Recipients of GPR109A−/− T cells have fewer donor T cells post allo-HCT compared to WT. Lethally irradiated BALB/c recipients received B6 WT TCD BM and 0.5 × 106 WT or KO T cells. (A-B) Live, CD45+, CD3+, H-2kb+ donor CD4+ and CD8+ T cell percentages (top) and numbers (bottom) are shown from spleen, small intestine (SI) lamina propria and colon lamina propria on day 7 and day 14 post allo-HCT. (C-D) Live, CD45+, CD3+, H-2kb+ donor effector memory CD4+ and CD8+ T cell percentages and numbers were analyzed from indicated tissues. (E) Live, CD45+, CD3+, H-2kb+, CD4+ donor regulatory T cell percentages analyzed for the 3 tissues on day 7 and 14 and (F) ratio of Tregs to CD4+ T cells analyzed. (G) Percent and number of T-bet+ Th1 cells on day 7 post-BMT. (H) Percent and number of Rorgt+ Th17 cells on day 7 post allo-HCT. All comparisons in (A) to (H) were performed by two-tailed unpaired Mann-Whitney Test. Values are means ± standard deviation. *P < .05, **P < .01, ***P < .001, ****P < .0001, n = 5-15 mice per group. All results from two to three independent experiments.