Author: Isobel Ozra Khoshbooie
Khoshbooie, Isobel Ozra, 2024 Engineering probiotic bacteria to express vaccine derived antigens to enhance immune responses to vaccination, Flinders University, College of Medicine and Public Health
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Immune responses to vaccination are highly variable between different individuals and within any given population. Further, those most vulnerable to infectious often show suboptimal immune responses to vaccination, leaving them more susceptible to infection following vaccination. Thus, developing strategies that can enhance vaccine-specific immune responses would be an enormous benefit. Most licensed vaccines are delivered intramuscularly and only induce a systemic immune response, however, they do not prime an immune response at mucosal tissues. This is a major limitation of current vaccine technologies as mucosal-induced immunity generates a resident B and T cell response and the production of mucosal Immunoglobulin (Ig) A which, combined, provide protection at the entry site for many vaccine-targeted pathogens. A challenge in developing strategies that promote mucosal immunity is finding a delivery method for the antigen of interest that is immunogenic enough without driving potentially harmful inflammation. Recent evidence suggests that the commensal bacteria that occupy our mucosal surfaces are a major source of foreign antigen that can prime effector and helper T cell responses, are capable of priming microbiota-pathogen cross-reactive T and B cell responses within mucosal tissue. Importantly, the priming of these cross-reactive responses seemingly occurs in the absence of inflammation, suggesting that commensal bacteria may be the perfect vehicle for the delivery of antigen to mucosal tissues to safely prime an antigen-specific immune response. Thus, I conclude that this potential mechanism can be exploited by engineering a commensal / probiotic bacterium to express antigen of interest. I hypothesized that treating specific opportunistic pathogen free (SOPF) mice with an engineered probiotic bacterium expressing a vaccine-derived antigen will prime vaccine specific immunity in mucosal tissues and enhance vaccine specific immune responses upon subsequent vaccination. To investigate this, I constructed a pUC57 plasmid to express Ovalbumin- (Ova) derived peptides in the bacterial cytoplasm and transformed this plasmid into the probiotic Escherichia coli Nissle 1917 (EcN) strain (EcN-Ova Cyto). Two weeks prior to intramuscular vaccination with an mRNA-Ova vaccine I demonstrated that there was a significant increase in vaccine-specific IgGtotal and IgM in the serum, and vaccine-specific IgA in the faces. Additionally, EcN-Ova treated mice had significant increase in splenic germinal Centre B cells, and antibody secreting cells. These finding confirmed that probiotic bacteria (EcN) engineered to express vaccine-derived peptides can enhance subsequent immune response to vaccination. To confirm these observations in a more relevant model of vaccination, I expressed a component of the polysaccharide conjugate vaccine-13 valent (PCV13) cross-reactive material 197 (CRM) in the Escherichia coli strain BL21 and administer it to mice prior to vaccination with PCV13. Despite successful expression of CRM as a full-length protein on the surface of BL21 we saw no major differences in the outcome of PCV13 vaccination in mice. Together my data demonstrates that probiotics engineered to express vaccine-derived antigens can alter subsequent immune responses to vaccines containing the same antigen. However, careful consideration of the bacterial strain used, and the nature of the antigen expressed in the bacteria, may be required to exploit this mechanism to its full potential.
Keywords: Engineering probiotic bacteria, Antigens, Enhance, Immune response, Vaccination
Subject: Medical Biotechnology thesis
Thesis type: Masters
Completed: 2024
School: College of Medicine and Public Health
Supervisor: Professor David Lynn