other. A person or entity need not have actual knowledge of this statute or specific intent to violate it;

•
the federal False Claims Act (FCA), which prohibits, among other things, individuals or entities from knowingly presenting, or causing to be presented, claims for payment from Medicare, Medicaid or other federal healthcare programs that are false or fraudulent. Federal Anti-Kickback Statute violations and certain marketing practices, including off-label promotion, also may implicate the FCA;

•
federal criminal laws that prohibit executing a scheme to defraud any healthcare benefit program or making false statements relating to healthcare matters;

26

Table of Contents

•
the federal Physician Payment Sunshine Act, which requires certain manufacturers of drugs, devices, biologics and medical supplies to report annually to the Centers for Medicare & Medicaid Services (CMS) information related to payments and other transfers of value to physicians and teaching hospitals, and ownership and investment interests held by physicians and their immediate family members;

•
the Health Insurance Portability and Accountability Act of 1996 (HIPAA) imposes criminal and civil liability for executing a scheme to defraud any healthcare benefit program or making false statements relating to healthcare matters;

•
regulations promulgated under HIPAA, as amended by the Health Information Technology for Economic and Clinical Health Act, which govern the conduct of certain electronic healthcare transactions and protects the security and privacy of protected health information; and

•
state and foreign law equivalents of each of the above federal laws, such as anti-kickback and false claims laws which may apply to: items or services reimbursed by any third-party payor, including commercial insurers; state laws that require pharmaceutical companies to comply with the pharmaceutical industry’s voluntary compliance guidelines and the relevant compliance guidance promulgated by the federal government or otherwise restrict payments that may be made to healthcare providers and other potential referral sources; state laws that require drug manufacturers to report information related to payments and other transfers of value to physicians and other healthcare providers or marketing expenditures; and state laws governing the privacy and security of health information in certain circumstances. Many of these state and foreign laws differ from federal law and from each other in significant ways and may not have the same effect, thus complicating compliance efforts.

Violation of any of the laws described above or any other governmental laws and regulations may result in penalties, including civil and criminal penalties, damages, fines, the curtailment or restructuring of operations, the exclusion from participation in federal and state healthcare programs and imprisonment. Furthermore, efforts to ensure that business activities and business arrangements comply with applicable healthcare laws and regulations can be costly for manufacturers of branded prescription products.

Coverage and Reimbursement

Significant uncertainty exists as to the coverage and reimbursement status of any products for which we may obtain regulatory approval. In the United States and markets in other countries, sales of any product candidates for which regulatory approval for commercial sale is obtained will depend in part on the availability of coverage and adequate reimbursement from third-party payors. Third-party payors include government authorities, managed care providers, private health insurers and other organizations. The process for determining whether a payor will provide coverage for a drug product may be separate from the process for setting the reimbursement rate that the payor will pay for the drug product. Third-party payors may limit coverage to specific drug products on an approved list, or formulary, which might not include all FDA-approved drugs for a particular indication. Moreover, a payor’s decision to provide coverage for a drug product does not imply that an adequate reimbursement rate will be approved.

Third-party payors are increasingly challenging the price and examining the medical necessity and cost-effectiveness of medical products and services, in addition to their safety and efficacy. New metrics frequently are used as the basis for reimbursement rates, such as average sales price, average manufacturer price and actual acquisition cost. To obtain coverage and reimbursement for any product that might be approved for sale, it may be necessary to conduct expensive pharmacoeconomic studies in order to demonstrate the medical necessity and cost-effectiveness of the products, in addition to the costs required to obtain regulatory approvals. If third-party payors do not consider a product to be cost-effective compared to other available therapies, they may not cover the product after approval as a benefit under their plans or, if they do, the level of payment may not be sufficient to allow a company to sell its products at a profit. Health Technology Assessment, which is intended to take account of medical, social, economic and ethical issues when determining the suitability of a medicinal product for reimbursement, has increasingly become an element of the pricing and reimbursement decisions of the competent authorities in EU Member States.

