Human secreted programmed cell death 1 (PD-1)-Fc fusion protein, also known as, PDCD1, SLEB2, CD279 and HPD-L, GenBank Accession No. NM_005018, a.a 25-167, fused at the Cterminus to the Fc portion of human IgG1, expressed in a HEK293 cell expression system. This protein runs at a higher M.W. by SDS-PAGE due to glycosylation. The protein was randomly labeled with RPE on accessible lysine residues.