Blimp1 controls the proliferative potential of NK cells. (A) Rag2^−/−Blimp1^+/+ or Rag2^−/−Blimp1^gfp/gfp mice, generated as described in Figure 3C, were injected subcutaneously with 5 × 10⁵ RMAS cells. Tumor growth was measured and is presented as mean tumor size ± SEM. Results are representative of 3 independent experiments, each with 4-7 mice per group. (B-C) Wild-type (Ly5.1⁺) or Blimp1^gfp/gfp (Ly5.2⁺) TCRβ⁻NK1.1⁺CD49b⁺ NK cells were sorted from the spleens of mixed bone-marrow chimeric mice, generated as described in Figure 3D, and either subjected to an ex vivo killing assay using RMAS-Rae1β target cells (B) or cultured in titrated amounts of IL-15 as indicated (C). Proliferation was measured 48 hours later. Data in (B) and (C) are the means of triplicate measurements ± SEM. (D) Purified wild-type (Ly5.1⁺) or Blimp1^gfp/gfp (Ly5.2⁺) TCRβ⁻NK1.1⁺CD49b⁺ NK cells were cultured in IL-15 for 7 days before being mixed at a 1:1 ratio (total 2 × 10⁶ cells), injected into Rag2^−/−γc^−/− hosts, and analyzed after 6 days by flow cytometry. Total numbers of the NK-cell population in spleen and total bone marrow (BM) are shown as the means ± SEM. P values compare the indicated genotypes. Results are representative of 2-3 individual experiments