Perforin-deficient CAR T cells recapitulate late-onset inflammatory toxicities observed in patients.

Late-onset inflammatory toxicities resembling hemophagocytic lymphohistiocytosis (HLH) or macrophage activation syndrome (MAS) occur after chimeric antigen receptor T cell (CAR T cell) infusion and represent a therapeutic challenge. Given the established link between perforin deficiency and primary HLH, we investigated the role of perforin in anti-CD19 CAR T cell efficacy and HLH-like toxicities in a syngeneic murine model. Perforin contributed to both CD8+ and CD4+ CAR T cell cytotoxicity but was not required for in vitro or in vivo leukemia clearance. Upon CAR-mediated in vitro activation, perforin-deficient CAR T cells produced higher amounts of proinflammatory cytokines compared with WT CAR T cells. Following in vivo clearance of leukemia, perforin-deficient CAR T cells reexpanded, resulting in splenomegaly with disruption of normal splenic architecture and the presence of hemophagocytes, which are findings reminiscent of HLH. Notably, a substantial fraction of patients who received anti-CD22 CAR T cells also experienced biphasic inflammation, with the second phase occurring after the resolution of cytokine release syndrome, resembling clinical manifestations of HLH. Elevated inflammatory cytokines such as IL-1β and IL-18 and concurrent late CAR T cell expansion characterized the HLH-like syndromes occurring in the murine model and in humans. Thus, a murine model of perforin-deficient CAR T cells recapitulated late-onset inflammatory toxicities occurring in human CAR T cell recipients, providing therapeutically relevant mechanistic insights.