Reconstructed Adeno-Associated Virus with the Extracellular Domain of Murine PD-1 Induces Antitumor Immunity

Background: The negative signaling provided by interactions of the co-inhibitory molecule, programmeddeath-1 (PD-1), and its ligands, B7-H1 (PD-L1) and B7-DC (PD-L2), is a critical mechanism contributing totumor evasion; blockade of this pathway has been proven to enhance cytotoxic activity and mediate antitumortherapy. Here we evaluated the anti-tumor efficacy of AAV-mediated delivery of the extracellular domain ofmurine PD-1 (sPD-1) to a tumor site. Material and
Methods: An rAAV vector was constructed in which theexpression of sPD-1, a known negative regulator of TCR signals, is driven by human cytomegalovirus immediateearly promoter (CMV-P), using a triple plasmid transfection system. Tumor-bearing mice were then treated withthe AAV/sPD1 construct and expression of sPD-1 in tumor tissues was determined by semi quantitative RT-PCR,and tumor weights and cytotoxic activity of splenocytes were measured.
Results: Analysis of tumor homogenatesrevealed sPD-1 mRNA to be significantly overexpressed in rAAV/sPD-1 treated mice as compared with controllevels. Its use for local gene therapy at the inoculation site of H22 hepatoma cells could inhibit tumor growth, alsoenhancing lysis of tumor cells by lymphocytes stimulated specifically with an antigen. In addition, PD-1 was alsofound expressed on the surfaces of activated CD8+ T cells.
Conclusion: This study confirmed that expression ofthe soluble extracellular domain of PD-1 molecule could reduce tumor microenvironment inhibitory effects onT cells and enhance cytotoxicity. This suggests that it might be a potential target for development of therapiesto augment T-cell responses in patients with malignancies.