Polyhydroxyalkanoate beads as a particulate vaccine against Streptococcus pneumoniae and Neisseria meningitidis : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Microbiology at Massey University, Manawatu, New Zealand
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Date
2017
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Massey University
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Abstract
Streptococcus pneumoniae and Neisseria meningitidis are the major causes of
pneumonia and meningitis, respectively, worldwide. Capsular polysaccharide-protein
vaccines (conjugate vaccines) provide protection against these diseases but not protection
against infections caused by serotypes and serogroups not included in these vaccines.
Proteins have been increasingly considered as antigens for vaccine development due to
their more structurally conserved composition when compared to capsular
polysaccharides. Proteins subunit vaccines are safe and protective; however, they have
limitations such as serotype-dependent immunity, and low immunogenicity of the
proteins, requiring adjuvant to be included in these formulations or delivery systems that
enhance the desired immune response. In addition, complex production procedures are
required, increasing production costs and therefore market prices making these vaccines
inaccessible for many people affected by these diseases. Recently, bacterial storage
polymer inclusions have been developed as protein antigen carriers.
Polyhydroxyalkanoate, in particular 3-polyhydroxybutyrate (PHB) inclusions have been
successfully bioengineered to display antigens from pathogens like Mycobacterium
tuberculosis and Hepatitis C virus. These particulate vaccine candidates elicited both a
Th1 and Th2 immunity patterns combined with a protective immune response against
Mycobacterium bovis in mice.
This thesis focuses on the study of polyhydroxybutyrate (PHB) beads properties as
a carrier/delivery system engineered to display antigens from extracellular bacteria. The
antigens Pneumococcal adhesin A, Pneumolysin (proteins) and 19F capsular
polysaccharide (CPS) from Streptococcus pneumoniae, and Neisserial adhesin A, factor
H binding protein (proteins) and serogroup C CPS from Neisseria meningitidis were
displayed on the PHB bead surface. These antigenic proteins were produced as fusion
proteins on the PHB bead surface, while the CPS was covalently attached by chemical
conjugation. Mice vaccinated with these PHB beads produced strong and antigen-specific
antibody levels. In addition, splenocytes from the same mice generated both IL-17A and
IFN-ɣ production.
The antibodies elicited against antigenic pneumococcal proteins were able to
recognise the same protein in the context of an Streptococcus pneumoniae whole cell
lysate from more than six different strains, while antibodies produced after vaccination
with 19F CPS conjugate to PHB showed high opsonophagocytic titers against the
homologous strain. In the case of Neisseria meningitidis, bactericidal antibodies were
elicited in mice vaccinated with PHB beads displaying proteinaceous and CPS antigens.
Overall, this thesis shows that PHB as particulate vaccine candidate holds the
promise of a broadly protective vaccine that can be produced cost-effectively for
widespread application to prevent diseases caused by Neisseria meningitidis and
Streptococcus pneumoniae.
Description
Listed in 2018 Dean's List of Exceptional Theses
Keywords
Vaccines, Biotechnology, Streptococcus pneumoniae, Neisseria meningitidis, Dean's List of Exceptional Theses