CCR5^-/- and WT T_regs sorted from target organ–infiltrating cells are suppressive in vitro. Lethally conditioned recipients were given transplants containing WT TCD-BM and WT CD25^- T cells, with column-purified WT/eGFP (black bars) or CCR5^-/-/eGFP (hatched bars) T_regs or with WT/eGFP CD4⁺CD25^- T cells (dark gray bars). GFP⁺CD4⁺ cells were isolated from spleen and liver infiltrates by flow cytometric sorting on day 14, from 3 mice per group. These were used in the indicated T_reg/responder cell ratios in an in vitro suppression assay, as described in “Materials and methods.” (Note: From previous work [Figure 5], a significant proportion of GFP⁺CD4 T cells sorted from target tissues are FoxP3-negative cells. The indicated ratios therefore overestimate T_reg numbers and should not be compared to suppression by freshly isolated cells in Figure 3.)