OFA-I (oncofetal antigen-immunogenic) was first described in 1976 as a major tumor-associated antigen that was present on human cancer cells and fetal brain tissues. Although the amount of this antigen is consistently higher on tumors and fetal brain tissues, we later detected the antigen in adult brain and tissues of neural crest origin. OFA-I stimulates an appreciable immune response in man. We have developed two human monoclonal antibodies to OFA-I. These antibodies were produced by human B-lymphoblastoid cell lines (L55 and L72) immortalized by Epstein-Barr virus (EBV). Antibody produced by the L55 cell line reacts to an antigen (OFA-I-1) expressed on a variety of human cancer tissues. Antibody produced by the L72 cell line reacts to an antigen (OFA-I-2) on tumors of neuroectodermal origin. The chemical nature of OFA-I-1 was identified as the ganglioside GM2, and of OFA-I-2 as the ganglioside GD2. L72 has produced anti-GD2 antibody for the entire period of our observation (5 years), whereas antibody production by L55 eventually ceased during its long-term culture. The antibody production of both lines was relatively low, up to 5 to 10 micrograms of IgM/ml. Therefore, the projects set for the current research are: (1) augmentation of production of antibody from L72 and L55 cells by fusing these cells with human myeloma or lymphoid cells to form hybrids and by inoculating L55, L72, or the hybrid cells in immunologically suppressed animals; (2) establishment of new B-cell lines stable for the production of human monoclonal antibody to GM2 by EBV transformation techniques; (3) the production of a third human monoclonal antibody, antiganglioside GD3 antibody. GD3 is one of four gangliosides, GD2, GM2, GD3, and GM3, expressed by human melanomas, and our preliminary test has suggested that GD3 induces immune responses in man; and (4) the immunoglobulin class of the anti-GD2 and anti-GM2 are IgM. In the current research, we will investigate the feasibility of the production of human IgG monoclonal antibodies to GD2, GM2, and GD3. Production of both immunoglobulin classes to these melanoma-associated gangliosides should for the first time provide us with human monoclonal antibodies for immunodiagnosis and treatment of melanomas and other human cancer. (AG)
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