PD-1 signaling to T cells is not required for molecular shield. (A) Schematic of wild-type PD-1 (PD-1) and intracellular domain-truncated PD-1 (ΔPD-1) genes. IgV indicates IgV domain; TM, transmembrane domain; CY, cytoplasmic domain, GFP, gene encoding for GFP. (B) The expression of PD-1 on 2C × PD-1KO T cells upon transduction. PD-1KO (PD-1⁰) 2C T cells were transduced with lentiviruses containing either wild-type PD-1 (PD-1) or truncated PD-1 (ΔPD-1), and each cell line was examined for PD-1 expression by flow cytometry using anti-mouse PD-1 mAb (G4). (C,D) Cytolytic activity of PD-1 transduced PD-1⁰2C against P815 tumor cells. Activated PD-1/PD-1⁰2C, ΔPD-1/PD-1⁰2C, or nontransduced PD-1⁰2C CTL was incubated at indicated E/T ratios with ⁵¹Cr-labeled mock/P815 (C) or B7-H1/P815 (D) cells in the presence of control IgG or anti-mouse B7-H1 mAb (10B5) for 4 hours. CTL activity was determined in a ⁵¹Cr release assay. Each point is the mean of triplicates with SD. Data are representative of 3 experiments.