CD4⁺CD25⁺CD62L^- T cells are quantitatively less efficient suppressors in vivo. Lethally irradiated BALB/c mice received TCD BM and CD4⁺CD25^- T cells from congenic C57BL/5 without (control hosts) or together with (experimental hosts) CD4⁺CD25⁺CD62L⁺ or CD4⁺CD25⁺CD62L^- Treg cells from wild-type (WT) C57BL/6 donors. All mice were killed 5 days after transfer. Single cell suspensions were prepared from mesenteric LN (MLN), spleen, and liver of individual mice. Viable cells were counted, stained with appropriate antibodies, and analyzed by flow cytometry. The progeny of CD4⁺CD25^- and CD4⁺CD25⁺ T cells was identified as CD4⁺H-2K^b+[congenic marker]^+/-. Results for individual mice are shown. The horizontal line represents the group median. P values are given above the figures. Data were pooled from 4 experiments with 9 to 11 mice per group. (A) Recovery of CD4⁺CD25⁺ T cells after transfer of the CD62L⁺ or CD62L^- subset. (B) Expansion of CD4⁺CD25^- T cells in mesenteric LN, spleen, or liver after cotransfer of CD4⁺CD25⁺CD62L⁺ or CD4⁺CD25⁺CD62L^- Treg cells. (C) Fraction of CD4⁺CD25⁺ T-cell progeny among all donor CD4⁺ T cells in individual mice.