EN2: A Candidate Antigen for the Development of Targeted Therapies in Breast Cancer

Engrailed (En) is a homeodomain-containing transcription factor with a multifunctional role in neural development. In vertebrates there are two engrailed genes, En-1 and En-2, each with their own specific functions. A unique feature of these proteins is their ability to regulate both transcription and translation at different stages of normal development. EN2 is normally involved in brain development in the embryo then silenced in adulthood. However, initial studies have shown that EN2 is over-expressed in a variety of cancers including prostate, ovarian and colon carcinomas. Furthermore, EN2 has been characterised as an oncogene in breast cancer due to its aber- rant expression and its tumor-promoting role in human breast cancer. The oncogenic nature of EN2 and its over-expression specifically in tumours makes it an ideal immunotherapeutic target. To date we have confirmed by immunohistochemistry on high density tissue arrays that EN2 protein is expressed in >90% of early and late-stage breast cancer including triple nega- tive breast cancers. In addition, we have shown that EN2 pro- tein is immunogenic. Cell-mediated immune responses to EN2 have been generated in vitro from HLA-A2 positive healthy donors and the EN2 epitopes inducing the response identified. Importantly, these EN2 specific T cells were able to recognise and kill breast cancer cell lines in an HLA-restricted manner. Preliminary work has also demonstrated an antibody response to EN2 in a significant proportion of breast cancer patients de- rived from three independent cohorts. To our knowledge this is the first study demonstrating the human immune reactivity to this protein EN2. The key role of EN2 in breast cancer develop- ment, its over-expression specifically in breast tumours and its immunogenicity makes it an interesting antigen to exploit as a novel target for breast cancer immunotherapy.