Kyverna reports that mobility gains persisted for a year in its trial of miv-cel, a treatment designed to remove immune cells linked to the disease, as it seeks US approval.
Kyverna is submitting its experimental stiff person syndrome treatment miv-cel for US Food and Drug Administration approval, Science News reported on October 22. The treatment engineers patients’ immune cells and has shown improvements in walking. Kyverna reports that those gains persisted for a year, but researchers caution that this does not yet establish a cure.
Stiff person syndrome can cause severe muscle spasms and rigidity, leading to falls, pain and difficulty moving. No treatment is FDA-approved for the disease. Existing options include medicines used outside their approved indications to ease symptoms, and infusions of healthy antibodies to reduce spasms and stiffness.
In autoimmune disease, the immune system attacks the body’s own tissues. Scientists think antibodies—proteins that normally help defend against threats—attack a nerve network that helps muscles relax in stiff person syndrome. CAR T-cell therapy targets B cells involved in making antibodies, rather than the antibodies themselves.
Doctors collect a patient’s T cells, immune cells that can destroy other cells. In a laboratory, scientists add a chimeric antigen receptor, or CAR: a molecular receptor that directs the T cells toward their target. Before receiving the engineered cells, patients undergo low-dose chemotherapy to reduce existing T cells and make room for the infused cells.
The treatment removes most B cells, including those thought to drive the disease. Rheumatologist Georg Schett describes the intended effect as an “immune reset”: harmful B cells disappear, and healthy replacement cells can emerge. That is the aim, not proof that the conditions causing the disease have permanently gone away.
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In September, Kyverna reported that mobility improvements persisted at one year. The company said a third of patients completed a 25-foot walk about as fast as a healthy adult, and nearly all no longer relied on drugs that suppress immune activity. These were company-reported follow-up findings, distinct from Piquet’s earlier conference observations.
CAR T therapy was first developed for cancer; the FDA approved its first uses for two blood cancers in 2017. Published lupus research later helped establish the case for testing it in autoimmune disease. Lupus can damage the kidneys and other organs.
In 2021, Schett’s team published a report of a woman with severe lupus whose disease signs began disappearing within five weeks of CAR T treatment. The following year, the team reported remission—an absence of disease activity—in five more lupus patients. Schett says the first patient’s lupus has not returned more than five years later. Those small published reports concern lupus, not proof of a cure for stiff person syndrome.
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Removing B cells also removes cells that help protect against infection. Treatment can bring fever, inflammation and potentially dangerous infections, while the chemotherapy preparation can cause nausea, vomiting, diarrhea and hair thinning. In Kyverna’s trial, 15 percent of participants developed severely low white blood cell counts after treatment. Piquet said these effects were expected and easily treated.
Other products have raised serious safety concerns. Science News reported that Novartis paused autoimmune trials of rap-cel in August after three patients died. Citing The Wall Street Journal, it also reported that Bristol Myers Squibb paused similar studies after some patients experienced neurological complications.
Those events do not establish that all CAR T products carry the same risks, cautioned Johns Hopkins Medicine rheumatologist Maximilian Konig. Designs and manufacturing processes differ, and their effects on toxicity are not always predictable. A Kyverna spokesperson said miv-cel had been consistently well tolerated in more than 100 treated patients; that is the company’s assessment, not a finding that long-term safety is settled.
University of Pennsylvania immunologist Carl June cautioned that too few people have been treated to identify all possible adverse effects, including long-term complications, or to establish a cure for stiff person syndrome. Durability also remains an open question: doctors do not know all the genetic and environmental triggers of autoimmune disease, so removing harmful B cells may not permanently prevent its return.
Miv-cel remains experimental. Kyverna is seeking priority FDA review and hopes the treatment could become available in 2027. Approval would make it the first FDA-approved treatment for stiff person syndrome and the first CAR T therapy approved for an autoimmune condition; that decision still lies ahead.
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