HB0045 is a 1:1 mixture of two humanized monoclonal IgG1 antibodies (mAbs), HB0038 and HB0039. In various animal models of syngeneic and xenograft tumors, HB0045 inhibits tumor growth more potently than the single mAbs. Collectively, our findings provide functional and structural insights into the mechanism of a CD73-targeting antibody cocktail.