Organizational update to advance the development of Duchenne’s gene therapy pipeline programs • Solid Biosciences

Dear Duchenne community,

In a press release issued this morning, we shared an update on our company’s strategy and reiterated our commitment to advancing our two gene therapy programs for Duchenne: SGT-001 and SGT-003. We wanted to provide you with a little more context and what this means for the future of these ongoing programs.

SGT-001

Last month, we provided an update on patients who received SGT-001 two years after treatment. These data show sustained benefit two years post-treatment compared to natural history trajectories of functional, pulmonary, and patient-reported outcomes.

In the update provided this morning, we announced that we have decided to complete enrollment in the IGNITE DMD Phase I/II clinical trial to move into FDA engagement and plan future clinical activities. . According to the study protocol, all treated patients will continue their scheduled follow-up visits 5 years after the infusion. As part of the clinical activities for IGNITE DMD, we will develop a primary analysis of data from the nine patients who were treated in IGNITE DMD through the primary endpoint at one year. We plan to make information about the full study, as well as individual patient data, available to all study participants.

We will also transition to a commercial-scale transient transfection-based manufacturing process for SGT-001. Following robust manufacturing analysis, we believe that by moving to a transient-based process, we will be able to produce a high quality drug and see improvements in manufacturability and clinical supply capabilities.

This was a natural opportunity for the company to complete its study enrollment. We will move aggressively through the transition process and have already contacted the FDA to determine how we can quickly return to the clinic with SGT-001. We plan to resume dosing with SGT-001 in the first half of 2023.

We would like to take this opportunity to express our immense gratitude to the patients who participated in IGNITE DMD, and to all patients and families who choose to participate in clinical trials. Without your courage and willingness to participate in clinical trials, we would not be able to advance this important science in our quest to develop meaningful therapies for Duchenne.

SGT-003

We also shared new data in support of SGT-003, a novel next-generation capsid candidate that we believe may have significant benefits for the delivery of muscle-related gene therapies. New data from a non-human primate study using a reporter transgene in our novel capsid demonstrated increased muscle tropism, decreased hepatic biodistribution, and improved efficacy compared to AAV9. These results are consistent with previous in vitro and live studies in mouse models, which suggested improved muscle tropism with our new capsid as well as better expression of Solid’s microdystrophin compared to AAV9. In the SGT-003 program for Duchenne, we combine this new muscle tropic capsid with our differentiated microdystrophin. We are excited about this compelling new data and remain on track for an IND submission expected in early 2023.

Following our decision to align Solid behind these two promising gene therapy programs, we had to make difficult choices to refocus our resources. As part of the organizational changes, we will reduce our workforce by approximately thirty-five percent and reduce the activities of our other research and development programs unrelated to SGT-001, SGT-003 and Next Generation Capsids. We are grateful for the efforts and contributions of every employee who has worked tirelessly to advance our mission.

Thank you for your continued support of Solid. As always, our commitment to the Duchenne community is unwavering. We will continue to work with determination and urgency every day toward the unified goal of developing meaningful treatments and improving the lives of patients with Duchenne.

Upcoming Community Presentations

  • CureDuchenne FUTURES National Conference: May 27-29, 2022
  • Parent Project Muscular Dystrophy Annual Conference: June 23-26, 2022

As always, we appreciate your continued support. #TogetherWeAreSolid

Sincerely,

Your Solid Biosciences team

Aubrey L. Morgan