A rat model system for radioimmunodetection of kappa myeloma antigen on malignant B cells.

A novel experimental model was established in normal rats for studying the localisation and tissue distribution of a murine monoclonal antibody directed against kappa light chain B cell malignancies. The antibody, K-1-21 was raised against human kappa Bence Jones Proteins and reacts with a cell membrane antigen KMA which is restricted to some kappa myeloma and lymphoma cells. In the rat model, kappa or lambda Bence Jones protein-conjugated sepharose was implanted subcutaneously on either flank 24 h before the injection of 131I-labelled K-1-21 or its F(ab')2 fragment. Gamma camera imaging and tissue distribution studies showed specific localisation of the K-1-21 antibody in the kappa sepharose. Injection of F(ab')2 antibody fragments resulted in faster background clearance, earlier delineation of the specific image and significantly higher target to blood ratios than those obtained with the intact antibody. These results suggest that the model may provide an alternative system to tumour xenograft bearing nude mice for studying localisation of antibodies with therapeutic potential.