Kyverna Therapeutics, Inc. said adults with stiff person syndrome completed a 25-foot walk in a median 49% less time one year after CAR T-cell therapy in a 26-person trial without a control group.
The results were presented Oct. 21 at MSToronto 2026 in Toronto. KYSA-8 is an open-label phase 2 study of mivocabtagene autoleucel, or miv-cel, given once to adults whose condition had responded inadequately to at least one immunotherapy. The main walking assessment was at 16 weeks; the new figures track participants to one year.
Twenty participants, or 77%, met the study’s benchmark of reducing their 25-foot walking time by at least 20%. Among 12 people who used a walking aid in the initial test, eight completed the one-year test without one.
The trial cannot show how much of the change miv-cel caused because it had no comparison group. The walking-aid finding applies to the test alone; it does not establish whether participants stopped using aids in daily life.
Miv-cel is made from patients’ modified T cells and targets B cells with CD19 on their surface. Stiff person syndrome is a rare autoimmune neurological disease in which muscle stiffness and painful spasms can limit movement. The U.S. Food and Drug Administration (FDA) has not approved a treatment specifically for the disease.
Kyverna reported that 24 of 26 patients, or 92%, had no immunomodulatory or immunosuppressant treatment for the disease at one year.
The poster recorded cytokine release syndrome in 24 patients and neurological toxicity in three. Five patients experienced grade 3 or 4 neutropenia, and three had serious adverse events linked to the treatment. It reported no high-grade cases of cytokine release syndrome or neurological toxicity.
Amanda Piquet, the trial’s principal investigator and director of the autoimmune neurology program at the University of Colorado Anschutz School of Medicine, called the findings a “major step forward.”
Kyverna says it aims to complete its rolling biologics license application to the FDA in the fourth quarter of 2026. That target is for finishing the submission, not for an FDA decision.