The U.S. government, state legislatures and foreign governments have shown significant interest in implementing cost containment programs to limit the growth of government-paid health care costs, including price controls, restrictions on reimbursement and requirements for substitution of generic products for branded prescription drugs. By way of example, the enactment of the Inflation Reduction Act (IRA) in August 2022 includes significant changes to potential Medicare drug product reimbursement through government negotiation of certain drug prices, as well as manufacturer discount and inflation rebate obligations. The Trump Administration has issued Executive Orders seeking to reduce prescription drug costs in the U.S. by requiring manufacturers to sell certain drugs in the U.S. at no higher than the lowest prices paid for those same drugs in other developed countries, including through direct-to-consumer (“DTC”) purchasing programs for prescription drugs at the most-favored-nation (“MFN”) price that may bypass traditional supply chain intermediaries. The Administration has announced deals with specific manufacturers to address the Administration’s MFN goals. In addition, in late 2025, HHS proposed three payment models that would test MFN pricing in Medicaid (the voluntary “GENEROUS” model), Medicare Part D (the mandatory “GUARD” model), and Medicare Part B (the mandatory “GLOBE” model) If GLOBE and GUARD are finalized, pharmaceutical manufacturers would be required to pay MFN-based rebates on eligible products for 25% of eligible Medicare beneficiaries during the applicable testing

27

Table of Contents

period. MFN pricing pressures and DTC mechanisms could lead to voluntary or involuntary manufacturer price changes, which could be either temporary or long term, but all of which could adversely affect our business. Adoption of government controls and measures, and tightening of restrictive policies in jurisdictions with existing controls and measures, could limit payments for pharmaceuticals.

U.S. Foreign Corrupt Practices Act

The U.S. Foreign Corrupt Practices Act (FCPA), to which we are subject, prohibits corporations and individuals from engaging in bribery and corruption when dealing with foreign government officials. It is illegal to pay, offer to pay, promise or authorize the payment of money or anything of value, directly or indirectly, to any foreign government official, political party or political candidate in an attempt to secure an improper advantage in order to obtain or retain business or to otherwise improperly influence a foreign official in his or her official capacity. Comparable laws have been adopted in other countries that impose similar obligations. We are also subject to the FCPA’s accounting provisions, which require us to keep accurate books and records and to maintain a system of internal accounting controls sufficient to assure management’s control, authority, and responsibility over our assets. The failure to comply with the FCPA and similar laws could result in civil or criminal sanctions or other adverse consequences.

Government Regulation Outside of the United States

In addition to regulations in the United States, we will be subject to a variety of regulations in other jurisdictions governing, among other things, clinical studies and any commercial sales and distribution of our products. Because biologically sourced raw materials are subject to unique contamination risks, their use may be restricted in some countries.

Whether or not we obtain FDA approval for a product, we must obtain the requisite approvals from regulatory authorities in foreign countries prior to the commencement of clinical studies or marketing of the product in those countries. Many countries outside of the United States have a similar process that requires the submission of a clinical study application much like the IND prior to the commencement of human clinical studies.

In the EU, for example, clinical trials are governed by the EU Regulation on Clinical Trials (Reg. EU No. 536/2014), or CTR, which became applicable in January 2022 and established a centralized process of obtaining competent authority approval for clinical trials in the EU. Under the CTR, trial sponsors submit their application for approval via an EU Portal. The approvals are still granted by the competent authorities of each EU Member State where the trial takes place; however, the procedure for approval is conducted in a coordinated manner among the concerned EU Member States as provided under the CTR. While the process for the application and granting of the approvals was streamlined, it remains a complex process that can significantly delay the start of a multinational clinical trial.

In the United Kingdom of Great Britain and Northern Ireland (UK), clinical trials are governed by the Medicines for Human Use (Clinical Trials) Regulations 2004 (UK CTRs). Under the UK CTRs, an approval is required from the Medicines and Healthcare products Regulatory Agency (MHRA) together with a positive ethics committee opinion. Clinical trials which take place in the UK and on NHS hospital sites, typically do so on the basis of standardized documentation which set out indemnification provisions. In the UK, new regulations, the Medicines for Human Use (Clinical Trials) (Amendment) Regulations 2025, which update the current UK CTRs, were approved and will come into force on 28 April 2026. These amendment regulations include changes with respect to transparency, approval pathways and regulatory requirements.

