Peripheral CD4 T cells deficient in CTLA-4 resist establishment of mixed chimerism in mice receiving CD8 depletion, 3 Gy TBI, anti-CD154 mAb, and allogeneic BM transplant. (A) The percentage of CD4 cells derived from WT, DKO, or TKO progenitors (CD45.2) is shown at 5, 8, and 11 weeks after lethal irradiation for lethally irradiated B6 (CD45.1) recipients reconstituted with (CD45.2) WT, DKO, or TKO BMCs in combination with TCRβ^−/− (CD45.2) BMCs. The 11-week time point is 2 weeks after allogeneic BMT, before allogeneic donors contribute to T-cell chimerism. (B) The mean percentage of donor cells in WBC B-cell, monocyte, and granulocyte lineages (from left to right) is shown in reconstituted recipients at 2 and 4 weeks after alloBMT with anti-CD154. Results are shown as mean plus or minus SEM for each lineage. (C) Nine weeks after lethal irradiation and reconstitution, mice received allogeneic B10.A BM transplant with anti-CD154, anti-CD8, and 3 Gy TBI and were assessed for chimerism by flow cytometry. In WT (5 of 5), TCRβ^−/− (5 of 5), T-WT (5 of 5), and T-DKO (9 of 9) mice, donor-derived cells were detected in the CD4, CD8, B-cell, monocyte, and granulocyte populations, whereas none of the T-TKO recipients (0 of 5) developed lasting mixed chimerism.