Kyverna Therapeutics’ miv-cel showed improved mobility and a favorable safety profile at one year in patients with stiff person syndrome, further derisking an upcoming FDA application, William Blair said on Thursday. The biotech plans to file for priority review this year.
Not a month after Novartis and Bristol Myers Squibb paused several trials of their investigational CAR T therapies in autoimmune diseases due to patient deaths and other safety signals, Kyverna Therapeutics is heading in a much different direction. The California biotech reported durability data Thursday that could bolster its chances of scoring the first CAR T approval for an autoimmune condition.
Mivocabtagene autoleucel (miv-cel) improved mobility and leg function and showed a favorable safety profile in 26 patients with stiff person syndrome (SPS) through one year, meeting the registrational Phase 2 KYSA-8 trial’s primary endpoints, Kyverna said in a press release.
In SPS, the typical disease trajectory is significantly decreased mobility and increased use of walkers, wheelchairs and immunosuppressants, Kyverna CEO Warner Biddle told BioSpace on Wednesday. “You compare that to our KYSA-8 study, we’re showing the complete opposite. We’re showing significantly improved mobility, actually a reversal of disease,” he said.
Trial participants saw a median improvement from baseline of 46% at 16 weeks, which grew to 49% at 12 months. In addition, 95% of patients who at the primary analysis had achieved a clinically meaningful improvement—defined as a 20% or greater improvement from baseline—sustained this benefit.
Kyverna shares rose more than 7% to $7.55 in premarket trading following the news.
Miv-cel also reversed disability in some patients; of the 12 patients who entered the trial requiring a walking aid, 67% no longer need assistance, Kyverna said.
These durability data serve to bolster Kyverna’s initial topline readout from KYSA-8 in December 2025, which William Blair analysts at the time called “impressive” and “extremely positive and supportive” of an upcoming biologics license application (BLA) for miv-cel. If approved, Kyverna would have the first CAR T on the market for an autoimmune disease.
Indeed, a rolling BLA submission is on track for completion before the end of this year, according to Kyverna’s release. The company is seeking priority review, Biddle said.
In a Thursday morning note to investors, William Blair called the one-year miv-cel results in SPS “strong,” adding that they further derisk the BLA submission and strengthen the therapy’s commercial value.
A broader reach for Kyverna’s CAR T?
Also in Thursday’s announcement, Kyverna revealed positive longer-term data from the Phase 2 portion of its registrational Phase 2/3 KYSA-6 trial in generalized myasthenia gravis (gMG).
The company reported in April that all seven patients in the trial achieved clinically meaningful improvement on two scales measuring symptom severity and functional impact of the disease at 24 weeks. Both scales are co-primary endpoints in the ongoing Phase 3 portion of the trial.
Clinically meaningful improvements were maintained through one year or longer in all five patients who have reached this time point, Kyverna said on Thursday.
“I think both of these data sets reinforce that Kyverna is leading the way in bringing these transformative cell therapies to autoimmune patients,” Biddle told BioSpace.
“In both cases, we’re showing an extension on the clinical benefits that we read out earlier this year . . . where we demonstrated dramatic clinical improvements in patients—never-been-seen-before clinical improvements,” he said. “But now with these longer-term follow ups, up to one year and beyond, we’re showing that this can be a durable effect in patients and give patients a chance at a disease-free remission, which is ultimately what they want.”
As for safety, miv-cel was well-tolerated in both studies, with no high-grade cytokine release syndrome or immune effector cell-associated neurotoxicity syndrome (ICANS) and no immune effector cell-associated hemophagocytic lymphohistiocytosis-like syndrome (IEC-HS).
This safety profile is particularly notable after Novartis reported the deaths of three patients who received the CAR T therapy rap-cel following “serious immune effector cell-associated hemophagocytic syndrome (IEC-HS) events,” a Kyverna spokesperson told BioSpace in an emailed statement on Sept. 1.
Novartis subsequently paused several immunology and neurology studies of the candidate. BMS followed suit, voluntarily freezing autoimmune trials for its own CAR T asset zolacabtagene autoleucel after observing “transient and reversible inflammatory events,” according to William Blair earlier this month.
In light of these developments, Biddle attributed miv-cel’s positive safety profile to the “unique” design of the construct and a well-established manufacturing process, noting that the therapy is the only CD19 CAR in the autoimmune space that has a fully human CD28 co-stimulatory domain that was specifically designed for safety.
