Subsequently, we structurally characterized the trio of constructs, interrogated their ability to bind recombinant HER2 as well as human and mouse FcγRI, explored their in vitro behavior with HER2-positive BT474 human breast cancer cells, and evaluated their in vivo performance in two different mouse models of HER2-expressing human breast cancer, including one using humanized NSG (huNSG) mice. The gene discussed is ERBB2; the disease is breast cancer.