Characterization of two human small cell lung carcinoma-reactive monoclonal antibodies generated by a novel immunization approach.

Two human small cell lung carcinoma cell lines, NCI-H69 and NCI-H128, were used as alternating sources of immunogen to generate monoclonal antibodies to small cell lung carcinoma-associated antigens. BALB/c mice were sensitized with seven injections of live tumor cells, four with NCI-H69 cells and three with NCI-H128 cells. Somatic cell hybridization was performed by fusion of the immune murine splenocytes using syngeneic myeloma cells from the SP2/0 Ag14 cell line. Hybridoma colonies were screened against small cell lung carcinoma cells and normal lung fibroblasts with an enzyme-linked immunosorbent assay. Compared to animals immunized with only NCI-H69 or NCI-H128 cells, alternate immunization resulted in the generation of a significantly higher number of hybridomas that reacted selectively with both tumor cell lines. Monoclonal antibodies from two reactive hybrid clones generated by alternate immunization, SCLC 2051 and SCLC 5023, were uniformly negative to normal human tissues including lung, kidney, liver, spleen, breast, thyroid, brain, small intestine, and colon. While both monoclonal antibodies were nonreactive to paraffin-embedded, formalin-fixed, nonmalignant lung biopsies, the monoclonal antibody SCLC 5023 reacted with tumor cell infiltrates in biopsies from small cell lung carcinoma patients (14 of 14 cases positive), using the immunoperoxidase technique. This monoclonal reagent also reacted with other lung tumor cell types, including atypical carcinoid (5 of 5 positive), epidermoid (4 of 6 positive), undifferentiated and bronchoalveolar (3 of 4 cases each positive) carcinomas. By contrast, monoclonal antibody SCLC 2051 apparently identified an antigen expressed preferentially on small cell lung carcinoma cells (12 of 14 positive) and only rarely reacted with other lung tumor cell types (2 of 34 positive). Both monoclonal antibodies were negative to colon carcinoma, epidermoid carcinoma of the floor of the mouth, breast adenocarcinoma, and B- and T-cell leukemia and lymphoma cells, as determined by the enzyme-linked immunosorbent assay, indirect immunofluorescence, and immunoperoxidase techniques. These observations suggest that SCLC 2051 and SCLC 5023 may be of value in identifying tumor-associated antigens expressed in small cell and other lung carcinomas. In addition, the generation of antibody-producing cells towards common tumor-associated antigens may be enhanced by immunization with multiple tumor cell lines of the same histological type.