TITLE: Identification of Tumor Rejection Antigens for Breast Cancer Using a Mouse Tumor Rejection Model PRINCIPAL INVESTIGATOR:

Pre-menopausal patients whose breast cancers are, in general, estrogen receptor (ER) negative and biologically more aggressive, are particularly in need of novel therapeutic interventions. A breast cancer vaccine to prevent relapse after conventional treatment would be of enormous clinical value. Several cancer vaccine studies have demonstrated that breast cancer patients can develop tumor antigen specific immune responses after a vaccine is given. Most of these approaches target a single immunogenic protein or antigen thus limiting the vaccine to those patients whose tumor expresses that antigen. We propose the development of a multi-antigen vaccine that could potentially benefit any ER negative breast cancer patient; the category of patient at highest risk of relapse. Several high throughput antigen discovery tools have been developed that have greatly helped the identification of immunogenic proteins in breast cancer patients. One such technique, SEREX (serological analysis of cDNA expression libraries) identifies tumor antigens based on spontaneous antibody immunity that can occur in breast cancer patients. To date, over 2,000 tumor antigens have been identified from a variety of cancers using SEREX. In fact, so many tumor antigens have been identified a major question facing tumor immunologists today iswhich antigen will induce anti-tumor immunity? Investigators evaluating immunity to leukemia have recently utilized patients who develop an anti-tumor response after immunotherapy to identify true “tumor rejection” antigens, that is, those immunogenic proteins which, if targeted, would induce an anti-tumor response. This work was possible because one of the treatments of relapsed leukemia is immunotherapy using donor lymphocyte infusions. The investigators could identify which immunogenic proteins were associated with the development of a remission after immunotherapy. Unfortunately, immunotherapy has not yet advanced to a stage in the treatment of breast cancer where we can reproducibly induce tumor regression. We have recently determined that the neu transgenic (neu-tg) mouse can serve as an excellent model for identifying human breast cancer antigens. These mice were genetically engineered to develop breast cancer that is almost identical to human breast cancer. The breast cancers that occur in these mice are ER negative and drug resistant mimicking pre-menopausal breast cancer in women. Preliminary experiments have shown that neu-tg FVB/N mice may share the same pool of tumor antigens with breast cancer patients. Our goal in this proposal is to identify antigens that are associated with tumor rejection. Whereas this study would not be possible in humans, we have recently established a tumor rejection model by implanting the mouse tumors derived from neu-tg mice into the parental FVB/N mouse, who are identical in every way except were NOT engineered to develop breast cancer. In our model, none of the parental FVB/N mice develop tumor while all of the neu-tg mice that received tumor implantation succumb to their disease despite having endogenous immunity to some proteins expressed by the tumor. Interestingly, the tumor rejection that occurs is not solely mediated by immunity to neuthe major cause of the cancer (similar to human HER-2/neu). We proposed to use subtractive SEREX, a method established in the laboratory to screen for antigens that are specifically induced by tumor rejection. The tumor antigens that have immunogenic human homologues will be further studied by using them to vaccinate the neu-tg mice to see if such a vaccine will prevent the cancers. The human homologues of these proteins, identified as described in this proposal, will be the basis for a multi-antigen vaccine to prevent breast cancer relapse in pre-menopausal patients with ER negative breast cancer.