Table of Contents

i

CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This Annual Report on Form 10-K includes forward-looking statements, which involve risks and uncertainties. These forward-looking statements can be identified by the use of forward-looking terminology, including the terms “believe,” “estimate,” “project,” “anticipate,” “expect,” “seek,” “predict,” “aim,” “continue,” “possible,” “intend,” “may,” “might,” “will,” “could,” “would” or “should” or, in each case, their negative, or other variations or comparable terminology. These forward-looking statements include all matters that are not historical facts. They appear in a number of places throughout this Annual Report on Form 10-K. We derive many of our forward-looking statements from our operating budgets and forecasts, which are based upon many detailed assumptions. While we believe that our assumptions are reasonable, we caution that it is very difficult to predict the impact of known factors, and, of course, it is impossible for us to anticipate all factors that could affect our actual results. All forward-looking statements are based upon information available to us on the date of this Annual Report on Form 10-K.

The forward-looking statements in this Annual Report on Form 10-K include, among other things, statements about:

By their nature, forward-looking statements involve risks and uncertainties because they relate to events and depend on circumstances that may or may not occur in the future. We caution you that forward-looking

ii

statements are not guarantees of future performance and that our actual results of operations, financial condition, business and prospects may differ materially from those made in or suggested by the forward-looking statements contained in this Annual Report on Form 10-K. In addition, even if our results of operations, financial condition, business and prospects are consistent with the forward-looking statements contained in this Annual Report on Form 10-K, those results may not be indicative of results in subsequent periods.

ii

You should read this Annual Report on Form 10-K completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of our forward-looking statements by these cautionary statements.

As used in this Annual Report on Form 10-K, the terms “Solid,” “the Company,” “we,” “us” and “our” refer to Solid Biosciences Inc. unless the context indicates otherwise.

RISK FACTOR SUMMARY

Our business is subject to a number of risks that if realized could materially affect our business, operating results and financial condition and the trading price of our common stock could decline. These risks are discussed more fully in the “Risk Factors” section of this Annual Report on Form 10-K. These risks include the following:

iii

PART I

Overview

Our mission is to cure Duchenne muscular dystrophy, or DMD,Duchenne, a genetic muscle-wasting disease predominantly affecting boys, with symptoms that usually manifest between three and five years of age. DMDboys. Duchenne is a progressive, irreversible and ultimately fatal disease that affects approximately one in every 3,500 to 5,000 live male births and has an estimated prevalence of 10,0005,000 to 15,000 cases in the United States alone. DMDDuchenne is caused by mutations in the dystrophin gene, which result in the absence or near-absence of dystrophin protein. Dystrophin protein works to strengthen muscle fibers and protect them from daily wear and tear. Without functioning dystrophin and certain associated proteins, muscles suffer excessive damage from normal daily activities and are unable to regenerate, leading to the build-up of fibrotic, or scar, and fat tissue. There is no cure for DMDDuchenne and, for the vast majority of patients, there are no satisfactory symptomatic or disease-modifying treatments. Our efforts are focused on our lead product candidate, SGT-001, is a gene transfer candidate under developmentinvestigation for its ability to restoredrive functional dystrophin protein expression in patients’ muscles. Based on our preclinical program that included multiple animal species of different phenotypesmuscles and genetic variations, we believeimprove the mechanism of action of SGT-001, if our clinical trials prove to be successful, has the potential to slow or even halt the progression of DMD, regardlesscourse of the typedisease, as well as SGT-003, our next-generation gene therapy candidate for the treatment of genetic mutation or stage of the disease.

SGT-001 has been granted Rare Pediatric Disease Designation, or RPDD, in the United States and Orphan Drug Designations in both the United States and European Union. In November 2017, we initiated a Phase I/II clinical trial for SGT-001, called IGNITE DMD, and in February 2018 we dosed the first patient, a non-ambulatory adolescent. On March 14, 2018, we announced that IGNITE DMD was placed on full clinical hold following a serious adverse event reported in the clinical trial.Duchenne.

For patients suffering from DMD,Duchenne, symptoms usually begin to manifest between three and five years of age, when they fail to reach developmental milestones or experience motor function challenges, such as difficulty walking or climbing stairs. As the disease progresses, patients with DMDDuchenne experience frequent falls; can no longer run, play sports or perform most daily functions; and are further weakened by physical activity. By their early teens, DMDDuchenne patients typically lose their ability to walk and ultimately become dependent on a wheelchair for mobility. By their 20s, patients essentially become paralyzed from the neck down and require a ventilator to breathe. Though disease severity and life expectancy vary, a DMDDuchenne patient’s quality of life dramatically decreases over time, with death typically occurring by early adulthood from either cardiac or respiratory complications.

Our founders, who are personally touched by the disease, created a biotechnology company purpose-built to accelerate the discovery and development of meaningful therapies for all patients affected by DMD.Duchenne. Through this disease-focused business model, our research team, led by experts in DMDDuchenne biology and drug development, along with key opinion leaders in DMD,Duchenne, continuously evaluate emerging science to identify high-potential product candidates. Our selection process includes extensive diligence and initial pharmacology research with highly specific, predefined criteria, which provide us with confidence in our development program decisions. Through this data-driven selection process, we have evaluated a number of programs and identified gene therapy as a potentially beneficial approach for DMD,Duchenne, and thus initiated development of our lead product candidate SGT-001. We will continue to apply this rigorous approachcandidates SGT-001 and reject the majority of the candidates we evaluate in our effort to develop only programs that we believe have the greatest likelihood of becoming therapies for DMD patients.SGT-003.

Our product candidates

SGT-001 is our leadand SGT-003 are gene transfer candidate.candidates. Gene transfer, a type of gene therapy, is designed to address diseases caused by mutated genes through the delivery of functional versions of those genes, called transgenes. The transgenes are then utilized by the body to produce proteins that are absent or not functional prior to

treatment, potentially offering long-lasting beneficial clinical effects. SGT-001 isand SGT-003 are designed to address the underlying genetic cause of DMDDuchenne by delivering a synthetic transgene that produces dystrophin-like protein that is only expressed in muscles of the body, including cardiac and respiratory muscles. Our SGT-001 vector isand SGT-003 vectors are derived from a naturally occurring, non-pathogenic virus called adeno-associated virus, or AAV, which waswere selected for itstheir ability to efficiently enter skeletal, diaphragm and cardiac muscle tissues. The vector isvectors are designed to carry a synthetic dystrophin transgene construct, called microdystrophin, that retains the most critical components of the full-size dystrophin gene yet is small enough to fit within AAV packaging constraints.SGT-001 is designed These components not only include the domains necessary to confer protection against muscle damage, but also to drive the expression of key dystrophin associated proteins, such as neuronal Nitric Oxide Synthase, or nNOS. Inclusion of this nNOS coding region of the dystrophin protein may result in microdystrophin protein expressionthat has unique activity, restore nitric oxide production in affected muscles throughout the body. Wemuscle and potentially provide important functional benefits such as diminished muscle fatigue and protection against ischemic muscle damage.

SGT-001

SGT-001 is our lead gene transfer candidate and utilizes an AAV9 vector. In our Investigational New Drug Application, or IND, enabling preclinical program, we have studied the efficacy, safety and durability of SGT-001 in multiple preclinical models and its functional benefits in DMDDuchenne animal studies. In contrast to some other therapeutic approaches, that areSGT-001 is not designed to target specific mutations in the dystrophin gene, we believe gene.

SGT-001 is a mutation agnostic approach.

Inhas been granted Rare Pediatric Disease Designation, and Fast Track Designation, in the fourth quarterUnited States and Orphan Drug Designations in both the United States and European Union. The safety and efficacy of 2017, we initiated a randomized, controlled,SGT-001 are under evaluation in an open-label, single-ascending dose Phase I/II clinical trial called IGNITE DMD.

1

We initiated IGNITE DMD in the fourth quarter of 2017 to evaluate SGT-001 in ambulatory and non-ambulatory males with DMDDuchenne aged four to 17 years. The primary objectives of IGNITE DMD are to assess the safety and tolerability of SGT-001, as well as efficacy as defined by SGT-001 microdystrophin protein expression. The clinical trial is also designed to assess other parameters of muscle function and mass, respiratory and cardiovascular function, serum and muscle biomarkers associated with SGT-001 microdystrophin production, SGT-001 microdystrophin associated biochemical properties (e.g., nNOS binding) and patient and parent reported outcomes and quality of life measures, among other endpoints.

Patient Dosing

To date, nine patients have been dosed in IGNITE DMD is anticipated to enroll 16 to 32with SGT-001. In 2021, we dosed three patients with DMD, who will be randomly assigned to either an active treatment group or a delayed treatment group. It is planned so that adolescents aged 12 to 17 years will receive treatmentin February (Patient 7), April (Patient 8) and at a later stage of the clinical trial, children aged four to 11 years will be dosed. Efficacy will be assessed by comparing microdystrophin protein expression in muscle biopsy before treatment and 12 months after treatment for each patient. ParticipantsNovember (Patient 9) in the control group who continue2E14 vg/kg cohort with SGT-001. All three patients were dosed with our second generation manufacturing process. Patients 7 and 9 were safely dosed, with transient and manageable adverse events, none of which were serious. Patient 8 experienced a systemic inflammatory response which has since fully resolved. The event was classified as a serious adverse event, or SAE, and considered to meetbe drug related. The type of event is described in our Investigators Brochure and is not considered unexpected. Following the dosing of Patient 8, we conducted an extensive review of all clinical trial criteria would receive active treatment after 12 months.

In March 2018,data from IGNITE DMD, which resulted in a strengthened risk mitigation plan that was submitted to the U.S. Food and Drug Administration, or the FDA, placedand implemented prior to the dosing of the Patient 9.

Clinical Data

In 2021, we reported long-term biomarker data from biopsies of skeletal muscle from IGNITE DMD on full clinical hold following our reportPatients 4-6 taken 24 months, 18 months and 12 months post-dosing, respectively. In addition, we reported interim safety and efficacy data for motor function as assessed by North Star Ambulatory Assessment, or NSAA, and 6-Minute Walk Test, or 6MWT, pulmonary function as assessed by pulmonary function tests, or PFTs, including forced vital capacity, or FVC, peak expiratory flow, or PEF, and forced expiratory volume in one second, or FEV1, as well as patient reported outcome measures, or PROMs, as assessed by the key functional domains of a serious adverse eventthe Pediatric Outcomes Data Collection Instrument, or PODCI.

In March 2022, we announced two-year interim safety and efficacy data from the first three Patients (Patients 4-6) treated with SGT-001 in the clinical trial. On February 14, 2018,2E14 vg/kg dose cohort of IGNITE DMD. Results suggested durable benefit 24-months post-administration of SGT-001, when compared to natural history. These data were consistent with results reported at the first patient12-month and 18-month time periods for the same patients. The average age of Patients 4-6 at the two year timepoint was 10.4 years.

Data from Patients 4-6 suggested sustained motor function at two years post-infusion, as assessed by 6MWT and NSAA, against expected natural history declines. In addition, the data suggested improved pulmonary function, as measured by FVC and PEF, and sustained or improved PROMs as assessed in key functional domains of the PODCI when compared to both baseline and natural history.

