Novel polyhydroxyalkanoate beads for use as a vaccine against tuberculosis : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Microbiology at Massey University, Manawatū, New Zealand

Abstract

Tuberculosis was in 1993 declared as a re-emerging disease by the World Health Organization. The only vaccine currently available, BCG, an attenuated strain of Mycobacterium bovis, does not protect adults against the pulmonary disease, which is the form of transmission. New vaccine candidates are being developed to provide protection against tuberculosis. Subunit vaccines offer a safer alternative than whole cell preparations and provide the possibility of utilizing only the components that mediate protective immune responses. This thesis describes the production of bacterially derived polyhydroxyalkanoate (PHA) beads for use as a delivery system for Mycobacterium tuberculosis reverse vaccinology antigens and immune modulators. In the first study, the immunogenicity of beads derived from an endotoxin-free host, Clear coli, displaying M. tuberculosis antigens Rv1626, Rv2032 and Rv1789 was evaluated in mice. Beads displaying Rv1626 were selected for further studies based on the magnitude and specificity of the immune response elicited. In a final study, the immune modulators Cpe30, CS.T3378-395 and Flagellin were co-displayed with Rv1626 antigen on beads and the immunogenicity of these functionalised beads evaluated in mice. Vaccinations with Rv1626 beads and the immune modulators Cpe30 and CS. T3378-395 induced a Th1/Th17 skewed immune response. These beads were then assessed for their ability to protect mice against aerosol challenge with Mycobacterium bovis. Rv1626 beads reduced the bacterial loads in 0.48 log10 compared with the negative control group but the inclusion of immune modulators did not enhance the immunogenicity or protection induced by Rv1626 beads. This study has demonstrated the potential of PHA beads delivering a single reverse vaccinology antigen for protection against tuberculosis infection in mice. While the co-display of immune modulators did not improve the protection induced by the antigen, further studies are needed to determine optimal doses for delivery of immune modulators to enhance protective immunity.