Kyverna's Miv-Cel Nears FDA Filing With One-Year Data in Stiff Person Syndrome

A potential first: CAR-T crosses over into autoimmune disease

Cell therapy's biggest expansion in years may be about to arrive. On September 24, 2026, Kyverna Therapeutics reported positive one-year topline data from KYSA-8, its registrational trial of miv-cel (mivocabtagene autoleucel, formerly KYV-101) in stiff person syndrome, describing sustained clinical benefit and reversal of disability through a full year of follow-up.

The stakes are unusually high for a rare-disease readout. CAR-T therapies are currently approved only for blood cancers. If miv-cel clears the FDA, it would become the first approved therapy for stiff person syndrome (SPS) and the first CAR-T therapy approved for an autoimmune disease of any kind — a proof point that engineered T cells can treat something other than malignancy.

How miv-cel works

Miv-cel is a one-time, autologous CD19-targeted CAR T-cell therapy. Rather than suppressing inflammation on an ongoing basis, it is designed to eliminate CD19-positive B cells — the cells that produce the autoantibodies implicated in many autoimmune diseases — and thereby reset the immune system.

The construct's design is meant to reinforce that effect. Miv-cel's CAR incorporates a CD28 co-stimulatory module intended to enhance cell persistence and potency, with the goal of producing a more durable response from a single infusion.

The KYSA-8 efficacy data in stiff person syndrome

KYSA-8 is a registrational Phase 2 trial in which 26 SPS patients received a single dose of miv-cel. The headline result was functional rather than biochemical: the average time patients took to complete a 25-foot walk test fell 46% at Week 16 versus baseline, with a p-value of 0.0002.

• Statistically significant benefit on the primary endpoint and on all secondary endpoints, per the company
• 81% of patients achieved a clinically meaningful response threshold
• One-year follow-up characterized by Kyverna as sustained clinical benefit and reversal of disability

For a progressive disease in which loss of mobility is the defining outcome, a walk-test improvement of that size is the kind of result that translates directly into daily function.

Safety profile through one year

Safety has been the central question hanging over the idea of using oncology-grade cell therapy in non-malignant disease. Kyverna described miv-cel's profile as consistent and well tolerated through one year of follow-up.

• No high-grade cytokine release syndrome (CRS)
• No high-grade immune effector cell-associated neurotoxicity syndrome (ICANS)
• No cases of immune effector cell-associated hemophagocytic lymphohistiocytosis-like syndrome (IEC-HS)

The absence of severe CRS, ICANS and IEC-HS matters for a patient population that is not facing a terminal cancer diagnosis and for whom the risk-benefit calculus is therefore very different.

The regulatory path and shifting timelines

Kyverna says its rolling biologics license application for miv-cel is on track to be completed in the fourth quarter of 2026. That would put the company at the door of a first-in-class approval decision.

The date has moved, though. Fierce Biotech reported in December 2025 that an FDA filing was expected in the first half of 2026, and STAT reported in April 2026 that a submission would come by mid-2026. The current Q4 2026 completion target reflects a later finish line than either of those earlier signals, a reminder that rolling submissions in novel regulatory territory rarely land exactly where they were first penciled in.

Beyond SPS: generalized myasthenia gravis

Stiff person syndrome is the lead indication, but it is not the only one. Longer-term follow-up from the Phase 2 portion of KYSA-6 in generalized myasthenia gravis (gMG) showed effects sustained for up to 1.5 years, with a majority of patients maintaining minimal symptom expression (MSE) — the benchmark clinicians use to describe near-complete symptom control.

That duration is among the longest reported for a CD19 CAR-T in an autoimmune setting, and it directly addresses the field's biggest open question about whether a one-time B-cell reset holds. Kyverna expects to complete Phase 3 enrollment in gMG in mid-2027.

Why stiff person syndrome is a high unmet need

SPS is a rare, progressive neurological autoimmune disease estimated to affect roughly one to two people per million. Muscle stiffness and spasms cause up to 80% of patients to lose mobility as the disease advances.

There are no FDA-approved therapies. Care today relies on off-label immunotherapies and supportive treatment, which leaves clinicians improvising against a condition that steadily takes away the ability to walk. Public awareness of the disease grew after Céline Dion disclosed her diagnosis, but awareness has not been matched by approved options — which is precisely the gap miv-cel is aiming at.

The broader autoimmune CAR-T field

Kyverna is not working alone. Other autologous CD19 CAR-T candidates are being tested in autoimmune disease, including zorpocabtagene autoleucel from Miltenyi Biomedicine and zolacabtagene autoleucel from Bristol Myers Squibb.

The indications under study span much of rheumatology and neurology:

• Systemic lupus erythematosus
• Systemic sclerosis
• Idiopathic inflammatory myopathies
• Multiple sclerosis
• Myasthenia gravis

In early basket trials, CRS and ICANS occurred at acceptable rates with no severe cases, disease activity improved, and some patients achieved a drug-free "treatment-free period" — a genuinely new concept in diseases usually managed with lifelong therapy. The major caveat across the field is the same one Kyverna's gMG data begins to address: durability still requires longer follow-up.

About Kyverna Therapeutics

Kyverna Therapeutics is a late-stage clinical immunology company based in Emeryville, California. It trades on Nasdaq under the ticker KYTX and is led by CEO Warner Biddle.