IL15 and lymphopenia: To further investigate the differential contribution of IL-15 relative to IL-7 with respect to the prolonged survival and enhanced memory of transferred T-cells in lymphopenia, we isolated naïve CD8+ T-cells from transgenic OT-I mice, stimulated them with OVA I peptide and IL-2 for 4 days, transferred them into WT B6 and irradiated B6 mice, and quantified changes in the expression of IL-7Rα and IL-15Rβ over time.