Host-derived IL-12 enhances erythroid and T-cell engraftment 30 days post-transplant. Radiation chimeras (B6 or BA and IL-12p40 KO) were conditioned with 9 Gy irradiation and transplanted with 5 × 106 FVB TCD BM cells along with 3 × 105 MACS-purified luc + FVB T-cells. A syngeneic transplant was also performed using non-radiation chimera FVB mice as recipients. The levels of red blood cells (RBC) (A), hemoglobin (B), white blood cells (WBC) (C), and platelets (D) were measured in the blood 30 days post-transplant. The percentage of cells of donor–origin (FVB) in the T-cell compartment on day 30 post-transplant was determined by flow-cytometric analysis of congenic markers (CD45.1, CD45.2, CD90.1, CD90.2) after gating on CD3+ cells (E). The percentage of mice in each group (WT or IL-12p40 KO) that exhibited greater than 50% FVB T-cell chimerism are shown in (F). **, p < 0.01 comparing RBC of WT vs. IL-12p40 KO at day 30; *, p < 0.05 comparing Hemoglobin of WT vs. IL-12p40 KO at day 30. Data shown is combined from 2 independent experiments of 4 mice per group (WT and IL-12p40 KO) or 3 mice per group (syngeneic).