CD274 and neoplasm: The blockade of the PD-1/PD-L1 axis by monoclonal antibodies improved cytokine production and lymphocyte proliferation in canine immune cell cultures [17,21,22], strongly suggesting that clinical intervention with anti-PD-1 or anti-PD-L1 antibody drugs could exert antitumor effects in dogs with OMM by reinvigorating T cell-mediated immunity against the tumor.