Homeostatic expansion of CD4⁺ and CD8⁺ GVHD T cells after transfer into secondary recipients. Lethally irradiated (1100 cGy) AKR mice from Figure 1 that were transplanted with Rag-1 BM (5 × 10⁶) and a spleen cell-adjusted dose of either 4 to 5 × 10⁵ naive or GVHD T cells were killed 90 to 119 days after transplantation and examined for the extent of T-cell expansion in the spleen. (A) Absolute numbers of CD3⁺, CD4⁺, and CD8⁺ splenic T cells in mice transplanted with naive (n = 3; □) or GVHD (n = 13; ■) T cells. (B) CD4/CD8 ratio before and after transfer of naive or GVHD splenic T cells into secondary AKR hosts is shown. Analysis in panels A and B was performed on 13 (76%) of 17 animals transplanted in Figure 1 that had received Rag-1 BM plus chimeric (B6→AKR) spleen cells and had a mean thymus size of 2.4 ± 0.6 × 10⁶ cells with a mean percentage of double-positive thymocytes (CD4⁺CD8⁺) of 11% ± 2.5%, indicative of limited de novo T-cell generation. Data are presented as mean ± SEM and are cumulative results from 6 experiments.