B7-H3^−/− donor T cells augment GVHD. (A) BALB/c mice were lethally irradiated and infused with 10⁷ B6 NTCD BM and 1 × 10⁶ B6-WT or B7-H3^−/−–purified T cells. Survival plot of WT (solid circle) vs B7-H3^−/− (open circle) is shown (n = 16 per group; P < .0001). Two experiments with comparable results were pooled. (B) BALB/c mice were lethally irradiated and infused with 10⁷ B6 NTCD BM and 1 × 10⁶ B6 or B7-H3^−/−-purified T cells. Mice were analyzed for weights and clinical scores, the latter of which were not scored beyond day 41 because they had reached mean values of >8 in both groups (n = 8 per group). One experiment was performed. (C) BALB/c mice were lethally irradiated and infused with 10⁷ B6 NTCD BM, 1 × 10⁶ B6-purified T cells, and 0.5 × 10⁶ B6-WT or B7-H3^−/−-purified Tregs. Survival plot of B6-WT Tregs (solid triangle) vs B7-H3^−/− Tregs (open triangle) is shown (n = 8-9 per group; P < .0001). One experiment was performed. (D) BALB/c mice were lethally irradiated and infused with 10⁷ B6 NTCD BM and 1 × 10⁶ B6-WT or B7-H3^−/− CD25-depleted–purified T cells. Survival plot of WT (solid circle) vs B7-H3^−/− (open circle) is shown (n = 8 per group; P < .05). One experiment was performed. *P < .05; **P < .01. KO, knockout.