Melioidosis is a potentially fatal bacterial disease caused by Burkholderia pseudomallei and is estimated to cause 89,000 deaths per year in endemic areas of Southeast Asia and Northern Australia. People with diabetes mellitus are most at risk of melioidosis, with a 12-fold increased susceptibility for severe disease. Interferon gamma (IFN-γ) responses from CD4 and CD8 T cells, but also from natural killer (NK) and natural killer T (NKT) cells, are necessary to eliminate the pathogen. We previously reported that immunization with B. pseudomallei OmpW (BpOmpW antigen) protected mice from lethal B. pseudomallei challenge for up to 81 days. Elucidating the immune correlates of protection of the protective BpOmpW vaccine is an essential step prior to clinical trials. Thus, we immunized either non-insulin-resistant C57BL/6J mice or an insulin-resistant C57BL/6J mouse model of type 2 diabetes (T2D) with a single dose of BpOmpW. BpOmpW induced strong antibody responses, stimulated effector CD4+ and CD8+ T cells and CD4+ CD25+ Foxp3+ regulatory T cells, and produced higher IFN-γ responses in CD4+, CD8+, NK, and NKT cells in non-insulin-resistant mice. The T-cell responses of insulin-resistant mice to BpOmpW were comparable to those of non-insulin-resistant mice. In addition, as a precursor to its evaluation in human studies, humanized HLA-DR and HLA-DQ (human leukocyte antigen DR and DQ isotypes, respectively) transgenic mice elicited IFN-γ recall responses in an enzyme-linked immune absorbent spot (ELISpot)-based study. Moreover, human donor peripheral blood mononuclear cells (PBMCs) exposed to BpOmpW for 7 days showed T-cell proliferation. Finally, plasma from melioidosis survivors with diabetes recognized our BpOmpW vaccine antigen. Overall, the range of approaches used strongly indicated that BpOmpW elicits the necessary immune responses to combat melioidosis and bring this vaccine closer to clinical trials.
Melioidosis is a fatal disease caused by Burkholderia pseudomallei Gram-negative bacteria. It is the causative of 89,000 deaths per year in endemic areas of Southeast Asia and Northern Australia. Diabetes mellitus is the most risk factor, increasing 12-fold the susceptibility for severe disease. IFN-y responses from CD4 and CD8 T cells, but also from NK and NKT cells are necessary to eliminate the pathogen. Elucidating the immune correlates of protection of our previously described protective BpOmpW vaccine is an essential step of any vaccine before clinical trials. Thus, we immunized non-insulin resistant C57BL/6j mice and an insulin resistant C57BL/6j mouse model of Type 2 Diabetes (T2D) with BpOmpW using Sigma Adjuvant System (SAS) (treatment) or SAS only (control). Two weeks later bloods and spleens were collected and serological analysis & in vitro exposure of splenocytes to the antigen for 60 hours were performed in both controls and treatment groups to finally analyze the stained splenocytes by flow cytometry. BpOmpW induced strong antibody response, stimulated effector CD4+ and CD8+ T cells and CD4+ CD25+ Foxp3+regulatory T cells and produced higher IFN-y; responses in CD4+, CD8+, NK and NKT cells relative to the control group in non-insulin resistant mice. T cell responses of insulin resistant mice to BpOmpW were comparable to those in non-insulin resistant mice. In addition, as a precursor to its evaluation in human studies, humanised HLA-DR and HLA-DQ transgenic mice elicited IFN-y; recall responses in an ELISPoT-based study and PBMCs from donors that were in contact to BpOmpW for seven days experienced T cell proliferation. Finally, plasma from melioidosis survivors with diabetes recognized our BpOmpW vaccine antigen. Overall, these range of approaches used strongly indicate that BpOmpW elicits the required immune correlates of protection to combat melioidosis and bring the vaccine closer to clinical trials.
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