2

The following table summarizes the interim efficacy results of Patients 4-6 of the 2E14 vg/kg cohort in IGNITE DMD a non-ambulatory adolescent, received a dose of 5E13 vg/kg of SGT-001,at 12-months, 18-months and 24-months post-dosing. Data are presented as mean change from baseline at each respective timepoint and as the low dose inmean change from natural history at the clinical trial. Several days after administration24-month timepoint. Mean difference from natural history is calculated as the patient was hospitalized due to laboratory findings that included a decrease in platelet count followed by a reduction in red blood cell countdifference between mean change from baseline for Patients 4-6 at 24-months and evidence of complement activation. The patient showed no signs or symptoms of coagulopathy (bleeding disorder), had no relevantthe expected changes from baseline in liver function tests and responded well to medical treatment.each measure over 24 months, based on published natural history studies:

We

^{(1): -84.6m expected decline in 24 months after age 7 (Mercuri et al 2016)}

^{(2): -6.0 unit expected decline in 24 months after age 6.3 (Muntoni eta al 2019)}

^{(3): -10.0%p expected decline in 24 months after age 6 (Mayer et al 2015)}

^{(4): -10.0%p expected decline in 24 months after age 6 (Mayer et al 2015)}

^{(5): -10.1 point expected decline in 24 months (Henricson et al 2013)}

^{(6): -19.9 point expected decline in 24 months (Henricson et al 2013)}

^{(7): -6.2 point expected decline in 24 months (Henricson et al 2013)}

In March 2022, we reported the serious adverse event to the FDA and, because it was unexpected, classified it as a Suspected Unexpected Serious Adverse Reaction, or SUSAR. We have halted enrollment and dosing in IGNITE DMD and are awaiting the formal clinical hold letterdata from skeletal muscle biopsies collected three months after infusion of SGT-001 from the FDA.

Assuming successful resolutionmost recently dosed Patients 7-9.  The range by immunofluorescence of 1% to 50% and by western blot of Below the full clinical hold and based on data from5% Limit of Quantification (BLQ) to 6.8%, were within the clinical trial, we will determine next steps for SGT-001 clinical development, including additional clinical trials that may include other patient populations, as well as the need for larger confirmatory clinical trials.

In addition, pursuant to a letter we received from the FDA in November 2017, we are not permitted to dose patientsrange of previously dosed Patients 4-6 in the higher-dose grouphigh dose cohort. Microdystrophin expression levels for all six patients dosed in the high dose cohort (Patients 4-9) ranged from 1 to 70% by immunofluorescence and BLQ to 17.5% by western blot. All six patients dosed with SGT-001 in the high dose cohort have demonstrated microdystrophin expression and proper membrane localization.

No new drug-related safety findings have been identified in Patients 1-9 in post-dosing periods of IGNITE DMD due90 days to a partial clinical hold. The hold relatesapproximately four years. We continue to the number of vialsfollow dosed patients and manufacturing lots utilized per patient, as well as manufacturing processescollect data to support the higher-dose group. We have submitted our response to the FDA and are awaiting their feedback.potential benefit of SGT-001.

If successfully developed and approved, we intend to commercialize SGT-001 in the United States and European Union, and we may enter into licensing agreements or strategic collaborations to commercialize the product candidate in other markets.

Taking into account the prevalence and incidence of DMDDuchenne and the anticipated dosing requirements for gene transfer, we anticipate that there will be a need for a substantial supply of SGT-001 for clinical trials and, if approved, for commercial markets. Through significant targeted investments to address this challenge, we generated sufficient drug product supplyhave developed a manufacturing process that we believe can scale to initiateadequately support our IGNITE DMD. We continueneeds for clinical trials, commercial launch and beyond. Our in-house scientists are continuing to developwork to increase the productivity, efficiency and purity of our manufacturing process.

SGT-003

SGT-003 is our next-generation gene transfer candidate. It is comprised of our nNOS binding domain microdystrophin transgene and muscle-specific promoter present in SGT-001 and uses a novel, rationally designed AAV capsid, candidate, selected for potentially enhanced muscle tropism, to deliver these components to target tissues. We believe that the properties of this novel capsid may allow for enhanced benefit over therapies using traditional capsids, potentially both in terms of efficacy and safety.

We plan to submit an Investigational New Drug, or IND, application for SGT-003 in early 2023 and initiate IND-enabling studies in 2022.

We have selected a manufacturing process that we believe can scale to meet future clinical and commercial productionadequately support our needs for SGT-001.

While we believe gene transfer may be ableclinical trials, commercial launch and beyond. Our in-house scientists are continuing to slowwork in close partnership with our Contract Development and Manufacturing, or halt DMD disease progression, many patients would still suffer from the manifestations of the disease, such as tissue damageCDMO, partner to their muscles, inflammation, cardiac dysfunctionincrease both yield and fibrosis. As partquality of our disease-focused business model, we are also building a portfolio of complementary disease modifying therapies to address these manifestations. Our portfolio currently includes an initial disease modifying candidate, SB-001, a monoclonal antibody designed to reduce fibrosis and inflammation, as well as a number of emerging and complementary programs. We intend to commence preclinical activities for the SB-001 program in 2018.manufacturing.

3

Platform technologies

In addition to developing our gene transfer candidates, we have development programs focusing on platform technologies, including dual gene expression, a technology that allows us to package multiple transgenes into one vector, as well as novel capsids. These programs are part of our ongoing research efforts to develop innovative technologies that we believe may hold potential to translate into meaningful treatments and drive our future pipeline expansion.

Preclinical data in both wild-type and disease animal models demonstrate that we have developed a library of product candidates,novel capsids that have shown increased muscle tropism with concomitant decreased liver biodistribution, resulting in improved efficiency compared to AAV9.  

In conjunction with our development of SGT-001 and SGT-003,we believe it is critical to invest time and resources incontinue to investigate tools and technologies designed to help us more effectively understand DMD,Duchenne, accurately monitor disease progression and assist patients in daily life. As part of this goal, we are developing biomarkers and sensorsevaluating the use of sensor-based technologies that may allow us to identify treatment targets faster,biomarkers that measure the therapeutic impact of potential product candidates better and reach decision points earlier. In addition, through our Solid Suit program, we are developing a linebetter measure the therapeutic impact of soft, wearable assistive devices with the goal of providing functional and therapeutic benefits to DMD patients.

Our pipeline

We seek to protect our proprietary and intellectual property position through a combination of patents, trade secret laws, proprietary know-how, continuing technological innovation, and entering into non-disclosure, confidentiality and invention assignment agreements. We have exclusively licensed three issued U.S. patents, one pending U.S. non-provisional patent application, and seven issued patents and eleven pending patent applications in foreign jurisdictions. We have filed three pending U.S. provisional patent applications. We intend to continue building out our intellectual property protection to further strengthen our position in the DMD field.potential product candidates.

Who we are

Solid Biosciences was founded in 2013 by our Chief Executive Officer, Ilan Ganot, our former Chairman of the Board, Andrey Zarur, and our former President, Gilad Hayeem, a former board member, Matthew Arnold, and our Vice President, Patient Advocacy, Annie Ganot, with the goal of developing meaningful therapies for patients with DMD.Duchenne. Solid is the English translation of Eytani, the Hebrew name of Ilan and Annie Ganot’s son,

who was diagnosed with the disease in 2012. Our founders, unsatisfied with the existing therapeutic landscape, proceeded to raise funds to execute on our disease-focused business model. We assembled a passionate management team and scientific advisory board composed of individuals with extensive experience in DMD,Duchenne, gene therapy, product discovery, research and development, manufacturing, business strategy and finance.

In 2015, we began exclusively licensing the elements of the construct for SGT-001 and other elements of ourthe SGT-001 gene transfer program from the University of Michigan, the University of Missouri and the University of Washington. Since then, we have continued to use our extensive network across the academic, business and patient communities to identify, vet and pursue high-potential complementary product candidates to address the needs of DMDDuchenne patients.

Since our inception, we have raised private capital from a group of top-tier corporate and private investors. In addition, three leading U.K.-based DMD charities provided initial seed funding for our gene transfer program in return for equity in our company, and we have accepted additional contributions from several DMD charities to fund our early-stage research programs. In January 2018, we completed our initial public offering resulting in net proceeds of $129.3 million, after deducting underwriting discounts and commissions and offering expenses.

We operated as a Delaware limited liability company under the name Solid Biosciences, LLC until immediately prior to the effectiveness of our registration statement on Form S-1 on January 25, 2018, at which time we converted into a Delaware corporation pursuant to a statutory conversion and changed our name to Solid Biosciences Inc.

Mission

Our mission, which guides every aspect of our operations, is to cure DMD.Duchenne. Underscoring this mission, our disease-focused business model is founded on the following fundamental values:

About Duchenne muscular dystrophy

DMDDuchenne is an X-chromosome-linked, muscle-wasting disease, predominantly affecting boys. Progressive, irreversible and ultimately fatal, DMDDuchenne occurs in approximately one in every 3,500 to 5,000 live male births and has an estimated prevalence of 10,0005,000 to 15,000 cases in the United States alone. In DMD,Duchenne, mutations in the dystrophin gene result in the body’s inability to produce functioning dystrophin protein, which works to strengthen muscle fibers and protect them from daily wear and tear. Dystrophin protein also serves as the cornerstone of the dystrophin glycoprotein complex, or DGC, a group of proteins that links the inner and outer components of muscle cells to ensure proper muscle function.

Without dystrophin and the DGC, muscles suffer excessive damage from normal daily activities and are unable to regenerate, leading to the build-up of scar and fat tissue. More than 1,000 dystrophin gene mutations, which can be inherited or can occur spontaneously, have been identified in people with DMD.Duchenne.

For patients suffering from DMD,Duchenne, symptoms usually begin to manifest between three and five years of age, when they fail to reach developmental milestones or experience motor function challenges, such as difficulty walking or climbing stairs. Muscle wasting initially presents in the legs and pelvic area, then in the muscles of the shoulders, neck and arms. As the disease progresses, patients with DMDDuchenne experience frequent falls, can no longer run, play sports or perform most daily

4

functions, and are further weakened by physical activity. In addition to physical challenges, DMDDuchenne also commonly involves cognitive difficulties and behavioral challenges.

By their early teens, DMDDuchenne patients typically lose their ability to walk and become dependent on a wheelchair for mobility. By their 20s, patients essentially become paralyzed from the neck down and require a ventilator to breathe. Though disease severity and life expectancy vary, a patient’s quality of life dramatically decreases over time, with death typically occurring by early adulthood from either cardiac or respiratory complications.

Need for effective therapies

There is no cure for DMDDuchenne and, for the vast majority of patients, there are no satisfactory symptomatic or disease-modifying treatments.

Glucocorticoid treatment, the current standard-of-care, has been shown to temporarily improve muscle strength, prolong the period of ambulation and slow the progression of DMD.Duchenne. However, glucocorticoid use is associated with well-known adverse events, such as severe weight gain, stunted growth, weakening of bone structure and metabolic dysfunctions, among others. The most commonly used glucocorticoids include prednisone and deflazacort (EMFLAZA). Deflazacort has been commercially available in several countries outside of the United States and was approved in the United States for the treatment of DMD in 2017.

In recent years, certain regulators have conditionally approved two new therapies eteplirsen (EXONDYS 51) and ataluren (Translarna), which target specific mutations in the dystrophin gene. These therapies are indicated for only a small portion of the DMDDuchenne patient population, and their respective efficacy profiles still need to be fully understood.

