(A) B6 bm1 mice were sublethally irradiated and transplanted with 1 × 106 purified CD8+ cells per recipient from WT, CD28 KO, ICOS KO, or DKO B6 donors. Recipient survival is shown, and the data are from 2 replicate experiments with 6-15 recipients per group. CD28 KO vs. WT: p < 0.01. (B) Lethally irradiated BALB/c mice were transplanted with TCD-BM alone or plus 1-2 × 106 T cells (CD4 and CD8) from WT, CD28 KO, ICOS KO or dKO B6 donors. Recipient survival is shown, and the data are pooled from 3 replicate experiments with 11-16 mice per group. CD28 KO vs. WT: p < 0.001; ICOS KO vs. WT: p < 0.001; CD28 vs. ICOS: p = 0.7; DKO vs. CD28 KO: p = 0.06; DKO vs. ICOS KO: p = 0.01.