Exploratory study on Th1 epitope-induced protective immunity against Coxiella burnetii infection

Synthetic Particulate Subunit Vaccines for the Prevention of Q Fever

Coxiella burnetti is an intracellular bacterium that causes Q fever, a disease of worldwide importance. Q-VAX® , the approved human Q fever vaccine, is a whole cell vaccine associated with safety concerns. Here a safe particulate subunit vaccine candidate is developed that is ambient-temperature stable and can be cost-effectively manufactured. Endotoxin-free Escherichia coli is bioengineered to efficiently self-assemble biopolymer particles (BPs) that are densely coated with either strings of 18 T-cell epitopes (COX-BP) or two full-length immunodominant antigens (YbgF-BP-Com1) all derived from C. burnetii. BP vaccine candidates are ambient-temperature stable. Safety and immunogenicity are confirmed in mice and guinea pig (GP) models. YbgF-BP-Com1 elicits specific and strong humoral immune responses in GPs with IgG titers that are at least 1 000 times higher than those induced by Q-VAX® . BP vaccine candidates are not reactogenic. After challenge with C. burnetii, YbgF-BP-Com1 vaccine leads to reduced fever responses and pathogen burden in the liver and the induction of proinflammatory cytokines IL-12 and IFN-γ inducible protein (IP-10) when compared to negative control groups. These data suggest that YbgF-BP-Com1 induces functional immune responses reducing infection by C. burnetii. Collectively, these findings illustrate the potential of BPs as effective antigen carrier for Q fever vaccine development.

Q fever - immune responses and novel vaccine strategies

Q fever is a zoonotic disease caused by the bacterium Coxiella burnetii. It is an occupational risk for employees of animal industries and is associated with contact with wildlife and domestic animals. Although Q fever infection may be asymptomatic, chronic sequelae such as endocarditis occur in 5% of symptomatic individuals. Disease outcomes may be predicted through measurement of immune correlates. Vaccination is the most efficient method to prevent Q fever. Currently, Q-VAX is the only licenced human vaccine. Q-VAX is highly effective; however, individuals previously exposed to C. burnetii are at risk of adverse reactions. This review examines the immunological responses of acute and chronic Q fever and the efforts to provide a safer and cost-effective Q fever vaccine.

Genome-wide epitope mapping across multiple host species reveals significant diversity in antibody responses to Coxiella burnetii vaccination and infection

Coxiella burnetii is an important zoonotic bacterial pathogen of global importance, causing the disease Q fever in a wide range of animal hosts. Ruminant livestock, in particular sheep and goats, are considered the main reservoir of human infection. Vaccination is a key control measure, and two commercial vaccines based on formalin-inactivated C. burnetii bacterins are currently available for use in livestock and humans. However, their deployment is limited due to significant reactogenicity in individuals previously sensitized to C. burnetii antigens. Furthermore, these vaccines interfere with available serodiagnostic tests which are also based on C. burnetii bacterin antigens. Defined subunit antigen vaccines offer significant advantages, as they can be engineered to reduce reactogenicity and co-designed with serodiagnostic tests to allow discrimination between vaccinated and infected individuals. This study aimed to investigate the diversity of antibody responses to C. burnetii vaccination and/or infection in cattle, goats, humans, and sheep through genome-wide linear epitope mapping to identify candidate vaccine and diagnostic antigens within the predicted bacterial proteome. Using high-density peptide microarrays, we analyzed the seroreactivity in 156 serum samples from vaccinated and infected individuals to peptides derived from 2,092 open-reading frames in the C. burnetii genome. We found significant diversity in the antibody responses within and between species and across different types of C. burnetii exposure. Through the implementation of three different vaccine candidate selection methods, we identified 493 candidate protein antigens for protein subunit vaccine design or serodiagnostic evaluation, of which 65 have been previously described. This is the first study to investigate multi-species seroreactivity against the entire C. burnetii proteome presented as overlapping linear peptides and provides the basis for the selection of antigen targets for next-generation Q fever vaccines and diagnostic tests.

