Proliferative response of neonatal CD4⁺ and CD8⁺ T cells to IL-7 and IL-15. Lymphocytes were purified from cord blood, labeled with CSFE, and cultured in the absence or presence of IL-7 (10 ng/mL) and IL-15 (24 ng/mL). Cell division patterns of CD4⁺ and CD8⁺ T cells were evaluated by flow cytometric analysis on day 7. Representative results from 4 experiments are shown. Results gated on CD4⁺ (A, B) and CD8⁺ T cells (C, D) are shown as scatter plots (A, C) and histograms (B, D). Cells were cultured in the absence (gray line) and the presence of IL-7 and IL-15 (shaded area). The dark line represents autofluorescence.