DETERMINATION OF THE IMMUNOREACTIVITY OF RADIOLABELED MONOCLONAL-ANTIBODY FRAGMENTS BY BINDING TO IMMOBILIZED ANTIIDIOTYPIC ANTIBODIES

The feasibility of using immobilised anti-combining site (anti-idiotyp ic) antibodies as targets for assessing the immunoreactivity of radiol abelled anti-tumour monoclonal antibodies has been assessed. With two anti-tumour monoclonal antibodies (anti-CEA and anti-gp72) it was poss ible to quantify binding of their I-125 labelled Fab fragment preparat ions to their anti-idiotypic monoclonal antibodies immobilised on cyan ogen bromide activated Sepharose. Binding was specific for immobilised anti-idiotypic antibodies reactive with the anti-tumour antibody frag ments. Moreover binding was inhibited by unlabelled Fab or intact mono clonal 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 tar get antigen, which may be available only in inconvenient forms, such a s cultured tumour cells.