Bispecific HER2 × CD3 Antibodies Enhance T-Cell Cytotoxicity in Vitro and Localize to HER2-Overexpressing Xenografts in Nude Mice

Abstract Recently, we reported the development of fully humanized bispecific F(ab′) 2 antibodies with dual binding specificities to human T-lymphocytes and to tumor cells overexpressing HER2. These antibodies were shown to effectively mediate targeted HER2 -overexpressing tumor cell killing by freshly isolated human T-cells. In this report we extend our studies to describe the interaction of the bispecific antibody with activated T-lymphocytes (ATL) maintained in culture for an extended period of time. A microtiter plate radioreceptor assay was used to elucidate the affinity of bispecific antibody binding to ATL. The data show that ATL maintained in vitro for up to 5 weeks continued to express high-affinity CD3 surface markers that bound to bispecific antibody with a Kd of 2.49 nM and exerted cytolytic activities against targets overexpressing HER2. In addition, we demonstrated the specific localization of HER2 × CD3 bispecific antibody to HER2 -overexpressing tumor xenografts in nude mice. Furthermore, HER2 × CD3 bispecific antibody has the ability to inhibit the proliferative activities of breast tumor (SKBR-3) cells in vitro. The clinical implications of these data are discussed.