Effect of sGITRL contained in cancer patient sera on NK cell anti-tumor reactivity. (A) NK cells were incubated with PC3 tumor cells in the absence (diamonds) or presence of sGITRL-containing patient serum (squares). Where indicated, 10 ng/mL human IgG1 (circles) or GITR-Ig fusion protein (triangles) was added to patient serum 30 minutes before the cocultures. Cytotoxicity was analyzed by chromium release assays. (B) IFN-γ production of NK cells after 24 hours of culture alone or with PC3 cells in the absence or presence of patient serum and/or GITR-Ig with human IgG1 as control was determined by ELISA. (Left panels) Serum of a colon cancer patient. (Middle panels) Serum of lung cancer patient. (Right panels) Serum of a gastric cancer patient. Means of triplicates and SD of one representative experiment each of a total of at least 4 experiments with similar results are shown.