CAR T Cell Therapy Eliminates Rogue Antibodies and Improves Walking Speed in Stiff Person Syndrome Patients

An experimental cell therapy called miv-cel has shown promising results in improving mobility and reducing stiffness in people with stiff person syndrome, a rare autoimmune disorder that affects the nervous system and has no FDA-approved treatments.

After a single infusion of miv-cel, which uses chimeric antigen receptor (CAR) T-cell technology to target CD19-positive antibody-producing cells, patients demonstrated meaningful improvements in walking speed, muscle stiffness, and disability scores, according to findings presented by neurologist Amanda Piquet of the University of Colorado Anschutz at the American Academy of Neurology annual meeting in Chicago on April 21, 2026.

The therapy works by eliminating the long-lived plasma cells and plasmablasts that produce the rogue antibodies responsible for attacking the brain and spinal cord in stiff person syndrome. By addressing the root cause of the autoimmune response rather than merely managing symptoms, miv-cel represents a shift from current treatment approaches, which rely on off-label immunomodulatory drugs and symptom-focused therapies with limited long-term benefits.

In the registrational trial, 26 patients who had not adequately responded to existing off-label treatments received a single dose of 1×10⁸ miv-cel CAR T cells. The primary analysis showed statistically significant and durable clinical benefit across all measured endpoints, including improvements in neurologic function and mobility, with the majority of patients gaining function by week 16 post-treatment.

Stiff person syndrome is estimated to affect more than 5,000 people in the United States. The disorder is characterized by progressive muscle rigidity, painful spasms triggered by noise or stress, and chronic pain so severe it can lead to fractures and disability requiring walking aids or wheelchairs. While the exact prevalence remains uncertain due to diagnostic challenges, the condition is often underrecognized and misdiagnosed as other neurological or psychiatric disorders.

Currently, We find no cures for stiff person syndrome, and no treatments are specifically approved by the U.S. Food and Drug Administration for the condition. Existing therapies include benzodiazepines for muscle spasms, immunosuppressants like rituximab, and intravenous immunoglobulin, but these provide inconsistent relief and do not halt disease progression for many patients.

CAR T-cell therapy has previously been investigated in other refractory neuroautoimmune conditions such as myasthenia gravis, neuromyelitis optica, and multiple sclerosis, with case series showing promise in reducing pathogenic antibody production. The application of this technology to stiff person syndrome builds on that emerging evidence, suggesting a potential broader role for immune-resetting therapies in treating autoimmune disorders of the central nervous system.

While the initial results are encouraging, researchers emphasize that longer-term follow-up is needed to assess the durability of response, potential late effects, and whether retreatment may be necessary. The therapy carries risks associated with CAR T-cell treatments, including cytokine release syndrome and neurotoxicity, though specific safety data from this trial were not detailed in the reported findings.

Kyverna Therapeutics, the Emeryville, California-based biopharmaceutical company that developed miv-cel, plans to pursue regulatory pathways based on the trial results. The presentation at the American Academy of Neurology meeting was designated as an oral late-breaker session, indicating the novelty and potential significance of the findings within the neurology community.

For patients living with stiff person syndrome, the prospect of a treatment that targets the underlying autoimmune mechanism offers hope for improved quality of life and functional independence. However, medical experts caution that the therapy remains investigational, and access outside of clinical trials is not currently available.