Immunologic quantitation of the carcinoma specific human carcinoma antigen in clinical samples

Based on the cross-reactivity of the human carcinoma antigen, HCA, with epiglycanin, a mouse mammary carcinoma cell surface glycoprotein, HCA has been detected in the tissue and blood of patients with every type of epithelium-derived cancer tested.

Competitive binding assays utilized the following antiepiglycanin antibodies: a polyclonal rabbit antiserum (immunoglobulin [Ig] G and IgM) in a radioimmunoassay; mouse monoclonal antibodies (Ab-1, IgM) on immunoplates; anti-idiotypic (Ab-2) and anti-anti-idiotypic (Ab-3) monoclonal antibodies (both IgG) from spleen cells of C57BL mice immunized, respectively, with Ab-1 and Ab-2, and utilized on immunoplates. IgG and IgM antibodies were evaluated for their ability to detect HCA and to distinguish between the blood of patients with, or without, carcinomas.

Assays with the rabbit antiserum distinguished plasmas of metastatic breast carcinoma patients from those of patients with benign breast disease with a sensitivity of approximately 93% (specificity 90%). Antiepiglycanin IgM monoclonal antibodies (i.e., AE3) showed high specificity and sensitivity (> 90%) with sera from advanced carcinoma patients when compared with normal sera. The IgG anti-anti-idiotypic (Ab-3) monoclonal antibodies (i.e., AF2), which bind the same epitope as Ab-1, appear to possess less nonspecific binding capacity, however, than the Ab-1 (IgM) antibodies. Anti-Ab-1 (i.e., C8F2) anti-idiotypic monoclonal antibodies, which bear an idiotope equivalent to the epitope present in epiglycanin and the HCA, demonstrated greater consistency as a standard calibrator and for coating wells than epiglycanin.

The concentration of the HCA in the body fluids of patients with carcinomas may be accurately determined by competitive binding assays. It is suggested that the use of anti-idiotypic antibodies (IgG), rather than epiglycanin/HCA, and Ab-3 anti-anti-idiotypic antibodies (IgG), rather than Ab-1 (IgM), will improve the consistency, as well as the sensitivity and specificity, of the assay.