Kyverna Therapeutics Reports One-Year Phase 2 Results for CAR T-Cell Therapy in Stiff Person Syndrome

Key Points

• Kyverna Therapeutics reported a 49% median improvement in timed walking at one year in its 26-patient, single-arm Phase 2 trial of miv-cel for stiff person syndrome.
• At one year, 92% (24/26) of patients remained free of chronic immunotherapies for stiff person syndrome.
• Kyverna reported no high-grade cytokine release syndrome or neurotoxicity; serious treatment-related adverse events occurred in three patients and had fully resolved.

Kyverna Therapeutics, a clinical immunology company focused on neurologic autoimmune diseases, announced the full one-year data set from KYSA-8, its registrational Phase 2 trial of miv-cel (mivocabtagene autoleucel, KYV-101) in patients with stiff person syndrome (SPS). The data were presented at MS Toronto 2026, the joint ACTRIMS-ECTRIMS meeting, on October 21, 2026.

KYSA-8 is a single-arm trial in which 26 adults with SPS who had an inadequate response to at least one immunotherapy received a single dose of miv-cel. The primary endpoints are change from baseline in the timed 25-Foot Walk (T25FW) at 16 weeks and the incidence and severity of adverse events. Secondary endpoints assess disability, stiffness, hypersensitivity and mobility.

Amanda Piquet, M.D., FAAN, 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: “Through one year, patients experienced significant improvements across multiple measures of disease burden, including disability, mobility, stiffness, hypersensitivity, physical functioning and mental health, with a well-tolerated safety profile.”

One-year outcomes

Kyverna said the primary endpoint and all key secondary endpoints were achieved with statistical significance. The company reported the following one-year findings in the 26-patient cohort:

• Median improvement from baseline in T25FW was 46% at week 16 and 49% at one year, with significant improvement sustained at one year (p < 0.0001).
• Clinically meaningful improvement in T25FW, defined as a reduction of at least 20% from baseline, was achieved by 81% (21/26) of patients at week 16 and 77% (20/26) at one year.
• Over one-third of patients completed T25FW in less than 5 seconds, which Kyverna described as comparable to a typical time for healthy adults.
• Of the 12 patients who required a walking aid before treatment, 67% (8/12) no longer required assistance.
• 92% (24/26) of patients remained free of chronic immunotherapies for SPS.

Kyverna reported that all secondary endpoints continued to be met at one year. Mean changes from baseline were -1.0 on the Modified Rankin Scale (p = .0003), -1.7 on the Hauser Ambulation Index (1.38; p < .0001), -1.6 on the Distribution-of-Stiffness Index (1.75; p < .0001) and -2.8 on the Heightened Sensitivity Scale (2.11; p < .0001).

For exploratory endpoints, the company reported that median improvement in the 6-minute walk test increased from 89 meters at week 16 to 119 meters at one year. The source identified 20 meters as the clinical minimally important change. Kyverna also reported sustained improvements in physical functioning and mental health on the 36-item short form health survey, describing one-year findings as comparable to those of healthy adults. B-cell reconstitution was observed alongside sustained efficacy and antibody reduction.

Safety findings

In the one-year data set, Kyverna reported:

• No 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).
• Grade 3/4 neutropenia in five patients, which the company described as manageable.
• Serious treatment-related adverse events in three patients, all of which had fully resolved.

Miv-cel and stiff person syndrome

Miv-cel is an autologous (sourced from the patient), CD19-targeting chimeric antigen receptor (CAR) T-cell therapy with CD28 co-stimulation. It is under investigation for B-cell-driven autoimmune diseases. Kyverna reported that more than 100 patients had received miv-cel across autoimmune diseases. The therapy has received FDA Regenerative Medicine Advanced Therapy (RMAT) designation for SPS.

SPS is a rare, progressive neurologic autoimmune disease characterized by muscle stiffness and painful spasms that affect mobility and gait. Most patients have antibodies to glutamic acid decarboxylase 65 (GAD65) or the glycine receptor, which disrupt normal inhibitory neurotransmission. There are no FDA-approved treatments for SPS. Treatment options include symptomatic therapies, off-label immunotherapies such as intravenous immunoglobulin and rituximab, plasmapheresis, supportive care and rehabilitation therapies.

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