To obtain regulatory approval of a biological medicinal product in the EU, we must submit a marketing authorization application. The grant of marketing authorization in the EU for products containing viable human tissues or cells such as gene therapy medicinal products is governed by Regulation (EC) No 1394/2007 on advanced therapy medicinal products, read in combination with Directive 2001/83/EC on the Community code relating to medicinal products for human use and Regulation (EC) No 726/2004 laying down Community procedures for the authorization and supervision of medicinal products for human and veterinary use and establishing the EMA. Regulation (EC) No 1394/2007 lays down specific rules concerning the authorization, supervision and pharmacovigilance of gene therapy medicinal products, somatic cell therapy medicinal products and tissue engineered products. The EMA’s Committee for Advanced Therapies (CAT) is responsible for assessing the quality, safety and efficacy of ATMP. ATMP include gene therapy medicinal products, somatic cell therapy medicinal products and tissue engineered products. The role of the CAT is to prepare a draft opinion on an application for marketing authorization for an ATMP candidate that is submitted to the EMA. The EMA then provides a final opinion regarding the application for marketing authorization. The European Commission grants or refuses marketing authorization after the EMA has delivered its opinion.

Innovative medicinal products are authorized in the EU on the basis of a full marketing authorization application (as opposed to an application for marketing authorization that relies, in whole or in part, on data in the marketing authorization dossier for another, previously approved medicinal product). Applications for marketing authorization for innovative medicinal products must contain the results of pharmaceutical tests, preclinical tests and clinical trials conducted with the medicinal product for which marketing authorization is sought. Innovative medicinal products for which marketing authorization is granted are entitled to eight years of data exclusivity. During this period, applicants for approval of generics or biosimilars of these innovative products cannot rely on data

28

Table of Contents

contained in the marketing authorization dossier submitted for the innovative medicinal product to support their application. Innovative medicinal products for which marketing authorization is granted are also entitled to ten years of market exclusivity. During these ten years of market exclusivity, no generic or biosimilar medicinal product may be placed on the EU market even if a marketing authorization application for approval of a generic or biosimilar of the innovative product has been submitted to the EMA or to the competent regulatory authorities in the EU Member States and marketing authorization has been granted. The ten years of market exclusivity will be extended to a maximum of eleven years if, during the first eight years of those ten years, the marketing authorization holder obtains an authorization for one or more new therapeutic indications which, during the scientific evaluation prior to their authorization, are held to bring a significant clinical benefit in comparison with existing therapies. However, there is no guarantee that the EU’s regulatory authorities will consider a product to be an innovative medicinal product which is eligible for the relevant periods of data and market exclusivity.

Products authorized as “orphan medicinal products” in the EU are entitled to benefits additional to those granted in relation to innovative medicinal products. In accordance with Article 3 of Regulation (EC) No 141/2000 on orphan medicinal products, a medicinal product may be designated as an orphan medicinal product if (i) it is intended for the diagnosis, prevention or treatment of a life-threatening or chronically debilitating condition; (ii) either (a) such condition affects no more than five in 10,000 persons in the EU when the application is made, or (b) the product, without the incentives derived from orphan medicinal product status, would not generate sufficient return in the EU to justify investment; and (iii) there exists no satisfactory method of diagnosis, prevention or treatment of such condition authorized for marketing in the EU, or if such a method exists, the product will be of significant benefit to those affected by the condition. Further guidance on such criteria is provided in Regulation (EC) No 847/2000 laying down the provisions for implementation of the criteria for designation of a medicinal product as an orphan medicinal product and definitions of the concepts “similar medicinal product” and “clinical superiority”. Orphan medicinal products are eligible for financial incentives such as reduction of fees or fee waivers and following grant of a marketing authorization, the EMA and the EU Member States’ competent authorities are not permitted to accept another application for a marketing authorization, or grant a marketing authorization or accept an application to extend an existing marketing authorization, for the same therapeutic indication of a similar medicinal product for ten years following grant or authorization. The application for orphan drug designation must be submitted before the application for marketing authorization. The applicant may receive a fee reduction for the marketing authorization application if the orphan drug designation has been granted, but not if the designation is still pending at the time the marketing authorization is submitted. Orphan drug designation does not convey any advantage in, or shorten the duration of, the regulatory review and approval process.

