Development of antimicrobial vaccines and monoclonal antibodies against carbapenem-resistant Acinetobacter baumannii
File(s)
Author(s)
Higham, Sophie
Type
Thesis
Abstract
Acinetobacter baumannii is a Gram negative bacterium associated with high levels of antibiotic resistance and difficult to treat hospital acquired infections such as ventilator associated pneumonia. The development of carbapenem resistance by A. baumannii has left colistin as a last resort antibiotic treatment option. However, colistin resistance is developing resulting in an urgent requirement for the development of new antimicrobials and preventatives. Using clinically relevant A. baumannii isolates from ventilator associated pneumonia patients in Vietnam, a robust and reproducible murine respiratory infection model was developed. Intranasal challenge of mice resulted in significant weight loss, inflammation and bacterial burden. Outer membrane vesicles naturally produced by A. baumannii clinical isolates were used to immunise mice intramuscularly, subcutaneously and intranasally. Immunisation with OMVs provided high levels of protection against challenge, reducing weight loss and bacterial burden with intranasal immunisation being the most protective and completely preventing bacterial dissemination. Using serum from immunised mice to measure reactivity, three highly conserved antigens were identified using phage expression cloning and western blotting. The three proteins FilF, OXA-23 and PAL showed high levels of similarity across different A. baumannii strains collected from the National Center for Biotechnoloy Information database and potential for use in future vaccine development. Fully human monoclonal antibodies generated using the Kymouse platform at Kymab were raised against OMVs from the same clinical strains. These mAbs were tested in the infection model, showing mixed results. An antibody directed to the carbohydrate capsule antigen was the most effective at reducing disease severity. This work developed clinically relevant in vivo infection models in BALB/c mice that allowed for effective testing of the use of OMVs as vaccines against respiratory A. baumannii infection. Intramuscular and subcutaneous vaccination with OMVs provided some protection against challenge but intranasal vaccination was the most effective. OMVs delivered intranasally in a prime boost approach prior to challenge led to a significant IgA response and more effective protection against challenge which was most likely due to a stronger mucosal immune response. The three potential vaccine antigens identified require further testing to determine if they have any protective efficacy in vivo. Additionally, individual antibodies showed mixed results when tested in vivo with capsular targeting antibodies being more effective than protein or lipooligosaccharide targeting antibodies, which could be due to capsule preventing antibody binding to the target. The work performed within this thesis highlighted the importance of immunisation route and the likelihood of a multivalent approach being the most efficacious for future A. baumannii vaccine and monoclonal antibody development.
Version
Open Access
Date Issued
2022-12-23
Date Awarded
01/07/2023
License URL
Advisor
Tregoning, John S
Reece, Stephen
Kellam, Paul
Sponsor
Biotechnology and Biological Sciences Research Council (Great Britain)
Medical Research Council (Great Britain)
Grant Number
4050789012
Publisher Department
Department of Infectious Disease
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)