Absence of CCR1 expression on both donor T cells and accessory cells contributes to improved survival following allo-SCT. Lethally irradiated B6D2F1 mice underwent transplantation as described in Figure 2 (syngeneic: · · ·, ■; allogeneic CCR1^+/+: —, ●; allogeneic CCR1^−/−: solid gray line, *). Two additional allogeneic groups were evaluated in this “mixing” experiment as described in “Materials and methods”: allogeneic CCR1^+/+ bone marrow cells mixed with allogeneic CCR1^−/− T cells (light gray dashed line, ◆) and allogeneic CCR1^−/− bone marrow cells mixed with allogeneic CCR1^+/+ T cells (dark gray dashed line, ▴). Survival was monitored daily, and GVHD clinical scores were assessed weekly; n = 8 to 10 per group for survival and GVHD clinical score data; *P < .002 (allogeneic CCR1^−/− and allogeneic CCR1^+/+ BM + CCR1^−/− T vs allogeneic CCR1^+/+); **P < .03 (allogeneic CCR1^−/− BM + CCR1^+/+ T vs allogeneic CCR1^+/+); ***P = .01 (allogeneic CCR1^−/− vs allogeneic CCR1^+/+); ****P = .001 (allogeneic CCR1^+/+ BM + CCR1^−/− T vs allogeneic CCR1^+/+).