CD27-trunc enhances the activity of tumor-infiltrating NK cells. (A-F) Analysis of NK cells in spleens (A) and tumor tissue (B-F) of MC57 or MC57-CD27-trunc tumor-bearing mice, 12 days after tumor transplantation. (A) Frequencies and numbers of NK cells in spleens of BL/6 mice. (B) Numbers of tumor-infiltrating NK cells. (C-F) MACS-sorted CD45⁺ cells from tumor tissue were restimulated with PMA/ionomycin for 4 hours and IFN-γ was analyzed by FACS. (C) One representative FACS plot of IFN-γ⁺ NK cells out of 3 is shown. (D) Frequencies of IFN-γ⁺ NK cells in tumor are shown as Δ (PMA/Iono-unstimulated). (E) Numbers of tumor-infiltrating IFN-γ⁺ NK cells. (F) Δ MFI, [MFI-stimulated – MFI-unstimulated], of IFN-γ expression in tumor-infiltrating NK cells. Data are shown as mean ± SEM of 3 to 5 mice in each group and are representative of 3 independent experiments. Statistics: Student t test (A-B,D-F). lono, ionomycin; SSC, side scatter.