IL-7 and IL-15 instruct the expansion of a novel CD62L⁺CD45RA⁺ memory T-cell population from naive precursors. (A) Diagram summarizing the procedure to generate T_(TN), T_(TCM), and T_(TEM) subsets. FACS-sorted T_N (CD62L⁺CD45RA⁺), T_CM (CD62L⁺CD45RA⁻), and T_EM (CD62L⁻CD45RA⁻) lymphocytes were activated with anti-CD3/CD28 beads (bCD3/CD28) and cultured with IL-7 (5 ng/mL) and IL-15 (5 ng/mL). Forty-eight hours after activation, cells were transduced with retroviral (RV) or lentiviral (LV) vectors. (B) RV and LV transduction efficiency measured in each T-cell subset by flow cytometry. (C) T-cell expansion (measured as fold increase) analyzed for each cell subset. (D) Representative FACS plots of CD45RA and CD62L expression. (E) Quantification of CD62L⁺CD45RA⁺ double-positive cells 16 days after initial activation (left) and longitudinal analysis of CD62L/CD45RA coexpression over 30-day culture (right) in each T-cell subset. Graphs depict the percentages of CD62L⁺CD45RA⁺ cells gated on CD8⁺ T cells. (F) Representative FACS plots of CD45RA and CD45R0 coexpression gated on CD62L⁺CD8⁺ T_(TN), T_(TCM), and T_(TEM) subsets. (G) Quantification of CD62L⁺CD45RA⁺CD45R0⁺ triple-positive CD8⁺ cells 16 days after activation. (H) Absolute numbers of CD62L⁺CD45RA⁺CD8⁺ T cells generated from purified T_N treated with different stimulation (bCD3/CD28 in black or OKT3 in gray) and culture conditions (IL-7 and IL-15 together, IL-7, IL-15, or IL-2 alone). (I) Percentages of CD62L⁺CD45RA⁺ cells (gated on CD8⁺ T cells) on bCD3/CD28-stimulated T_N cells cultured with different cytokines. Mean data from at least 3 healthy donors are presented, and error bars represent SEM.