The 10-year market exclusivity that an orphan drug enjoys may be reduced to six years if, at the end of the fifth year, it is established that the product no longer meets the criteria for orphan designation, for example, if the product is sufficiently profitable not to justify maintenance of market exclusivity. Additionally, marketing authorization may be granted to a similar product during the 10-year period of market exclusivity for the same therapeutic indication at any time if:

•
The second applicant can establish in its application that its product, although similar to the orphan medicinal product already authorized, is safer, more effective or otherwise clinically superior;

•
The holder of the marketing authorization for the original orphan medicinal product consents to a second orphan medicinal product application; or

•
The holder of the marketing authorization for the original orphan medicinal product cannot supply enough orphan medicinal product.

Similar to obligations imposed in the United States, medicinal products authorized in the EU may be subject to post-authorization obligations, including the obligation to conduct Post Marketing Safety Studies (PASS) or Post Marketing Efficacy Studies (PAES).

In April 2024, the European Parliament adopted its position on the European Commission's proposal for a new Directive and a new Regulation, which would revise and replace the existing general pharmaceutical legislation. The proposed changes include a proposal to recast Directive 2001/83/EC, i.e., the Community code on medicinal products and the creation of a new Regulation laying down EU marketing authorization of medicinal products that will replace Regulation (EC) No 726/2004, Regulation (EC) No 141/2000 on orphan drugs and Regulation (EC) No 1901/2006 on pediatric medicines, and amend Regulation (EC) No 1394/2007 on ATMP and Regulation (EU) No 536/2014, i.e., the CTR. After the European Parliament’s position, the so-called trilogue negotiations among the Commission, the Parliament, and the Council commenced.

On December 11, 2025, a press release was issued by the European Council stating that an agreement was achieved. The texts of the draft legislation are not available yet, but according to the press release, an agreement was reached on one of the main diverging points, the data exclusivity and market protection periods, to the effect that an eight-year data exclusivity period for new medicines will be provided, plus one year of market protection, which may be extended by an additional year for innovative medicines that satisfy two out of three conditions.

29

Table of Contents

Other key elements of the proposed framework were also agreed upon, including a provision giving EU countries the power to require companies to supply medicines benefiting from regulatory protection in sufficient quantities to meet patient needs, clarified wording on the so-called Bolar-exemption (an intellectual property exemption allowing generics manufacturers to start research of a medicine before patent expiry), and an extension of its scope to include submissions for procurement tenders, and a new transferrable exclusivity voucher incentivizing pharmaceutical companies to help combat antimicrobial resistance by developing priority antibiotics.

The provisional agreement now needs to be endorsed by both the Council of the European Union and the European Parliament, before being formally adopted and entering into force upon publication in the EU’s Official Journal.

Reimbursement for medicinal products is still an area that is not harmonized in the EU and is largely governed by EU Member States’ laws. However, there are some EU level legal frameworks that must be considered, including Directive 89/105/EEC (the Price Transparency Directive). The aim of the Price Transparency Directive is to ensure that pricing and reimbursement mechanisms established in EU Member States are transparent and objective, do not hinder the free movement and trade of medicinal products in the EU and do not hinder, prevent or distort competition on the market. The Price Transparency Directive does not, however, provide any guidance concerning the specific criteria on the basis of which pricing and reimbursement decisions are to be made in individual EU Member States. Neither does it have any direct consequence for pricing or levels of reimbursement in individual EU Member States. The national authorities of the individual EU Member States are free to restrict the range of medicinal products for which their national health insurance systems provide reimbursement and to control the prices and/or reimbursement of medicinal products for human use. Individual EU Member States adopt policies according to which a specific price or level of reimbursement is approved for the medicinal product. Other EU Member States adopt a system of reference pricing, basing the price or reimbursement level in their territory either on the pricing and reimbursement levels in other countries, or on the pricing and reimbursement levels of medicinal products intended for the same therapeutic indication. Furthermore, some EU Member States impose direct or indirect controls on the profitability of the company placing the medicinal product on the market.

