Trastuzumab and single hinge cleaved trastuzumab binding to Fcγ receptors and antibody-dependent cellular cytotoxicity activity. (A) Trastuzumab and single hinge cleaved trastuzumab (scIgG-T) binding to Fc gamma receptor (FcγR) I. (B) Trastuzumab and scIgG-T binding to FcγRIIA. (C) Trastuzumab and scIgG-T binding to FcγRIIIA. (D) Antibody-dependent cellular cytotoxicity (ADCC) activity induced by trastuzumab and scIgG-T using the high-HER2-expressing SKOV-3 ovarian cancer cells as target cells and human peripheral blood mononuclear cells (PBMC) as effector cells (n = 3). Cell index was compared after treatment of trastuzumab and scIgG-T for 24 hours. Percentage of cell lysis calculated as: (cell index of control group - cell index of treatment group)/cell index of control group×100. RFU, relative fluorescence units.