Sangamo Therapeutics has announced positive topline results from its registrational Phase 1/2 STAAR study evaluating isaralgagene civaparvovec (ST-920), a wholly-owned, investigational one-time gene therapy for adults with Fabry disease. The study demonstrated a positive mean annualized estimated glomerular filtration rate (eGFR) slope of 1.965 mL/min/1.73m2/year at 52 weeks across all 32 dosed patients, a key outcome that the U.S. FDA has agreed will serve as an intermediate clinical endpoint for Accelerated Approval. This positive eGFR slope compares favorably to the observed decline in kidney function seen with currently approved Fabry disease treatments, which range from -2.2 to -0.4 mL/min/1.73m2/year.

Beyond kidney function, isaralgagene civaparvovec showed sustained elevation of alpha-galactosidase A (α-Gal A) activity for up to 4.5 years in the longest-treated patient. Notably, all 18 patients who started the study on enzyme replacement therapy (ERT) have successfully withdrawn from it and remain off ERT, with stable plasma lyso-Gb3 levels. Patients also experienced a range of other significant clinical benefits, including improvements in disease severity as measured by the Fabry Outcome Survey Mainz Severity Score Index (FOS-MSSI) and statistically and clinically significant improvements in multiple domains of the short form-36 (SF-36) quality of life scores at week 52. Additional benefits included reduced or eliminated pain medication use and the resumption of sweating in some individuals.

The gene therapy demonstrated a favorable safety and tolerability profile without the need for preconditioning, with most adverse events being mild to moderate and resolving with clinical management. Isaralgagene civaparvovec has received several expedited designations, including Orphan Drug, Fast Track, and RMAT from the FDA. Based on these compelling results, Sangamo intends to submit a Biologics License Application (BLA) as early as the first quarter of 2026 under the Accelerated Approval pathway, aiming to provide a durable, one-time treatment option for Fabry disease.