Multiformat T-Cell-engaging bispecific antibodies targeting human breast cancers

Four different formats of bispecific antibodies (bsAbs) were generated that consist of anti-Her2 IgG or Fab site-specifically conjugated to anti-CD3 Fab using the genetically encoded noncanonical amino acid. These bsAbs varied in valency or in the presence or absence of an Fc domain. Different valencies did not significantly affect antitumor efficacy, whereas the presence of an Fc domain enhanced cytotoxic activity, but triggered antigen-independent T-cell activation. We show that the bsAbs can efficiently redirect T cells to kill all Her2 expressing cancer cells, including Her2 1+ cancers, both in vitro and in rodent xenograft models. This work increases our understanding of the structural features that affect bsAb activity, and underscores the potential of bsAbs as a promising therapeutic option for breast cancer patients with low or heterogeneous Her2 expression. Bispecific antibodies are highly effective for targeting breast cancer cells with antigens of low abundance. It is suggested that the monovalent BiFab in the absence of an Fc domain may be the best bispecific antibody format to trigger antigen-dependent T-cell activation and target tumor eradication for low or heterogeneous Her2-expressing cancers.