Engineering Protein Nanoparticles Functionalized with an Immunodominant Coxiella burnetii Antigen to Generate a Q Fever Vaccine

Coxiella burnetii is the causative agent of Q fever, for which there is yet to be an FDA-approved vaccine. This bacterial pathogen has both extra- and intracellular stages in its life cycle, and therefore both a cell-mediated (i.e., T lymphocyte) and humoral (i.e., antibody) immune response are necessary for effective eradication of this pathogen. However, most proposed vaccines elicit strong responses to only one mechanism of adaptive immunity, and some can either cause reactogenicity or lack sufficient immunogenicity. In this work, we aim to apply a nanoparticle-based platform toward producing both antibody and T cell immune responses against C. burnetii. We investigated three approaches for conjugation of the immunodominant outer membrane protein antigen (CBU1910) to the E2 nanoparticle to obtain a consistent antigen orientation: direct genetic fusion, high affinity tris-NTA-Ni conjugation to polyhistidine-tagged CBU1910, and the SpyTag/SpyCatcher (ST/SC) system. Overall, we found that the ST/SC approach yielded nanoparticles loaded with the highest number of antigens while maintaining stability, enabling formulations that could simultaneously co-deliver the protein antigen (CBU1910) and adjuvant (CpG1826) on one nanoparticle (CBU1910-CpG-E2). Using protein microarray analyses, we found that after immunization, antigen-bound nanoparticle formulations elicited significantly higher antigen-specific IgG responses than soluble CBU1910 alone and produced more balanced IgG1/IgG2c ratios. Although T cell recall assays from these protein antigen formulations did not show significant increases in antigen-specific IFN-γ production compared to soluble CBU1910 alone, nanoparticles conjugated with a CD4 peptide epitope from CBU1910 generated elevated T cell responses in mice to both the CBU1910 peptide epitope and whole CBU1910 protein. These investigations highlight the feasibility of conjugating antigens to nanoparticles for tuning and improving both humoral- and cell-mediated adaptive immunity against C. burnetii.

Q fever immunology: the quest for a safe and effective vaccine

Q fever is an infectious zoonotic disease, caused by the Gram-negative bacterium Coxiella burnetii. Transmission occurs from livestock to humans through inhalation of a survival form of the bacterium, the Small Cell Variant, often via handling of animal parturition products. Q fever manifests as an acute self-limiting febrile illness or as a chronic disease with complications such as vasculitis and endocarditis. The current preventative human Q fever vaccine Q-VAX poses limitations on its worldwide implementation due to reactogenic responses in pre-sensitized individuals. Many strategies have been undertaken to develop a universal Q fever vaccine but with little success to date. The mechanisms of the underlying reactogenic responses remain only partially understood and are important factors in the development of a safe Q fever vaccine. This review provides an overview of previous and current experimental vaccines developed for use against Q fever and proposes approaches to develop a vaccine that establishes immunological memory while eliminating harmful reactogenic responses.

Construction of an inhalable recombinant M2e-FP-expressing Bacillus subtilis spores-based vaccine and evaluation of its protection efficacy against influenza in a mouse model

Influenza A virus (IAV) is a deadly zoonotic pathogen that remains a burden to global health systems despite continuous vaccinations, indicating the need for an improved vaccine strategy. In this work, we constructed a new recombinant influenza vaccine using Bacillus subtilis spores expressing M2e-FP protein (RSM2eFP) and assessed its potency and efficacy in BALB/c mouse immunized via aerosolized intratracheal inoculation (i.t.) or intragastric (i.g.) administration. Immunization via i.t. route conferred 100 % protection against 20 × LD50 A/PR/8/34 (H1N1) virus compared with only 50 % via the i.g. route. Even when challenged with 40 × LD50 virus, the RSM2eFP vaccine immunized via i.t. provided 80 % protection. Consistently, i.t. inoculation of RSM2eFP spore vaccine induced a stronger lung mucosal immune response and a greater cellular immune response than i.g. administration, as indicated by the high production of IgG and SIgA. In addition, the RSM2eFP spore vaccine diminished the yield of infectious virus in the lung of mice immunized via i.t. These results suggest that i.t. immunization of the RSM2eFP spore vaccine may be a promising strategy for the development of mucosal vaccines against IAV infections.

