Host Treg cells compose the predominant component of the CD4⁺FoxP3⁺ compartment in lymph nodes 5 weeks after autologous HCT. (A) B6-CD45.1 congenic mice were conditioned with 9.5 Gy TBI and 1 day later transplanted with TCD-BMC from B6-wt (CD45.2) donors. Lymph nodes were collected and CD4 T cells were assessed 5 weeks posttransplant. (Left panels) Dot plots from 2 individual mice stained for CD4 and CD25. Numbers outside of boxes represent the percentage of CD4⁺ T cells, which were CD25⁺. (Right panels) Dot plots of gated CD4⁺CD25⁺ cells analyzed for expression of donor CD45.2 and FoxP3. Numbers represent the percentage of positive staining cells in each quadrant. (B) BALB.B (H2^b, Ly9.1⁺) mice were conditioned with 9.5 Gy TBI and 1 day later transplanted with TCD-BMC from major histocompatibility complex–identical B6 (H2^b, Ly9.1⁻). The panels and numbers represent the same populations as those described in panel A with the exception that gated CD4⁺CD25⁺ cells were analyzed for expression of host Ly9.1 and FoxP3. The percentage of CD4 T cells expressing CD25 in the rectangles ranged between 12% and 18%.