In 2011, Directive 2011/24/EU on the application of patients’ rights in cross-border healthcare was adopted at the EU level. The Directive is intended to establish rules for facilitating access to safe and high-quality cross-border healthcare in the EU.

Health Technology Assessment (HTA) of medicinal products is becoming an increasingly common part of the pricing and reimbursement procedures in some EU Member States. HTA is the procedure according to which the assessment of the public health impact, therapeutic impact and the economic and societal impact of the use of a given medicinal product in the national healthcare systems of the individual country is conducted. HTA generally focuses on the clinical efficacy and effectiveness, safety, cost, and cost-effectiveness of individual medicinal products as well as their potential implications for the national healthcare system. Those elements of medicinal products are compared with other treatment options available on the market.

The outcome of HTA may influence the pricing and reimbursement status for specific medicinal products within individual EU member states. The extent to which pricing and reimbursement decisions are influenced by the HTA of a specific medicinal product vary between the EU Member States.

A new Regulation on HTA on EU level was adopted in December 2021: Regulation (EU) 2021/2282 on health technology assessment (the HTA Regulation) and has been applicable since January 12, 2025. The HTA Regulation covers new medicines and certain new medical devices. Member states will be able to use common HTA tools, methodologies and procedures across the EU, working together in four main areas: (i) joint clinical assessments focusing on the most innovative health technologies with the most potential impact for patients; (ii) joint scientific consultations whereby developers can seek advice from HTA authorities; (iii) identification of emerging health technologies to identify promising technologies early; and (iv) continuing voluntary cooperation in other areas. Individual member states will continue to be responsible for assessing non-clinical (e.g., economic, social, ethical) aspects of health technology and making decisions on pricing and reimbursement. For other countries outside of the EU, such as countries in Eastern Europe, Latin America or Asia, the requirements governing the conduct of clinical studies, product licensing, pricing and reimbursement vary from country to country. In all cases, again, the clinical studies are conducted in accordance with GCP and the applicable regulatory requirements and the ethical principles that have their origin in the Declaration of Helsinki.

As a consequence of Brexit, the UK formally left the EU and as of January 1, 2021, the UK is a “third country” with respect to the EU (subject to the terms of the EU UK Trade Agreement), so that EU law ceased to apply directly in the UK. However, the UK has retained the EU regulatory regime with certain modifications as standalone UK legislation, while certain aspects of the EU medicines laws remain applicable in Northern Ireland pursuant to the Northern Ireland Protocol, as amended by the Windsor Framework with effect from January 1, 2025. Therefore, the UK regulatory regime is currently substantially similar to EU regulations, but under the Medicines and Medical Devices Act 2021, the UK may adopt changed regulations for medicines, including their research, development and commercialization. Currently, new regulations with respect to clinical trials are due to come into force in April 2026, as referred to above.

30

Table of Contents

In the UK, gene therapy medicinal products are classified as advanced therapy medicinal products. To place an advanced therapy medicinal product on the UK market, a person must hold a marketing authorization for the medicinal product. There are various routes to applying for a marketing authorization in the UK. These include a UK-wide national application for a medicinal product, which operates on a 150-day assessment procedure if all issues are resolved following one round of questions (if they are not, a 210 assessment procedure applies), or on a rolling review basis. The UK also permits submissions for applications via the “Access Consortium” process which allows simultaneous submission to the UK, Australia, Canada, Singapore and/or Switzerland, and which follows a standard 180-day procedure, with the UK aiming to make a decision within 210 days. From 1 January 2024, the UK adopted an international recognition procedure which is a route open to applicants that have already received an authorization for the same product from one of the MHRA reference regulators. Reference regulators include the European Medicines Agency and the FDA. Under the international recognition procedure, there are two recognition routes (Route A and Route B). Advanced therapy medicinal products must follow Route B, which sets out a 110-day timetable, which runs from the date on which the submission has been validated by the MHRA. In order to make an application for a marketing authorization, the applicant must be established in the UK or the EU/EEA.

