Disruption of the CD24–Siglec-G interaction enhances allogeneic T-cell responses. BMDCs from WT-B6 and Siglec-G^−/− mice were used as stimulators in an MLR with T cells from either CD24^−/− BALB/c (allogeneic) or C57BL/6 (syngeneic) mice and analyzed for (A) T-cell proliferation based on ³H-thymidine incorporation at 96 hours. The data are the mean ± SEM of quadruplicate cultures and are from 1 of 3 similar experiments. (B-C) Supernatants from the cultures were collected at 80 hours and analyzed for IFN-γ (B) and IL-2 (C) by ELISA. The data are the mean ± SEM of quadruplicate cultures and are from 1 of 3 similar experiments. (D) Survival. WT-B6 mice were lethally irradiated with 13 Gy and infused with 2.5 × 10⁶ CD90⁺ T cells along with 5 × 10⁶ TCD-BM cells from either syngeneic B6 or allogeneic MHC-mismatched BALB/c or CD24^−/− donors (n = 4 to 15 per group, pooled from 2 experiments). The bar shows the mean ± SEM. (E) Clinical GVHD score. For ▲ vs ●, **P < .01 and *P < .05. (F) Survival. WT-B6 mice were lethally irradiated with 13 Gy and infused with 2.5 × 10⁶ CD90⁺ T cells along with 5 × 10⁶ TCD-BM cells from either syngeneic B6 or allogeneic MHC-mismatched CD24^−/− donors. The recipients were injected with the CD24 Fc protein on day −1 (5 mg/kg) or diluent control on day −1 before allo-HCT (n = 4 to 10 per group, pooled from 2 experiments). For ♦ vs ◊, P = .02. The bar shows the mean ± SEM.