Both Novartis and Bristol Myers Squibb have paused multiple trials of their respective CAR-T cell therapies in several autoimmune disorders after worrisome safety incidents occurred.

Novartis, which is testing a personalized cell therapy Rap-cel in a handful of autoimmune studies, found three cases of immune effector cell-associated hemophagocytic syndrome (IEC-HS), a rare and possibly life-threatening reaction; complications from those events led to "fatal outcomes," according to a Novartis spokesperson.¹ Bristol Myers described its own incidents, observed in its CAR-T treatment zolacabtagene autoleucel, (Zola-cel), as "transient and reversible inflammatory events."¹

What happened to Novartis' trials?

On August 24, 2026, Novartis began initiating holds on the affected trials evaluating Rap-cel in lupus, myasthenia gravis, multiple sclerosis, and more. According to a spokesperson, the company is "engaged" with regulators and is reviewing the findings.¹

"The temporary halt will allow for a more comprehensive review of the evolving clinical and safety data across the program," the spokesperson added.

Novartis is testing Rap-cel in eight different immunology and neuroscience indications in total, and the scale of Novartis’ pause has drawn particular attention from investors. Rather than a single halted study, eight trials were suspended at once raising wider concerns about the safety profile and development timeline of the entire platform.^1,3

Studies testing Rap-cel in cancer are still ongoing and were not affected by the hold, a spokesperson said.³

How Bristol Myers is responding?

Bristol Myers has voluntarily paused enrollment in its autoimmune trials evaluating Zola-cel, though it has not halted the studies outright. A company spokesperson says the move was made "out of an abundance of caution" to "review clinical data across our zola-cel program," noting that Bristol Myers detected the transient and reversible inflammatory events during routine safety surveillance.^1,3

The company is aiming to complete its evaluation and resume testing "as quickly as possible."³

Results published in February already detailed one case of IEC-HS in a Phase I study of Zola-cel, and the drug's safety profile "remains consistent with the known profile of CAR-T therapies," according to the spokesperson, who added: "We continue to have confidence in zola-cel, which has demonstrated transformational, treatment-free responses in systemic lupus erythematosus and other autoimmune diseases."³ Bristol Myers was previously planning to begin a trial of Zola-cel in patients with systemic sclerosis in September.

Why analysts are pointing to manufacturing speed

Both Rap-cel and Zola-cel are being developed with technology meant to speed up production compared with earlier CAR-T products, and that technology "could be driving increased cell expansion and the reported toxicities," William Blair analyst Sami Corwin wrote in a Monday client note, though she cautioned other factors could be involved too.³

CAR-T therapies already approved for cancer work by rewiring a patient's own immune defenders to hunt down and kill diseased cells in conditions such as leukemia and multiple myeloma, and have driven certain malignancies into deep, long-lasting remissions, but the approach carries notable downsides. Patients' T cells must be extracted, sent to a specialized manufacturing facility, modified and eventually reinfused, a process that can take multiple weeks, with patients also requiring extensive post-infusion monitoring for potentially severe immune or neurological side effects.

Novartis and Bristol Myers have been seeking to compress those production times using a speedier approach to grow modified cells more quickly, and multiple analysts have zeroed in on that strategy as a possible culprit behind the reported safety issues, noting that companies including Cabaletta Bio, Kyverna Therapeutics ,and Autolus Therapeutics make their therapies via more traditional processes.^1,3

How does this effect the broader market?

Several other biotechs are actively pursuing their own CAR-T therapies for autoimmune conditions in parallel to Bristol Myers and Novartis. Cabaletta Bio has multiple trials underway, including a late-stage study in myositis, Kyverna Therapeutics has the potential to submit an approval application in stiff person syndrome by the end of the year, and is currently enrolling patients in a pivotal study in myasthenia gravis.¹

Shares of Kyverna, Cabaletta, Allogene, CRISPR Therapeutics, and Fate dropped abruptly before recovering as the news broke. "This will clearly need to be monitored to determine how it could impact the total market adoption of these products in the future," Corwin wrote.¹

Sources

1. Autoimmune CAR-T faces tough questions after Novartis, Bristol Myers study halts BioPharmaDive September 2, 2026, https://www.biopharmadive.com/news/autoimmune-cell-therapy-safety-novartis-bristol-kyverna-cabaletta/829413/?utm_source=Sailthru&utm_medium=email&utm_campaign=Issue:%202026-09-02%20BioPharma%20Dive%20%5Bissue:88775%5D&utm_term=BioPharma%20Dive
2. Novartis Halts Eight Trials After Three Patient Deaths Yahoo Finance September 1, 2026,https://finance.yahoo.com/healthcare/articles/novartis-halts-eight-trials-three-134359980.html?guccounter=1&guce_referrer=aHR0cHM6Ly93d3cuZ29vZ2xlLmNvbS8&guce_referrer_sig=AQAAAM6yps_RbpuYFclVq7uUg4XHXy75jfS28UxezSydxvDyDQjCymJYFizD_6u1WHMmpwX8960pUubsyfBHmIFC24Q7sCkcyJow_GONSrdfpBMOSJq69v6hS_Fj7MZb-5dtW1eWbxwynED4mgcbtjjZVJYEI19FoA0mQZdbVuRDBI3N 
3. Novartis, Bristol Myers pause autoimmune CAR-T trials due to safety concerns BioPharmaDive August 31, 2026, https://www.biopharmadive.com/news/novartis-bristol-myers-autoimmune-cell-therapy-trial-halt/829218/