Identification of a 220-kDa membrane tumor-associated antigen by human anti-UK114 monoclonal antibodies selected from the immunoglobulin repertoire of a cancer patient

Human monoclonal antibodies (HuMAb) specific for a 14-kDa perchloric acid-s oluble protein (defined as UK114) were produced by somatic fusion of the hu man-mouse myeloma K6H6/B5 with Epstein-Barr virus-transformed peripheral B lymphocytes from a cancer patient previously treated with UK101 preparation s, containing the UK114 protein. Three IgM-secreting clones were selected o n the criteria of specificity for the purified UK114 protein immobilized on to plastic and adapted to grow in a serum-free medium. The reactivity of th ese antibodies showed a broad distribution pattern restricted to fresh tumo r tissues and tumor cell lines, mainly of the adenocarcinoma type. None of the normal cells, nonmalignant cell lines, and normal tissues surrounding t he neoplastic lesions were reactive. The immunochemical analysis of the tar get antigens showed that the HuMAb recognize a molecule of 220 kDa selectiv ely expressed by the surface of tumor cells, as well as a cytoplasmic 14-kD a protein. The 220-kDa antigen was different from other tumor-associated an tigens with similar molecular mass and, so far, unique. In the presence of human complement, two of three HuMAb are cytotoxic for tumor cells expressi ng the 220-kDa surface antigen. The tumor specificity and the lytic ability attributed to these HuMAb are promising features for the exploration of fu ture clinical applications. (C) 1999 Academic Press.