Evaluation of a Human T Cell-Targeted Multi-Epitope Vaccine for Q Fever in Animal Models of Coxiella burnetii Immunity

T cell-mediated immunity plays a central role in the control and clearance of intracellular Coxiella burnetii infection, which can cause Q fever. Therefore, we aimed to develop a novel T cell-targeted vaccine that induces pathogen-specific cell-mediated immunity to protect against Q fever in humans while avoiding the reactogenicity of the current inactivated whole cell vaccine. Human HLA class II T cell epitopes from C. burnetii were previously identified and selected by immunoinformatic predictions of HLA binding, conservation in multiple C. burnetii isolates, and low potential for cross-reactivity with the human proteome or microbiome. Epitopes were selected for vaccine inclusion based on long-lived human T cell recall responses to corresponding peptides in individuals that had been naturally exposed to the bacterium during a 2007-2010 Q fever outbreak in the Netherlands. Multiple viral vector-based candidate vaccines were generated that express concatemers of selected epitope sequences arranged to minimize potential junctional neo-epitopes. The vaccine candidates caused no antigen-specific reactogenicity in a sensitized guinea pig model. A subset of the vaccine epitope peptides elicited antigenic recall responses in splenocytes from C57BL/6 mice previously infected with C. burnetii. However, immunogenicity of the vaccine candidates in C57BL/6 mice was dominated by a single epitope and this was insufficient to confer protection against an infection challenge, highlighting the limitations of assessing human-targeted vaccine candidates in murine models. The viral vector-based vaccine candidates induced antigen-specific T cell responses to a broader array of epitopes in cynomolgus macaques, establishing a foundation for future vaccine efficacy studies in this large animal model of C. burnetii infection.

Immunogenicity and Reactogenicity in Q Fever Vaccine Development

Coxiella burnetii is an obligate intracellular bacterium which, in humans, causes the disease Q fever. Although Q fever is most often a mild, self-limiting respiratory disease, it can cause a range of severe syndromes including hepatitis, myocarditis, spontaneous abortion, chronic valvular endocarditis, and Q fever fatigue syndrome. This agent is endemic worldwide, except for New Zealand and Antarctica, transmitted via aerosols, persists in the environment for long periods, and is maintained through persistent infections in domestic livestock. Because of this, elimination of this bacterium is extremely challenging and vaccination is considered the best strategy for prevention of infection in humans. Many vaccines against C. burnetii have been developed, however, only a formalin-inactivated, whole cell vaccine derived from virulent C. burnetii is currently licensed for use in humans. Unfortunately, widespread use of this whole cell vaccine is impaired due to the severity of reactogenic responses associated with it. This reactogenicity continues to be a major barrier to access to preventative vaccines against C. burnetii and the pathogenesis of this remains only partially understood. This review provides an overview of past and current research on C. burnetii vaccines, our knowledge of immunogenicity and reactogenicity in C. burnetii vaccines, and future strategies to improve the safety of vaccines against C. burnetii.

Complete Protection Against Yersinia pestis in BALB/c Mouse Model Elicited by Immunization With Inhalable Formulations of rF1-V10 Fusion Protein via Aerosolized Intratracheal Inoculation

Pneumonic plague, caused by Yersinia pestis, is an infectious disease with high mortality rates unless treated early with antibiotics. Currently, no FDA-approved vaccine against plague is available for human use. The capsular antigen F1, the low-calcium-response V antigen (LcrV), and the recombinant fusion protein (rF1-LcrV) of Y. pestis are leading subunit vaccine candidates under intense investigation; however, the inability of recombinant antigens to provide complete protection against pneumonic plague in animal models remains a significant concern. In this study, we compared immunoprotection against pneumonic plague provided by rF1, rV10 (a truncation of LcrV), and rF1-V10, and vaccinations delivered via aerosolized intratracheal (i.t.) inoculation or subcutaneous (s.c.) injection. We further considered three vaccine formulations: conventional liquid, dry powder produced by spray freeze drying, or dry powder reconstituted in PBS. The main findings are: (i) rF1-V10 immunization with any formulation via i.t. or s.c. routes conferred 100% protection against Y. pestis i.t. infection; (ii) rF1 or rV10 immunization using i.t. delivery provided significantly stronger protection than rF1 or rV10 immunization via s.c. delivery; and (iii) powder formulations of subunit vaccines induced immune responses and provided protection equivalent to those elicited by unprocessed liquid formulations of vaccines. Our data indicate that immunization with a powder formulation of rF1-V10 vaccines via an i.t. route may be a promising vaccination strategy for providing protective immunity against pneumonic plague.

