Augmented Binding Of Radiolabeled Monoclonal Antibodies To Melanoma Cells Using Specific Antibody Combinations

Antigenic heterogeneity may limit effective cancer therapy using monoclonal antibodies (Mabs). To address this problem, combinations of two,three, or four 125I-labeled antimelanoma Mabs (NRML-05, P94, 96.5,and CL207) were incubated in vitro with three different melanoma celllines (HS294t, A375SM, and DX3). Binding of the various Mab combinations was expressed as total cpm/10^5 cells and was compared to bindingof each Mab alone. Saturating amounts (10 μg/ml)of two, three, or fourMabs bound to a significantly greater extent (P < 0.05) than eachindividual Mab except for NRML-05. Combinations of three Mabs at anonsaturating concentration (1.5 μg/ml) bound to a greater extent thansingle Mabs (P < 0.05), depending on the cell line examined and theamount of antigen sites present for each Mab. Saturating or nonsaturatingconcentrations of unlabeled Mab 96.5 combined with 125I-labeled NRML-05 enhanced binding of the latter to HS294t by significantly modifyingits affinity and by increasing the number of binding sites 3-fold. Modulation occurred only at 37°Cand was dependent upon protein synthesis.These data demonstrate that the effectiveness of various Mab combinations over single Mabs varies, depending on Mab concentration and thecell lines used. In addition, one Mab may significantly (P < 0.05) enhancebinding of another Mab to its antigen.