Peptide vaccine strategy for immunotherapy of HER-2/neu overexpressing cancers

HER-2 is a member of epidermal growth factor receptors (EGFR) and preferentially heterodimerizes with other members of EGFR family (EGFR, HER-3, and HER-4) signaling cells for division. In humans, HER-2 is expressed in fetal tissues and is weakly detectable in normal tissues of adults. HER-2 is overexpressed in unmutated form in 3040% of breast and ovarian cancers and to a lesser extent in adenocarcinoma of uterus, cervix, fallopian tube and endometrium [1]. HER-2 overexpression is associated with poor prognosis, aggressive disease and resistance to chemotherapy [2]. Monoclonal antibodies directed against the extracellular domain (ECD) of HER-2 confer inhibitory effects on tumor growth in vitro and in animal models. Phase II and III clinical trials with humanized MAb to HER-2 ECD (HerceptinTM) in patients with HER-2 overexpressing breast cancers were promising. Although HER-2 is a self-protein, HER-2 specific immune responses were detectable in patients with HER-2 positive breast cancer [3]. Therefore, active specific immunotherapy offers the possibility of sustained anti-HER-2 immune responses and is potentially more applicable than passive approaches. We have identified B-cell epitopes in HER-2 ECD by computer aided analyses of protein antigenicity [4]. Four high ranking B-cell epitopes (amino acid sequences 115136, 376-395, 410-429, and 628-647) were synthesized co-linearly with a promiscuous T helper cell epitope from measles virus (sequence 288-302, designated MVF) to enhance immunogenicity and circumvent MHC restriction. High titered antibodies were raised in rabbits by immunization with chimeric B-cell epitopes. These peptide antibodies recognized the native HER-2 receptor and had tumor inhibitory effects on HER-2 overexpressing breast cancer cells in vitro and in xenografted nude mice [5]. To validate a proposed phase Ib vaccine trial in humans, we immunized transgenic mice bearing rat neu gene overexpressing mammary tumors with HER-2 B-cell epitope constructs. At least 50% of these female transgenic mice (Jackson Labs, ME) develop focal mammary tumors by twenty five weeks of age. Rat neu is a human homolog of HER-2 and has 89% amino acid sequence similarity.