Antigen-specific antibody and polyfunctional T cells generated by respiratory immunization with protective Burkholderia ΔtonB Δhcp1 live attenuated vaccines

BpOmpW antigen administered with CAF01 adjuvant stimulates comparable T cell responses to Sigma adjuvant system

There are no licensed vaccines to protect vulnerable populations from the potentially fatal tropical infection, melioidosis, despite its causative agent, Burkholderia pseudomallei, being endemic in tropical and subtropical regions. A promising vaccine candidate, BpOmpW protected mice from melioidosis infection for up to 81 days and stimulated robust interferon gamma responses in CD4+, CD8+, NK and NKT cells. In order to progress to human studies, selection of an adjuvant with an acceptable human safety profile that stimulates appropriate correlates of protection is essential. Here we demonstrate that the CAF01 vaccine adjuvant elicits optimal immune correlates of protection when administered with our BpOmpW vaccine. Specifically, we demonstrate that CAF01 administered with BpOmpW elicits robust Th1 responses, with potent IFN-γ responses in CD4+ and CD8+ T cells and NKT cells, in addition to Th17 and Th2 responses. This formulation will be particularly effective in protecting susceptible populations including people with type 2 diabetes from melioidosis.

Helper T cell bias following tuberculosis chemotherapy identifies opportunities for therapeutic vaccination to prevent relapse

Therapeutic vaccines have promise as adjunctive treatment for tuberculosis (TB) or as preventives against TB relapse. An important development challenge is the limited understanding of T helper (Th) cell roles during these stages of disease. A murine model of TB relapse was used to identify changes in Th populations and cytokine microenvironment. Active TB promoted expansion of Th1, Th2, Th17, and Th22 cells and cytokines in the lung. Following drug therapy, pulmonary Th17 and Th22 cells contracted, Th1 cells remained elevated, while Th cells producing IL-4 or IL-10 expanded. At relapse, Th22 cells failed to re-expand in the lung despite a moderate re-expansion of Th1 and Th17 cells and an increase in Th cytokine polyfunctionality. The dynamics of Th populations further differed by tissue compartment and disease presentation. These outcomes identify immune bias by Th subpopulations during TB relapse as candidate mechanisms for pathogenesis and targets for therapeutic vaccination.

Intranasal immunization with a Bucl8-based vaccine ameliorates bacterial burden and pathological inflammation, and promotes an IgG2a/b dominant response in an outbred mouse model of Burkholderia infection

Burkholderia pseudomallei is a gram-negative bacterium that is the etiological agent of the tropical disease melioidosis. Currently, there is no licensed vaccine for melioidosis, but numerous candidates are being tested for protective efficacy and characterization of the elicited immune response. Our lab has previously reported the immunogenicity of a Bucl8-protein-based peptide antigen, designated L1-CRM197 (Cross-reacting material 197). When given subcutaneously, this vaccine formulation promoted a strong Th2 (IgG1) antibody response, however immunization did not protect from death. In this study, we hypothesized that an intranasally administered L1-CRM197 vaccine would induce protective mucosal immunity. To evaluate vaccine efficacy, we developed a surrogate Burkholderia infection model that employs outbred CD-1 mice which imitates the immunogenetic diversity of humans. Mice were immunized with either L1-CRM197 adjuvanted with fluorinated cyclic diguanosine monophosphate (FCDG) or with FCDG-only control. These mice were then challenged intranasally with an infectious dose of a luminescent strain of B. thailandensis E264 two weeks post-immunization, and correlates of protection were assessed in euthanized mice on days 1, 2, 3, and 7 post-infection. Overall, intranasal vaccination, compared to subcutaneous administration, induced a stronger Th1 (IgG2a/2b) to Th2 (IgG1) antibody response and promoted anti-L1 nasal, pulmonary, and systemic IgA. Additionally, sera IgG from L1-CRM197-vaccinated mice recognized whole-cell B. thailandensis and B. pseudomallei, a select agent exempt strain Bp82. Vaccination ameliorated disease indicators, including luminescent signal and bacterial cell counts, weight and temperature loss, and organ weight, which negatively correlated with IgG2a antibody levels and mucosa-stimulating cytokines IL-13 and IL-9. L1-CRM197-vaccinated mice also had earlier resolution of inflammatory and tissue-damaging cytokines compared to the FCDG-only controls. These results suggest a balanced humoral and cell-mediated response, along with mucosa-based immunity are beneficial for protection. Future efforts should further assess mucosal cellular and humoral mechanisms of protection and test such protection, using aerosolized B. pseudomallei select agent strain(s).

