Efficient generation of useful monoclonal antibodies reactive with globotriaosylceramide using knockout mice lacking Gb3/CD77 synthase

Efficient generation of useful monoclonal antibodies (mAbs) with high performance in cancer therapeutics has been expected. Generation of mAbs reactive with globotriaosylceramide (Gb3/CD77) was compared between A/J mice and Gb3/CD77 synthase-deficient (A4GalT-knockout) mice by immunizing Gb3-liposome. Specificity and functions of established antibodies were examined by ELISA, TLC- immunostaining, cytotoxicity of cancer cells and immunoblotting. Compared with results with conventional mice, better generation of mAbs with higher functions has been achieved with A4GalT-knockout mice, i.e. acquisition of IgG class antibodies, activities in antibody-dependent cell-mediated cytotoxicity, complement-dependent cytotoxicity, and aggregation activity toward a Burkitt’s lymphoma line Ramos. Binding of mAb k52 induced tyrosine phosphorylation of several proteins in Ramos cells. One of the strongest phosphorylation bands turned out to be c-Cbl. Pretreatment of B cell lines with mAbs resulted in the attenuation of BCR-mimicking signaling. All these results suggested that A4GalT-knockout mice are very useful to generate mAbs against globo-series glycolipids, and that suppressive signaling pathway driven by endogenous Gb3-ligand molecules might be present in B cells.