CAR-T Cells Linger in the Gut and Drive Severe Intestinal Inflammation, Mount Sinai Study Finds

Chimeric antigen receptor T cell therapy has redefined the treatment of multiple myeloma, offering deep and durable remissions to patients whose disease had resisted every conventional option. Yet a small fraction of those treated with BCMA-directed CAR-T cells develop a debilitating complication: a severe inflammation of the intestine known as CAR-T cell-associated enterocolitis, marked by chronic diarrhea, abdominal pain, nausea, and progressive weight loss. A new study from the Icahn School of Medicine at Mount Sinai, published in Nature Medicine, now provides the most detailed picture to date of what is happening inside the gut of these patients, and points to a plausible therapeutic strategy.

The research team, led by corresponding author Dr. Saurabh Mehandru, Professor of Medicine in Gastroenterology, set out to map the intestinal immune landscape in patients who developed enterocolitis after BCMA-directed CAR-T therapy. Using single-cell analysis of intestinal tissue, the investigators found something striking: CAR-T cells can persist in the intestinal mucosa long after the infusion, in a subset of patients. Rather than disappearing once their anti-cancer mission is complete, these engineered cells appear to take up residence in gut tissue, where they may sustain inflammatory signals indefinitely.

The study also revealed that the condition is not simply a matter of losing protective immune cells. Patients with enterocolitis showed a substantial depletion of B cells and plasma cells in the intestinal lining, the very cells that normally produce protective antibodies and help maintain mucosal integrity. But critically, some patients who never developed enterocolitis showed similar losses, indicating that B cell depletion alone cannot explain the severe inflammation. Something else must be driving the disease in susceptible individuals.

That something else, the data suggest, is a broad remodeling of the intestinal immune environment. Multiple cell types are affected simultaneously: immune cells, structural and vascular support cells, and the epithelial cells that line the intestine itself. This widespread disruption implies that CAR-T-associated enterocolitis is not a narrow, cell-specific side effect but a systemic disturbance of the gut’s immune architecture, involving crosstalk between many cellular compartments at once.

Among the pathways the researchers identified, one stood out with particular therapeutic relevance. JAK proteins, intracellular signaling molecules that help cells communicate and regulate inflammation, showed increased activity across multiple cell types in the intestine of affected patients. This finding suggested that the inflammatory cascade driving enterocolitis might be amenable to pharmacological interruption with drugs that already exist and are approved for other inflammatory conditions.

To test that idea, the team turned to upadacitinib, a selective JAK1 inhibitor. Two patients with CAR-T-associated enterocolitis who received the drug experienced meaningful improvements in symptoms, intestinal inflammation, and other measures of disease activity. In one of these patients, treatment was also associated with a substantial reduction in the number of CAR-T cells detectable in intestinal tissue, hinting that blocking JAK signaling may not only calm inflammation but may also affect the persistence of the engineered cells themselves.

Dr. Samir Parekh, Professor of Medicine and Director of the Center of Excellence for Multiple Myeloma at Mount Sinai, who co-supervised the study, emphasized the growing clinical urgency of the problem. As CAR-T therapies are deployed in more patients and earlier in the course of myeloma, understanding and managing complications becomes increasingly important. The findings, he noted, offer both an explanation for why some patients develop severe intestinal inflammation and a potential roadmap for treating or preventing it.

Dr. Nikhit Kethidi, the study’s first author, described the work as providing a detailed cellular view of the condition and demonstrating that it involves multiple components of the intestinal immune environment. Understanding these changes, he suggested, may help identify new therapeutic approaches and guide future studies aimed at preventing or managing the complication before it takes hold.

The scale of the collaboration reflects the rarity and complexity of the condition. Investigators from Mount Sinai worked alongside researchers at Weill Cornell Medicine, Johns Hopkins University, Memorial Sloan Kettering Cancer Center, Stanford University School of Medicine, Harvard Medical School, Boston Children’s Hospital, Northwestern University Feinberg School of Medicine, Charité-Universitätsmedizin Berlin, Friedrich-Alexander-Universität Erlangen-Nürnberg, University Hospital Leipzig, and other national and international institutions, pooling tissue samples and clinical expertise from centers that treat large volumes of myeloma patients with CAR-T therapy.

For the myeloma community, the study marks a turning point in how CAR-T-associated enterocolitis is understood. What was previously a poorly characterized and frightening complication now has a defined cellular signature: persistent mucosal CAR-T cells, loss of antibody-producing lineages, widespread immune remodeling, and heightened JAK-mediated inflammatory signaling. With a plausible drug target already validated in a small number of patients, the path from mechanistic insight to clinical intervention appears shorter than it does for many rare treatment toxicities, offering hope that future patients can receive the transformative benefits of CAR-T therapy without paying the price of chronic intestinal disease.

Subject of Research: Mechanisms of severe intestinal inflammation after BCMA CAR-T therapy for multiple myeloma

Article Title: Mount Sinai study identifies why some patients develop severe intestinal inflammation after CAR-T therapy

Article References: Mount Sinai study identifies why some patients develop severe intestinal inflammation after CAR-T therapy. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: CAR-T cell therapy, multiple myeloma, enterocolitis, BCMA, intestinal inflammation, JAK inhibitors, upadacitinib, Nature Medicine, immune remodeling, gastrointestinal toxicity, Mount Sinai, mucosal immunity