Polyclonal antibodies against gp185(HER2) peptides: Their putative role inthe identification of a particular HER2 status in patients with breast cancer

The HER2 oncogene and its relative oncoprotein, gp185(HER2), a transmembran e glycoprotein belonging to the epidermal growth factor receptor family, ar e overexpressed in a wide range of solid tumors including breast and ovaria n cancer. In patients with breast cancer, both humoral and cell-mediated HE R2 immune responses have been found as well as in some patients with gp185( HER2) nonoverexpressing tumors. To establish whether peptide sequences iden tified as HLA-A2-restricted T-cell epitopes are expressed in breast tumor c ell lines and tissues, we produced and characterized by different methodolo gic approaches polyclonal antibodies raised against four gp185(HER2) peptid es. Two of the antibodies recognized peptides eluted from the HLA-A2 groove of the mDAmB231 breast cancer cell line expressing a basal level of gp185( HER2). Paraffin-embedded primary and metastatic breast tumors were specific ally immunostained by all four reagents, thereby showing an overlapping rea ctivity. When this immunoreactivity was compared with that obtained using t wo different monoclonal antibodies, in 105 breast primary tumors and 36 cor responding lymph node metastases, we identified a subset of tumors that wer e negative with anti-gp185(HER2) monoclonal antibodies and positive with th e four antipeptide antibodies. Our novel observations provide in vivo evide nce of the complexity involved in evaluating HER2 expression, and open a ne w path for understanding the biologic significance of HER2 status in breast tumors.