| Popis: |
Cancer vaccines are a novel method of treating cancer by harnessing the patient's own immune system to recognise and attack malignant cells. Viral vectors can be used to encode tumour antigens to be presented to the immune system. However this field is hindered by immunity to the viral vectors themselves, which are often more immunogenic than tumour antigens. This thesis describes the production of a novel cancer vaccine based on murine leukaemia retrovirus (MLV), where the enveloped vaccine particles express only tumour antigens on the surface with internal viral proteins physically shielded from B cells. This is designed to stimulate B cells specific for the weak tumour antigens by exploiting T cell recognition of strong viral MHC class II epitopes to confirm their activation. Having cloned tumour antigens HER2 and 5T4 into the genome of MLV, the recombinant virus particles were purified and characterised thoroughly to ensure correct expression and presentation of tumour antigens. A vaccination schedule was also optimised, involving a homologous prime-boost strategy. Several prime vaccines were trialled with different results, highlighting the importance of priming CD4+ T cells and avoiding off-target effects. In vivo testing of the vaccine particles in BALB/c mice showed that mice with pre-existing immunity to MLV (those that were "primed" beforehand) had higher antibody responses against the tumour antigen than non-primed mice. This supports the hypothesis that the presence of viral specific T cells will amplify the immune response to the tumour antigen after the subsequent "boost" vaccination, based on the requirement for T cell help for B cell activation and antibody production. This thesis demonstrates that tolerance to endogenous tumour antigens can be overcome by using a self-adjuvanting viral vaccine particle. This method of homologous prime-boosting has important implications for cancer vaccination and immunotherapy. |
