Phenotypical and functional shift from early mature toward regenerating B cells begins around day 60 after allo-HSCT. (A) PBMCs of adult allo-HSCT patients were analyzed for CD19⁺ B- and CD3⁺ T-cell counts, as well as CD3⁺CD4⁺ T-helper and CD3⁺CD8⁺ cytotoxic T-cell subset counts by flow cytometry at indicated time points after allo-HSCT (D14, n = 27; D28, n = 44; D60, n = 35; D90, n = 36; D180, n = 18). (B) Within CD19⁺ B cells, cell numbers of indicated B-cell subsets were analyzed by flow cytometry at indicated time points after allo-HSCT (D14, n = 27; D28, n = 44; D60, n = 35; D90, n = 30; D180, n = 11). Shown are mean values per microliter of blood ± SEM. Gray bars in A and B indicate mean reference values ± SEM of HCs (n = 12). (C) Total CD19⁺ B cells and separately transitional B cells were analyzed by flow cytometry for the expression of CD86, CD95, and Baff-R within 6 months after allo-HSCT. Graphs show expression of indicated markers on total CD19⁺ B cells (white bars) and transitional B cells (gray bars) of HCs (n = 12) and of allo-HSCT patients at indicated time points after allo-HSCT (CD19⁺ B cells/transitional B cells: D14, n = 20/data not available [N/A]; D28, n = 37/N/A; D60, n = 30/18; D90, n = 33/21; D180, n = 17/14). Graphs illustrate percentages of cells expressing the indicated marker represented as mean values ± SEM. Statistically significant differences in cell counts or percentages between HCs and allo-HSCT patients are shown. *P ≤ .05; **P ≤ .001.