Kyverna rises on stiff person syndrome data

Shares in Kyverna Therapeutics were up nearly 40% today after the biotech reported that its cell therapy for rare autoimmune disease stiff person syndrome (SPS) had met its objectives in a potentially pivotal trial.

Emeryville, California-based Kyverna said that mivocabtagene autoleucel (miv-cel, formerly KYV-101) showed clinical benefit across all the primary and secondary endpoints in the phase 2 KYSA-8 study, which enrolled 26 patients with SPS.

The disease is a progressive immune-mediated disorder of the central nervous system (CNS) that is characterised by progressive rigidity and painful spasms of muscle, particularly the limbs, head, and neck, that can be triggered by being startled, experiencing stress, cold, and/or exercise. It is thought to affect one to two people per million in the US.

The condition gradually worsens over time, and if untreated, can lead to permanent disability and even death in some cases. Current treatment is aimed at treating symptoms, for example through the use of muscle relaxants, but miv-cel is designed to suppress autoreactive B cells that are considered to be one of the main drivers of the disorder.

After a single dose, miv-cel achieved a "robust and sustained improvement" in mobility, according to Kyverna, with a statistically significant 46% improvement in timed 25-foot walk (T25FW) at 16 weeks, compared to baseline.

Overall, 81% of patients exceeded a 20% improvement in T25FW, a threshold that Kyverna said was "clinically meaningful," with additional positive results on a range of secondary endpoints measuring muscle stiffness, walking ability, sensitivity to stimuli like sounds and bright lights, and neurological disability.

Kyverna is one of a clutch of companies trying to develop CAR-Ts for autoimmune diseases, extending their use beyond cancer. Miv-cel is an anti-CD19 CAR-T and also stimulates CD28, a strategy designed to reduce the risk of serious side effects.

Chief executive Warner Biddle said the results could "pave the way for miv-cel to become the first and only approved therapy in SPS and CAR T-cell therapy for autoimmune disease," and put the firm on target to file the cell therapy for approval in SPS in the first half of 2026.

Kyverna has previously reported positive midstage data with miv-cel in generalised myasthenia gravis (gMG), another autoimmune disorder, and is poised to start patient dosing in a phase 3 stage of the trial before the end of this year. It is also exploring the cell therapy's potential role in treating multiple sclerosis and rheumatoid arthritis.