Abstract B62: A novel combination HER2, brachyury, and MUC1 adenovirus based vaccines for a multitargeted immunotherapy approach to treat breast cancer
Authors: Latchman Yvette , Rice Adrian , Balint Joseph , Gabitzsch Elizabeth , Schlom Jeffrey , Jones Frank 
Published: May 2016

Abstract
Many studies have shown that most breast cancers express a diverse array of tumor associated antigens (TAA), and the ability to simultaneously target multiple TAA as opposed to targeting a single TAA by immunotherapy could be of clinical benefit, especially in terms of breaking tolerance, impacting tumor growth and increasing overall survival. We report here the development and testing of two new recombinant TAA vaccines containing MUC1 and Brachyury that will be combined with our Ad5 [E1-, E2b-]-HER2/neu vaccine as a multi-target immunotherapeutic. MUC1 is a TAA that is over expressed in 70% of breast cancers and has been recognized as a priority TAA target for tumor immunotherapy. One of the major barriers to immunotherapy is the inability to target antigens that are involved in the progression of primary tumors to a metastatic state. Brachyury represents a new and attractive target as it plays an essential role in epithelial mesenchymal transition and targets cancer stem cells. A recently published study showed that Brachyury is over-expressed in breast cancer and is associated with poor prognosis. Our vaccines are based on an Ad5 [E1-, E2b-]- gene delivery platform that has an E1 gene deletion and additional early 2b (E2b) gene region deletions by removing the DNA polymerase (pol) and pre-terminal protein (pTP) genes. Potent T cell and antibody responses can be induced against vector-expressed antigens even in the presence of hyper Ad5 immunity. Using a truncated non-oncogenic HER2/neu gene in our delivery platform, we reported that this product candidate induces HER2/neu directed humoral and T cell directed immune responses. In addition, the Ad5 [E1-, E2b-]-HER2/neu significantly inhibits tumor growth of HER2/neu expressing tumors in a mouse model. This product candidate has been manufactured under cGMP and will initiate Phase I/2 clinical trials to evaluate immunotherapy treatment of patients with HER2+ breast cancer. To characterize our two new vaccines, Ad5 [E1-, E2b-]-MUC1 and Ad5 [E1-, E2b-]-Brachyury, immunogenicity studies were performed in mice. In collaboration with Dr. Jeffrey Schlom at the NCI we have generated an Ad5 [E1-, E2b-]-MUC1c vaccine that is modified with agonist peptides that results in increased immunogenic activity. In our studies, cell mediated immune (CMI) responses were determined by ELISpot assays and intracellular cytokine staining. Robust T cell responses and TNF-α/IFN-γ expressing polyfunctional CD4+ and CD8+ cells were detected in mice immunized with Ad5 [E1-, E2b-]-MUC1c but not control mice. In immunotherapy protocols, significant anti-tumor activity and increased survival was observed in mice bearing MUC1 expressing tumors and treated with Ad5 [E1-, E2b-]-MUC1c. These results indicate that our Ad5 [E1-, E2b-]-MUC1c can induce anti MUC1 directed anti-tumor responses. We have also generated an Ad5 [E1-, E2b-]-Brachyury modified to contain a HLA-A2 binding epitope that increases immunogenicity. After mice were immunized with this vaccine, splenocytes from immunized mice when stimulated with Brachyury peptide pools gave significant T cell responses compared to controls. As seen with our MUC1 vaccine, Ad5 [E1-, E2b-]-Brachyury also induced polyfunctional TNF-α/IFN-γ expressing CD4+ and CD8+ T cells. These results indicate that Ad5 [E1-, E2b-]-Brachyury can induce an immune response in vivo. This study lays the foundation to test whether a multi-targeted immunotherapy employing HER2/neu, MUC1 and Brachyury vaccines can result in greater anti-tumor activity against established tumors as well as prevent the development of metastatic disease in breast cancer patients.
Citation Format: Yvette Latchman, Adrian Rice, Joseph Balint, Elizabeth Gabitzsch, Jeffrey Schlom, Frank Jones. A novel combination HER2, brachyury, and MUC1 adenovirus based vaccines for a multitargeted immunotherapy approach to treat breast cancer. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr B62.