B7-H3 expression is upregulated in target organs during acute GVHD. (A) B6-WT mice were lethally irradiated and infused with 10⁷ BALB/c non-T-cell–depleted (NTCD) BM with or without 2 × 10⁶ BALB/c-purified T cells (3 experiments were performed). (B) BALB/c mice were lethally irradiated and infused with 10⁷ B6-WT BM only, B7-H3^−/− BM only, or B7-H3^−/− BM plus 1 × 10⁶ purified B7-H3^−/− T cells. Mice were euthanized on day 21 after transplantation, and the colon, liver, and lung were examined for B7-H3 mRNA by qPCR. Two experiments were performed with 5 mice per group per experiment; 1 representative experiment is depicted. (C) Representative colon sections of a patient without GVHD (left) and a patient with intestinal GVHD grade 4 (right) are shown. Red signal: detection of B7-H3⁺ cells. (D) Quantification of B7-H3 staining in intestinal sections from multiple patients is shown. *P < .05; **P < .01. ns, not significant. HPF, high power field.