DIFFERENTIAL TUMOR IMMUNOGENICITY OF L1210 AND ITS SUBLINES .1. EFFECT OF AN INCREASED ANTIGEN DENSITY ON TUMOR-CELL SURFACES ON PRIMARY B-CELL RESPONSES INVITRO
The differential immunogenicity of DBA/2 [mouse] lymphoma L1210 and 3 L1210 sublines, each resistant to a different anti-leukemic agent (guanazole, methylglyoxal-bis-guanylhydrazone, and 4,4-diacetyldiphenylurea-bis-guanylhydrazone), was evaluated in vitro. Syngeneic spleen cells from nonimmunized DBA/2 mice were cultured in the presence of graded numbers of irradiated cells of L1210 or its sublines. The stimulation elicited a T[thymus-derived cell]-independent primary antibody response in vitro which was measured by determining the number of plaque-forming cells by using the immunizing lymphoma cells as target. Cells of all 3 sublines exhibited an increased immunogenicity, as compared to that of the parental L1210 cells, in eliciting the response directed to tumor-associated antigens which were common to all sublines. Dose-response experiments showed that high doses of the parental cells stimulated responses which were detectable with subline cells as target. The differential immunogenicity of L1210 and its sublines, as demonstrated in the present assay system, is primarily quantitative, and was apparently due to increased amount or density of common tumor-associated antigens on the subline cells. The implications of these observations are discussed in relation to the possible mechanisms underlying the emergence of highly immunogenic drug-resistant sublines.