Primary resistance to CD19-directed chimeric antigen receptor T-cell therapy (CART19) occurs in 10% to 20% of patients with acute lymphoblastic leukemia (ALL); however, the mechanisms of this resistance remain elusive. Using a genome-wide loss-offunction screen, we identified that impaired death receptor signaling in ALL led to rapidly progressive disease despite CART19 treatment. This was mediated by an inherent resistance to T-cell cytotoxicity that permitted antigen persistence and was subsequently magnified by the induction of CAR T-cell functional impairment. These findings were validated using samples from two CAR T-cell clinical trials in ALL, where we found that reduced expression of death receptor genes was associated with worse overall survival and reduced T-cell fitness. Our findings suggest that inherent dysregulation of death receptor signaling in ALL directly leads to CAR T-cell failure by impairing T-cell cytotoxicity and promoting progressive CAR T-cell dysfunction. SIGNIFICANCE: Resistance to CART19 is a significant barrier to efficacy in the treatment of B-cell malignancies. This work demonstrates that impaired death receptor signaling in tumor cells causes failed CART19 cytotoxicity and drives CART19 dysfunction, identifying a novel mechanism of antigenindependent resistance to CAR therapy.