A novel monoclonal antibody-defined antigen which distinguishes human non-small cell from small cell lung carcinomas

Spleen cells from BALB/c mice hyperimmunized with the human epidermoid lung carcinoma cell line T222 were fused with NS-1 mouse myeloma cells to produce monoclonal antibodies to human lung cancer antigens. Hybridoma culture supernatants were tested by an enzyme-linked immunosorbent assay for reactivity against a panel of human lung tumor cell lines. Supernatant from hybridoma EA1 (immunoglobulin G1) displayed strong reactivity with four of four non-small cell lung carcinomas but did not react with three of three small cell lung carcinoma (SCLC) cell lines. This hybridoma was cloned by limiting dilution and utilized to generate ascites antibody for subsequent immunohistochemical and antigen characterization studies. Evaluation of fresh frozen tumor tissue sections by immunoperoxidase staining methods revealed EA1 reactivity with the vast majority of non-SCLCs tested (21 of 21 epidermoid, 17 of 18 adenocarcinomas, four of four large cell, two of two bronchioloalveolar) and no reactivity with nine of nine small cell lung carcinomas. EA1 also stained bronchial epithelium and other benign and malignant epithelial tissues. The EA1 antigen was determined to have a molecular weight of 75,000 by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of human non-SCLC tumor extracts. These data imply that EA1 recognizes a novel antigen expressed by non-SCLCs and other epithelial tissues. The absence of EA1 reactivity with SCLCs suggests that this monoclonal antibody may find future application in distinguishing non-SCLC from SCLC and prove useful in furthering our understanding of the histogenesis of lung carcinomas.