Doherty Institute - Theses
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ItemAn evaluation of charged Pam2Cys-based lipopeptides as novel adjuvants for subunit-based vaccines( 2017)The use of subunit antigens in modern vaccines generally requires the addition of an adjuvant due to the lack of immunostimulatory features that would otherwise allow them to induce strong immune responses. A problem facing the use of classical adjuvants such as Alum is that it is not known for inducing effective Th-1 responses that are important for clearing viral and intracellular bacterial infection. There is a shortage of adjuvants that are appropriate for use in animals including humans and as a consequence there is a wealth of research being carried out to discover and design novel and safe ways of delivering vaccines that will induce strong antibody- and/or cell-based immune responses. The TLR2 agonist-based adjuvant R4Pam2Cys is a synthetic adjuvant with a branched structure that has been shown to enhance humoral and also CD8+ T cell responses when formulated with soluble protein antigens. The studies presented in this thesis describe experiments that were designed to improve the economies of chemical synthesis, with a view to improving manufacturing conditions, and to better understand the role played by geometry of the final Pam2Cys-based adjuvant in its in vitro and in vivo biological activities. The results demonstrate that the efficiency of synthesis process could be improved without affecting biological activity by solid phase assembly of the lipid moiety prior to assembly of the R4 moiety. This also saved consumption, and hence costs, of reagents. The branched structure of the peptide portion of R4Pam2Cys was shown to confer resistance to trypsin hydrolysis and to play an important role in providing optimum binding to protein antigens. Finally R4Pam2Cys was compared with the clinically approved and commercially available hepatitis B virus (HBV) vaccine in which Alum is used to improve immunogenicity of the HBV antigen HBsAg. Clear immunological benefits were apparent using R4Pam2Cys over Alum; not only were better antibody titres obtained but robust CD8+ T cell responses were elicited by HBsAg-R4Pam2Cys complexes whereas the commercially available vaccine elicited few if any CD8+ T cells. The use of R4Pam2Cys also resulted in an improvement of protective efficacy in an animal model against HBV infection when used in prophylactic and therapeutic settings. These are promising findings and encourage the lipopeptide’s future application in development of an HBV therapeutic vaccine.