Molecular shield is observed generally. (A) B7-H1⁺ P815 cells are resistant to allospecific CTL-mediated lysis. Allospecific T cells were incubated at indicated E/T ratios with ⁵¹Cr-labeled mock/P815 or B7-H1/P815 cells in the presence of control IgG or anti-mouse B7-H1 mAb (clone 10B5) for 4 hours. CTL activity was determined in a ⁵¹Cr release assay. Each point is the mean of triplicates with SD. The data are representative of 3 experiments. (B) B7-H1⁺ Renca cancer cells are resistant to allospecific CTL-mediated lysis. Renca cells were incubated with IFN-γ (5 ng/mL) for 48 hours to up-regulate B7-H1 expression (data not shown). Activated 2C CTLs were incubated at indicated E/T ratios with ⁵¹Cr-labeled Renca cells with control IgG or antimurine B7-H1 antibody (clone 10B5) for 4 hours. CTLs activity was determined in a ⁵¹Cr release assay. Each point is the means of triplicates with SD. The data are representative of 3 experiments.