Recombinant human PD-1 (programmed cell death 1), encompassing amino acids 25-167. The construct contains a C-terminal FLAG-tag followed by an Avi-Tag™ and a His-tag (10xHis). 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.