Tumor growth inhibits NK-cell development at stage IV. (A) Schematic depiction of the stages of NK-cell differentiation in vivo. (B-E) The effect of tumor growth on the development of NK cells in the bone marrow. Bone marrow cells were obtained from control and EL4 tumor-bearing mice and stained with CD3 and CD122 (A,B,D) or CD3 and NK1.1 (C,E) in conjunction with other markers. The CD122⁺CD3^- cells were evaluated for expression of NK1.1 (B); CD94 (C); Ly49A, Ly49C, Ly49D, Ly49H, and Ly49I (D), as well as BrdU and CD11b (E). The numbers shown in the panels are mean ± SEM (n = 4) of the percentage of cells in the gates. The decreases of CD11b expression (P ≤ .001) and increase in proliferation (P ≤ .001) in tumor-bearing mice were highly significant. (F) Multiple lineages of syngeneic tumors caused developmental defects of NK cells in the bone marrow. NK cells from syngenic mice bearing mammary tumors (4T1 or TSA), melanoma (B16F1), or colon adenocarcinoma (MC38) were evaluated for NK-cell maturation. NK cells were identified based on their phenotypes, that is, CD122⁺CD3^- in BALB/c mice and NK1.1⁺CD3^- in C57BL/6 mice. Fluorescence-activated cell sorting (FACS) profiles depict CD11b expression among NK cells. The numbers of mice with indicated defects over the number of mice tested are shown next to the tumor cells used.