Kyverna Therapeutics’ Phase III trial of a CAR-T therapy in stiff-person syndrome (SPS) has seen sustained benefit after one year.
In the registrational KYSA-8 study (NCT06588491), patients treated with miv-cel (mivocabtagene autoleucel) saw a sustained 49% improvement in timed 25-Foot Walk (T25FW) at month 12, compared to 46% at week 16. More than one-third of patients completed T25FW in less than 5 seconds, comparable to a typical time for healthy adults.
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Of those who achieved a clinically meaningful improvement at the primary analysis, 95% sustained their benefit.
Miv-cel, an anti-CD19 CAR-T that stimulates CD28, continued to be well-tolerated with no high-grade cytokine release syndrome (CRS) or immune effector cell-associated neurotoxicity syndrome (ICANS). There were also no cases of immune effector cell-associated hemophagocytic lymphohistiocytosis-like syndrome (IEC-HS).
At the American Academy of Neurology (AAN) Annual Meeting, which was held in April 2026, Kyverna confirmed that the study met its primary and secondary endpoints after 16 weeks of treatment.
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 the KYSA-8 trial, 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.”
Kyverna will include the one-year data in its rolling Biologics License Application (BLA) submission to the US Food and Drug Administration (FDA).
SPS is a rare, progressive autoimmune neurological disorder that causes severe muscle stiffness, rigidity, and painful spasms in the trunk, abdomen, and limbs. While the syndrome is incredibly rare, it has become more known publicly in recent years after Céline Dion was diagnosed with the disease in 2022.
There are currently no FDA-approved drugs specifically for SPS and the pipeline also remains sparse. Kedrion is one of those working towards a therapy, with its asset Qivigy (immune globulin Intravenous human 10% solution) winning FDA orphan drug designation earlier this week. The drug is currently in a Phase III clinical study (NCT07552987) for SPS.
gMG data also promising
Kyverna also shared longer-term data from the Phase II/III KYSA-6 study (NCT06193889) of miv-cel in generalised myasthenia gravis (gMG), with analysis of up to 18 months. In the Phase II portion, all seven patients achieved clinically meaningful improvement in Myasthenia Gravis Activities of Daily Living (MG-ADL) and Quantitative Myasthenia Gravis (QMG) at 24 weeks, with mean reductions of 8.3 and 11.7 points, respectively.
These improvements were sustained at the one-year point for those who have been receiving treatment for that period.
MG-ADL and QMG are the co-primary endpoints of the ongoing Phase III portion of the study.
According to a GlobalData market forecast report, the gMG market across the seven major markets (7MM: US, France, Germany, Italy, Spain, UK, and Japan) is projected to reach $13bn by 2034, growing from a valuation of $4.5bn in 2024.
GlobalData is the parent company of Clinical Trials Arena.
