Frequency of CD8⁺T-cell memory subsets in human peripheral blood. (A) Flow cytometric analysis of PBMCs from 4 different human donors gated on the lymphoid population by forward and side scatter (left panel) and analyzed for CD45RO, CD62L, and CD8 expression. CD45RO⁺ lymphocytes were then gated for CD8⁺CD62L⁺ T_CM and CD8⁺CD62L⁻ T_EM (middle and right panels) and analyzed by multicolor flow cytometry with anti-CCR7, anti-perforin, or anti-granzyme A mAbs (B). Percentage of cells in each gate (red) is indicated, and mean percentage of the CD8⁺ T_CM or T_EM cells that were CCR7, perforin, or granzyme A positive (± SE; n = 3 donors) is indicated. *P < .05, CD8⁺ T_CM versus T_EM cells (unpaired Student t test). (C) Cytokine production profiles of the freshly isolated CD8⁺ T_CM and T_EM. Supernatants were collected after overnight coincubation with LCL-OKT3, and cytokine levels (mean ± SE of triplicate wells) were determined as described in “Cytokine production assays.” *P < .0001, cytokine levels of CD8⁺ T_CM versus T_EM cells (unpaired Student t test).