CD19 and acute lymphoblastic leukemia: While CD19 loss is likely to contribute to ALL relapse in this model, we were unable to harness DR upregulation by LD-TBI to elicit CD19-independent ALL killing by CAR T cells during leukemic remission as previously done in models of PDAC [11], most likely because CAR T cells were exhausted or in insufficient numbers when we delivered LD-TBI as a salvage approach (Fig. 3).