Proliferative response of purified CD8 cells from spleen and BM to IL-21, in combination with either IL-15 or IL-7. Purified CD8⁺ cells (5 × 10⁴ cells/well) from spleen and BM of untreated B6 mice were cultured for 5 days in the presence of graded concentrations of either IL-15 or IL-7, alone or in combination with IL-21. H³-thymidine incorporation was determined after a 12-hour pulse. (A,B) IL-21 and IL-15. Spleen (A) and BM (B) CD8-cell response to graded dose of IL-15, alone or in combination with 50 ng/mL of IL-21. (C,D) IL-21 and IL-7. Spleen (C) and BM (D) CD8-cell response to graded dose of IL-7, alone or in combination with 50 ng/mL of IL-21. For both organs, background proliferation with medium resulted in less than 60 cpm and incubation with 10, 50, and 100 ng/mL of IL-21 in approximately 100 cpm. One representative experiment is shown of 3. For each experiment, cells were pooled from 4 to 5 mice.