Characterization of a new surface epitope specific for human epithelial cells defined by a monoclonal antibody and application to tumor diagnosis.

In an attempt to characterize the antigens attached to cells of a line established from a human squamous cell carcinoma of the tongue (CAL 27), BALB/c mice were immunized with whole CAL 27 cells; hybridomas were then produced using spleen cells of the animals and cells of an NS1 syngeneic myeloma. A hybridoma secreting a monoclonal antibody was obtained (CALAM 27); CALAM 27 was directed against an epitope attached to the CAL 27 cells. CALAM 27, IgG2a, reacted with a membrane antigen specific to all epithelial cells. After immunoprecipitation, this antigen corresponded to two bands (Mr 22,000 and 54,000). Reactivity disappeared when the tissue was embedded in paraffin but was conserved after fixation with acetone or methanol. This antigen was conserved for both benign and malignant epithelial cell pathologies. The action of CALAM 27 was tested on 80 samples of pleural effusions, ascites, and cerebrospinal fluid samples; after conventional cytological examinations, CALAM 27 failed to recognize either reactive mesothelial cells or meningothelial cells. In addition, the cell structure recognized by CALAM 27 is not found on certain lymphoid tissue cells. CALAM 27 also failed to react with small cell carcinoma of the lung. Its strictly epithelial specificity therefore permits its use for the diagnosis of micrometastases of carcinoma in ascites and cerebrospinal fluid, in pleural effusions, and in bone marrow. CALAM 27 may also prove useful in confirming diagnosis of pathologies suspected to be of epithelial origin.