CAR T-cell therapy eases stiff person syndrome in Phase 2 trial

Walking across a room is something most people never think about. For many patients with stiff person syndrome, it becomes a struggle, and 80% of them eventually need walking assistance or a wheelchair.

Stiff person syndrome is a rare, progressive autoimmune neurological disease. In autoimmune diseases, the immune system attacks the body's own tissue, and here the result is debilitating muscle stiffness, painful spasms and difficulty walking. Many patients face a risk of permanent disability, and until now there were no approved therapies for the condition.

The experimental treatment, mivocabtagene autoleucel or miv-cel, works differently from standard care. It is a CAR T-cell therapy: the patient's own immune cells are modified so that they target the cells involved in the disease. Standard treatments usually require ongoing medication to manage symptoms and suppress immune activity. The researchers say this approach aims to address the underlying autoimmune processes instead, potentially offering longer-lasting benefits after a single treatment.

The one-year results, presented at MSToronto26 by Amanda Piquet of the University of Colorado Anschutz, cover all 26 patients in the Phase 2 trial. Patients completed a 25-foot walking test in a median of 49% less time than before treatment. Of the 12 patients who initially needed a walking aid, eight (67%) no longer did. More than one-third of patients, 35%, completed the walking test in under five seconds, a time comparable to that of typical healthy adults. Lasting reductions in stiffness, sensitivity to stimuli and overall disability were also reported. The researchers note that in 65% of patients, the targeted immune cells had begun returning by one year, yet the clinical gains held.

For patients, the most concrete change would be a therapy that could reduce the need for ongoing immune-suppressing drugs; 24 of 26 patients (92%) remained free of them at one year. Kyverna has said it intends to complete its rolling biologics license application in the fourth quarter of 2026. If the FDA approves miv-cel, it could become the first approved treatment for stiff person syndrome and the first CAR T-cell therapy approved for an autoimmune disease. Those outcomes depend on the regulator's review, and the data still come from one trial of 26 patients, sponsored by the company that developed the drug.