PRECLINICAL STUDIES WITH FC-GAMMA-R BISPECIFIC ANTIBODIES AND GRANULOCYTE-COLONY-STIMULATING FACTOR-PRIMED NEUTROPHILS AS EFFECTOR-CELLS AGAINST HER-2 NEU OVEREXPRESSING BREAST-CANCER/

Immunotherapies directed to the proto-oncogene product HER-2/neu, whic h is overexpressed on a subset of breast and other carcinomas, current ly receive considerable attention, We have investigated cell-mediated effector mechanisms of HER-2/neu antibodies against breast cancer cell lines, Compared to unfractionated control blood, whole blood from pat ients during granulocyte colony-stimulating factor (G-CSF) treatment e xhibits significantly enhanced lysis (P < 0.001) of SK-BR-3 cells in t he presence of HER-2/neu antibody 520C9. The extent of tumor cell kill ing correlated positively (r = 0.74) to polymorphonuclear neutrophil ( PMN) blood counts, Fractionation of whole blood into plasma, mononucle ar cells, and PMNs showed major killing capacity to reside in the gran ulocyte fraction. PMNs were efficiently cytolytic with a panel of HER- 2/neu antibodies and against various breast cancer cell lines. Experim ents with blocking antibodies to Fc gamma R documented Fc gamma RII (C D32) as the major trigger molecule for monoclonal antibody 502C9-media ted cytotoxicity, Killing via 520C9 was significantly influenced by an allotypic polymorphism of Fc gamma RIIa, the CD32 molecule expressed on PMNs. In reverse antibody-dependent cell-mediated cytotoxicity expe riments with a panel of HER-2/neu-directed bispecific antibodies, Fc g amma RIII (CD16) proved to be an efficient trigger molecule in blood f rom healthy volunteers, During G-CSF treatment, however, Fc gamma RI ( CD64)-expressed on monocytes and G-CSF primed, but not on healthy dono r PMNs-became the predominant cytotoxic trigger molecule, Thus, G-CSF application increased effector cell numbers for HER-2/neu-directed imm unotherapy, and G-CSF primed PMNs proved particularly effective with a [HER-2/neu x Fc gamma RI] bispecific antibody. These findings support clinical trials with HER-2/neu-directed antibodies in combination wit h G-CSF in breast cancer patients overexpressing HER-2/neu.