Determination of the immunoreactivity of radiolabelled monoclonal antibody fragments by binding to immobilised antiidiotypic antibodies

Abstract

The feasibility of using immobilised anti-combining site (anti-idiotypic) antibodies as targets for assessing the immunoreactivity of radiolabelled anti-tumour monoclonal antibodies has been assessed. With two anti-tumour monoclonal antibodies (anti-CEA and anti-gp72) it was possible to quantify binding of their 125I labelled Fab fragment preparations to their anti-idiotypic monoclonal antibodies immobilised on cyanogen bromide activated Sepharose. Binding was specific for immobilised anti-idiotypic antibodies reactive with the anti-tumour antibody fragments. Moreover binding was inhibited by unlabelled Fab or intact monoclonal antibody, but not by an irrelevant antibody or its Fab fragment. The use of antiidiotypic antibodies for quantifying immunoreactions of radiolabelled antibodies has advantages over the use of initial target antigen, which may be available only in inconvenient forms, such as cultured tumour cells.