Identification of a malignant cell associated antigen recognized by a human monoclonal antibody

A human X human hybridoma, CLNH11, derived from a lymphocyte of a patient with cervical carcinoma, produces a human monoclonal antibody of gamma 1 and kappa isotypes (CLN-IgG). Immunoperoxidase staining showed that CLN-IgG reacted with frozen tissue sections of human malignant tumors (cervical carcinoma, gall bladder carcinoma, glioblastoma), but not with their normal counterparts. Enzyme-linked immunosorbant assay also demonstrated that CLN-IgG reacted with various human tumor cell lines, but not with non-tumorigenic cells such as some fibroblasts, peripheral blood lymphocytes and red blood cells. Indirect and direct immunofluorescence staining indicated that the tumor antigens recognized by CLN-IgG were located in restricted areas close to the cell surface and exposed on the outer surface of the cell membrane. A protein antigen of Mr 226,000 was purified to homogeneity by affinity chromatography with CLN-IgG from the plasma membrane fraction of A549 lung tumor cell line. The antigen consisted of alpha (Mr 60,000) and beta subunit (Mr 53,000) which were linked by disulfide bond(s) (TA60K/53K). The TA60K/53k antigens were expressed commonly in other tumor cell lines originated from histologically different tissues.