Eteplirsen is an antisense oligonucleotide indicated for DMD patients who have a confirmed mutation of the dystrophin gene amenable to exon 51 skipping, which affects approximately 13% of DMD patients. Eteplirsen is administered as a weekly intravenous infusion. In 2016, eteplirsen was granted accelerated approval from the FDA based on an increase in dystrophin in skeletal muscle observed in some patients who received the therapy. However, the FDA concluded that a clinical benefit, including improved motor function, has not been established. Eteplirsen is still under review by regulatory authorities outside of the United States.

Ataluren is a small molecule indicated for the treatment of patients who have DMD resulting from nonsense mutations in the dystrophin gene, which also affect approximately 13% of DMD patients. In 2014, ataluren received conditional marketing authorization from the European Commission, and has since been approved in several other countries outside of the United States. Ataluren’s indication is currently limited to ambulatory patients five years of age and older. In February 2018, the FDA reiterated its denial of PTC Therapeutics, Inc.’s appeal of the complete response letter for the new drug application for ataluren.

Current best practices for treating DMDDuchenne patients also dictate a multidisciplinary approach to disease management, which includes physical and occupational therapy to preserve strength, function and flexibility, orthopedic management to reduce the risk of scoliosis and other bone and joint problems, pulmonary, cardiac and gastrointestinal management, and psychosocial management to support behavior and learning.

We are actively involved in engaging with the Duchenne patient, clinical and research communities to support advancement of therapies for patients with Duchenne. In November 2021, in collaboration with REGENXBIO Inc., we formally launched the Pathway Development Consortium, or the PDC, a multistakeholder initiative which aims to identify, develop, expand and maintain pathways to effective therapies for patients diagnosed early in life with rare diseases, including Duchenne. The PDC seeks to achieve these goals by bringing together a broad and diverse group of stakeholders from the rare disease and AAV gene therapy communities, including patients, industry, regulators, academia and payers, among others, for meaningful scientific and policy discussions.

Burden of disease

Despite recent therapeutic advances, DMDDuchenne represents a significant societal and economic burden. The economic burden, estimated at $1.2 billion annually in the United States (excluding costly mortality and end-of-life care expenses), includes costs associated with hospital admissions, medication, frequent doctor visits and investment in assistive devices, as well as indirect costs related to productivity losses for the caregivers and costs due to pain, anxiety and social handicap. Of this amount, approximately 45% is represented by indirect costs. Only a small proportion of DMDDuchenne patients are employed and many caregivers reduce their hours or stop working altogether to care for their children, who progressively require more help with everyday tasks, such as eating, dressing and using the bathroom. In some cases, patients also experience serious mental health issues that require additional support and treatment.

Solid’s 360-degree solution

We aim to address the full spectrum of DMD disease manifestation, from its underlying genetic cause to other disorders that result from disease progression. We are advancing corrective therapies, disease-modifying therapies and assistive devices, as well as tools to accelerate drug development.

Gene transfer—A corrective therapy

Gene therapy is a therapeutic approach that aims to address diseases caused by gene mutations. A gene is a portion of deoxyribonucleic acid, or DNA, that provides the instructions for the body to construct proteins that perform functions needed for life. Genes are prone to mutations, which can either be inherited or occur spontaneously. While many mutations are harmless, some lead to the absence of crucial proteins, resulting in serious genetic diseases like DMD.Duchenne.

Gene transfer, a type of gene therapy, is designed to address diseases caused by mutated genes through the delivery of functional versions of those genes, called transgenes. The transgenes are then utilized by the body to produce proteins that are absent or not functional prior to treatment, potentially offering long-lasting beneficial effects.

We have focused our initial efforts on gene transfer because we believe it has the greatest potential to address the root cause of DMD:Duchenne: the absence or near-absence of dystrophin protein. If successful, we believe gene transfer can slow or stop the

5

progression of DMDDuchenne in a majority of patients, irrespective of their genetic mutation, by producing long-term, muscle-specific expression of a functional dystrophin-like protein.

Our gene transfer candidate, or vector, includes three components:

SGT-001

SGT-001, our lead gene transfer candidate, is designed to preserve muscle function in DMDDuchenne patients after a single administration.administration and is based on some of the most recent understanding of dystrophin biology in the field. The SGT-001 vector is comprised of a functional transgene and a muscle-specific promoter, which are delivered via an AAV capsid.  We believe that the SGT-001 construct is differentiated from other gene transfer candidates and may provide unique clinical benefit.

The vector is modified to no longer self-replicate, yet retains its ability to effectively introduce new genetic material directly into patients’ cells. AAV vectors have been extensively studied in human clinical trials in multiple disease indications, including in clinical trials of high-dose, systemically delivered AAV gene therapies being conducted by third parties.

Capsid: The capsid of the SGT-001 vector is derived from a naturally occurring, non-pathogenic virus called AAV. There are several subtypes of AAV capsids that differ based on the proteins that make up their structure. These capsids have affinities for different sites in the body. We selected the AAV9 serotype capsid for clinical development based on our preclinical data, which demonstrated the capsid’s ability to efficiently enter skeletal, diaphragm and cardiac muscle tissues.tissues, as well as its favorable tolerability reported in other gene transfer clinical programs.

Transgene: Dystrophin, the largest gene in the body, exceeds the carrying capacity of AAV vectors. To overcome this challenge, we advanced development of the SGT-001 transgene, a synthetic, dystrophin-like gene that fits into AAV and has the ability to drive functional protein expression in skeletal, diaphragm and cardiac muscle tissue.

The concept of a modified therapeutic dystrophin gene originated from research on Becker muscular dystrophy, or BMD, where researchers discovered that certain BMD patients had mutations in the dystrophin gene that drove expression of a functional form of dystrophin protein, allowing patients to live relatively normal lives. This discovery led scientists to engineer a number of synthetic, dystrophin transgene constructs, called microdystrophins, that retained only the most critical components of the full-size dystrophin gene yet were small enough to fit within AAV packaging constraints. There are several types of microdystrophins that differ based on the configuration of their components. Microdystrophins were subsequently demonstrated to functionally protect muscle in mouse models of DMD.Duchenne.

TheOur SGT-001 microdystrophin construct which is our lead clinical candidate for DMD, is based on three decades of development and optimization work at the University of Missouri and the University of Washington as well as other academic institutions. In preclinical studies, the laboratories of Jeffrey Chamberlain, Ph.D., from the University of Washington, and Dongsheng Duan, Ph.D., from the University of Missouri, identified a proprietary configuration of genetic components that, when administered systemically, produces functional microdystrophin protein expression that not only stabilizes muscle membranes and protects muscle against injury, but also simultaneously restores the localization of DGC to the muscle membrane, notably increasing neuronal nitric oxide synthase, or nNOS concentration. In subsequent published studies, Dr.Drs. Duan and Chamberlain demonstrated in animal models that, in comparison to earlier configurations, nNOS-restoring microdystrophins were more effective in improving muscle function and blood circulation.resistance to fatigue. We believe the unique functionality of our SGT-001 microdystrophin may result in functional benefits including diminished muscle fatigue and protection against ischemic muscle damage, which can lead to loss of functional muscle.

Promoter:The expression of the SGT-001 microdystrophin transgene is regulated by a modified, synthetic muscle-specific promoter cassette called CK8, which is derived from the naturally occurring muscle creatine kinase promoter. Regulatory cassettes, such as CK8, are used to prompt gene expression specifically in muscle tissues. In comparison to other regulatory cassettes, we chose CK8 due to its small size and its ability to drive microdystrophin transgene expression in skeletal, diaphragm and cardiac muscle tissues. In our preclinical studies in small and large animal models, CK8 restricted microdystrophin transgene expression to these muscles.

6

SGT-001 preclinical program

Our comprehensive preclinical program for SGT-001 iswas comprised of studies that inform efficacy, durability and safety, as well as dose response and the kinetics of transgene expression. Our program includes three different animal species: mice, dogs and non-human primates, or NHPs. Our preclinical studies were performed by third-party collaborators over the last three years.collaborators.

Well establishedWell-established mouse and dog disease models for DMDDuchenne offered us the opportunity to better evaluate the potential translatability of SGT-001 to humans. While studies in dystrophic mice, such as the mdx mouse, provide important efficacy rationale, we chose to perform additional functional studies in dystrophic dogs because they exhibit a more severe dystrophic phenotype and progress similarly to human patients at earlier stages of the disease. Dog models enabled us to assess various endpoints, including biodistribution, expression, durability and function in a large animal species.

Because DMDDuchenne is a disease defined by a lack of dystrophin protein, it is important to reliably detect microdystrophin expression in muscle after SGT-001 treatment. As part of our core preclinical program, we developed well characterizedwell-characterized and well recognizedwell-recognized analytic approaches to confirm transgene expression and localization, using the following assays:

We also employed immunofluorescence to confirm if our microdystrophin construct restored the DGC, including key proteins such as sarcoglycan and nNOS.

Efficacy in dystrophic mice

Multiple studies in both dystrophic, or mdx, and healthy, or wild-type, mice have demonstrated that a single intravenous administration of SGT-001 induces measurable levels of microdystrophin protein expression. Muscle strength assessments in mild and severe mouse models of Duchenne demonstrated functional improvements in animals treated with SGT-001 in comparison to untreated dystrophic controls. In all studies, microdystrophin protein expression was measured using immunofluorescence, Westernwestern blot and mass spectrometry.

In an mdx dose-response study, a clear dose-dependent pattern of transgene expression was observed at day 28 by all three assays. As an example, at a dose of 1E14 vg/kg, transgene expression as quantified by positive immunoflouresenceimmunofluorescence staining in the quadriceps and heart muscle tissues was 50% and 80%, respectively, of the full-length dystrophin levels quantified in healthy wild-type control muscles. Similar levels of microdystrophin expression were found in all mdx studies completed to date. Efficacy studies performed in dystrophic mice treated with SGT-001 demonstrated significant, dose-responsive improvements in both muscle morphology and multiple physiological parameters. In a blinded efficacy study performed in mdx mice dosed at approximately six weeks of age, SGT-001 treatment showed a statistically significant improvementimprovements in gripmultiple muscle strength which assesses arm and leg strength, at multiple doses.parameters as well as resistance to treadmill-induced fatigue.

In addition, using a treadmill exhaustion assay, the total distance run by the SGT-001-treated mdx mice was approximately two- to fifteen-fold longer compared to the untreated mice at all time points five-weeks post-dose.

At study termination, muscle force was measuredex vivo in the extensor digitorum longus muscle in all animals. SGT-001-treated mdx mice, dosed at either 2E14 or 4.5E14 vg/kg, exhibited a 1.3-fold increase in specific muscle force over untreated controls when compared to the untreated mdx mice.

In a second efficacy study employing a more severe dystrophic mouse model, or DBA/2J-mdx, a version of SGT-001 was administered at a dose of 1E15 vg/kg. Treated mice exhibited functional results that were similar to untreated wild-type animals. In the SGT-001-treated DBA/2J-mdx mice, the specific muscle force was similar to wild-type mice. Further, the treated animals were protected against muscle damage associated with eccentric contractions, a type of contraction related to muscle lengthening under load that is known to be highly damaging to dystrophic muscles. In contrast, untreated DBA/2J-mdx mice showed significantly reduced specific force and no protection against eccentric contraction induced muscle damage.

