PDCD1 and neoplasm: Indeed, systemic (intraperitoneal (i.p.)) injection of uridine-5′-O-α,β-methylene-diphosphate (UMP-CP; a hydrolytically stable analog of UDP) in anti-PD-1-treated sgCda KPC FC1245 tumor-bearing mice restored tumor weight to the same level as observed in anti-PD-1-treated sgNT tumor-bearing mice (Fig. 8b).