Kyverna Therapeutics has announced that its investigational CAR T therapy, mivocabtagene autoleucel (miv-cel), showed significant improvement in mobility for patients with stiff person syndrome (SPS) during a pivotal mid-stage study. The company plans to submit a biologics license application for the treatment in the first half of 2026.
Analysts from William Blair described the results as “impressive” and stated in a note to investors that the data are “extremely positive and supportive of the upcoming BLA submission for miv-cel in SPS, setting it up to potentially be the first FDA-approved CAR-T for the treatment of an autoimmune disease.”
Following this announcement, Kyverna’s stock rose by 23%, closing at $10.82 per share on Monday.
In its news release, Kyverna reported that patients treated with miv-cel experienced a median improvement of 46% at 16 weeks on the timed 25-foot walk (T25FW), which is a key measure of mobility. William Blair commented that this result “exceeded our expectations.” Additionally, 81% of patients achieved at least a 20% improvement on the T25FW.
The therapy also met all secondary endpoints, which included improvements in ambulation, sensitivity, disability, and distribution of stiffness across the body. At the time of data readout, all patients had discontinued immunotherapies and none required rescue therapy. Kyverna stated this outcome highlights “miv-cel’s potential to provide unprecedented clinical benefit while significantly reducing or eliminating chronic treatment burden.”
Regarding safety outcomes, no high-grade cases of cytokine release syndrome or immune effector cell-associated neurotoxicity syndrome were observed. Cases of grade 3/4 neutropenia were reported but considered manageable.
Stiff person syndrome affects fewer than 5,000 people in the United States. It is characterized by progressive muscle stiffening and painful spasms due to antibodies attacking cells in the brain and central nervous system. Other symptoms include pain, difficulty walking, and interference with daily activities.
Miv-cel works by targeting CD19 protein on B cells and CD28 protein on T cells. This approach depletes autoimmune B cells and aims to reset the immune system.
Kyverna is also developing miv-cel for other autoimmune disorders such as generalized myasthenia gravis—where it recently demonstrated a 100% response rate in a Phase III trial—and is exploring its use in multiple sclerosis and rheumatoid arthritis.