Soluble antigens derived from Coxiella burnetii elicit protective immunity in three animal models without inducing hypersensitivity

Q fever is caused by the intracellular bacterium Coxiella burnetii, for which there is no approved vaccine in the United States. A formalin-inactivated whole-cell vaccine (WCV) from virulent C. burnetii NMI provides single-dose long-lived protection, but concerns remain over vaccine reactogenicity. We therefore sought an alternate approach by purifying native C. burnetii antigens from the clonally derived avirulent NMII strain. A soluble bacterial extract, termed Sol II, elicits high-titer, high-avidity antibodies and induces a CD4 T cell response that confers protection in naive mice. In addition, Sol II protects against pulmonary C. burnetii challenge in three animal models without inducing hypersensitivity. An NMI-derived extract, Sol I, enhances protection further and outperforms the WCV gold standard. Collectively, these data represent a promising approach to design highly effective, non-reactogenic Q fever vaccines.

A T-Cell Epitope-Based Multi-Epitope Vaccine Designed Using Human HLA Specific T Cell Epitopes Induces a Near-Sterile Immunity against Experimental Visceral Leishmaniasis in Hamsters

Visceral leishmaniasis is a neglected tropical disease affecting 12 million people annually. Even in the second decade of the 21st century, it has remained without an effective vaccine for human use. In the current study, we designed three multiepitope vaccine candidates by the selection of multiple IFN-γ inducing MHC-I and MHC-II binder T-cell specific epitopes from three previously identified antigen genes of Leishmania donovani from our lab by an immuno-informatic approach using IFNepitope, the Immune Epitope Database (IEDB) T cell epitope identification tools, NET-MHC-1, and NET MHC-2 webservers. We tested the protective potential of these three multiepitope proteins as a vaccine in a hamster model of visceral leishmaniasis. The immunization data revealed that the vaccine candidates induced a very high level of Th1 biased protective immune response in-vivo in a hamster model of experimental visceral leishmaniasis, with one of the candidates inducing a near-sterile immunity. The vaccinated animals displayed highly activated monocyte macrophages with the capability of clearing intracellular parasites due to increased respiratory burst. Additionally, these proteins induced activation of polyfunctional T cells secreting INF-γ, TNF-α, and IL-2 in an ex-vivo stimulation of human peripheral blood mononuclear cells, further supporting the protective nature of the designed candidates.

Q Fever Vaccine Development: Current Strategies and Future Considerations

Q fever is a zoonotic disease caused by the intracellular pathogen Coxiella burnetii. This disease typically manifests as a self-limiting, febrile illness known as acute Q fever. Due to the aerosol transmissibility, environmental persistence, and infectivity of C. burnetii, this pathogen is a notable bioterrorism threat. Despite extensive efforts to develop next-generation human Q fever vaccines, only one vaccine, Q-Vax®, is commercially available. Q-Vax® is a phase I whole-cell vaccine, and its licensed use is limited to Australia, presumably due to the potential for a post-vaccination hypersensitivity response. Pre-clinical Q fever vaccine development is a major area of interest, and diverse approaches have been undertaken to develop an improved Q fever vaccine. Following a brief history of Q fever vaccine development, current approaches will be discussed along with future considerations for an improved Q fever vaccine.

Intratracheal inoculation of AHc vaccine induces protection against aerosolized botulinum neurotoxin A challenge in mice

Botulinum neurotoxin (BoNT), produced by Clostridium botulinum, is generally known to be the most poisonous of all biological toxins. In this study, we evaluate the protection conferred by intratracheal (i.t.) inoculation immunization with recombinant Hc subunit (AHc) vaccines against aerosolized BoNT/A intoxication. Three AHc vaccine formulations, i.e., conventional liquid, dry powder produced by spray freeze drying, and AHc dry powder reconstituted in water are prepared, and mice are immunized via i.t. inoculation or subcutaneous (s.c.) injection. Compared with s.c.-AHc-immunized mice, i.t.-AHc-immunized mice exhibit a slightly stronger protection against a challenge with 30,000× LD₅₀ aerosolized BoNT/A. Of note, only i.t.-AHc induces a significantly higher level of toxin-neutralizing mucosal secretory IgA (SIgA) production in the bronchoalveolar lavage of mice. In conclusion, our study demonstrates that the immune protection conferred by the three formulations of AHc is comparable, while i.t. immunization of AHc is superior to s.c. immunization against aerosolized BoNT/A intoxication.

