Donor Tregs added to CD4^−/− donor transplants protect against donor CD8⁺ T-cell infiltration in the colon. (A) Mean absolute number (± SD) H-2K^b+TCRαβ⁺CD8⁺ cells recovered from MLN of wild-type BALB/c hosts given 800 cGy TBI/ATS and wld-type C57BL/6 donor bone marrow and splenocytes, or TLI/ATS and transplantation of 50 × 10⁶ bone marrow and 60 × 10⁶ splenocytes from CD4^−/− C57BL/6 donors with and without addition of 1.5 × 10⁶ purified wild-type C57BL/6 CD4⁺CD25⁺ Tregs (n = 3, TBI/ATS; n = 5, CD4^−/− TLI/ATS; n = 4, CD4^−/− TLI/ATS + Treg). Each group represents data combined from 2 separate experiments. (B) FACS analyses of gated donor H-2K^b+TCRαβ⁺ cells, showing CD4 versus CD8 in MLN at day 6 after bone marrow and splenocyte transplantation in 1 representative host from each group shown in panel A. (C) Mean absolute number (± SD) H-2K^b+TCRαβ⁺CD8⁺ cells recovered from colons of wild-type BALB/c hosts shown in panel A. (D) FACS analyses of gated donor H-2K^b+TCRαβ⁺ cells, showing CD4 versus CD8 in colon at day 6 after bone marrow and splenocyte transplantation in 1 representative host from each group shown in panel C.