Figure 2.

In vitro expansion of NK cells. (A) CD45^−/− and control NK1.1⁺CD49b⁺TCR-β⁻ cells were sorted and cultured in various concentrations of IL-15 for 60 h. Cultures were pulsed with [³H]thymidine for the final 8 h and radioactive incorporation counted. (B) CD45^−/− and control NK1.1⁺CD49b⁺TCR-β⁻ cells were cultured for 48 or 72 h in 50 ng/ml IL-15 with or without 100 ng/ml IL-21. Cultures were pulsed with [³H]thymidine for the final 8 h and radio-labeled DNA counted. For A and B data are representative of four independent experiments. (C) Cells cultured in IL-15 with or without IL-21 for 72 h were analyzed for surface expression levels of NK1.1 by flow cytometry. Data are representative of three independent experiments.