Proteome-wide analysis of Coxiella burnetii for conserved T-cell epitopes with presentation across multiple host species

Background

Coxiella burnetii is the Gram-negative bacterium responsible for Q fever in humans and coxiellosis in domesticated agricultural animals. Previous vaccination efforts with whole cell inactivated bacteria or surface isolated proteins confer protection but can produce a reactogenic immune responses. Thereby a protective vaccine that does not cause aberrant immune reactions is required. The critical role of T-cell immunity in control of C. burnetii has been made clear, since either CD8⁺ or CD4⁺ T cells can empower clearance. The purpose of this study was to identify C. burnetii proteins bearing epitopes that interact with major histocompatibility complexes (MHC) from multiple host species (human, mouse, and cattle).

Results

Of the annotated 1815 proteins from the Nine Mile Phase I (RSA 493) assembly, 402 proteins were removed from analysis due to a lack of inter-isolate conservation. An additional 391 proteins were eliminated from assessment to avoid potential autoimmune responses due to the presence of host homology. We analyzed the remaining 1022 proteins for their ability to produce peptides that bind MHCI or MHCII. MHCI and MHCII predicted epitopes were filtered and compared between species yielding 777 MHCI epitopes and 453 MHCII epitopes. These epitopes were further examined for presentation by both MHCI and MHCII, and for proteins that contained multiple epitopes. There were 31 epitopes that overlapped positionally between MHCI and MHCII across host species. Of these, there were 9 epitopes represented within proteins containing ≥ 5 total epitopes, where an additional 24 proteins were also epitope dense. In all, 55 proteins were found to contain high scoring T-cell epitopes. Besides the well-studied protein Com1, most identified proteins were novel when compared to previously studied vaccine candidates.

Conclusion

These data represent the first proteome-wide evaluation of C. burnetii peptide epitopes. Furthermore, the inclusion of human, mouse, and bovine data capture a range of hosts for this zoonotic pathogen plus an important model organism. This work provides new vaccine targets for future vaccination efforts and enhances opportunities for selecting multiple T-cell epitope types to include within a vaccine.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12859-021-04181-w.

T-B cell epitope peptides induce protective immunity against Mycoplasma pneumoniae respiratory tract infection in BALB/c mice

Mycoplasma pneumoniae is the most common pathogen of community-acquired pneumonia in humans. Due to its high rates of antibiotic resistance, vaccination has become the best method to control the dissemination of M. pneumoniae. The recombinant carboxyl terminus of the P1 (P1C) protein is an immunodominant antigen, but it has negative effects such as poor stability and lower purity. In the current study, T-B epitopes of the P1C protein were predicted according to bioinformatics analysis and assessed for efficacy in peptide vaccination. BALB/c mice were subcutaneously inoculated with the T-B epitope peptides four times and then infected with M. pneumoniae through the respiratory tract. The results showed that the T-B epitope peptides of the P1C protein (P1C_103-117, P1C_155-169, P1C_224-238 and P1C_244-258) induced strong antigen-specific serum antibody responses and cellular immune responses with high levels of serum IgG, IgA antibodies and Th1-biased (IFN-γ and IL-2) cytokines. Immunization with T-B epitope peptides significantly reduced the M. pneumoniae burden and the degree of inflammation in the challenged mice. Furthermore, the levels of IFN-γ and TNF-α in the supernatants of lung homogenates were observably reduced compared to those in the PBS group. Overall, our findings demonstrate that T-B epitopes (P1C_103-117, P1C_155-169, P1C_224-238 and P1C_244-258) play significant roles in the P1C protein and can be used to induce powerful humoral and cellular immune responses to provide significant protection against M. pneumoniae pulmonary infection, which provides new insight into the design of potential multiepitope vaccines to prevent host infection by M. pneumoniae.

