Recombinant Expression and Purification of Extracellular Domain of the Programmed Cell Death Protein Receptor

The programmed cell death protein 1 (PD-1), which is a member of the CD28 receptor family, can negatively regulate antitumor immune responses by interacting with its ligands, PD-L1 or PD-L2. The PD-1–PD-L1 signaling pathway is a checkpoint mechanism that plays essential roles in downregulating immune responses in cancerous tissues. Thus, blocking this signaling pathway leads to enhanced antitumor immunity, potentially preventing tumor progression. Methods: We synthesized the extracellular domain of the PD-1 receptor (rPD-1) de novo by using a two-step polymerase chain reaction and the Phusion® DNA polymerase. The synthesized gene was cloned into the pET28 expression plasmid and transformed into competent Escherichia coli. Purification of rPD-1 was performed by metal-affinity chromatography, using a HisTrap column. Purified rPD-1 was characterized by western blotting and mass spectrometry using the SwissProt database and the Mascot program. Results: Designed and synthesized construct of rPD-1 was 500 bp in size. Analysis of the electrophoresis data of purified rPD-1 showed the presence of a protein with a molecular mass of 21 kDa. Mass spectrometry data using the SwissProt database and the Mascot program outputted the highest-scoring sequence to correspond to rPD-1. Conclusions: Synthesized de novo rPD-1 may have potential therapeutic applications in enhancing antitumor immune responses