Recombinant human PD-1 (Programmed Cell Death 1), encompassing amino acids 25-167. The C-terminus is fused with the Fc fragment of a human IgG1 followed by an Avi-Tag™. This protein contains mutation of interest (E136A). The recombinant protein was enzymatically biotinylated using the Avi-Tag™ and affinity purified. HiP™ indicates a high purity protein (≥90% pure) and less than 10% aggregation as measured by gel filtration.