Tumor metastasis into bone marrow is not responsible for developmental defects of NK cells. Congenic mice (CD90.1) were injected with EL4 (CD90.2) or PBS. Mice were killed when tumors reached an average diameter of 20 mm. Box in the top right of each histogram indicates the tumor-cell gates. (A) Splenocytes and bone marrow cells were evaluated for the presence of tumor. (B) Expression of CD11b on NK1.1⁺CD3^- cells. Data from 2 representative EL4 tumor-bearing mice, called EL4-1 and EL4-4, are presented.