Analysis of recombinant proteins for Q fever diagnostics

Serology is essential for Q fever diagnostics, a disease caused by the bacterial pathogen Coxiella burnetii. The gold standard test is an immunofluorescence assay utilizing whole cell antigens, which are both dangerous and laborious to produce. Complexities of the antigen coupled with the subjective nature of the assay lead to decreased uniformity of test results and underscore the need for improved methodologies. Thirty-three C. burnetii proteins, previously identified as immunoreactive, were screened for reactivity to naturally infected goat serum. Based on reactivity, 10 proteins were analyzed in a secondary screen against human serum from healthy donors. Assay sensitivity and specificity ranged from 21 to 71% and 90 to 100%, respectively. Three promising antigens were identified based on receiver operating characteristic curve analysis (CBU_1718, CBU_0307, and CBU_1398). Five multiplex assays failed to outperform the individual proteins, with sensitivities and specificities ranging from 29 to 57% and 90 to 100%, respectively. Truncating the top antigen, CBU_1718, had no effect on specificity (90%); yet sensitivity decreased dramatically (71% to 21%). Through this study, we have expanded the subset of C. burnetii immunoreactive proteins validated by enzyme-linked immunosorbent assay and demonstrate the effect of novel antigen combinations and protein truncations on assay performance.

Construction of a Live-Attenuated Vaccine Strain of Yersinia pestis EV76-B-SHUΔpla and Evaluation of Its Protection Efficacy in a Mouse Model by Aerosolized Intratracheal Inoculation

Plague, which is caused by Yersinia pestis, is one of the most dangerous infectious diseases. No FDA-approved vaccine against plague is available for human use at present. To improve the immune safety of Y. pestis EV76 based live attenuated vaccine and to explore the feasibility of aerosolized intratracheal inoculation (i.t.) route for vaccine delivery, a plasminogen activator protease (pla) gene deletion mutant of the attenuated Y. pestis strain EV76-B-SHU was constructed, and its residual virulence and protective efficacy were evaluated in a mouse model via aerosolized intratracheal inoculation (i.t.) or via subcutaneous injection (s.c.). The residual virulence of EV76-B-SHUΔpla was significantly reduced compared to that of the parental strain EV76-B-SHU following i.t. and s.c. infection. The EV76-B-SHUΔpla induced higher levels of mucosal antibody sIgA in the bronchoalveolar lavage fluid of mice immunized by i.t. but not by s.c.. Moreover, after lethal challenge with Y. pestis biovar Microtus strain 201 (avirulent in humans), the protective efficacy and bacterial clearance ability of the EV76-B-SHUΔpla-i.t. group were comparable to those of the EV76-B-SHUΔpla-s.c. and EV76-B-SHU immunized groups. Thus, the EV76-B-SHUΔpla represents an excellent live-attenuated vaccine candidate against pneumonic plague and aerosolized i.t. represents a promising immunization route in mouse model.

Evaluation of a tandem Chlamydia psittaci Pgp3 multiepitope peptide vaccine against a pulmonary chlamydial challenge in mice

Chlamydia psittaci is the pathogen of psittacosis, and it has emerged as a significant public health threat. Because most infections are easily overlooked, a vaccine is recognized as the best solution to control the spread of C. psittaci. Our previous study showed that Pgp3 protein is efficacious as a subunit vaccine while not the best candidate due to the negative effects. Thus, in this study, we tested the ability of a tandem epitope vaccine candidate designated SP based on Pgp3-dominant epitopes to induce protective immunity against pulmonary chlamydial infection. BALB/c mice were intraperitoneally inoculated with multiepitope peptide antigens followed by intranasal infection with C. psittaci. We found that the multiepitope peptide antigens induced strong humoral and cellular immune responses with high Th1-related (IFN-γ and IL-2) and proinflammatory (IL-6) cytokine levels. Meanwhile, the pathogen burden and inflammatory infiltration were significantly reduced in lungs of SP-immunized mice after chlamydial challenge. In addition, the IFN-γ and IL-6 secretion levels in the infected lungs were substantially reduced. Overall, our findings demonstrate that the peptide vaccine SP plays a significant role with good immunogenicity and protective efficacy against C. psittaci lung infection in BALB/c mice, providing important insights towards understanding the potential of peptide vaccines as new vaccine antigens for inducing protective immunity against chlamydial infection.