Heterologous mRNA-protein vaccination with Tc24 induces a robust cellular immune response against Trypanosoma cruzi, characterized by an increased level of polyfunctional CD8+ T-cells

Tc24 is a Trypanosoma cruzi-derived flagellar protein that, when formulated with a TLR-4 agonist adjuvant, induces a balanced immune response in mice, elevating IgG2a antibody titers and IFN-γ levels. Furthermore, vaccination with the recombinant Tc24 protein can reduce parasite levels and improve survival during acute infection. Although some mRNA vaccines have been proven to elicit a stronger immune response than some protein vaccines, they have not been used against T. cruzi. This work evaluates the immunogenicity of a heterologous prime/boost vaccination regimen using protein and mRNA-based Tc24 vaccines. Mice (C57BL/6) were vaccinated twice subcutaneously, three weeks apart, with either the Tc24-C4 protein + glucopyranosyl A (GLA)-squalene emulsion, Tc24 mRNA Lipid Nanoparticles, or with heterologous protein/mRNA or mRNA/protein combinations, respectively. Two weeks after the last vaccination, mice were euthanized, spleens were collected to measure antigen-specific T-cell responses, and sera were collected to evaluate IgG titers and isotypes. Heterologous presentation of the Tc24 antigen generated antigen-specific polyfunctional CD8+ T cells, a balanced Th1/Th2/Th17 cytokine profile, and a balanced humoral response with increased serum IgG, IgG1 and IgG2c antibody responses. We conclude that heterologous vaccination using Tc24 mRNA to prime and Tc24-C4 protein to boost induces a broad and robust antigen-specific immune response that was equivalent or superior to two doses of a homologous protein vaccine, the homologous mRNA vaccine and the heterologous Tc24-C4 Protein/mRNA vaccine.

Hcp1-loaded staphylococcal membrane vesicle vaccine protects against acute melioidosis

Burkholderia pseudomallei is the causal agent of melioidosis, a deadly tropical infectious disease that lacks a vaccine. On the basis of the attenuated Staphylococcus aureus RN4220-Δagr (RN), we engineered the RN4220-Δagr/pdhB-hcp1 strain (RN-Hcp1) to generate B. pseudomallei hemolysin-coregulated protein 1 (Hcp1)-loaded membrane vesicles (^hcp1MVs). The immunization of BALB/c mice with ^hcp1MVs mixed with adjuvant by a three-dose regimen increased the serum specific IgG production. The serum levels of inflammatory factors, including TNF-α and IL-6, in ^hcp1MV-vaccinated mice were comparable with those in PBS-challenged mice. The partial adjuvant effect of staphylococcal MVs was observed with the elevation of specific antibody titer in ^hcp1MV-vaccinated mice relative to those that received the recombinant Hcp1 protein (rHcp1) or MVs derived from RN strain (^ΔagrMVs). The ^hcp1MVs/adjuvant vaccine protected 70% of mice from lethal B. pseudomallei challenge. Immunization with ^hcp1MVs only protected 60% of mice, whereas vaccination with rHcp1 or ^ΔagrMVs conferred no protection. Moreover, mice that received ^hcp1MVs/adjuvant and ^hcp1MVs immunization had low serum TNF-α and IL-6 levels and no inflammatory infiltration in comparison with other groups. In addition, all surviving mice in ^hcp1MVs/adjuvant and ^hcp1MVs groups exhibited no culturable bacteria in their lungs, livers, and spleens five days postinfection. Overall, our data highlighted a new strategy for developing B. pseudomallei vaccine and showed that Hcp1-incorporated staphylococcal MV is a promising candidate for the prevention of acute melioidosis.

Melioidosis and Burkholderia pseudomallei : progress in epidemiology, diagnosis, treatment and vaccination

PURPOSE OF REVIEW

Melioidosis and its causative bacterium Burkholderia pseudomallei are being found in unexpected locations and bacterial genotyping is providing new insights into global spread and where and how individuals are being infected. This review summarizes recent studies covering the epidemiology, diagnosis, treatment, and prevention of melioidosis.

RECENT FINDINGS

Whole-genome sequencing of B. pseudomallei from patients and environmental sampling is informing the phylogeography of B. pseudomallei at regional, continental, and global levels, while also defining the epidemiology for individual cases. The situation in Africa remains the most unresolved, while the evolving story of B. pseudomallei in the Americas may establish that B. pseudomallei is endemic in parts of southern USA. Guidelines for diagnosis and treatment of melioidosis are well established, and published mortality has decreased from 50% or higher to 10% or lower in some countries but access to laboratory and therapeutic resources are not available or are extremely limited in many melioidosis-endemic regions.

SUMMARY

The enormous clinical diversity of melioidosis and the complexities of laboratory diagnosis and of treatment make it a sentinel disease for highlighting the continuing global disparities in access to and provision of healthcare.

