GVL activity is maintained following CCR1^−/− SCT. Lethally irradiated B6D2F1 mice received transplants from syngeneic B6D2F1 (gray solid line; ) and allogeneic CCR1^+/+ (— ■), or CCR1^−/− (gray dashed line; ▩) donors as described in Figure 2. P815 (H2K^d) tumor cells were added to the BM inoculum on day 0 as described in “Materials and methods.” A second syngeneic group without P815 tumor cells served as the negative control (gray dotted line; □). (A,B) GVL activity is maintained in CCR1^−/− transplant recipients at 500 (A) and 2000 (B) P815 tumor cells, but the survival advantage compared with allogeneic CCR1^+/+ transplant recipients is lost at the higher tumor burden. (*P < .001; allo-CCR1^−/− vs allo-CCR1^+/+ in panel A and allo-CCR1^−/− vs syngeneic tumor in panel B). (C) Histopathology of the liver and spleen was assessed for tumor infiltration and GVHD severity. Shown are data represented from experiments in which 2000 P815 tumor cells were administered. Data are expressed as means plus or minus SEM and are combined from at least 2 comparable experiments at each tumor dose, n = 8 to 20 per group for survival data and 6 to 18 per group for pathology (*P < .01; allo-CCR1^−/− vs allo-CCR1^+/+).