Efficacy in dystrophic dogs

Two independent studies in dystrophic dogs assessed durability of microdystrophin expression and efficacy, respectively. These studies were performed in two distinct dystrophic dog models (mixed breed dystrophic dogs, or cDMD, and Golden Retriever Muscular Dystrophy, or GRMD), collectively encompassing a number of genetic mutations that lead to the absence of dystrophin protein. This enabled us to assess SGT-001 across multiple mutations, which is more reflective of the composition of the DMDDuchenne patient population. Both studies used a canine-optimized version of the microdystrophin gene.

In a long-term dose-ranging study, five three-month-old, juvenile cDMD dogs received an intravenous dose of either 5E13 vg/kg (n=1), 1E14 vg/kg (n=2), 3E14 vg/kg (n=1) or 5E14 vg/kg (n=1). In this study, muscle biopsies were collected from the skeletal muscles at one, three, six, 12, 16, 20, 24 and 30 months after injection. Robust transgene expression was detected by immunofluorescence at all biopsy time points and at all of the dose levels. In animals dosed with 1E14 vg/kg, approximately 70-90% of the muscle fibers were positive for microdystrophin. In treated muscle samples, transgene expression was associated with stabilization of the DGC, including nNOS. To date, all doses have been well toleratedmicrodystrophin and there has been no observed immune responsecorrelated to the transgene. This study is currently ongoing.restoration of DGC associated proteins, including nNOS.

7

A blinded dose-ranging study in the GRMD model assessed the general safety and efficacy of the canine construct of SGT-001. The three dose levels (1E13, 1E14 and 2E14 vg/kg) were administered at three months of age and animals were followed for three months following administration. All doses were well tolerated and there was no observed immune response to the transgene.

Dose-dependent transgene expression was detected in interim biopsies of skeletal muscles at day 28 and 45 and at the end of the study at day 91 in skeletal, diaphragm and cardiac muscles. A blinded histological evaluation of the muscle tissue revealed a reduction of dystrophic pathology at the higher dose levels. In the mid- and high-dose groups, all muscles biopsied at the end of the study exhibited improved pathology compared to low dose and untreated controls. Biodistribution studies demonstrated dose dependent transgene expression that was only detectable in the muscle tissues.

The observed dose response was detectable by both immunofluorescence and Westernwestern blot. Quantification by Westernwestern blot averaged less than 10% of wild-type in the low-dose (1E13 vg/kg) animals. In the mid-dose animals, the level of expression among the skeletal muscles ranged from an average of approximately 20% to approximately 50% of wild-type control muscles. At 2E14 vg/kg, the level of expression ranged from 30% to 70% of wild-type dystrophin. This data also correlates to quantification of microdystrophin via mass spectrometry.

Dose-dependent, sustained expression of microdystrophin not only correlated with histological improvements in muscle, but also provided statistically significant improvements in measures of muscle function. At day 90, muscle force generation was improved in both the 1E14 vg/kg and 2E14 vg/kg cohorts, indicating that the microdystrophin produced by SGT-001 is highly protective in a large animal dystrophic species.

The efficacy data collectively described above in both dystrophic mouse and dog models was incorporated into an overall nonclinical model to inform dose selection for our clinical program. All doses were well tolerated and there was no observed immune response to the transgene.

Manufacturing comparability

As part of our manufacturing process development, we have run comparability studies at each stage of our process scale-up. These comparability studies were carried out usingin vivo mouse models to ensure that our drug product produced at different scales is comparable to each other.

Safety

As part of our preclinical program, we performed necessary good laboratory practices, or GLP, toxicology studies to establish the overall safety profile of SGT-001 in wild-type mice and NHPs. The data and our conclusions from these studies were included in our Investigational New Drug application, or IND submission to the FDA. Systemic administration of SGT-001 was generally well tolerated in both species. We observed no evidence of test-article-related toxicity for up to 13 weeks after systemic administration of SGT-001 in either species that would prevent us from initiating clinical trials. In the NHP study, test-article-related effects were self-limited, mild chemistry and hematology changes with no microscopic correlates at the end of the study. There was a transient and asymptomatic increase in liver function enzymes observed in NHPs starting on day 9, which returned to normal levels by day 21. We believe there were no other relevant test-article-related adverse events associated with SGT-001 administration in either GLP study. In the NHP toxicology study, a single animal from the high dose cohort was euthanized after it did not recover from an anesthetic procedure. We believe this event was attributed to procedural errors. However, AAV vector cannot be completely ruled out as a contributing factor to the toxicity that gave rise to the event.

Clinical development of SGT-001

We are developing SGT-001 for the treatment of DMDDuchenne through a single intravenous administration. In the fourth quarter of 2017, we announced the initiation of IGNITE DMD, as a randomized, controlled, open-label, single-ascending dose Phase I/II clinical trial designed to evaluate SGT-001 in ambulatory and non-ambulatory males with DMDDuchenne aged four to 17 years. The primary objectives of IGNITE DMD are to assess the safety and tolerability of SGT-001, as well as efficacy as defined by microdystrophin protein expression. The clinical

trial is also designed to assess muscle function and mass, respiratory and cardiovascular function, serum and muscle biomarkers associated with microdystrophin production, SGT-001 microdystrophin associated biochemical properties (e.g., nNOS binding), functional outcome, patient and parent reported outcomes and quality of life measures, among other endpoints. IGNITE DMD is anticipated to enroll 16 to 32 patients with DMD. Key inclusion criteria include:include established clinical diagnosis of DMDDuchenne and documented dystrophin gene mutation predictive of DMDDuchenne phenotype; anti-AAV9 antibodies below pre-specified thresholds; stable cardiac and pulmonary function; and a stable daily dose of oral corticosteroids for 2412 weeks. There is no enrollment restriction in the clinical trial protocol based on a patient’s underlying dystrophin gene mutation.

8

In the current IGNITE DMD protocol, as amended, participants will be randomlyare all assigned to either an activeopen label treatment group or a delayed treatment control group.with SGT-001. The selection of ourthe original starting dose in our first cohort, 5E13 vg/kg, was based on safety and efficacy data observed in our preclinical studies. Dose escalation between cohorts and decisions regarding clinical trial progression will occur after review by the Data Safety Monitoring Board,data safety monitoring board, or the DSMB. ItEfficacy is planned so that adolescents aged 12 to 17 years will be treated initially, followed by children aged four to 11 years. Efficacy will bebeing assessed by comparing microdystrophin protein expression in muscle biopsy before and 12 months after treatmentinfusion for each patient. Other endpointsAn intermediate biopsy at either 45 days, three months, six months or nine months will be compared againstinform the control group. We anticipate that the delayed treatment control group will be rolled into an active treatment phase after 12 months, as long as participants continue to meet clinical trial criteria. time course of microdystrophin expression.Long-term follow up will continue per regulatory guidelines.

Patient Dosing and U.S. Regulatory Engagement

To date, nine patients have been dosed in IGNITE DMD with SGT-001. The first three patients were infused with 5E13 vg/kg of SGT-001 (low dose cohort). The subsequent six patients were all dosed in the high dose cohort at 2E14vg/kg of SGT-001.

In November 2019, we announced that the third patient in the 2E14 vg/kg cohort of IGNITE DMD, dosed in late October 2019, experienced an SAE deemed related to the study drug and that IGNITE DMD was placed on clinical hold by the FDA as a result of the SAE. The SAE was characterized by complement activation, thrombocytopenia, a decrease in red blood cell count, acute kidney injury, and cardio-pulmonary insufficiency. Neither cytokine- nor coagulopathy-related abnormalities were observed. In December 2019, we reported that the SAE had fully resolved and the patient had resumed his normal activities.  

In April 2020, we submitted a response to the FDA that included changes to the clinical protocol designed to enhance patient safety, as well as information related to improvements to our manufacturing process. The FDA responded by maintaining the clinical hold and requesting further data and analyses relating to this manufacturing process.  In June 2020, we submitted a response to the FDA that provided data related to manufacturing process improvements. In July 2020, we announced that the FDA responded by maintaining the clinical hold and requesting further manufacturing information and updated safety and efficacy data for all patients dosed in the trial, as well as providing direction on the total viral load to be administered per patient. In October 2020, we announced that the FDA lifted the clinical hold placed on IGNITE DMD. In connection with the lifting of the clinical hold, we determined to reduce the maximum weight of the next two patients dosed in IGNITE DMD to 18 kg per patient, with safety outcomes from these two patients driving potential weight increase of patients dosed subsequently. This reduction, in conjunction with the delivery of fewer viral particles as a result of our manufacturing process improvements, will reduce patients’ total viral load while continuing dosing at the 2E14 vg/kg dose. Additionally, to mitigate the risk of serious drug-related adverse events, we amended the IGNITE DMD clinical protocol to include the prophylactic use of both anti-complement inhibitor eculizumab and C1 esterase inhibitor, and increase the prednisone dose in the first month post dosing.

In March 2018,2021, we announced that Patient 7 was safely dosed with SGT-001 in the FDA placed IGNITE DMD on full2E14 vg/kg cohort under the amended clinical hold following our reportprotocol, with transient and manageable adverse events, none of which were serious.  

In April 2021, Patient 8 was treated with SGT-001 in the 2E14 vg/kg cohort. The patient experienced a systemic inflammatory response which has since fully resolved. The event was classified as a serious adverse event and considered by the investigator to be drug related. This type of event is described in our Investigators Brochure and is not considered unexpected. Following dosing, we conducted an extensive review of all IGNITE DMD clinical data, resulting in an amended protocol with a strengthened risk mitigation plan including an optimized eculizumab regimen utilized prophylactically and in the first two weeks, elimination of the C1 esterase inhibitor, and new patient monitoring guidance, all of which was submitted to the FDA.        

In January 2022, we announced that in November 2021 Patient 9 was safely dosed with SGT-001 in the 2E14 vg/kg cohort under the amended clinical trial. Onprotocol, with transient and manageable adverse events, none of which were serious.  

No new drug-related safety findings have been identified in Patients 1-9 through nine in post-dosing periods of 90 days to approximately four years. We continue to follow dosed patients and collect data to support the potential benefit from dosing with SGT-001.

Clinical Data

In February 14, 2018,2019, we announced preliminary findings based on three-month biopsy data from the first patient in IGNITE DMD, a non-ambulatory adolescent, received a dose ofthree patients dosed with 5E13 vg/kg of SGT-001, the lowest dose outlined in the trial protocol. In one patient, SGT-001 microdystrophin was detected via western blot below the five percent level of quantification, or BLQ, of the assay and in approximately 10

9

percent of fibers via immunofluorescence. Due to these findings, and in consultation with the DSMB, in May 2019 we announced that we had initiated dosing of the next cohort of patients at 2E14 vg/kg. In August 2019, we amended our protocol to remove the matched patient control arm for the rest of the 2E14 vg/kg cohort in the IGNITE DMD trial and to provide measures to potentially improve safety, such as initially proceeding to dose patients weighing 25 kg or less.

