Tumors impede the maturation of adoptively transferred CD11b^-NK cells. Congenic (CD45.1) immature NK cells (NK1.1⁺CD11b^-) from bone marrow were adoptively transferred into control and EL4-bearing mice (CD45.2). Two weeks after the adoptive transfer, splenocytes were analyzed by flow cytometry. (A) Expression of CD11b and NK1.1 in presorted and postsorted samples. The postsorted NK1.1⁺CD11b^- cells were used for adoptive transfer. (B) Histogram of adoptively transferred NK cells in PBS-treated host or in tumor-bearing host. The profiles depict the expression of CD11b among the CD45.1⁺NK1.1⁺ cells and are representative of data from 2 separate experiments.