Absence of IFN-γ synthesis by donor T cells leads to enhanced cell division among donor CD8⁺ T cells. CD90.1⁺ BA.B10 mice received 3 × 10³ FACS-sorted HSCs and 3 × 10⁵ CFSE-labeled CD90.2⁺ T cells from WT (closed symbols) or IFN-γ^−/− (open symbols) B6 donors with or without 5 × 10⁴ FACS-purified pDCs (n = 3/group). Recipient splenocytes were prepared at day 3 after transplant and analyzed for the proliferation of donor T cells. (A) Representative CFSE proliferation profiles of CD4 and CD8 T cells for each transplant combination. Gating indicates the average percentage of cells in the undivided T-cell peak. (B) Average percentage of cells in each division peak (CD4 panel, ***P < .001 comparing percentage of undivided T cells in HSCs + WT T vs all other groups; *P < .05 comparing percentage of T cells divided 5 times for HSCs + WT T vs HSCs + IFN-γ^−/− T + pDCs and P < .05 comparing percentage of T cells divided 6 times for HSCs + WT T vs HSCs + WT T + pDCs; CD8 panel, ***P < .001 comparing percentage of undivided T cells and T cells divided 1 or 2 times in HSCs + WT T vs all other groups; *P < .05 comparing percentage of T cells divided 5 or 6 times for HSCs + WT T vs HSC + IFN-γ^−/− T and divided 6 or 7 times for HSCs + WT T vs HSCs + IFN-γ^−/− T + pDCs). (C) Calculated proliferation indices (*P ≤ .05 compared with HSCs + T group by 1-tailed Mann-Whitney U test).