Development of therapeutic PD-1 monoclonal antibodies for treatment of canine tumor.
The use of monoclonal antibodies to block PD-1 binding to its ligand PD-L1 as a strategy for cancer treatment has already proven successful in the clinical management of human cancers. However, the clinical application of anti-PD-1 monoclonal antibodies in canine cancer immunotherapy still requires systematic and in-depth research. In this study, an anti-canine PD-1 monoclonal antibody (designated 2H4) was developed that can be used for therapeutic purposes. In an Indirect Enzyme-Linked Immunosorbent Assay (ELISA), the minimum binding concentration of 2H4 for PD-1E (a recombinant canine PD-1 extracellular domain protein) was 0.48 ng/mL. In the PD-1/PD-L1 blocking assay, the minimum concentration of 2H4 required to block PD-1/PD-L1 interaction was 3.9 ng/mL. Further studies identified the spatial region containing three PD-1 amino acid residues-Y68, K78, and E136-as the binding site for 2H4. In therapeutic trials using a Beagle tumor model, the 2H4 antibody demonstrated the ability to activate the Beagles' anti-tumor immune response without causing any side effects. However, due to the limitations of xenograft animal models and the potential impact of murine antibodies on therapeutic efficacy, there was no significant difference in the rate of tumor shrinkage between the 2H4 antibody treatment group and the control group. Nevertheless, following subsequent tumor implantation, tumor volume in the antibody treatment group decreased significantly. The results suggest that 2H4 has potential for the treatment of tumors. In future, this antibody will need to undergo canine-specific modification, and dogs with spontaneous cancer will need to be selected to further evaluate its clinical efficacy.