CAR T cell Toxicities: Bedside to Bench - How Novel Toxicities Inform Laboratory Investigations

• CAR-T indications and patient numbers are growing, yet toxicities are a limitation. Complications beyond CRS and ICANS are reported.

• The pathophysiology of novel toxicities need to be comprehensively studied to develop effective treatment and prevention strategies.

Multiple chimeric antigen receptor (CAR) T cell therapies are FDA approved, and several are under development. While effective for some cancers, toxicities remain a limitation. The most common toxicities, i.e. cytokine release syndrome (CRS) and immune effector cell associated neurotoxicity syndrome (ICANS), are well described. With increasing utilization, providers worldwide are reporting on other emergent, and often complicated toxicities. Given the evolving toxicity profiles and urgent need to catalogue these emerging and emergent CAR T toxicities and describe management approaches, the American Society of Hematology Subcommittee on Emerging Gene and Cell Therapies organized the first Scientific Workshop on CAR T cell toxicities during the annual society meeting. The workshop functioned to 1) aggregate reports of CAR T emergent toxicities, including movement disorders after BCMA CAR T, coagulation abnormalities, and prolonged cytopenias; 2) disseminate bedside to bench efforts elucidating pathophysiological mechanisms of CAR-T toxicities, including the intestinal microbiota and systemic immune dysregulation; and 3) highlight gaps in the availability of clinical tests such as cytokine measurements, which could be utilized to expand our knowledge around the monitoring of toxicities. Key themes emerged. First, while clinical manifestations may develop before the pathophysiologic mechanisms are understood, these must be studied to aid in the detection and prevention of such toxicities. Second, systemic immune dysregulation appears central to these emergent toxicities and research is needed to elucidate links between tumor, CAR T, and microbiota. Finally, there was consensus around an urgency to create a repository to capture emergent CAR-T toxicities and the real-world management.