Exploring bacteriophage qbeta virus like particle as a platform for anticancer vaccine development

Vaccination is a powerful strategy to combat different diseases and provide long term immunity with no overt toxicities. Our lab has been exploring the ability of bacteriophage Qβ, a virus like particle (VLP) in eliciting immune response against several antigens. Qβ is an attractive candidate for vaccine applications due to its exceptionally stable and highly organized icosahedral structure. It provides a platform to overcome the low immunogenicity of many peptide antigens and tumor-associated carbohydrate antigens (TACA). This thesis will focus on the design and development of Qβ-based anticancer vaccine against human breast cancer and Bovine Leukemia Virus causing enzootic bovine leukosis. Human Mucin-1 (MUC1) is a high molecular weight transmembrane glycoprotein that is found on the apical borders for luminal or glandular epithelial cellular surfaces of many tissues. Of the ~1.4 million tumor patients diagnosed each year in the US, about 900,000 patients were found to overexpress MUC1 and were associated with poor prognosis compared to those with low levels of MUC1. It can be aberrantly overexpressed (>100-fold) on the cell surface of a wide range of human carcinoma including prostrate, lung, ovarian pancreatic, colon and more than 90% of breast cancer. MUC1 protein is cleaved into two subunits MUC1-N (N-terminus) and MUC1-C (C-terminus), which are associated by non-covalently interactions. MUC1 has thus become a highly attractive target for the development of new anti-cancer agents. In chapter 1, the current MUC1-C based immunotherapies including monoclonal antibodies, peptide vaccines, antibody-drug conjugates and cytotoxic T cells were reviewed for a deeper understanding of MUC1-C glycoprotein as an oncogenic target. In the following chapters (chapter 2 and chapter 3) both domains of MUC1 protein; MUC1-N and MUC1-C were investigated as antigenic epitopes for Qβ-based vaccines against human breast cancer. In chapter 2, a spontaneous mouse breast cancer model (MUC1/MMTV) was developed by crossing mouse mammary tumor virus (MMTV)-polyoma middle T (PyMT) mice with human MUC1 transgenic (MUC1.Tg) mice. While the xenograft tumor model is relatively straightforward to establish, it is unable to represent well the genetic and histological complexity of human tumors. To better mimic the immunosuppressive environment and heterogeneity of human breast cancer, spontaneous tumor models are attractive. The translational potential of the Qβ-tMUC1 vaccine with a short glycopeptide (tMUC1) SAPDT*RPAP (* denotes O-linked glycan) from the MUC1-N domain was evaluated. The Qβ-tMUC1 conjugate produced a robust immune response including binding and killing a wide range of MUC1-expressing tumor cells. It also significantly prolonged the overall survival of MUC1/MMTV mice vaccinated with Qβ-tMUC1 conjugate laying the groundwork for its clinical translation to human patients. In chapter 3, preliminary results for Qβ-MUC1-C vaccine were demonstrated, which explored two MUC1-C epitopes. The MUC1-C vaccine displayed encouraging results to be developed as an anti-metastatic therapeutic candidate.Bovine leukemia virus (BLV) is a C-type retrovirus of cattle that causes huge economic losses with the infection rate escalated in the majority of countries worldwide. The National Animal Health Monitoring System estimated that BLV is present in 89% of US dairy operations. BLV causes enzootic bovine leukosis including frequent persistent lymphocytosis and lymphoma. In chapter 4, an anti-BLV vaccine was developed by constructing a peptide-Qβ conjugate using the envelope glycoprotein gp51 peptide-epitope. The gp51-peptide epitope is known to be putative receptor-binding site and directly implicated in virus infectivity. Qβ-gp51 peptide vaccine construct elicited robust immune response with long lasting antibodies persisting for over 539 days, making it the first BLV peptide-based vaccine candidate to generate such a long-term immunity, an important criterion for an effective vaccine.