In December 2019, we announced preliminary findings based on three-month biopsy data from the first two patients dosed with 2E14 vg/kg of SGT-001 (Patients 4 and 5). Using two independent immunofluorescence assays, 10% to 20% of microdystrophin positive muscle fibers were determined to express SGT-001 microdystrophin in Patient 4 and 50% to 70% of microdystrophin positive muscle fibers in Patient 5. Immunofluorescence also showed clear stabilization and co-localization of nNOS and beta-sarcoglycan with SGT-001 microdystrophin in both patients. Using western blot, the expression levels for Patient 4 were detectable and estimated to be near the assay’s level of quantification which is 5% of non-dystrophic control samples, with one assay replicate at 5.5%. Expression for Patient 5 was 17.5% of normal control samples. The levels of serum creatine kinase, a highly variable biochemical marker of muscle damage, declined from baseline in both patients.

In March 2020, we announced data from the third patient dosed in the 2E14 vg/kg dose cohort of IGNITE DMD (Patient 6), including three-month biopsy data. Using immunofluorescence assays, 50% to 70% of the muscle fibers were determined to express SGT-001 microdystrophin.Immunofluorescence also showed stabilization and co-localization of nNOS and beta-sarcoglycan with SGT-001 microdystrophin. Using western blot, microdystrophin expression was 8% of normal control samples. In addition, the level of serum creatine kinase decreased from baseline.

In March 2021 and September 2021, we announced interim data collected from the first six patients dosed in IGNITE DMD twelve months after treatment, including data from three patients (Patients 4-6) dosed at the high dose (2E14 vg/kg). Data from the delayed treatment cohort, analyzed as an untreated control cohort, was evaluated as was representative natural history data. The average age at baseline of Patients 4-6 was 8.4 years. Functional data collected included 6MWT, NSAA and PFTs, which provided evidence of potential benefit in functional endpoints one year after a single infusion of SGT-001 at a dose of 2E14 vg/kg. This data demonstrated stable or improved function compared to both baseline and natural history over the same time period.

PROM assessments using the PODCI revealed a trend towards dose-response improvements in motor function subscales and fatigability assessments 12-months following infusion with SGT-001, providing real-world evidence to support the clinical and biomarker findings of varying degrees of benefit in high dose patients.

The March 2021 data also included the following biomarker data:

10

The following tables summarize the interim efficacy results for patients in IGNITE DMD at 12-months post-dosing:

^{(1): -42.3m expected decline in 12 months after age 7 (Mercuri et al 2016)}

^{(2): -3.0 unit expected decline in 12 months after age 6.3 (Muntoni eta al 2019)}

^{(3): -5.0%p expected decline in 12 months after age 6 (Mayer et al 2015)}

^{(4): -5.0%p expected decline in 12 months after age 6 (Mayer et al 2015)}

^{(5): -5.05 point expected decline in 12 months (Henricson et al 2013)}

^{(6): -9.95 point expected decline in 12 months (Henricson et al 2013)}

^{(7): -3.11 point expected decline in 12 months (Henricson et al 2013)}

^{(1): -42.3m expected decline in 12 months after age 7 (Mercuri et al 2016)}

^{(2): -3.0 unit expected decline in 12 months after age 6.3 (Muntoni eta al 2019)}

^{(3): -5.0%p expected decline in 12 months after age 6 (Mayer et al 2015)}

^{(4): -5.0%p expected decline in 12 months after age 6 (Mayer et al 2015)}

^{(5): -5.05 point expected decline in 12 months (Henricson et al 2013)}

^{(6): -9.95 point expected decline in 12 months (Henricson et al 2013)}

^{(7): -3.11 point expected decline in 12 months (Henricson et al 2013)}

11

In May 2021, we reported long-term biopsy data collected from Patients 4-6, who were dosed at the 2E14 vg/kg dose level. Analyses of the biopsies, taken 24 months, 18 months and 12 months post-dosing, respectively, demonstrated durable and widespread expression of the microdystrophin protein. The long-term results were consistent with the day 90, interim data reported in March 2021 and continued to demonstrate the functionality of the SGT-001 microdystrophin, as highlighted by the recruitment of key dystrophin associated proteins: beta-sarcoglycan and neuronal nNOS. The long-term muscle biopsy results were analyzed by two methods, western blot and immunofluorescence.

*Below the limit of quantification (5%)

Further morphological analysis of the muscle biopsies indicated that sustained microdystrophin protein expression and function resulted in membrane stabilization, evidenced by minimal progression of muscle deterioration since the day 90 timepoint. These long-term pathophysiological improvements support the recently reported positive trends in the clinical trial. Several days after administrationbiomarker and functional data.

In September 2021, we announced interim data collected from the patient was hospitalized due to laboratory findings that included a decreasefirst three patients infused in platelet count followed by a reduction in red blood cell count and evidence of complement activation. The patient showed no signs or symptoms of coagulopathy (bleeding disorder), had no relevant changes from baseline in liver function tests and responded well to medical treatment.

We reported the serious adverse event to the FDA and, because it was unexpected, classified it as a Suspected Unexpected Serious Adverse Reaction, or SUSAR. We have halted enrollment and dosinghigh dose cohort (2E14 vg/kg) in IGNITE DMD 18-months months after treatment. The average age at baseline of Patients 4-6 was 8.4 years. Data collected from 6MWT, NSAA and PFTs provided evidence of continued potential benefit in functional endpoints 18-months after a single infusion of SGT-001 at a dose of 2E14 vg/kg. Patient reported outcome measures showed meaningful sustained improvements at 18-months compared with baseline and natural history as assessed using the PODCI Global Functions, PODCI Transfer/Basic Mobility and PODCI Sports/Physical Functioning over the same period of time. These data are awaitingconsistent with results reported at the formal clinical hold letter12-month time period for the same patients.

The following table summarizes the interim efficacy results for Patients 4-6 in IGNITE DMD at 18-months post-doing:

^{(1). -63.5m expected decline in 18 months after age 7 (Mercuri et al 2016)}

^{(2). -4.5 unit expected decline in 18 months after age 6.3 (Muntoni eta al 2019)}

^{(3). -7.5%p expected decline in 18 months after age 6 (Mayer et al 2015)}

^{(4). -7.5%p expected decline in 18 months after age 6 (Mayer et al 2015)}

^{(5). -7.6 point expected decline in 18 months (Henricson et al 2013)}

^{(6). -14.9 point expected decline in 18 months (Henricson et al 2013)}

^{(7). -4.7 point expected decline in 18 months (Henricson et al 2013)}

In March 2022, we announced two-year interim safety and efficacy data from the FDA.first three Patients (Patients 4-6) treated with SGT-001 in the 2E14 vg/kg dose cohort of IGNITE DMD. Results suggested durable benefit 24-months post-administration of SGT-001, when compared to natural history. These data were consistent with results reported at the 12-month and 18-month time periods for the same patients. The average age of Patients 4-6 at the two year timepoint was 10.4 years.

Assuming successful resolution12

Data from Patients 4-6 suggested sustained motor function at two years post-infusion, as assessed by 6MWT and NSAA, against expected natural history declines. In addition, the data suggested improved pulmonary function, as measured by FVC and PEF, and sustained or improved PROMs as assessed in key functional domains of the full clinical holdPODCI when compared to both baseline and natural history.

The following table summarizes the interim efficacy results for Patients 4-6 in IGNITE DMD at 24-months post-dosing:

^{(1): -84.6m expected decline in 24 months after age 7 (Mercuri et al 2016)}

^{(2): -6.0 unit expected decline in 24 months after age 6.3 (Muntoni eta al 2019)}

^{(3): -10.0%p expected decline in 24 months after age 6 (Mayer et al 2015)}

^{(4): -10.0%p expected decline in 24 months after age 6 (Mayer et al 2015)}

^{(5): -10.1 point expected decline in 24 months (Henricson et al 2013)}

^{(6): -19.9 point expected decline in 24 months (Henricson et al 2013)}

^{(7): -6.2 point expected decline in 24 months (Henricson et al 2013)}

In March 2022, we reported data from skeletal muscle biopsies collected three months after infusion of SGT-001 from the most recently dosed Patients 7-9.  The range by immunofluorescence of 1% to 50% and by western blot of Below the 5% Limit of Quantification (BLQ) to 6.8%, were within the range of previously dosed Patients 4-6 in the high dose cohort. Microdystrophin expression levels for all six patients dosed in the high dose cohort (Patients 4-9) ranged from 1 to 70% by immunofluorescence and BLQ to 17.5% by western blot. All six patients dosed with SGT-001 in the high dose cohort have demonstrated microdystrophin expression and proper membrane localization.

We believe the unique functionality of our SGT-001 microdystrophin may result in functional benefits including diminished muscle fatigue and protection against ischemic muscle damage, which can lead to loss of functional muscle. Collectively, we believe these data provide evidence supporting the biological activity of SGT-001 and provide support for continued development. Based on data from the clinical trial, we will determine next steps for SGT-001 clinical development, including additional clinical trials that may include other patient populations, as well as the need for larger confirmatory clinical trials.

In additionNo new drug-related safety findings have been identified in Patients 1-9 in post-dosing periods of 90 days to the full clinical hold on IGNITE DMD, we also must resolve a partial clinical hold on the higher-dose group in the clinical trial. Pursuantapproximately four years. We continue to a letter we received from the FDA in November 2017, we are not permitted to dosefollow dosed patients in the higher-dose group of the clinical trial until we decrease the number of vials and utilize no more than a single production lot per patient, as well as demonstrate that we have the appropriate manufacturing processes in placecollect data to support the higher-dose group. We have submitted our responsepotential benefit of SGT-001.

The most common drug related clinical adverse reactions at the time of initial dosing were nausea, experienced by the nine patients dosed; fever experienced by seven of the nine patients dosed; and vomiting, experienced by eight of the nine patients dosed. The most common drug related laboratory abnormalities were thrombocytopenia, increased fibrin D-dimer, increased soluble C5b9, increased lactate dehydrogenase, and proteinuria. Activation of the terminal pathway (sC5b9) of the classical complement system occurred in all nine patients resulting in three serious adverse events, which were previously resolved. Two other serious adverse events included an episode of immune hepatitis four weeks post dosing which resolved rapidly after a transient increase of corticosteroids, and giardiasis determined to the FDA and are awaiting their feedback.be unrelated to SGT-001.

Manufacturing SGT-001

The prevalence and incidence of DMD,Duchenne, combined with average patient weight and anticipated dosing requirements for SGT-001, result in a substantial supply need for clinical trials and, if approved, for commercial markets. To address this challenge, we developed a manufacturing process that we believe will be scalable to meetsupport clinical and commercial production needs for SGT-001.

13

Our suspension-based process is founded on seminal work by scientists at the University of Florida and has been optimized for manufacturability by our internal process development scientists with the support of our

Contract Development Manufacturing Organizations, or CDMO partners. The process consists of three steps. First, we produce two replication-incompetent Herpes Simplex Virus, or HSV, stocks, one containing our microdystrophin construct and the other containing the critical elements of the AAV9. WeSecond, we then use these two HSV stocks to coinfect suspension-adapted human embryonic kidney cells (HEK-293), which. Third, these cells are then purified and concentrated in our downstream process to produce our gene transfer candidate. Our team has developed the analytical testing methods needed to support consistency and strict standards of quality and potency. We believe that this approach will increase our speed of development, ensure consistent quality and regulatory compliance, and reduce the risk of delay or unexpected production costs.

