San Francisco, CA – [Insert Date] – In a significant development for patients battling Stiff-Person Syndrome (SPS), a rare and debilitating autoimmune neurological disorder, Kyverna Therapeutics has announced compelling one-year data from its Phase III KYSA-8 trial evaluating the CAR-T therapy, miv-cel (mivocabtagene autoleucel). The results demonstrate a sustained and significant improvement in motor function and a favorable safety profile, positioning miv-cel as a potential first-in-class therapy for a condition with no currently FDA-approved treatments.
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The trial, which met its primary and secondary endpoints at the 16-week mark and has now been extended to a full year of follow-up, offers a beacon of hope for individuals living with the progressive and often severe symptoms of SPS. The sustained efficacy observed after a single dose of miv-cel underscores its potential to offer long-lasting relief and significantly improve the quality of life for patients.
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Main Facts: A New Era for Stiff-Person Syndrome Treatment
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Kyverna Therapeutics’ miv-cel has demonstrated remarkable efficacy in the Phase III KYSA-8 study for Stiff-Person Syndrome (SPS). The investigational CAR-T therapy has shown a sustained 49% improvement in the timed 25-Foot Walk (T25FW) at 12 months post-treatment, a significant leap from the 46% improvement observed at week 16. This sustained benefit is particularly noteworthy, as over one-third of treated patients were able to complete the T25FW in under five seconds, a benchmark comparable to healthy adults. Crucially, 95% of patients who achieved a clinically meaningful improvement at the initial analysis maintained their gains one year later.
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This groundbreaking efficacy comes with an equally promising safety profile. Miv-cel, an anti-CD19 CAR-T therapy engineered to stimulate CD28, was well-tolerated by participants. The trial reported no instances of high-grade cytokine release syndrome (CRS) or immune effector cell-associated neurotoxicity syndrome (ICANS), two potential serious side effects associated with CAR-T therapies. Furthermore, no cases of immune effector cell-associated hemophagocytic lymphohistiocytosis-like syndrome (IEC-HS) were observed, further bolstering the therapy’s safety credentials.
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These pivotal findings are set to be integrated into Kyverna’s rolling Biologics License Application (BLA) submission to the U.S. Food and Drug Administration (FDA). The company’s proactive approach to data submission aims to expedite the regulatory review process, potentially granting miv-cel the distinction of being the first FDA-approved treatment for SPS.
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Chronology of Progress: From Initial Promise to Sustained Efficacy
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The journey of miv-cel in Stiff-Person Syndrome has been marked by progressive positive developments. The KYSA-8 study, officially registered as NCT06588491, was designed to rigorously evaluate the safety and efficacy of miv-cel in a patient population desperately seeking effective treatment options.
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The initial analysis of the KYSA-8 trial, presented at the American Academy of Neurology (AAN) Annual Meeting in April 2026, confirmed that the study had met its primary and secondary endpoints at the 16-week mark. This early success set the stage for further evaluation of long-term outcomes. The subsequent release of one-year data has now solidified the therapeutic potential of miv-cel, showcasing not just initial improvement but sustained benefit over an extended period.
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This one-year data is critical for regulatory approval, as it demonstrates the durability of miv-cel’s effects, a key factor in assessing the long-term value of a new therapy. The sustained improvements in mobility, stiffness, and other disease-specific measures, coupled with the favorable safety profile, are directly contributing to Kyverna’s ongoing regulatory submissions.
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Supporting Data: Quantifying the Impact on Patients’ Lives
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The quantitative data emerging from the KYSA-8 trial provides a clear picture of miv-cel’s transformative impact on patients with SPS. The primary endpoint, the timed 25-Foot Walk (T25FW), is a critical measure of mobility and functional capacity, directly reflecting the debilitating muscle stiffness and spasms characteristic of SPS.
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- T25FW Improvement: The sustained 49% improvement at 12 months signifies a substantial restoration of walking ability. This is not merely a statistical improvement; it translates to a tangible increase in independence and a reduction in the physical limitations imposed by the disease.
