A glyco-engineered heterodimeric bispecific monoclonal antibody, derived from trastuzumab and pertuzumab, directed against two distinct epitopes of the extracellular dimerization (ECD) domain of the tumor-associated antigen (TAA) human tyrosine kinase receptor epidermal growth factor receptor 2 (HER2; ErbB2; HER-2), with potential immunomodulating and antineoplastic activities. Upon administration, recombinant humanized anti-HER-2 bispecific monoclonal antibody MBS301 simultaneously targets and binds to two separate, non-overlapping epitopes of HER-2. This prevents the activation of HER-2 signaling pathways. Also, by binding to HER-2, MBS301 induces an antibody-dependent cell-mediated cytotoxicity (ADCC) against tumor cells that overexpress HER-2. This results in tumor cell apoptosis and inhibits tumor cell proliferation of HER-2-overexpressing tumor cells. HER-2, overexpressed on a variety of tumor cell types, plays an important role in tumor cell proliferation, differentiation and survival.