Current statusIn 2020, we implemented our second generation manufacturing process which collectively includes improvements to our AAV manufacturing methods as well as the introduction of a refined set of analytical methods for product release. Our second generation AAV manufacturing process includes a scalable purification step which results in a significant enrichment of microdystrophin-containing “full” capsids and plans forelimination of empty capsids. On average, drug product produced by the second generation manufacturing method contains 90% full capsids as measured by Transmission Electron Microscopy, whereas drug product produced by the first generation process is on average 50% full. This improvement in purification methods significantly reduces the total capsid load administered at any given dose level, allowing us to achieve the same effective dose of drug product with fewer total capsids. Since the first quarter of 2021, and following lift of the clinical and commercial scale-uphold, all patients dosed in IGNITE DMD have been dosed with material produced using our second generation manufacturing process.

We believe that our investmentdecision to invest early in our scalable manufacturing process over the last several years will allow uswas key to minimize the need for changes throughoutdeveloping a scalable process designed to support clinical development and upon commercialization, while ensuring supply at the high volume required at all stages.potential commercialization. We intend to supplyare supplying our clinical development program for SGT-001 with drug product produced at current good manufacturing practices, or cGMP, - compliant facilities located at partner CDMOs. We are currently operatinghave operated at 250-liter scale and have successfully produced multiple drug product batches at this scale. Our in-house scientists are continuing to work to increase the productivity, efficiency and efficiencypurity of our manufacturing process.

SGT-003

SGT-003 is our next-generation gene transfer candidate. It is comprised of our nNOS binding domain microdystrophin transgene and muscle-specific promoter present in SGT-001 and uses a lead candidate novel, rationally designed AAV capsid, developed for enhanced muscle tropism, to deliver these components to target tissues. We believe that the properties of this novel capsid may allow for enhanced benefit over therapies using traditional capsids, potentially both in terms of efficacy and safety.

SGT-003 preclinical program

We identified a lead novel capsid candidate through evaluation of muscle tropic AAV screening, in which increased muscle transduction was observed.

Translatability of in vitro data to in vivo systems was assessed in preclinical studies using the novel capsid. It was evaluated in a head-to-head study with AAV9-CK8-microdystrophin in the dystrophin-negative mouse model of DMD (mdx mouse). Separate groups of animals were administered a single intravenous dose of either construct and the biodistribution, microdystrophin protein expression, and biomarker analyses were performed at the conclusion of the study. Overall, the in vivo study data supported the results seen from in vitro assays and further demonstrated the potential benefits. The mdx mice dosed with the novel capsid showed increased biodistribution (vector genome copies) in representative muscle tissues and increased microdystrophin expression compared to those administered the AAV9 vector. In addition, welower vector genome copies in the liver compared to AAV9-administered animals, with the data supporting a preferential distribution of the novel capsid towards muscle tissue and away from the liver. These data supported the proof of concept for the novel capsid microdystrophin construct in Duchenne and formed a basis for establishing and advancing the SGT-003 program. We intend to establish the capability and capacityinitiate IND-enabling studies for SGT-003 in 2022 to supply SGT-001 at commercial scale from multiple sources, including potentially building our own GMP facility to ensure redundancy and reliability.support a planned IND submission in early 2023.

Complementary disease-modifying therapiesManufacturing SGT-003

WhileWe selected a manufacturing process that we believe will be scalable to support clinical and commercial production needs for SGT-003. The transient transfection process was selected in order to efficiently advance SGT-003 along its

14

development timeline. . In October 2021, we announced a partnership with a cell and gene therapy-focused CDMO, for the development and clinical stage manufacture of SGT-003.

Platform Technologies

In addition to our gene transfer candidates, we have development programs focusing on platform technologies, including novel capsids and dual gene expression, a technology that allows us to package multiple transgenes into one vector. These programs are part of our ongoing research efforts to develop innovative technologies that we believe may be ablehold potential to slow or halt DMD disease progression, many patients would still suffer from the manifestations of the disease, such as tissue damage to their muscles, impaired muscle strength, inflammation, cardiac dysfunctiontranslate into meaningful treatments and fibrosis. We are building a portfolio of complementary disease-modifying therapies designed to address these manifestations.

Our portfolio currently includes SB-001,drive our initial disease modifying candidate that is aimed at addressing fibrosis, as well as several emerging and complementary programs. We have chosen to focus our efforts on these programs following rigorous preclinical testing and our assessment of clinical potential given natural human modifiers. If initial preclinical studies are successful, we envision initiating additional studies for our disease-modifying programs in combination with SGT-001. We continue to assess additional emerging therapeutic approaches from academia and industry through our highly focused product candidate selection process to further build our portfolio.

SB-001 (LTBP4)

SB-001 is a monoclonal antibody intended to reduce fibrosis and inflammation. It is designed to target and stabilize the LTBP4 protein. LTBP4 is highly expressed in muscle and, when stable, prevents fibrosis and inflammation by inhibiting the activation of the TGF-beta pathway.

The rationale for targeting LTBP4 originated from observations in DMD natural history studies. Researchers found that subsets of patients with genetic variants in the LTBP4 gene maintained their ability to walk longer compared to patients in the study who did not. Researchers discovered that these genetic variants lead to reduced TGF-beta signaling. Elizabeth McNally, M.D., Ph.D., Director of the Center for Genetic Medicine at Northwestern University, hypothesized that stabilization of the LTBP4 protein in DMD patients could mimic the effect.

In order to assess the efficacy of potential human antibody clinical candidates in preclinical models, mice expressing the human version of LTBP4 were crossed with mdx mice to generate a DMD model that expressed human LTBP4 (hLTBP4:mdx). Preliminary studies showed that the hLTBP4:mdx animals treated with an anti-LTBP4 antibody showed significantly lower levels of fibrosis and inflammation due to the stabilization of the LTBP4 protein.

In partnership with Dr. McNally and Adimab LLC, SB-001 development efforts are underway to optimize lead candidate human immunoglobulin G, or IgG, antibodies directed against LTBP4. Additional selection and characterization are being employed to obtain high affinity antibodies. We plan to conduct preclinicalin vivo efficacy, biodistribution and safety studies utilizing these human antibodies in hLTBP4:mdx mice beginning in 2018, following finalin vitroantibody characterization and scale-up of manufacturing efforts.future pipeline expansion.

Tools to accelerate discovery and development

WeIn conjunction with our development of SGT-001 and SGT-003,we believe it is critical to invest timecontinue to investigate tools and research into toolstechnologies designed to help us more effectively measureunderstand Duchenne, accurately monitor disease progression and assist patients in daily life. As part of this goal, we are evaluating the therapeutic impactuse of our product candidates. We are focused on developingsensor-based technologies to potentially identify biomarkers and sensors that willmay allow us to identify treatment targets faster, better measure the therapeutic impact of potential product candidates.

Novel Capsids

We have developed a library of novel capsids through the insertion of unique peptide sequences into traditional capsids and initially evaluated these candidates through an in vitro screening platform. The primary goal of developing this library was to generate capsids that preferentially target and reachtransduce muscle cells, compared to traditional capsids such as AAV9. Candidate novel capsids were packaged with our microdystrophin under the control of a muscle-specific promoter, such as CK8, and used to transduce muscle cells. Evaluation of microdystrophin expression from in vitro studies performed in mouse muscle cell lines showed multiple-fold increases in numerous novel capsid candidates over AAV9. Further in vitro characterization of these capsids was performed in human Duchenne muscle cell lines. Results from these studies showed similar findings of multiple-fold increases in expression for novel capsid candidates over AAV9. We are continuing to further develop our novel capsid library.

Non-specific novel capsids were packaged comprised of a bioluminescent protein (luciferase) under the control of a ubiquitous promoter (CMV) able to allow expression across a wide range of tissue types. These constructs were further evaluated in vivo in both mdx and wild-type mice to understand the potential broader applicability of these capsids for other indications. Results from this study support preferential targeting of muscle, with increases in biodistribution and expression over AAV9 across muscle tissues and decreased biodistribution and expression compared to AAV9 in the liver, and the potential applicability  to a wide variety of indications that may benefit from such a targeting profile, in addition to Duchenne.

Tools to accelerate discovery and development

In conjunction with our development of SGT-001 and SGT-003,we believe it is critical to continue to investigate tools and technologies designed to help us more effectively understand Duchenne, accurately monitor disease progression and assist patients in daily life. As part of this goal, we are evaluating the use of sensor-based technologies to potentially identify biomarkers that may allow us to better measure the therapeutic decision points earlier.impact of potential product candidates.

Blood-basedNon-invasive biochemical and imaging biomarkers

We are working to identify non-invasive blood-basedbiochemical and imaging biomarkers that could potentially reduce or eliminate the need for muscle biopsies in clinical trials, reducing stress on patients and allowing better evaluation of potential product candidates. We are developing a platform technology that may enable the non-invasive measurement of changes associated with increased dystrophin and dystrophin-like protein expression in DMDDuchenne patients by using established imaging techniques.techniques, as well as methods still under development. We are also currently using leading, robust platforms to perform extensive analysis on blood-basedpatient samples to establish molecular signatures based on various stages of DMDDuchenne disease progression.

Sensor-less mobility tracking

We are working to develop naturalistic motor function measurement at home with an ambient measurement system, which is based on sensors such as Microsoft Kinect. This system uses infrared technology to detect body movement and is designed to collect mobility data for DMD patients without requiring wearable sensors. If successful, this new non-invasive technology would enable us to understand in greater detail the therapeutic impact of potential product candidates as they relate to everyday activities, and could provide information to establish and measure clinical endpoints in future clinical trials.

Assistive devices

Solid Suit

We are currently developing a line of soft, wearable assistive devices that may have both functional and therapeutic benefits, with the goal of helping patients perform day-to-day activities with greater ease and preserving their muscle function. We refer to these devices as the Solid Suit. This work is being done in collaboration with technology innovators and engineering and disease experts, and is informed by input from the patient community. The Solid Suit utilizes cutting-edge technologies to power soft, light-weight comfortable exoskeletons with the potential to offset muscle fatigue and augment muscle strength. We are developing the Solid Suit in three separate components, two of which are currently in prototype development.

Intellectual property

Our commercial success depends in part on our ability to obtain and maintain proprietary or intellectual property protection for our product candidates, including SGT-001 and SGT-003, our platform technologies and other know-how, to

15

operate without infringing, misappropriating or otherwise violating the intellectual property rights of others, and to prevent others from infringing, misappropriating or otherwise violating our intellectual property rights. We also rely on patents, trade secrets, know-how and continuing technological innovation to develop and maintain our proprietary and intellectual property position.

As of March 15, 2018,February 16, 2022, we have filed three pending U.S. provisionalPCT international patent applications, two pending U.S. non-provisional patent applications and eighteen pending patent applications in foreign jurisdictions. For our gene transfer programs, we have exclusively licensed three issued U.S. patents, onethree pending U.S. non-provisional patent application,applications, and seveneleven granted patents and eleventhirteen pending patent applications in foreign jurisdictions. The issued U.S. patents are projected to expire between 20212023 and 2028,2036, excluding any patent term adjustments and any patent term extensions, and any U.S. patents that may issue from the pending U.S. non-provisional patent application and U.S. provisional patent applications (assuming U.S. non-provisional patent applications are timely filed with respect to such provisional patent applications and all other applicable requirements are satisfied) would be projected to expire between 2036 and 2039,2040, excluding any patent term adjustments and any patent term extensions.

