Efficacy of Prototype Vaccines for Prevention of Tuberculosis
Tuberculosis (TB) is a pulmonary disease caused by Mycobacterium tuberculosis, which killed 1.5 million people in 2014. The current TB vaccine, live attenuated Mycobacterium bovis bacille Calmette Guérin (BCG), effectively protects against neonatal TB yet has variable efficacy against pulmonary TB in adults. Consequently, a more effective preventive vaccine is needed. This project aimed to characterise the ability of two innovative new vaccines to improve antigen delivery and induce protective mucosal immune responses against mycobacterial infection in mice. The first vaccine approach employed sustained release of protein antigen together with adjuvants to enhance immunogenicity. To that end, a vaccine comprising the mycobacterial antigen 85B (Ag85B) with poly lactic-co-glycolic acid nanoparticles in a thermoresponsive chitosan gel was developed. This vaccine was hypothesised to prolong antigen exposure, enhancing the development of an effective immune response, and reducing the need for booster vaccinations. The second approach was designed to activate mucosal immune responses, using non-pathogenic Lactococcus lactis as a vector. Genetically engineered to overexpress the model antigen Ovalbumin (Ova) on its surface via a Group A Streptococcus serotype M1 Pilus (L. lactis PilM1-Ova), this prototype vaccine was hypothesised to improve antigen delivery to the mucosal immune system. The chitosan gel vaccine containing Ag85B, and the L. lactis PilM1-Ova vaccine were administered separately to groups of mice. For both vaccines, the activation state and cytokine responses of antigen-specific T cell populations were detected using flow cytometry. Compared to BCG, the chitosan gel vaccine did not induce higher frequencies of activated, proliferating, cytokine-producing, or memory Ag85B-specific T cells, and failed to protect against an intranasal BCG challenge. By contrast, L. lactis PilM1-Ova induced more activated, proliferating, cytokine-producing and memory Ova-specific T cells than recombinant BCG expressing Ova (BCG-Ova). Although L. lactis PilM1-Ova was not protective against intranasal BCG-Ova challenge, this may have been due to slow in vivo growth of the recombinant BCG-Ova. This work suggests that the chitosan gel vaccine requires further development to improve immunogenicity, for example by selecting a different antigen or antigen dose. L. lactis PilM1 shows promise as a vaccine delivery system for TB and is worthy of further studies, ideally with expression of an endogenous mycobacterial antigen to measure vaccine-induced antigen-specific T cell responses and protection against TB.
Advisor: Kirman, Joanna
Degree Name: Bachelor of Biomedical Sciences with Honours
Degree Discipline: Microbiology and Immunology
Publisher: University of Otago
Keywords: Tuberculosis; Vaccines; BCG; Lactococcus lactis; Chitosan gel; PLGA nanoparticles; Ag85B
Research Type: Thesis