BISPECIFIC ANTIBODY-DEPENDENT CELLULAR CYTOTOXICITY OF HER2 NEU-OVEREXPRESSING TUMOR-CELLS BY FC-GAMMA RECEPTOR-TYPE I-EXPRESSING EFFECTOR-CELLS/

A bispecific antibody, MDX-H210, was developed to target cytotoxic eff ector cells expressing Fc gamma receptor type I(Fc gamma RI, CD64) to HER2/neu-overexpressing tumor cells, HER2/neu is an appropriate target for immunotherapy due to the high level of expression of this proto-o ncogene in a variety of malignancies, The expression of Fc gamma RI is limited primarily to cytotoxic immune cells, including monocytes, mac rophages, and cytokine-activated polymorphonuclear (PMN) cells, Theref ore, tumor cells bound with MDX-H210 can be selectively recognized by effector cells with cytotoxic potential, MDX-H210 was prepared by chem ical conjugation of Fab' fragments derived from the HER2/neu-specific monoclonal antibody, 520C9, and the Fc gamma RI-specific monoclonal an tibody, H22, This bispecific molecule demonstrated specific, dose-depe ndent, and saturable binding to both HER2/neu- and Fc gamma RI-express ing cells, A solid-phase immunoassay that demonstrated simultaneous an d specific binding to both antigens was used to confirm the bispecific nature of MDX-H210. Monocytes and PMN cells mediated MDX-H210-depende nt lysis of HER2/neu-overexpressing cell lines derived from breast, ov arian, and lung carcinomas. IFN-gamma treatment of monocytes enhanced antibody-dependent cellular cytotoxicity, whereas IFN-gamma and granul ocyte colony-stimulating factor were required for PILIN cell-mediated tumor cell lysis. In addition, MDX-H210 elicited tumor necrosis factor -alpha secretion from monocytes when cultured in the presence of HER2/ neu-positive target cells, These in vitro data suggest that targeting tumor cells to Fc gamma RI with MDX-H210 may be an effective treatment for malignancies that overexpress HER2/neu. The in vivo cytotoxic pot ential of MDX-H210 may be enhanced by combination therapy with the cyt okines granulocyte colony-stimulating factor and IFN-gamma, which up-r egulate Fc gamma RI expression on cytotoxic effector cells.