PDCD1 and neoplasm: Pembrolizumab, a clinically approved anti-PD-1 Ab, was radiolabeled with 64Cu or zirconium-89 (89Zr) to detect tumor infiltration of adoptively transferred human peripheral blood mononuclear cells (hPBMCs) in NSG mice xenografted with human A-375 melanoma tumors (Natarajan et al. 2017).