Strategies to Improve the Efficacy of Vaccines by Selective Manipulation of the Immune System: A Translational Study
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Novel vaccine technologies are needed to induce protective immunity towards sophisticated diseases for which classical whole-cell vaccines have been inadequate. Modern vaccine development builds upon intricate understanding of immunology and disease pathology. Subunit vaccines containing highly purified protein or peptide antigens are safer than classical vaccines and can be developed for infectious and non-infectious diseases. Transitioning between in vitro and in vivo systems during pre-clinical development is daunted by the complexity of the vaccine and multifaceted immune response. In this thesis, translational vaccine research was explored with two projects. In the first project, a novel adjuvant system that can boost antibody responses to vaccines was developed in vitro. A combination of TLR agonists, poly I:C (TLR3) and Pam3CSK4 (TLR1/2), resulted in enhanced B cell activation characterized by expression of surface receptors, cytokine production and proliferation. The combination promoted B cell differentiation into antibody-producing plasma cells and increased their capacity to induce CD4+ T cell activation in a mixed lymphocyte reaction. When used as an adjuvant system for vaccines containing anthrax or influenza protein antigens in vivo, the combination resulted in significantly higher serum antibody titers than vaccines containing either agonist alone. Therefore, the poly I:C/ Pam3CSK4 combination is a promising adjuvant system for humoral vaccines containing protein antigens. The second project describes the development of a combinatorial immunotherapy for cancer using an in vivo model. Anti-tumour immune responses induced by vaccines containing tumour associated antigens are thwarted in advanced cancers by tumour-induced immune suppression. To address this, metronomic cyclophosphamide was evaluated as an immune modulator in combination with an HPV16E749-57 peptide vaccine in mice bearing HPV16-induced tumours. The combination provided significant long-term control of tumour growth. Metronomic cyclophosphamide had a pronounced lymphodepletive effect on the vaccine draining lymph node, yet did not reduce antigen-specific CD8+ T cells induced by the vaccine. This enrichment correlated with increased systemic cytotoxic activity and antigen-specific cytotoxic T cells in the tumour. The results provide important insights into the multiple mechanisms of metronomic cyclophosphamide induced immune modulation in the context of a peptide cancer vaccine that may be translated into more effective clinical trial designs.