Response to CAR T cell therapy can be explained by ecological cell dynamics and stochastic extinction events

Chimeric antigen receptor (CAR) T cell therapy is a remarkably effective immunotherapy that relies on in vivo expansion of engineered CAR T cells, after lymphodepletion by chemotherapy. The laws underlying this expansion and subsequent tumor eradication remain unknown. Still, about 60% of CAR T-treated patients are likely to progress; their tumors are not eradicated. Here we seek to understand and disentangle the multiple processes that contribute to CAR expansion and tumor eradication. We developed a mathematical model of T cell-tumor cell interactions, and demonstrate that CAR T cell expansion is shaped by immune reconstitution dynamics after lymphodepletion and predator prey-like dynamics. Our cell population model was parameterized using patient population-level data over time and recapitulates progression free survival. As an intrinsic property, we find that tumor eradication is a stochastic event. Our cell population-based approach renders CAR T cell therapy as an ecological dynamic process that drives tumors toward an extinction vortex. Even if a clinical event, such as progression, is likely, its timing can be highly variable. We predict how clinical interventions that increase CAR T memory populations could improve the likelihood of tumor eradication and improve progression free survival. Our model can be leveraged to propose new CAR composition and dosing strategies, assess the need for multiple doses, and identify patient populations most likely to benefit from CAR T with or without additional interventions.