With respect to our gene transfer programs, we exclusively licensed patent families that relate to microdystrophin genes. With respect to SGT-001 and SGT-003, we exclusively licensed onetwo issued U.S. patentpatents and onetwo pending U.S. non-provisional patent application,applications, which generally claim the structural elements of SGT-001 and SGT-003 and the promoter sequencesequences used in SGT-001. Thiseach. These issued U.S. patent ispatents are projected to expire in 2028 and 2036, excluding any patent term adjustments and any patent term extensions. We

Relating to SGT-001, SGT-003 and our platform technologies, we also own onethree pending U.S. provisionalPCT international patent application relating to SGT-001. Any U.S. patents that may issue from theapplications, two pending U.S. non-provisional patent applicationapplications and oureighteen pending U.S. provisional patent application (assuming a U.S. non-provisional patent application is timely filed with respect to such provisional patent application and all other applicable requirements are satisfied)applications in foreign jurisdictions. Any patents that may be issued from the pending PCTs would be projected to expire between 2036 and 2039,2041, excluding any patent term adjustments and any patent term extensions. Substantive prosecution of our provisional patent applicationapplications has not yet commenced at the U.S. Patent and Trademark Office, or USPTO. Our provisional patent application is not eligible to become an issued patent until, among other things, we file a non-provisional patent application within 12 months of the filing date of our provisional patent application. If we do not timely file the non-provisional patent application, we may lose our priority date with respect to our provisional patent application and any patent protection on the inventions disclosed in our provisional patent application. While we intend to file a non-provisional patent application, weWe cannot predict whether such futurepending patent applicationapplications will result in the issuance of a patent that effectively protects SGT-001, SGT-003 and our platform technologies, or if such issued patent or any of our licensor’s issued patents will effectively prevent others from commercializing competitive products. In any event, patent prosecution is a lengthy process, during which the scope of the claims initially submitted for examination by the USPTOpatent offices in various jurisdictions are often significantly narrowed by the time they issue, if they issue at all.

With respect to SB-001, we do not currently own or in-license any issued patents or patent applications relating to such product candidate. We have an exclusive option to negotiate for licenses of certain patents and patent applications relating to SB-001 from Ikaika Therapeutics, LLC. If we exercise such option, Ikaika Therapeutics, LLC is only required to negotiate the terms of a potential license agreement with us for certain specified periods of time and we may be unable to enter into such a definitive license agreement within the required timeframe or under terms that are acceptable to us. If we are unable to enter into such a definitive license agreement, we will not have any license to such patents and patent applications.

The term of individual patents depends upon the legal term for patents in the countries in which they are obtained. In most countries, including the United States, the patent term is 20 years from the earliest filing date of a non-provisional patent application. In the United States, a patent’s term may be lengthened by patent term adjustment, which compensates a patentee for administrative delays by the USPTO in examining and granting a patent, or may be shortened if a patent is terminally disclaimed over an earlier filed patent. The term of a patent that covers a drug or biological product may also be eligible for patent term extension when FDA approval is granted, subject to certain limitations and provided statutory and regulatory requirements are met (for more information, please see “Business—U.S. Government regulation and product approval —U.S. patent term restoration and marketing exclusivity”). In the future, if and when our product candidates receive approval from the FDA or foreign regulatory authorities, we expect to apply for patent term extensions on issued patents we may obtain in the future covering those products, depending upon the length of the clinical trials for each product and other factors. There can be no assurance that any of our pending patent applications will issue or that we will benefit from any patent term extension or favorable adjustment to the term of any of our patents.

As with other biotechnology and pharmaceutical companies, our ability to maintain and solidify our proprietary and intellectual property position for our product candidates will depend on our success in obtaining effective patent claims and enforcing those claims if granted. However, our owned and licensed pending patent applications, and any patent applications that we may in the future file or license from third parties may not result in the issuance of patents. We also cannot predict the breadth of claims that may be allowed or enforced in our patents. Any issued patents that we may receive in the future may be challenged, invalidated or circumvented. In addition, because of the extensive time required for clinical development and regulatory review of a product candidate we may develop, it is possible that, before any of our product candidates can be commercialized, any related patent may expire or remain in force for only a short period following commercialization, thereby limiting protection such patent would afford the respective product and any competitive advantage such patent may provide.

In addition to patents, we rely upon unpatented trade secrets and know-how and continuing technological innovation to develop and maintain our competitive position. We seek to protect our proprietary information, in part, by executing confidentiality agreements with our collaborators and scientific advisors, and non-competition, non-solicitation, confidentiality, and invention assignment agreements with our employees and consultants. We have also executed agreements requiring assignment of inventions with selected scientific advisors and collaborators. The confidentiality agreements we enter into are designed to protect our proprietary information and the agreements or clauses requiring assignment of inventions to us are designed to grant us ownership of technologies that are developed through our relationship

16

with the respective counterparty. We cannot guarantee, however, that these agreements will afford us adequate protection of our intellectual property and proprietary information rights.

We also seek trademark protection in the United States and internationally where available and when appropriate. We currently own U.S. federal registrations for the marks SOLID, SOLID GT and SOLID BIOSCIENCES and a European Union registration for the mark SOLID BIOSCIENCES and SOLID GT.

Strategic partnerships and collaborations/licenses

We have certain obligations under licensing agreements with third parties that include annual maintenance fees and payments that are contingent upon achieving various development, commercial and regulatory milestones. Pursuant to many of these license agreements, we are required to make milestone payments if certain development, regulatory and commercial sales milestones are achieved, and may have certain additional research funding obligations. Also, pursuant to the terms of many of these license agreements, when and if commercial sales of a licensed product commence, we must pay royalties to our licensors on net sales of the respective licensed products.

University of Washington License Agreement

In 2015, we entered into a license agreement with the University of Washington, acting through UW CoMotion, under which we obtained an exclusive, royalty-bearing, sublicensable, worldwide license under certain patent applications owned by the University of Washington relating to novel micro-dystrophins to develop, manufacture, and commercialize products for use in the treatment of DMDDuchenne and related disease indications caused by a lack of functional dystrophin. We have the right to grant sublicenses to third parties contingent upon written approval by the University of Washington prior to executing such sublicense, which approval may not be unreasonably withheld.

In consideration for the rights granted by the agreement, we paid a one-time, non-refundable license fee, which was recorded as a research and development expense in 2015. We are required to reimburse the University of Washington for costs incurred in applying for, prosecuting and maintaining patents and pay up to an aggregate of approximately $1 million upon the achievement of certain milestones. There were no milestones achieved as ofduring the years ended December 31, 20162021, 2020, and 2015.2019. In October 2017, the first milestone was achieved under this agreement. The

milestone payment was recorded as a research and development expense in the fourth quarter of 2017. In October 2020, the license agreement was amended such that we were required to pay the University of Washington $375 thousand in connection with the execution of the collaboration and license agreement with Ultragenyx, or the Collaboration Agreement, in October 2020. This payment was recorded as a research and development expense in the fourth quarter of 2020. The license agreement was also amended such that we are required to pay an aggregate of approximately $3.4 million upon the achievement of certain milestones. We must also pay royalties of a low single digit percentage of future sales by us and our sublicensees of products developed under the licensed patent rights. In addition, we must pay an annual maintenance fee until certain milestones are achieved, at which time a minimum annual royalty requirement will replace such maintenance fee and will apply to us and our sublicensees.

We are obligated to use our commercially reasonable efforts, consistent with sound and reasonable business practices and judgment, to commercialize the inventions covered by the licensed patent rights and to make and sell products based on that patent as soon as practicable and maximize sales thereof.

The University of Washington controls the prosecution and maintenance of the licensed patents in consultation with us and at our expense. In countries in which we have not requested prosecution or maintenance of licensed patents, the University of Washington may prosecute and maintain such licensed patents at its own cost. We have the first right to enforce such licensed patents at our expense. However, we may not enter into any settlement in any manner relating to the licensed patents without the University of Washington’s prior written consent.

The license agreement remains in effect until the expiration of the last-to-expire patent licensed under the agreement. We may terminate the agreement at any time upon providing sixty days’ written notice to the University of Washington. The University of Washington may terminate the agreement upon our uncured, material breach of the agreement or if we enter into an insolvency-related event.

17

The University of Missouri License Agreement

In 2015, we entered into a license agreement with the Curators of the University of Missouri, or the University of Missouri, a public corporation of Missouri, under which we obtained an exclusive, royalty-bearing, sublicensable, worldwide license under certain patents and patent applications owned by the University of Missouri relating to a novel synthetic microdystrophin gene to make, sell and distribute products for use in the treatment of DMDDuchenne and related disease indications resulting from a lack of functional dystrophin.

In consideration for the rights granted by the agreement, we paid a one-time, non-refundable license fee, which was recorded as a research and development expense in 2015. We arewere required to reimburse the University of Missouri for costs incurred in applying for, prosecuting and maintaining the licensed patents and pay up to an aggregate of approximately $1 million upon the achievement of certain milestones for each product developed based on the licensed patents. There

Under the agreement, in the event we grant a sublicense to another party, we are required to pay the University of Missouri a percentage of the consideration received. The license agreement was amended such that we were no milestones achievedrequired to pay, and did pay, the University of Missouri $0.8 million in February 2021 and $1.3 million in February 2022 as a result of December 31, 2016 and 2015. Inthe execution of the Collaboration Agreement with Ultragenyx in October 2017, the first milestone was achieved under this agreement. The milestone payment was2020. These amounts were recorded as a research and development expense in the fourth quarter of 2017.2020. The license agreement was also amended such that we are required to make aggregate milestone payments of approximately $1.9 million upon the achievement of certain milestones.

There were no milestones achieved during the years ended December 31, 2021, 2020, and 2019. We must pay a royalty of a low single digit percentage of future sales or by us or ourits sublicensees of products developed using the licensed patents. In addition, we must pay an annual maintenance fee until certain milestones are achieved, after which time a minimum annual royalty will replace such maintenance fee.

Under the agreement, we granted the University of Missouri a non-exclusive, royalty-free, irrevocable, paid-up license, with the right to grant sublicenses to non-profit, academic, educational or governmental institutions, to practice and use improvements made by us using the licensed patent rights, solely for non-commercial research purposes.

We are obligated to use our reasonable best efforts to introduce products based on the licensed patent rights into the commercial market as soon as possible, consistent with sound and reasonable business practices and judgment, and thereafter to keep such products reasonably available to the public.

The University of Missouri controls the prosecution and maintenance of the licensed patents in consultation with us and at our expense. In countries in which we have not requested prosecution or maintenance of licensed

patents, the University of Missouri may prosecute and maintain such licensed patents at its own cost. We have the first right to enforce such licensed patents at our expense. However, any settlement, consent judgment or other voluntary disposition of litigation that materially limits the scope, validity or enforceability of the licensed patent or admits fault or wrongdoing on the part of the University of Missouri must be pre-approved in writing by the University of Missouri.

The license agreement remains in effect until the expiration of the last-to-expire patent or the abandonment of the last to be abandoned patent application licensed under the agreement. The University of Missouri may terminate the agreement, or render the license granted thereunder non-exclusive, in individual countries if we and our sublicensees fail to achieve certain milestones. We may terminate the license agreement at any time upon providing six months’ written notice to the University of Missouri and paying a termination fee. Each of the University of Missouri and we may also terminate the agreement for an uncured default or breach of the agreement by the other party. Our ability to cure such breach only applies to the first two notices of such breach provided by the University of Missouri, and thereafter, the University of Missouri may terminate the agreement for our default or breach of the agreement upon thirty days’ written notice without an opportunity to cure such default or breach.

