Phenotypic characteristics of CD8⁺ T-cell populations specific for CMV pp65_495-503 and PR1 in peripheral blood and bone marrow. Cognate WT pHLA A*0201 tetramers were used to identify antigen-specific CD8⁺ T-cell populations in a polychromatic flow cytometric panel that included mAbs to determine the expression of surface markers commonly used to distinguish naive and memory T cells. (A) Pie charts depict the proportions of CMV-specific and PR1-specific CD8⁺ T cells that expressed various combinations of CD27, CD45RO, and CD57, as indicated by the adjoining key. The phenotypic composition of CMV-specific CD8⁺ T cells was not significantly different between the peripheral blood (PB) and bone marrow (BM) compartments; however, within the bone marrow, the phenotypic composition of CMV-specific and PR1-specific CD8⁺ T-cell populations was significantly different. (B) Bar graphs show the proportions of CMV-specific and PR1-specific CD8⁺ T cells that expressed each combination of CD27, CD45RO, and CD57 in the bone marrow. Compared with CMV-specific CD8⁺ T cells, PR1-specific CD8⁺ T-cell populations were significantly enriched for CD27⁺CD45RO⁺CD57⁻ (central memory–like) cells and depleted of CD27⁻CD45RO⁻CD57⁺ (terminally differentiated) cells.