Analysis of the interaction between a human high molecular weight melanoma-associated antigen and the monoclonal antibodies to three distinct antigenic determinants.

The restricted tissue distribution and the limited heterogeneity that appear in melanoma lesions of the high M.W. melanoma-associated antigen (HMW-MAA) suggest that this antigen may be an appropriate marker for radioimaging, and a useful target for immunotherapy in patients with melanoma. Therefore, in this study we analyzed other characteristics that are important in the selection of reagents for radioimaging and immunotherapy purposes. The affinities of the monoclonal antibodies (MoAB) 149.53, 225.28S, and 763.74T to distinct determinants of the HMW-MAA were found to be at least 1 X 10(8) mol/L. Furthermore, the effects of the concentrations of unlabeled MoAb on the dissociation rates suggest that the binding of MoAb 149.53 and 225.28S to melanoma cells (Colo 38) is preferentially bivalent, whereas that of MoAb 763.74T is preferentially univalent. These results suggest that the latter MoAb is the reagent of choice for assays that make use of soluble HMW-MAA, whereas the former two are the reagents of choice for assays with membrane-bound HMW-MAA, such as imaging with radiolabeled MoAb. The density of the HMW-MAA on cultured Colo 38 melanoma cells appears to be in the range of approximately 5 X 10(6) molecules/cell. The HMW-MAA was not susceptible to MoAb-mediated modulation under a variety of experimental conditions that included various concentrations of modulating MoAb, different incubation times, the use of an anti-mouse Ig antiserum, and the relaxation of equilibrium by diluting cells in MoAb-free medium. These results indicate that the HMW-MAA and the available corresponding MoAb meet the criteria to be reagents for radioimaging and immunotherapy in patients with melanoma.