CD274 and neoplasm: In a neoplastic state, PD-1 binds to its ligands PD-L1 (B7-H1) and PD-L2 (B7-DC), which are expressed on tumor cells; this inhibits T-cell proliferation, cytokine production, and cytolytic function, thereby causing immunosuppression and preventing the immune system from rejecting the tumor (Brahmer, Horn, & Antonia, 2013; Brahmer & Pardoll, 2013; Sundar, Soong, Cho, Brahmer, & Soo, 2014).