Kyverna’s CAR‑T Miv‑Cel Shows Durable One‑Year Benefit in Stiff‑Person Syndrome

Kyverna Therapeutics reported that its registrational Phase III study of the anti‑CD19 CAR‑T therapy miv‑cel (mivocabtagene autoleucel) demonstrated sustained clinical benefit for patients with stiff‑person syndrome (SPS) at one year.

Key Efficacy Results

In the KYSA‑8 trial (NCT06588491), participants treated with a single infusion of miv‑cel experienced a 49% improvement in the timed 25‑Foot Walk (T25FW) at month 12, up slightly from the 46% improvement observed at week 16. More than one‑third of treated patients completed the T25FW in under five seconds — a performance comparable to typical healthy adults.

Among patients who achieved a clinically meaningful improvement at the primary analysis, 95% maintained that benefit at the one‑year assessment.

Safety Profile

Miv‑cel continued to show a favorable tolerability profile in KYSA‑8. There were no reports of high‑grade cytokine release syndrome (CRS) or immune effector cell‑associated neurotoxicity syndrome (ICANS), and no cases of immune effector cell‑associated hemophagocytic lymphohistiocytosis‑like syndrome (IEC‑HS) were observed.

Regulatory and Presentation Updates

Kyverna confirmed at the American Academy of Neurology (AAN) Annual Meeting in April 2026 that KYSA‑8 met both its primary and secondary endpoints at the 16‑week analysis. The company plans to include the one‑year durability data in its rolling Biologics License Application (BLA) submission to the US Food and Drug Administration (FDA).

Dr Amanda Piquet, Director of Autoimmune Neurology at the University of Colorado Anschutz School of Medicine, Céline Dion Foundation Endowed Chair and lead investigator of KYSA‑8, said: "The results from KYSA‑8 are compelling, particularly given the severe burden of SPS and the absence of approved therapies. After a single dose of miv‑cel, the sustained improvements observed in mobility, stiffness and other disease‑specific measures, together with a well‑tolerated profile, underscore its potential to deliver significant, long‑lasting benefit to patients with SPS."

Context: Stiff‑Person Syndrome and Competing Programs

Stiff‑person syndrome is a rare, progressive autoimmune neurological disorder characterized by severe muscle stiffness, rigidity and painful spasms affecting the trunk, abdomen and limbs. Public awareness of SPS rose after singer Céline Dion disclosed her diagnosis in 2022. There are currently no FDA‑approved therapies specifically for SPS, and the development pipeline is limited.

Separately, Kedrion recently received FDA orphan drug designation for Qivigy (Immune Globulin Intravenous Human 10% Solution), which is being evaluated in a Phase III trial for SPS (NCT07552987).

Additional Kyverna Data: gMG Program

Kyverna also presented extended follow‑up from the Phase II/III KYSA‑6 study (NCT06193889) of miv‑cel in generalized myasthenia gravis (gMG), with analyses up to 18 months. In the Phase II cohort, all seven patients achieved clinically meaningful improvements in Myasthenia Gravis Activities of Daily Living (MG‑ADL) and Quantitative Myasthenia Gravis (QMG) scores at 24 weeks, with mean reductions of 8.3 and 11.7 points, respectively. Those gains have been sustained at the one‑year timepoint for patients who have reached that follow‑up.

MG‑ADL and QMG remain the co‑primary endpoints for the ongoing Phase III portion of KYSA‑6.

Market Outlook

According to a GlobalData market forecast, the gMG market across the seven major markets (7MM: US, France, Germany, Italy, Spain, UK and Japan) is projected to grow from approximately $4.5 billion in 2024 to about $13 billion by 2034. (GlobalData is the parent company of Clinical Trials Arena.)

Disclosure: This article is based on reporting originally published by Clinical Trials Arena, a GlobalData‑owned brand.