Kyverna Therapeutics, Inc. (KYTX) shares surged Monday on trading volume nearly 10 times the average, hitting new 52-week highs after the company released Phase 2 data that showed its experimental cell therapy helped patients with a devastating rare disorder regain the ability to walk.
The clinical-stage biotech shared topline results from its KYSA-8 Phase 2 trial testing mivocabtagene autoleucel (miv-cel, formerly KYV-101) in stiff person syndrome. The therapy is a fully human, autologous CD19-targeting CAR T-cell therapy with CD28 co-stimulation.
Stiff person syndrome is a brutal condition. This rare autoimmune neurological disorder causes progressive muscle stiffness, rigidity, and painful spasms, primarily in the torso and limbs. Random stimuli like noise or touch can trigger episodes, leading to falls and increasing disability over time. The root cause: the immune system mistakenly attacks nerve cells that control muscle movement.
Trial Design and Results
The single-arm registrational Phase 2 trial enrolled 26 patients who hadn't responded adequately to non-approved treatment options. Each received a single dose of miv-cel, then were followed through the primary analysis timepoint at Week 16 with additional follow-up continuing thereafter.
The results were striking. After just one dose, miv-cel achieved statistically significant benefits on the primary endpoint and all secondary efficacy measures at Week 16.
Primary Endpoint: The therapy demonstrated robust and sustained mobility improvement, with a highly statistically significant boost in the timed 25-foot walk test. The median improvement hit 46% at Week 16 compared to baseline. Perhaps more impressively, 81% of patients exceeded a 20% improvement in walking speed, a threshold considered clinically meaningful.
Secondary Endpoints: Highly statistically significant benefits showed up across all secondary measures, including the Modified Rankin Scale, Distribution-of-Stiffness Index, Hauser Ambulation Index, and Heightened Sensitivity Scale.
Here's a data point that really tells the story: Of the 12 patients who required a walking aid device before treatment, 67% no longer needed assistance to walk at Week 16.
Every single patient remained free of immunotherapies, and none required rescue therapy as of the last follow-up.
Safety Profile
Miv-cel was well-tolerated. Crucially, researchers observed no high-grade cytokine release syndrome or immune effector cell-associated neurotoxicity syndrome, two serious complications sometimes associated with CAR-T therapies.
What Comes Next
Kyverna plans to submit a Biologics License Application to the FDA for stiff person syndrome in the first half of 2026. The company has already secured both Regenerative Medicine Advanced Therapy and Orphan Drug designations for miv-cel in this indication, which should help smooth the regulatory path.
The full SPS data set will be presented at a medical conference in 2026.
Price Action: Kyverna Therapeutics shares jumped 38.15% to $12.13 at the time of publication Monday, reaching a new 52-week high. Session volume hit 6.80 million shares compared to the average volume of 696,680.