Nanomaterials-based vaccines to target intracellular bacterial pathogens

Development of novel immunization approaches to combat a growing list of emerging and ancient infectious agents is a global health priority. Intensive efforts over the last several decades have identified alternative approaches to improve upon traditional vaccines that are based on live, attenuated agents, or formulations of inactivated agents with adjuvants. Rapid advances in RNA-based and other delivery systems for immunization have recently revolutionized the potential to protect populations from viral pathogens, such as SARS-CoV-2. Similar efforts to combat bacterial pathogens, especially species with an intracellular niche, have lagged significantly. In the past decade, advances in nanotechnology have yielded a variety of new antigen/adjuvant carrier systems for use in vaccine development against infectious viruses and bacteria. The tunable properties of nanomaterial-based vaccines allow for balancing immunogenicity and safety which is a key hurdle in traditional antigen and adjuvant formulations. In this review, we discuss several novel nanoparticle-based vaccine platforms that show promise for use against intracellular bacteria as demonstrated by the feasibility of construction, enhanced antigen presentation, induction of cell mediated and humoral immune responses, and improved survival outcomes in in vivo models.

Evaluation of two different vaccine platforms for immunization against melioidosis and glanders

Burkholderia pseudomallei and the closely related species, Burkholderia mallei, produce similar multifaceted diseases which range from rapidly fatal to protracted and chronic, and are a major cause of mortality in endemic regions. Besides causing natural infections, both microbes are Tier 1 potential biothreat agents. Antibiotic treatment is prolonged with variable results, hence effective vaccines are urgently needed. The purpose of our studies was to compare candidate vaccines that target both melioidosis and glanders to identify the most efficacious one(s) and define residual requirements for their transition to the non-human primate aerosol model. Studies were conducted in the C57BL/6 mouse model to evaluate the humoral and cell-mediated immune response and protective efficacy of three Burkholderia vaccine candidates against lethal aerosol challenges with B. pseudomallei K96243, B. pseudomallei MSHR5855, and B. mallei FMH. The recombinant vaccines generated significant immune responses to the vaccine antigens, and the live attenuated vaccine generated a greater immune response to OPS and the whole bacterial cells. Regardless of the candidate vaccine evaluated, the protection of mice was associated with a dampened cytokine response within the lungs after exposure to aerosolized bacteria. Despite being delivered by two different platforms and generating distinct immune responses, two experimental vaccines, a capsule conjugate + Hcp1 subunit vaccine and the live B. pseudomallei 668 ΔilvI strain, provided significant protection and were down-selected for further investigation and advanced development.

Self-adjuvanting nanovaccines boost lung-resident CD4+ T cell immune responses in BCG-primed mice

Heterologous vaccine regimens could extend waning protection in the global population immunized with Mycobacterium bovis Bacille Calmette-Guerin (BCG). We demonstrate that pulmonary delivery of peptide nanofibers (PNFs) bearing an Ag85B CD4+ T cell epitope increased the frequency of antigen-specific T cells in BCG-primed mice, including heterogenous populations with tissue resident memory (Trm) and effector memory (Tem) phenotype, and functional cytokine recall. Adoptive transfer of dendritic cells pulsed with Ag85B-bearing PNFs further expanded the frequency and functional repertoire of memory CD4+ T cells. Transcriptomic analysis suggested that the adjuvanticity of peptide nanofibers is, in part, due to the release of damage-associated molecular patterns. A single boost with monovalent Ag85B PNF in BCG-primed mice did not reduce lung bacterial burden compared to BCG alone following aerosol Mtb challenge. These findings support the need for novel BCG booster strategies that activate pools of Trm cells with potentially diverse localization, trafficking, and immune function.

BpOmpW Antigen Stimulates the Necessary Protective T-Cell Responses Against Melioidosis

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.

Recent Progress in Shigella and Burkholderia pseudomallei Vaccines

Significant advancement has been made in the development of vaccines against bacterial pathogens. However, several roadblocks have been found during the evaluation of vaccines against intracellular bacterial pathogens. Therefore, new lessons could be learned from different vaccines developed against unrelated intracellular pathogens. Bacillary dysentery and melioidosis are important causes of morbidity and mortality in developing nations, which are caused by the intracellular bacteria Shigella and Burkholderia pseudomallei, respectively. Although the mechanisms of bacterial infection, dissemination, and route of infection do not provide clues about the commonalities of the pathogenic infectious processes of these bacteria, a wide variety of vaccine platforms recently evaluated suggest that in addition to the stimulation of antibodies, identifying protective antigens and inducing T cell responses are some additional required elements to induce effective protection. In this review, we perform a comparative evaluation of recent candidate vaccines used to combat these two infectious agents, emphasizing the common strategies that can help investigators advance effective and protective vaccines to clinical trials.