KYTX Stock Rallies 23% on Upbeat Stiff Person Syndrome Study Data

Core Insights - Kyverna Therapeutics (KYTX) shares increased by 23.2% following the announcement of positive top-line data from a mid-stage study of mivocabtagene autoleucel (miv-cel) for treating stiff person syndrome (SPS) [1][5] - Miv-cel is a fully human, autologous CD19-targeting CAR T-cell therapy that could become the first FDA-approved CAR T therapy for an autoimmune disease [1] Phase II SPS Study Data - In the Phase II KYSA-8 study, miv-cel met its primary efficacy endpoint, showing a median improvement of 46% in the timed 25-foot walk (T25FW) at week 16, with 81% of patients achieving over a 20% improvement [2][5] - The therapy also demonstrated consistent and statistically significant benefits across all secondary efficacy endpoints, indicating broad functional and symptom relief [3] Patient Outcomes - 67% of patients who required walking aids at baseline no longer needed assistance by Week 16, and all patients remained free of immunotherapies without requiring rescue treatment [4][7] - The therapy's safety profile was generally well tolerated, with no high-grade cytokine release syndrome or neurotoxicity reported, although some patients experienced manageable grade 3/4 neutropenia [7] Market Context - SPS is a rare autoimmune disorder with no FDA-approved therapies, leaving patients inadequately served by existing treatments [8] - Kyverna Therapeutics aims to fill this gap with miv-cel, which has shown significant potential in improving mobility and reducing stiffness [9] Future Developments - Following the positive results, Kyverna Therapeutics plans to file a biologics license application with the FDA for miv-cel in SPS in the first half of 2026 [10] - The company is also exploring miv-cel for other autoimmune conditions, including myasthenia gravis and multiple sclerosis, across various early to mid-stage studies [11]