An IgG human monoclonal antibody reactive with a surface membrane antigen expressed on malignant breast cancer cells

A human IgG3 monoclonal antibody (HMab), F86, that reacts with breast cancer cells was obtained by fusion of antibody-secreting Epstein-Barr virus (EBV)-transformed cells from a draining lymph node with the human fusion partner HMMA2.11TG/O. F86 reacts with an antigen expressed on the surface of five malignant human breast cancer cell lines and several human malignant myelomonocytic cell lines but is not detected on normal peripheral blood mononuclear cells. Studies with tissue sections of a human breast cancer line xenografted in nude mice have demonstrated that the F86 antigen is expressed both on the cell surface and in the cytoplasm of tumor cells. The F86 antigen is also expressed by the tumor cells in the original tumor specimen of a patient from whom one of the test cell lines and the xenografts were derived. Functionally, the F86 antibody does not mediate complement lysis or antibody-dependent cellular cytotoxicity in vitro. The F86 antigen could not be labeled by [35S] methionine or 125I and immunoprecipitated. The nature and expression of antigens such as that detected by the HMab F86 and how they became immunogenic and/or suppress an active immune response can be addressed through the use of HMab.