SCT with CCR1-deficient donor cells is associated with a significant decrease in GVHD severity. Lethally irradiated B6D2F1 mice received transplants from syngeneic B6D2F1 (- - -, ■), and allogeneic B6.129 CCR1^+/+ (—, ●) or B6.129 CCR1^−/− (dashed gray line, ▴) donors as described in “Materials and methods.” Transplant recipients were monitored daily for survival (A), and GVHD clinical scores were assessed weekly (B). *P < .01 (B6.129 CCR1^−/− vs B6.129 CCR1^+/+). Intestinal histopathology (C) and serum TNFα levels were assessed on day 7 (syngeneic, □; allo CCR1^+/+, ■; allo CCR1^−/−, ). *P < .01. Data are expressed as means plus or minus SEM (B-D) and are combined from 2 comparable experiments; n = 10 to 20 per group for survival data and 8 to 12 per group for pathology and TNFα data.