BISPECIFIC HER2 X CD3 ANTIBODIES ENHANCE T-CELL CYTOTOXICITY IN-VITROAND LOCALIZE TO HER2-OVEREXPRESSING XENOGRAFTS IN NUDE-MICE

Recently, we reported the development of fully humanized bispecific F( ab')(2) antibodies with dual binding specificities to human T-lymphocy tes and to tumor cells overexpressing HER2. These antibodies were show n to effectively mediate targeted HER2-overexpressing tumor cell killi ng by freshly isolated human T-cells. In this report we extend our stu dies to describe the interaction of the bispecific antibody with activ ated 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-a ffinity CD3 surface markers that bound to bispecific antibody with a K -d of 2.49 nM and exerted cytolytic activities against targets overexp ressing HER2. In addition, we demonstrated the specific localization o f HER2 x CD3 bispecific antibody to HER2-overexpressing tumor xenograf ts in nude mice. Furthermore, HER2 x CD3 bispecific antibody has the a bility to inhibit the proliferative activities of breast tumor (SKBR-3 ) cells in. vitro. The clinical implications of these data are discuss ed. (C) 1995 Academic Press, Inc.