Expression of CD27, CD28, CD11a, and CD62L in CD8⁺ T PBLs. (A-B) CD8-enriched PBLs were simultaneously stained for CD8, CCR7, CD45RA, CD27, and CD28. CD8^high cells were then subdivided using CCR7 and CD45RA expression in naive (T_N), central memory (T_CM), effector memory (T_EM), and effector memory CD45RA⁺ (T_EMRA) cell subpopulations (A), and CD27/CD28 coexpression was evaluated in each of these cell sets (B). (C-E) Comparison of CD27 (C), CD28 (D), and CD11a (E) expression levels on T_N cells (shaded histograms) with T_CM (dashed), T_EM (thick line), and T_EMRA (gray line). (F) CD8⁺ cells depleted for CCR7 were simultaneously stained for CD8, CD62L, CD45RA, CD27, and CD28. T_EM and T_EMRA subpopulations gated on CD8^high were subdivided according to their expression of CD27 and CD28 into CD27^high, CD28⁺CD27⁻ (CD28-SP), CD28⁺CD27⁺ (DP), CD28⁻CD27⁺ (CD27-SP), and CD28⁻CD27⁻ (DN) cell sets. Results show CD62L expression in each of these sets in 1 representative donor.