FDA Activity Recap: September 2025 Features New Draft Guidance Documents, RMAT Designation, and More

Last month, September 2025, the CGTLive^® team was diligently tracking the FDA's activities related to the development of cell and gene therapies for the treatment of rare, complex, and otherwise challenging diseases and disorders.

The agency has continued to ramp up its activities around these therapies as more of them progress through the pipeline in tandem. Last month proved no different, with the FDA releasing new draft "Guidance For Industry” documents for cell and gene therapy (CGT) development and granting regenerative medicine advanced therapy (RMAT) designation to Nanoscope Therapeutics' gene therapy MCO-010. Our team has highlighted these, and several other important actions, below.

Click the read more buttons for more details and information about each update.

FDA Publishes 3 New Draft Guidance for Industry Documents Aimed at Cell and Gene Therapy Development

September 30, 2025 — The FDA has published 3 new “Draft Guidance For Industry” documents intended to provide guidance for the development of CGT products.

The first of the 3 documents, entitled “Innovative designs for clinical trials of cellular and gene therapy products in small populations”, is intended to provide considerations for trial sponsors who are carrying out trials of such therapies intended to treat small populations of patients, such as those with a particular rare disease. Although the agency points out that in certain circumstances, the guidance provided may be applicable to trials for therapies for common diseases, as well, noting that in such cases the sponsor should hold a discussion with the relevant review division.

The goal of the guidance given in the document is to improve the efficiency of GCT trials. It covers topics including utilizing participants as their own control in single arm studies, disease progression modeling, externally controlled studies, adaptive clinical trial designs, Bayesian trial designs, master protocol designs, as well as considerations for selection of participants.

MavriX Bio’s Angelman Syndrome Gene Therapy MVX-220 Garners FDA Fast Track Designation

September 28, 2025 — MavriX Bio’s MVX-220, an investigational adeno-associated virus (AAV) vector-based gene therapy, has received fast track designation from the FDA for the treatment of Angelman syndrome (AS).

The therapy’s initial development was financially supported by the Foundation for Angelman Syndrome Therapeutics (FAST) and took place at the University of Pennsylvania. MavriX Bio later licensed the product and is carrying out clinical development in conjunction with partner GEMMA Biotherapeutics (GEMMABio). MavriX is a portfolio company of AS2Bio, a FAST drug development accelerator.

"GEMMABio has been deeply honored to support MavriX Bio on the MVX-220 development program,” James M. Wilson, MD, PhD, thechief executive officer at GEMMABio, said in a statement. “With fast track status, this program gains crucial momentum—it means the team can engage more closely with regulators and accelerate development milestones. For the AS community, fast track designation opens up a path toward bringing gene-targeted therapies to patients sooner.”

Sanofi's DM1 Gene Therapy SAR446268 Snags Fast Track Designation

September 26, 2025 — The FDA has granted fast track designation to Sanofi’s SAR446268, an investigational AAV vector-based gene therapy intended to treat noncongenital (juvenile and adult onset) DM1 myotonic dystrophy type 1 (DM1, also known as Steinert's disease).

The therapy, which is currently being evaluated in a first-in-human phase 1/2 clinical trial (NCT06844214), is given as a one-time treatment and is intended to silence expression of the DMPK gene through RNA interference. In addition to fast track designation, SAR446268 has previously received orphan drug designations from the FDA and European Medicines Agency.

“By reducing DMPK transcripts, the gene therapy aims to eliminate the abnormal and toxic RNA foci responsible for splicing defects in muscle tissue, thereby restoring normal splicing and improving muscular function,” Sanofi stated in a press release. “This approach has the potential to address key symptoms of the disease, including progressive muscle weakness, difficulty relaxing muscles (myotonia), and effects on multiple body systems including heart, lungs, and endocrine functions.”

Sanofi’s Neovascular Age-Related Macular Degeneration Gene Therapy SAR402663 Garners FDA Fast Track Designation

September 17, 2025 — Sanofi’s SAR402663, an investigational gene therapy, has received fast track designation from the FDA for the treatment of neovascular age-related macular degeneration, also known as wet AMD.

SAR402663 comprises a onetime intravitreal treatment and is intended to inhibit VEGF by providing a gene for soluble FLT01. Inhibition of abnormal blood vessel growth, a decrease in vascular leakage, minimization of retina damage, and a lowering of treatment burden are among the intended effects of SAR402663.

The gene therapy is currently being assessed in a phase 1/2 clinical trial (NCT06660667). The study, which consists of dose-escalation and dose-expansion portions, is expected to enroll 66 patients in total. According to the ClinicalTrials.gov page, which was most recently updated on July 4, 2025, the trial is currently recruiting patients aged 50 to 90 years at a number of sites in the United States. The estimated primary completion date for the trial is May 18, 2027.

Nanoscope Nabs RMAT Designation for Retinitis Pigmentosa Gene Therapy MCO-010

September 4, 2025 — Nanoscope Therapeutics has received FDA RMAT designation for MCO-010 (sonpiretigene isteparvovec), an investigational ambient-light activatable multicharacteristic opsin (MCO) gene therapy intended to treat various retinal diseases.

The RMAT designation specifically applies to Stargardt disease. Notably, the European Medicines Agency has also granted MCO-010 orphan drug designation for 5 retinal dystrophy categories, including macular dystrophies and nonsyndromic and syndromic rod-dominant and cone-dominant dystrophies. The FDA has also previously granted MCO-010 orphan drug designation and fast track designation.

“Securing RMAT designation for Stargardt disease in addition to our prior FDA designations for Stargardt disease and RP [retinitis pigmentosa] is a major validation for our therapies that warrant expedited development and review,” Sulagna Bhattacharya, the CEO of Nanoscope, said in a statement. “Combined with 5 EMA Orphan designations, these achievements highlight the global momentum behind our MCO platform as a potential vision-restoring therapy for patients with few or no treatment options.”