Enhanced protection against Q fever in BALB/c mice elicited by immunization of chloroform-methanol residue of Coxiella burnetii via intratracheal inoculation

Human Q fever is recognized as a worldwide public health problem. It often occurs by inhalation of airborne aerosols contaminated with Coxiella burnetii, a gram-negative intracellular bacterium, mainly from domestic livestock. In this study, we analyzed the possibility to establish mucosal and systemic immunity against C. burnetii infection using a pulmonary delivery of chloroform-methanol residue of C. burnetii (CMR) vaccine. Mice were immunized by the intratracheal inoculation of CMR (IT-CMR) or the subcutaneous injection of CMR (SC-CMR), and the immunized mice were challenged with C. burnetii by the intratracheal route. The levels of IFN-γ, IL-12p70, IL-5, and IL-4 in the IT-CMR group in splenic T cells stimulated ex vivo were significantly higher than in the SC-CMR group. Significantly elevated sIgA to C. burnetii was detected in the bronchoalveolar lavage fluid of mice immunized by IT-CMR but not by SC-CMR, which might have contributed to the significant reduction in C. burnetii load and pathological lesions in the lungs of the mice after the challenge of C. burnetii. These results suggest that compared with SC-CMR in mice, IT-CMR was more efficient to elicit cellular and lung mucosal immune responses against aerosol infection of C. burnetii.

Promiscuous Coxiella burnetii CD4 Epitope Clusters Associated With Human Recall Responses Are Candidates for a Novel T-Cell Targeted Multi-Epitope Q Fever Vaccine

Coxiella burnetii, the causative agent of Q fever, is a Gram-negative intracellular bacterium transmitted via aerosol. Regulatory approval of the Australian whole-cell vaccine Q-VAX® in the US and Europe is hindered by reactogenicity in previously exposed individuals. The aim of this study was to identify and rationally select C. burnetii epitopes for design of a safe, effective, and less reactogenic T-cell targeted human Q fever vaccine. Immunoinformatic methods were used to predict 65 HLA class I epitopes and 50 promiscuous HLA class II C. burnetii epitope clusters, which are conserved across strains of C. burnetii. HLA binding assays confirmed 89% of class I and 75% of class II predictions, and 11 HLA class II epitopes elicited IFNγ responses following heterologous DNA/DNA/peptide/peptide prime-boost immunizations of HLA-DR3 transgenic mice. Human immune responses to the predicted epitopes were characterized in individuals naturally exposed to C. burnetii during the 2007–2010 Dutch Q fever outbreak. Subjects were divided into three groups: controls with no immunological evidence of previous infection and individuals with responses to heat-killed C. burnetii in a whole blood IFNγ release assay (IGRA) who remained asymptomatic or who experienced clinical Q fever during the outbreak. Recall responses to C. burnetii epitopes were assessed by cultured IFNγ ELISpot. While HLA class I epitope responses were sparse in this cohort, we identified 21 HLA class II epitopes that recalled T-cell IFNγ responses in 10–28% of IGRA+ subjects. IGRA+ individuals with past asymptomatic and symptomatic C. burnetii infection showed a comparable response pattern and cumulative peptide response which correlated with IGRA responses. None of the peptides elicited reactogenicity in a C. burnetii exposure-primed guinea pig model. These data demonstrate that a substantial proportion of immunoinformatically identified HLA class II epitopes show long-lived immunoreactivity in naturally infected individuals, making them desirable candidates for a novel human multi-epitope Q fever vaccine.

Development of a rapid and visual detection method for Rickettsia rickettsii combining recombinase polymerase assay with lateral flow test

Objectives

Rickettsia rickettsii is the causative agent of Rocky Mountain spotted fever, which is the most severe spotted fever group (SFG) rickettsiosis. Developing a simple and reliable detection method is required.

Methods

A detection method for R. rickettsii was established based on a recombinase polymerase amplification (RPA) assay and the lateral flow (LF) test. A specific target sequence was screened, and corresponding primers and probes were designed, synthesized, and screened for establishing an RPA assay with high amplification efficiency. Reagent concentrations, amplification time, and loading volume for strip development were optimized. The detection limit, analytic sensitivity and specificity were evaluated.

Results

A rapid, visual, sensitive and specific method for the detection of R. rickettsii based on RPA and the LF test was successfully established. The novel method had a limit of detection of 10 to 50 copies/reaction without recognizing other organisms. Analytical sensitivity and specificity were ≥90% and 100%, respectively, as evaluated by animal and simulative human samples.

Conclusions

Using the established method, detection could be completed in 30 min with visually detectable results by the naked eye, without requirement of any instrument except a constant temperature equipment. The technique shows superior detection performance and is promising for wide use in the field as well as resource-limited areas for R. rickettsii detection.

