In a historic first for the field of cell therapy, Kyverna Therapeutics has initiated a rolling Biologics License Application (BLA) with the U.S. Food and Drug Administration for mivocabtagene autoleucel (miv-cel) — a CAR T-cell therapy targeting stiff person syndrome (SPS). If approved, it would become the first-ever CAR T therapy for an autoimmune disease and the first FDA-approved treatment for SPS.
Stiff person syndrome is a rare, progressive neurological autoimmune disorder affecting fewer than 5,000 people in the United States. The condition causes painful muscle stiffness and spasms, severely impairing mobility and quality of life. Currently, no FDA-approved therapies exist.
The pivotal KYSA-8 Phase 2 trial demonstrated remarkable results: patients receiving a single infusion of miv-cel showed a 46% median improvement on the Timed 25-Foot Walk test at 16 weeks, with 81% of patients achieving at least a 20% improvement. All secondary endpoints — including ambulation, sensitivity, disability, and distribution of stiffness — were also met with statistical significance.
Notably, 100% of patients remained free of any other immunotherapies through Week 16 and beyond, with early treated patients maintaining durable efficacy for over 15 and 26 months without needing chronic treatment. Kyverna CEO Warner Biddle called the achievement "a significant milestone for not only Kyverna but also the field."
The safety profile was favorable, with no high-grade cytokine release syndrome or neurotoxicity reported — a concern that has historically limited CAR T use beyond oncology. Cases of grade 3/4 neutropenia were manageable.
Kyverna gained FDA alignment on a single-arm trial design for the BLA submission, which is proceeding under the Regenerative Medicine Advanced Therapy (RMAT) designation, enabling priority review. The company expects to complete the submission in Q4 2026, with a potential launch in 2027.
Beyond SPS, Kyverna is advancing miv-cel in generalized myasthenia gravis (Phase 3 enrollment ongoing), where Phase 2 data showed a 100% response rate, and exploring its potential in multiple sclerosis and rheumatoid arthritis.
The milestone represents a paradigm shift: CAR T therapy, long confined to blood cancers, may be on the verge of transforming the treatment of autoimmune diseases by providing a one-time immune system reset rather than lifelong medication.
