par Bossi, Lorenzo 
Président du jury Vanhamme, Luc
Promoteur Andris, Fabienne
Co-Promoteur Giltaire, Severine GS
Publication Non publié, 2024-06-14
Président du jury Vanhamme, Luc
Promoteur Andris, Fabienne
Co-Promoteur Giltaire, Severine GS
Publication Non publié, 2024-06-14
Thèse de doctorat
| Résumé : | Vaccines are a promising strategy to tackle the issue of antibiotic resistant bacteria. In this thesis I tried to give insights regarding two novel vaccine candidates for the multidrug resistant pathogens Burkholderia pseudomallei and Acinetobacter baumannii. For both bacteria, there are many candidate vaccines that are being currently evaluated but none of them is approaching advanced phases of clinical trials. Subunit vaccines targeting proteins exposed on the outer membrane of gram-negative bacteria are attractive. In the study regarding B. pseudomallei, we took into consideration the outer membrane protein W (OmpW). This novel antigen has been shown protective in mice. My work assessed the reactivity of the antigen in the in vitro human context. We observed that despite inducing very low maturation of human dendritic cells, OmpW induced T cell proliferation in twenty donors covering distinct HLA alleles. These results show that a T cell repertoire is present in human peripheral blood cells reacting to OmpW. As the antigen preparation induced very low maturation of human dendritic cells by itself, it may be advisable to combine it with adjuvants with known safety profiles. These results pave the way for a possible clinical evaluation of this vaccine platform.The action of the innate immune system, mainly neutrophils, against A. baumannii infection was proved to be very important but the role of the adaptive immune response against this bacterium is not clarified. Our approach was directed to dissect the contribution of various actors of the adaptive immune system and to assess the efficacy of a vaccination platform using Heat-Killed (HK) bacteria. For the first goal we used a series of mice deficient for various actors of the adaptive immune system. The deficiencies that led to the poorest survival upon A. baumannii infection were the ones for IL-17RA, γδ T cells and CD8+ T cells. Particularly mice deficient of γδ T cells and IL-17RA were all dying after 24h. By qPCR we compared the cytokine production of the wild type with IL-17RA and γδ T cells KO. In WT mice, we observed the presence of IL-1β, IL-6 and TNF upon bacterial infection both at 4h and 24h with stronger stimulation due to the HK bacterium. We also detected IFN-γ at 24h upon live infection and IL-17 family cytokines (IL-17A, IL-17F and IL-22) especially at 4h post HK bacterial stimulation. Several hypotheses can be made for the susceptibility of these mice and further investigation is required.Regarding the second aim, HK bacteria were used for immunisation and this approach could protect both WT and the hereabove indicated immunodeficient mice from a lethal challenge with live bacteria. To further enhance the study of this vaccine strategy, we evaluated the immune response of human peripheral blood cells to the HK bacterium. We showed that HK A. baumannii induced human dendritic cells (DC) maturation in vitro, as assessed by up-regulation of costimulatory membrane receptors (CD40, CD80, CD83 and CD86). This maturation was accompanied by the production of IL-23 (a Th17 polarizing cytokine). T cell activation monitoring showed that CD4+, CD8+ and γδ T cells proliferate and produce IFN-γ, IL-17A and TNF in the presence of the HK bacterium. Altogether, these results indicate that HK A. baumannii is capable of inducing dendritic cells maturation and activating T cells. Protective in vivo response in mice and in vitro activation of human T cells and dendritic cells make this platform possibly suitable as a human vaccination strategy. Overall, our results enhance the knowledge of two promising candidate vaccine for two multidrug resistant pathogens, complementing their evaluation in mice with in vitro human studies. |
