Kyverna's CAR-T Therapy for Stiff Person Syndrome Advances to BLA Filing Based on Natural History Study
Key Insights
Kyverna Therapeutics has initiated a rolling Biologics License Application (BLA) for miv-cel (search), a CAR-T therapy targeting stiff person syndrome (search), following FDA acceptance of a single-arm trial design.
The company's 153-patient natural history study demonstrated that existing immunotherapies provide less than 20% improvement in mobility, contrasting with 100% immunotherapy-free rates achieved by miv-cel (search) at 16 weeks.
If approved in 2027, miv-cel (search) would become the first FDA-approved treatment for stiff person syndrome (search) and the first CAR-T therapy for autoimmune diseases.
Kyverna Therapeutics has initiated a rolling Biologics License Application (BLA) for its investigational CAR-T therapy miv-cel (search) (mivocabtagene autoleucel (search), KYV-101) in stiff person syndrome (search), marking a potential breakthrough for patients with this rare autoimmune neurological disorder. The FDA's acceptance of a single-arm trial design represents a significant regulatory precedent for autoimmune CAR-T therapies.
Regulatory Strategy Built on Natural History Data
The BLA filing is anchored by Kyverna's comprehensive 153-patient multicenter natural history study, which established the inadequacy of current treatment approaches. Among these patients, the majority showed less than 20% improvement in Timed 25-Foot Walk (T25FW) speed on existing immunotherapies. This benchmark creates what the company describes as a "categorical discontinuity" when compared to the 100% immunotherapy-free rate achieved at Week 16 in the KYSA-8 registrational trial.
The FDA's acceptance of this natural history cohort as the de facto control arm establishes a meaningful regulatory design precedent for autoimmune CAR-T broadly. The agency's willingness to approve based on single-arm data reflects the credibility of the historical comparator and the unmet medical need in this patient population.
Clinical Evidence and Durability Signals
The KYSA-8 Phase 2 trial demonstrated statistically significant, durable clinical benefit across all primary and secondary endpoints at 16 weeks, with reversal of disability scores following a single dose of miv-cel (search). All patients remained free of immunotherapies as of week 16 and through last follow-up.
Supporting the durability case, the first two patients treated through the individual hospital pathway in Germany have maintained efficacy at 15 and 26 months, respectively, without chronic immunotherapy. These long-term results reinforce the potential for sustained benefit from a single treatment.
Addressing Significant Unmet Medical Need
Stiff person syndrome (search) affects approximately one in a million people, with around 6,000 diagnosed cases in the United States. The condition, first identified at the Mayo Clinic in 1956, causes muscle stiffness and painful spasms that progressively impact mobility and quality of life. According to Naji Gehchan, chief medical and development officer of Kyverna Therapeutics, "80% of people with stiff person syndrome lose mobility and are unable to walk on their own."
Currently, no approved treatments exist for the condition. Patients rely on symptomatic treatments and off-label immunotherapies, including intravenous immunoglobulin, rituximab, and plasmapheresis. "Current off-label treatments fail the majority of people with stiff person syndrome (search), require chronic dosing, and do not stop the progression of the disease," Gehchan explained.
Mechanism of Action and Treatment Approach
Miv-cel (search) is a CAR-T therapy that involves extracting a patient's T cells and genetically reprogramming them to target CD19 (search), a marker found on B-cells. These engineered cells are infused back into the patient to target and eliminate B cells responsible for creating harmful antibodies implicated in autoimmunity.
Most people with stiff person syndrome (search) have antibodies to glutamic acid decarboxylase 65 (search) (GAD65 (search)) or the glycine receptor (search). GAD65 antibodies inhibit the synthesis of GABA, a neurotransmitter that functions as a brake for the nervous system, while glycine receptor antibodies affect inhibitory synaptic transmission, both contributing to muscle rigidity and spasms.
"Miv-cel (search) is administered as a single dose and works by eliminating B cells, which in turn helps the immune system to reset," said Gehchan. "This novel approach has the potential to deliver durable drug-free, disease-free remission, and may eliminate the burden of chronic or suboptimal therapies."
Broader Implications for Autoimmune CAR-T
If approved in 2027, miv-cel (search) would represent the first FDA-approved treatment for stiff person syndrome (search) and the first CAR-T therapy for autoimmune diseases. CAR-T therapies have previously been approved only for blood cancers, though a growing number of biopharmaceutical companies are exploring autoimmune applications.
The one-year T25FW responder rate from KYSA-8, expected in the second half of 2026, will be critical for maintaining the BLA's structural foundation. If the gains regress at nine or ten months, it could impact not only the SPS application but also the company's generalized myasthenia gravis (search) Phase 3 trial currently enrolling across 15 sites.
Gehchan emphasized the broader potential: "We are establishing a new therapeutic paradigm with the potential to deliver durable drug-free, disease-free remissions for patients" and "laying the foundation for a multi-indication neuroimmunology franchise that reinforces our leadership position in autoimmune CAR T."