Assessment of immunological responses to tumour antigens relevant to the development of therapeutic cancer vaccines

• Main Author: Rane, S.
• Published: Nottingham Trent University 2015
• Subjects: 616.99
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.686900

P53 protein that has been referred to as the "guardian of genome". It acts to suppress tumour development through mechanisms involving cell cycle arrest, DNA repair, senescence and apoptosis. Loss of the tumour-suppressive activity in p53 is a frequent event, occurring in more than 50% of all types of human cancers, mostly via point mutations. This very common genetic event is often associated with trans-dominant suppression of the wild type (wt) p53 or gain of oncogenic function independent of the wt protein. A wide range of p53 mutations are frequently found in the “hot spot” region responsible for promoting carcinogenesis. In the current study, two mutations, located at amino-acid 175 and 273 of the protein, were selected due to the two opposite effects they have on the protein conformation. Indeed, mutation at position 175 linearises the protein completely whereas mutation at position 273 retains the 3D structure of the protein but abolishes the DNA binding site. In both cases the protein loses its tumour suppressor characteristic. We hypothesise that these two mutants will be processed differently and give rise to a different peptide repertoire but maybe with some peptides in common. Therefore, HHDII/DR1 mice were immunised with the cDNA of either of these mutants and responses against predicted peptides were assessed ex-vivo using ELISpot assays. Responses against p53-193-201 was shown to be mutation specific and was not therefore pursued. On the other hand responses against peptides p53-322-329 (class I) and p53-249-264 (class II) could be detected in both the groups and were chosen for further study. Importantly the sequence of these peptides are the same in both human and murine p53 sequences. A vaccination strategy was developed using anti-CD-40 antibody and CpG TLR agonist to enhance the immunogenicity of the selected p53 peptides in the in vivo system. The developed strategy successfully demonstrated prolonged survival of the MC38 (naturally express mutated p53) cell-induced tumour bearer C57BL/6 mice in therapeutic vaccination setting and was found to be associated with enhanced tumour-infiltrating CD8+ lymphocytes (TILs). Prostate cancer (PrCa) is one of the most predominant types of cancer in the UK male population with high morbidity and mortality. Although studied for a long time and having a FDA approved PrCa vaccine (PROVENGE®), due to limitations of the vaccine a robust, and patient specific treatment for PrCa still remains to be determined. P53 is found to be overexpressed and/or mutated in the PrCa and is associated with advanced stage of cancer and age of the patient. In the current study, p53-322-329 (class I) and p53-249-264 (class II) peptides showed immunogenic responses in the patients with various grades of PrCa when assessed using different functional assays. Collectively, identified p53 class I and class II peptides appear to be highly relevant in the context of the PrCa vaccine development. Assessing the p53 mutation status in the cancer patient is essential in the development and success of the immunotherapy.