Reduced NK cell– and CD8 T cell–mediated suppression of tumors in DNAM-1^−/− mice. (A and B) B6 WT and DNAM-1^−/− mice were challenged i.v. with various doses (as indicated) of either (A) B16F10 or (B) RM-1, as described in Materials and methods. Lungs were harvested on day 14 and fixed in Bouin's solution, and tumor colonies were counted under a dissecting microscope. Data are depicted as mean tumor colonies ± SEM (n = 5–14 mice for each dose/group). Statistical differences between WT and DNAM-1^−/− mice are depicted by asterisks (P < 0.05 using the Mann-Whitney test). (C) WT and DNAM-1^−/− mice were injected with 5 × 10⁴ B16F10 tumor cells s.c., and tumor growth was monitored at least every second day using a caliper square to determine the product of two perpendicular tumor diameters. Some groups of WT mice were depleted of CD8 T cells or NK cells, as described in Materials and methods. Results were recorded as the means ± SEM of five mice and are representative of two to four independent experiments. Statistical differences between WT + cIg and DNAM-1^−/− mice are depicted by an asterisk (P < 0.05 using the Mann-Whitney test). (D) Expression of CD155 and CD112 on MC38-OVA cells as assessed by flow cytometry. Open histograms represent staining with the respective antibody, whereas shaded histograms show isotype staining. (E) WT or RAG1^−/− mice were injected with 10⁶ MC38-OVA tumor cells s.c., and tumor growth was monitored as described in C. Some groups of WT mice were depleted of CD8 T cells. (F) WT and DNAM-1^−/− mice were injected with 10⁶ MC38-OVA tumor cells s.c., and tumor growth was monitored as described in C. Results were recorded as the means ± SEM of five (E) or nine (F) mice.