Recommendations for Defining Chimeric Antigen Receptor T-Cell (CAR T) Dose-Limiting Toxicities (DLTs) for Future...

Chimeric antigen receptor T-cell (CAR T) therapies have demonstrated potential to provide long-term remission in incurable hematologic malignancies, and novel approaches for CAR T therapy continue to be developed for treating cancer and other indications. Acute class-effect toxicities, such as cytokine release syndrome, immune effector cell-associated neurotoxicity syndrome, and immune effector cell-associated hemophagocytic lymphohistiocytosis-like syndrome, remain significant concerns despite their potential reversibility. Given the complexities of balancing safety and efficacy of CAR T therapies, the US Food and Drug Administration (FDA) recently published Guidance for Industry, which included suggested definitions for dose-limiting toxicities (DLTs) for clinical trials of emerging CAR T therapies. However, the DLT definitions in the guidance do not reflect what was used in the phase 1 and/or registrational studies for the approved CAR Ts; for example, these studies defined DLTs as treatment-related, included exceptions, and/or allowed for time to resolve the adverse event. Using DLT definitions from the guidance could have prematurely stopped the early-phase studies of the now approved CAR Ts. In 2023, while designing a first-in-human, phase 1 study of a logic-gated cell therapy, an expert panel of academic cell therapists collaborated with industry partners at A2 Biotherapeutics to assess the practical implications of the FDA guidance. This led the panel to draft the revised recommendations contained herein, which integrate the permissibility of reversible events during dose-escalation for trial sponsors, investigators, health authorities, and other parties who may be involved in future CAR T therapy trials. These expert recommendations balance the safety of patients in early-phase trials with the potential long-term therapeutic opportunities for patients with terminal malignancies.