- Healthy Adult Benchmark: The fact that over one-third of patients achieved T25FW times comparable to healthy adults is a powerful testament to the therapy’s efficacy. This indicates a significant reversal of disease-related disability.
- Sustained Benefit: The 95% retention of clinically meaningful improvement among those who initially responded is a crucial indicator of long-term therapeutic value. This suggests that the benefits of miv-cel are not transient and can provide lasting relief.
- Safety Profile: The absence of high-grade CRS, ICANS, and IEC-HS is paramount. These potential adverse events can be serious and significantly impact patient outcomes. Kyverna’s data suggests miv-cel can be administered with a manageable risk profile, a critical factor for widespread adoption.
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These metrics, when viewed collectively, paint a compelling picture of a therapy that not only alleviates symptoms but also restores fundamental functional abilities in patients suffering from a disease that has historically offered limited therapeutic options.
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Official Responses: Expert Endorsement and Regulatory Momentum
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The significance of these findings has been echoed by leading experts in the field. Dr. Amanda Piquet, Director of Autoimmune Neurology at the University of Colorado Anschutz School of Medicine and lead investigator of the KYSA-8 trial, expressed considerable optimism.
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"The results from KYSA-8 are compelling, particularly given the severe burden of SPS and the absence of approved therapies," stated Dr. Piquet. "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."
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Dr. Piquet’s endorsement highlights the unmet need in SPS and the profound potential of miv-cel to address this gap. Her perspective, as a frontline clinician and researcher involved in the trial, carries significant weight in assessing the clinical impact of the therapy.
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Kyverna Therapeutics is now actively leveraging this robust data to advance its regulatory agenda. The inclusion of the one-year data in the rolling BLA submission to the FDA signifies a strategic move to streamline the review process and aims to bring this much-needed therapy to patients as quickly as possible. This proactive approach reflects the company’s commitment to addressing the urgent needs of the SPS community.
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Implications: A Paradigm Shift in Autoimmune Neurology and Beyond
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The implications of Kyverna’s success with miv-cel extend far beyond the immediate treatment of Stiff-Person Syndrome.
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- First-to-Market Advantage: With no FDA-approved drugs currently available for SPS, miv-cel has the potential to establish itself as the first disease-modifying therapy. This first-mover advantage could significantly shape the treatment landscape and Kyverna’s market position.
- Validation of CAR-T for Autoimmune Diseases: The successful application of CAR-T therapy in SPS, a neurological autoimmune disorder, further validates the potential of this innovative treatment modality for a broader range of autoimmune conditions. This could pave the way for similar CAR-T approaches in other challenging autoimmune diseases.
- Addressing Rare Disease Needs: SPS, while gaining public awareness due to high-profile diagnoses such as that of Céline Dion, remains a rare condition. Kyverna’s commitment to developing a therapy for such a rare and severe disease demonstrates a significant contribution to the field of rare disease therapeutics.
- Broader Market Potential for miv-cel: The company also presented promising longer-term data from its Phase II/III KYSA-6 study of miv-cel in generalized myasthenia gravis (gMG). In the Phase II portion, all seven patients achieved clinically meaningful improvements in key disease activity scores, with these gains sustained at the one-year mark. This dual success in two distinct autoimmune neurological disorders suggests a broader therapeutic applicability for miv-cel. The projected growth of the gMG market, estimated to reach $13 billion by 2034, further underscores the significant commercial and patient-care potential of Kyverna’s CAR-T platform.
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The current therapeutic landscape for SPS is characterized by a scarcity of options. While Kedrion is working on Qivigy (immune globulin intravenous human 10% solution), which recently received FDA orphan drug designation and is in Phase III trials, miv-cel’s CAR-T approach represents a fundamentally different and potentially more impactful therapeutic strategy.
In conclusion, Kyverna Therapeutics’ sustained positive results for miv-cel in Stiff-Person Syndrome mark a pivotal moment in the fight against this debilitating disease. The combination of sustained efficacy and a robust safety profile positions miv-cel as a strong candidate for FDA approval, offering a much-needed therapeutic breakthrough and potentially ushering in a new era of treatment for autoimmune neurological disorders.