The University of Michigan License Agreement

In 2016, we entered into a license agreement with the Regents of the University of Michigan, or the University of Michigan, a constitutional corporation of Michigan, under which we obtained an exclusive, royalty-bearing, sublicensable, worldwide license to make, sell and distribute products under certain patents owned by the University of Michigan related to microdystrophin and utrophin spectrin-like nucleic acid sequences for any use that, but for this agreement, would comprise an infringement of a valid claim included in the licensed patent rights.

In consideration for the rights granted by the agreement, we paid a one-time license fee and a separate fee to cover past patent prosecution costs. We recorded the upfront license fee as a research and development expense in 2016. We are required to reimburse the University of Michigan for costs incurred in applying for, prosecuting and maintaining patents, and pay up to an aggregate of approximately $1 million upon the achievement of certain milestones. There were no milestones achieved as of December 31, 2017 and 2016. We must also pay royalties of a low single-digit percentage of future sales by us or our sublicensees of products developed using the licensed rights, with a minimum annual royalty after certain milestones are achieved. In addition, we must pay an annual maintenance fee in any year in which the minimum annual royalty is not reached.

Under the agreement, the University of Michigan reserves for itself and its affiliates the right to use the licensed rights for non-commercial research, public service, internal and educational purposes and the right to grant the same limited non-commercial rights to other non-profit research institutions.

We are obligated to use commercially reasonable efforts to bring one or more products based on the licensed patents to market through a diligence program for utilizing the licensed patents, to continue diligent marketing efforts throughout the term of the agreement, and to make reasonable amounts of such products commercially available, in each case consistent with prudent business practices and judgment.

The University of Michigan controls the prosecution and maintenance of the licensed patents in consultation with us and at our expense. In countries in which we have not requested prosecution or maintenance of licensed patents, the University of Michigan may prosecute and maintain such licensed patents at its own cost. We have the first right to enforce such licensed patents at our expense. However, we may only enter into a settlement with the advice and consent of the University of Michigan.

The license agreement remains in effect until the expiration of the last-to-expire patent licensed under the agreement. The University of Michigan may terminate the agreement upon our uncured material breach of the

agreement, including failure to make required payments under the agreement or to achieve certain milestones, or if we become insolvent or bankrupt. We may terminate the license agreement at any time upon providing sixty days’ written notice to the University of Michigan.

Harvard College License Agreements

In 2016 and 2017, we entered into license agreements with the President and Fellows of Harvard College, or Harvard College, under which we obtained non-exclusive, royalty-bearing, sublicensable, worldwide licenses to use certain intellectual property owned by Harvard College to develop, manufacture, and commercialize products for use in the treatment of DMD.Duchenne.

18

In consideration for the rights granted by each agreement, we paid one-time, non-refundable license fees, which were recorded as a research and development expense in 2016 and 2017. We are required to pay an annual license maintenance fee until certain milestones are achieved, after which time the annual maintenance fee will increase annually. Such annual maintenance fees will further increase if we grant certain rights to a sublicensee or strategic partner with whom we collaborate on the development and commercialization of licensed products. The annual maintenance fees are creditable against royalty payments. We also must pay milestone payments within thirty days after achieving certain milestones. There were no milestones achieved as ofduring the years ended December 31, 20172021, 2020 and 20162019 under either agreement. We must pay a royalty on future sales by us or our sublicensees of products developed using the licensed technology.

The license agreements each remain in effect for an initial term of fifteen years, with automatic three-year renewal periods thereafter unless one of the parties provides notice of non-renewal. We may terminate the license agreements at any time upon providing sixty days’ written notice to Harvard College. Harvard College may terminate the agreements in the event we become bankrupt or insolvent. Both Harvard College and we may also terminate the agreements for an uncured material breach of the agreements by the other party.

Ultragenyx Collaboration Agreement

On October 22, 2020, or the Effective Date, we entered into a collaboration and license agreement with Ultragenyx, to focus on the development and commercialization of new gene therapies for Duchenne. We granted Ultragenyx an exclusive worldwide license for any pharmaceutical product that expresses our proprietary microdystrophin construct from AAV8 and variants thereof in clade E for the treatment of Duchenne and other diseases resulting from the lack of functional dystrophin. We are conducting certain activities agreed to by the parties with respect to the development of licensed products. Ultragenyx will reimburse us for personnel and out-of-pocket costs that we incur in conducting such development activities. Otherwise, Ultragenyx has decision-making authority with respect to the development, manufacturing and commercialization of licensed products. We retain exclusive rights to all other uses of our microdystrophin proteins, including under our existing SGT-001 program.

We are conducting certain activities agreed to by the parties with respect to the development of licensed products. Ultragenyx is obligated to reimburse us for personnel and out-of-pocket costs that we incur in conducting such development activities. Otherwise, Ultragenyx has decision-making authority with respect to the development, manufacturing and commercialization of licensed products. In connection with the execution of the Collaboration Agreement, we also entered into a stock purchase agreement and an investor agreement with Ultragenyx, pursuant to which we issued and sold 7,825,797 shares of our common stock to Ultragenyx at a price of $5.1113 per share for an aggregate purchase price of approximately $40.0 million. The shares purchased by Ultragenyx are subject to a lock-up period until the earliest to occur of (i) 18 months from the closing date, (ii) the termination of the Collaboration Agreement or (iii) other specified events. Pursuant to the terms of the investor agreement, Ultragenyx agreed that, so long as it holds at least 10% of our outstanding common stock, the shares will be subject to a voting agreement, such that until the earliest to occur of certain specified events, and subject to specified conditions, Ultragenyx will, and will cause its permitted transferees to, vote in accordance with the recommendation of our Board of Directors with respect to specified matters.

Ultragenyx also agreed to pay up to $255.0 million in cumulative milestone payments per product upon achievement of specified milestone events, and tiered royalties on worldwide net sales at low double digit to mid-teens percentages. Upon achievement of proof-of-concept, we have the right to opt-in to co-fund collaboration programs in return for participation in a profit share or increased royalty payments. None of the payments under the Collaboration Agreement are refundable.

For each licensed product for which Ultragenyx decides to initiate a registrational trial in humans, we have the option to fund 30% of the development costs in the United States and European Union for such licensed product and forgo the development milestones and regulatory milestones, or the Development Option, and receive tiered royalties on a licensed product-by-licensed product and country-by-country basis ranging from a mid-teens percentage to a low twenties percentage based on Ultragenyx’s, and any of its affiliates’ and sublicensees’ annual worldwide net sales of each such licensed product.

For each Licensed Product for which we exercise the Development Option, we may also elect to share 30% of the net income and net losses on net sales of such Licensed Product in the United States and European Union, or the Income Share Option. For licensed products for which we have exercised the Income Share Option, we will not be entitled to milestone payments and Ultragenyx will pay us tiered royalties on a licensed product-by-licensed product and country-by-country basis ranging from a mid-teens percentage to a low twenties percentage based on Ultragenyx’s, and any of its affiliates’ and sublicensees’, annual net sales of each such licensed product outside of the United States and European Union.

19

Other License Agreements

In 2016, we entered into a license agreement with Life Technologies Corporation, or Life Technologies. In consideration for obtaining a non-exclusive, royalty-free, worldwide license to use certain technologies and associated know-how to develop our product candidates, we paid a one-time, non-refundable license fee. This fee was recorded as a research and development expense in 2016. The license agreement will remain effective in perpetuity unless earlier terminated. Life Technologies has the right to terminate the agreement upon our material, uncured breach of the agreement or in the event that it determines that continued performance of the agreement may violate any laws. We are obligated to diligently pursue regulatory approval necessary for the development, manufacture and sale of the licensed products. We have the right to terminate the agreement at any time upon providing thirty days’ written notice to Life Technologies.

Competition

The biotechnology and pharmaceutical industries are characterized by rapidly changing technologies, significant competition and a strong emphasis on intellectual property. This is also true in treatments of DMD,Duchenne, as well as in gene therapy. While we believe that our focus, strength of team, expertise in gene therapy, scientific knowledge and intellectual property provide us with competitive advantages, we face competition from several different sources, including large and small biopharmaceutical companies, academic research institutions, government agencies and public and private research institutions. Not only must we compete with other companies that are focused on gene transfer technology, but any product candidates that we successfully develop and commercialize will compete with existing therapies and new therapies that may become available in the future.

Many of our competitors have significantly greater financial resources and expertise in research and development, manufacturing, preclinical testing, clinical trials, regulatory approvals and product marketing than

we do. 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. Mergers and acquisitions in the pharmaceutical and biotechnology industries may result in even more resources being concentrated among a smaller number of our competitors. Smaller or early stage companies may also prove to be significant competitors, particularly through collaborative arrangements with large and established companies.

We are aware of several companies and research institutions conducting clinical trials of product candidates focused on developing systemic gene transfers for DMD,Duchenne, including Pfizer Inc. and Sarepta Therapeutics, Inc. Any advanceswith product candidates currently in gene transfer technology made byPhase III clinical development,  Genethon with a competitor may be used to develop therapies that could compete with our lead product candidate.

For our gene transfer product candidate we are aware of the following competitors:

In addition to the investigationalits gene transfer programs discussed above, there are two therapies, which are intended to be disease modifying, that are currently approved for DMD by certain regulators. These products are eteplirsen (EXONDYS 51) and ataluren (Translarna), eachproduct in the first half of which is indicated for approximately 13% of DMD patients.2022.

20

Government regulation and product approvallicensure

U.S. government regulation and product approvallicensure

In the United States, biologic products including gene therapy products, such as our lead product candidate, are licensed for marketing by the FDA under the Public Health Service Act, or PHS Act, and regulated by the FDA under the Federal Food, Drug, and Cosmetic Act, or FD&C Act, as well as by other federal, state and local statutes and regulations. Both the FD&C Act and the PHS Act and their corresponding rules and regulations govern, among other things, the testing, manufacturing, safety, efficacy, labeling, packaging, storage, record keeping, distribution, reporting, advertising and other promotional practices involving biologic products. FDA approval must be obtained before conducting human clinical testing of biologic products. Additionally, each clinical trial protocol for a gene therapy product candidate is reviewed by the FDA and, in limited instances, the U.S. National Institutes of Health, or the NIH, through its Office of Biotechnology Activities’ Recombinant DNA Advisory Committee, or RAC. FDA must license a biologic product before it may be marketed within the United States.

Within the FDA, the Center for Biologics Evaluation and Research, or the CBER, regulates gene therapy products. Within CBER, the review of gene therapy and related products is consolidated in the Office of Tissues and Advanced Therapies, or the OTAT, and the FDA has established the Cellular, Tissue and Gene Therapies Advisory Committee to advise CBER on its reviews. CBER, which works closely with the NIH and the RAC, which makes recommendations to the NIH on gene therapy issues and engages in a public discussion of scientific, safety, ethical and societal issues related to proposed and ongoing gene therapy protocols. To date, theThe FDA has licensed one human gene therapy producttherapies products for sale in the United States, and the agency has provided guidance for the development of other gene therapy products. This guidance includes a growing body of guidance documents on chemistry, manufacturing and control, or CMC, clinical investigations and other areas of gene therapy development, all of which are intended to facilitate the industry’s development of gene therapy products.

U.S. biologic products development process

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