Humoral response of melanoma patients to two different tumor‐associated antigens

Sera of 8 stage II melanoma patients undergoing surgical adjunctive immunotherapy with bacille Calmette Guérin (BCG) plus melanoma cell vaccine (MCV) were assayed for humoral response by the complement-dependent antibody cytotoxicity (CDAC) assay and by the microcomplement fixation (MCF) test. The patients developed high levels of cytotoxic (CTX) and complement-fixing (CF) antibodies to the UCLA-SO-M14 (M14) cells, one of the three melanoma cell lines in the MCV. Significant rises in CTX and CF antibodies occurred one month post-immunotherapy. While the level of CTX antibodies was maintained for 11 months thereafter, the titer of CF antibodies was sustained for seven months, then gradually declined. When the sera were absorbed with lymphoblastoid (ML14) cells which are autologous to the M14 cells, two residual peaks of CTX antibodies, one and four months postimmunotherapy and two peaks of CF antibodies, one and seven months postimmunotherapy, emerged. Two sera that exhibited high levels of CTX and CF antibodies one month postimmunotherapy were absorbed with ML14 cells and human fetal brain tissue. The reactivity of one serum in both the CDAC and MCF assays were abolished, whereas the reactivity of the other serum was not significantly diminished in either assay. These data indicate that the stage II post-surgical melanoma patients developed a humoral immune response to at least two distinct tumor antigens on the membrane of the M14 cells. One of these antigens appeared to be of fetal origin (OFA), the other M14-associated (TAA). Both antigens, OFA and TAA, were involved in complement-dependent antibody cytotoxic and complement fixation reactions in vitro.