Monoclonal antibody identifies a distinctive epitope expressed by human multiple myeloma cells

Employing a technology called differential immunization for antigen and ant ibody discovery (DIAAD), we aimed to generate monoclonal antibodies (mAbs) specific to human multiple myeloma (MM) cells. The fundamental principles o f DIAAD rely on the induction of high zone tolerance to the "wild type" (no rmal) antigen, followed by immunization with the modified (diseased) antige n. Because chronic myelogenic leukemia (CML) cells are derived from a linea ge closely related to MM, we immunized mice by contrasting a pool of MM cel ls with CML cells. Monoclonal antibody VAC69 reacted exclusively with MM ce lls, identifying a membrane molecule composed of a single-chain glycoprotei n with a Molecular weight of 78-120 kd. This antigen exhibited narrow tissu e specificity and was not found on human cancers such as prostate, breast, or cervical carcinoma: leukemia, or lymphoma, nor was it seen on normal hum an peripheral lymphocytes or oil Epstein-Barr virus-transformed B-cell line s. By immunohistochemistry, mAb VAC69 showed no binding to antigens express ed on normal human ovary, breast, prostate, lung or colon tissue, nor did i t bind to human breast or prostate cancer. Conversely, mAb VAC69 bound stro ngly to human MM, although showing only slight binding to histiocytes or in flamed cells in human lymph nodes and human tumors of the colon, lung, and ovary. Monoclonal antibody VAC69 also triggered cancer-specific cytotoxicit y in vitro (in the presence of complement) as well as in vivo using a sever combined immunodeficiency model transplanted with human MM. Further studie s showed the ability or mAb VAC69 to be specifically internalized by human MM cells, indicating its potential use for therapeutic intervention in MM b y delivering drugs into cancer cells.