The Th1/Th17 axis regulates chimeric antigen receptor (CAR) T cell therapy toxicities.

CAR-T therapy has led to significant improvements in patient survival. However, a subset of patients experience high-grade toxicities, including cytokine release syndrome (CRS) and immune cell-associated hematologic toxicity (ICAHT). We utilized IL-2Rα knockout mice to model cytokine toxicities with elevated levels of IL6, IFNγ, and TNFα and increased M1-like macrophages. Onset of CRS was accompanied by a reduction in peripheral blood neutrophils due to disruption of bone marrow neutrophil homeostasis characterized by an increase in apoptotic neutrophils and a decrease in proliferative and mature neutrophils. Both non-tumor-bearing and Eμ-ALL tumor-bearing mice recapitulated the co-occurrence of CRS and neutropenia. IFNγ-blockade alleviated CRS and neutropenia without affecting CAR-T efficacy. Mechanistically, a Th1-Th17 imbalance was observed to drive co-occurrence of CRS and neutropenia in an IFNγ-dependent manner leading to decreased IL-17A and G-CSF, neutrophil production, and neutrophil survival. In patients, we observed an increase in the IFNγ-to-IL-17A ratio in the peripheral blood during high-grade CRS and neutropenia. We have uncovered a biological basis for ICAHT and provide support for the use of IFNγ-blockade to reduce CRS and neutropenia.