Donor T_SCM dominate the peripheral T-cell compartment following pt-Cy. (A) FACS analysis of PB T cells at day 7 post–haplo-HSCT. Donor (D; red) and recipient (R; dark gray) cells are identified by an antibody recognizing the mismatched HLA-A*02. Light-gray cells in the background are T cells from the PB of a healthy donor. (B) Median ± SEM frequency of D and R T cells (identified as in panel A) with a given differentiation phenotype in patients at day 7 post–haplo-HSCT (n = 7, CD4⁺; n = 6, CD8⁺). Only donor-recipient pairs whose mismatched HLA could be investigated by flow cytometry are included. *P < .05 vs day 7 D cells; Mann-Whitney test. (C) Percent CFSE^lo CD8⁺ T cell subsets from a healthy donor (HD) and a recipient (R) at day 41 post–haplo-HSCT after PBMC culture with 1 (gray, serving as a nonproliferating control) or 50 ng/mL IL-15 (black) for 8 days. N/D, not detected. (D) Mean ± SEM CFSE^lo CD8⁺ T-cell subsets (calculated as in panel C) from healthy donors (n = 6) and haplo-HSCT patients (n = 5). T_MEM, CD45RO⁺ memory T cells. *P < .05, Mann-Whitney test. (E) Combinations of IFN-γ, IL-2, and TNF production in gated T_SCM from patients (n = 3) and in T-cell subsets from healthy donors (HD; n = 4). *P < .05, permutation test.