Investigation of cytomegalovirus-basedcancer vaccines

Cytomegalovirus (CMV) is a highly immunogenic beta-herpesvirus that establishes asymptomatic infection in immune competent individuals. The ability of CMV to induce high frequencies of functional effector memory CD8+ T cells that increase over time (termed ‘memory inflation’) makes this virus an attractive vaccine vector. The primary focus of this thesis is centred on the hypothesis that engineering a CMV-based vector expressing a tumour-associated antigen will be able to induce a robust and long-lived anti-tumour CD8+ T cell response. Using the murine CMV (MCMV) infection model, several MCMV-based vectors were constructed to express the tumour-associated antigens 5T4 and NY-ESO-1, from different locations within the m123-m128 locus of the MCMV genome, which has been associated with the induction of memory inflation. Systemic immunisation with these vectors revealed that induction of tumour-specific CD8+ T cells correlated with high tumour antigen expression during MCMV replication in vitro and in turn, depended on the site of insertion within the MCMV genome. MCMV-based vectors were also examined in prime-boost strategies that incorporated recombinant adenovirus expressing the corresponding tumour-associated antigen. Prime-boost immunisation resulted in the generation of polyfunctional tumour-specific CD8+ T cells that delayed tumour onset. Interestingly, immunisation with the MCMV vector led to an increased influx of lymphocytes infiltrating the tumour. Finally, the immunogenicity of a spread-defective MCMV vector, DgL-MCMV, was investigated upon subcutaneous challenge. Encouragingly, although the magnitude of the response was reduced compared to wild-type MCMV, DgL-MCMV was able to drive memory inflation. Collectively, these data show the importance of vector construction in an effective CMV-based vaccine and highlight the potential of CMV in influencing lymphocyte infiltration into tumours. Ultimately, it provides further evidence of the potential use of CMV as a vaccine vector for cancer therapy