In the UK, following implementation of the Windsor Framework (an agreement which made changes to the Northern Ireland Protocol), from January 1, 2025, medicinal products may be designated as an orphan drug in the UK and will be valid UK-wide regardless of whether there is an EU orphan designation or EU authorization as an orphan medicinal product if the medicine meets certain criteria similar to those set out in European legislation. Unlike in the EU, there is no need to obtain orphan designation before the application for authorization is made, instead the criteria will be assessed with the application. On grant of a marketing authorisation with orphan status, the medicinal product will benefit from UK orphan rewards of up to 10 years of market exclusivity from similar products in the approved orphan indication. During that period a marketing authorisation will not be granted for a similar product in the approved orphan indication although the MHRA may request that market exclusivity be reduced from 10 to 6 years in certain circumstances if the orphan criteria are no longer met.

If we fail to comply with applicable foreign regulatory requirements, we may be subject to, among other things, fines, suspension or withdrawal of regulatory approvals, product recalls, seizure of products, operating restrictions and criminal prosecution.

Human Capital Resources

As of February 27, 2026, we employed 371 full-time employees, of which 296 were engaged in research and development activities, including preclinical, clinical and manufacturing related functions, and 75 were engaged in general administrative activities, including commercial, corporate development, finance, legal, human resources, information technology, facilities and other general and administrative functions. We have never had a work stoppage, and none of our employees are represented by a labor organization or under any collective bargaining arrangements. We consider our relationship with our employees to be good.

Talent, Growth and Retention

We appreciate the importance of retention, growth and development of our employees. We seek and value employees who have substantial experience in the discovery, development, manufacture and commercialization of innovative therapies in a complex regulatory environment. For certain key functions, especially in research and development and manufacturing activities, we require specialized scientific and gene therapy expertise. To attract and retain the talent we require, we believe we offer competitive compensation, including salary, cash incentive awards and equity awards, along with competitive benefits packages, including medical, dental, vision and life insurance, flexible spending accounts, short- and long-term disability and matching contributions to a 401(k) tax-deferred savings plan. All full-time employees are eligible to participate in the same health and welfare and retirement savings plans. Additionally, we provide professional development programs and on-demand learning opportunities to cultivate talent at all levels throughout our company.

Equal Opportunity

We believe that a diverse, equitable and inclusive culture fosters innovation, which is integral to our mission of improving lives through the curative potential of gene therapy. We have worked to ensure equal opportunity in all aspects of employment and appropriate merit-based representation of gender, race and ethnicity throughout our company. We emphasize an inclusive environment and equitable treatment as an important part of our company culture.

31

Table of Contents

Available Information

Our principal offices are located at 9804 Medical Center Drive, Rockville, MD 20850, and our telephone number is (240) 552-8181. Our website address is www.regenxbio.com. The information contained in, or that can be accessed through, our website is not a part of, or incorporated by reference in, this Annual Report on Form 10-K. We file annual, quarterly, and current reports, proxy statements, and other documents with the SEC under the Exchange Act. You may obtain any reports, proxy and information statements, and other information that we file electronically with the SEC at www.sec.gov.

You also may view and download copies of our SEC filings free of charge at our website as soon as reasonably practicable after we electronically file such material with, or furnish it to, the SEC. The information contained on, or that can be accessed through, our website will not be deemed to be incorporated by reference in, and is not considered part of, this Annual Report on Form 10-K. Investors should also note that we use our website, as well as SEC filings, press releases, public conference calls and webcasts, to announce financial information and other material developments regarding our business. We use these channels, as well as any social media channels listed on our website, to communicate with investors and members of the public about our business. It is possible that the information that we post on our social media channels could be deemed material information. Therefore, we encourage investors, the media and others interested in our company to review the information that we post on our social media channels.

32

Table of Contents