The benefit of low-dose total body irradiation before CAR T-cell therapy is primarily owing to direct tumor rather than host effects. (A) Schematic diagram of treatment delivery with low-dose RT being given to the mice alone (top), the tumor alone (middle), or the tumor and mice (bottom) separately followed by CAR T-cell therapy. (B) Bioluminescence imaging showing tumor burden over time of mice in the indicated treatment group. 10 000 CAR T cells were used in these studies, with 50% more tumor cells than Figures 1 and 2 to better assess differences in efficacy.