Rapid and Visual Detection of Coxiella burnetii Using Recombinase Polymerase Amplification Combined with Lateral Flow Strips

Coxiella burnetii, a global-distributed biological warfare agent, is the causative agent of Q fever. Correct diagnosis of Q fever is challenging and developing a fast, simple, and reliable detection method is necessary. In this study, recombinase polymerase amplification (RPA) assay combined with lateral flow (LF) test was developed targeting 23S rRNA gene of C. burnetii Xinqiao strain. Primers and probe were designed and synthesized, with one set with high amplification efficiency screened for establishment of the method. Reaction conditions were optimized. Sensitivity, specificity, and accuracy were evaluated. The established RPA-LF reaction could be completed in 30 minutes by combining RPA at 37°C with LF at room temperature, with visually judged results. The method showed good specificity without recognizing other bacteria evaluated. It detected positive plasmid and genomic DNA at levels of 10 copies/reaction and 7 copies/reaction, respectively, levels comparable to that of real-time quantitative PCR (RT-qPCR) targeting 23S rRNA gene established previously. Both RPA-LF and RT-qPCR were used to detect C. burnetii-infected mouse samples and the results were fully consistent. The method showed superior detection performance and will provide technical support against C. burnetii in resources-limited areas.

Development of a rapid and visual nucleotide detection method for a Chinese epidemic strain of Orientia tsutsugamushi based on recombinase polymerase amplification assay and lateral flow test

OBJECTIVES

Orientia tsutsugamushi is an obligate intracellular pathogen that causes scrub typhus. Diagnosing scrub typhus remains a challenge, and a sensitive, specific, simple, and rapid diagnostic test is still needed.

METHODS

A recombinase polymerase amplification (RPA) assay combined with a lateral flow (LF) test targeting the 56-kDa gene of a Karp-like strain of O. tsutsugamushi was developed and optimized. The detection limits, sensitivity, specificity, and simulative clinical performance were evaluated.

RESULTS

Primers and probe were screened to establish the RPA assay, and the reaction conditions were optimized. The detection limit was 10 copies/reaction in detecting plasmid DNA and 12 copies/reaction in detecting genomic DNA. The RPA-LF method could differentiate O. tsutsugamushi from other phylogenetically related bacteria. The sensitivity was 100% and specificity was over 90%, when evaluated using infected animal samples or simulative clinical samples. Furthermore, the method was completed in 20min at 37°C followed by a 3-5min incubation at room temperature for the development of an immunochromatographic strip, and the results could be determined visually.

CONCLUSIONS

This method is promising for wide-ranging use in basic medical units considering that it requires minimal instruments and infrastructure and is highly time-efficient, sensitive, and specific for diagnosing scrub typhus.

Th1 epitope peptides induce protective immunity against Rickettsia rickettsii infection in C3H/HeN mice

Rickettsia rickettsii is the causative pathogen of Rocky Mountain spotted fever (RMSF). Adr2, YbgF and OmpB are protective antigens of R. rickettsii. In this study, 90 candidate peptides were selected from these antigens based on their high-affinity binding capacity for the MHC class II molecule H2 I-A or H2 I-E using bioinformatic methods. Six peptides were determined using ELISPOT assay to be immunodominant based on the IFN-γ recall responses of CD4⁺ T cells from mice immunized with R. rickettsii. Six nucleotide sequences encoding the immunodominant peptides were linked in series and inserted into a plasmid for expression in Escherichia coli cells, resulting in a new, recombinant polypeptide termed GWP. After immunization and challenge, the rickettsial load or histopathological lesions in the organs of mice immunized with GWP or pooled peptides was significantly lower than that in organs of mice immunized with PBS or the individual peptide OmpB₃₉₉. An in vitro neutralization test revealed that sera from mice immunized with GWP, OmpB₃₉₉, or pooled peptides reduced R. rickettsii adherence to, and invasion of, vascular endothelial cells. Furthermore, significantly higher levels of IgG, IgG1, or IgG2a were detected in sera from mice immunized with GWP or pooled peptides, and significantly higher levels of IFN-γ or TNF-α secreted by CD4⁺ T cells from R. rickettsii-infected mice were detected after immunization with GWP. Altogether, our results indicated that polypeptides, especially GWP, could induce a Th1-type immune response against R. rickettsii infection, which might contribute to the rational design of peptide-based vaccines for RMSF.

Identification of Coxiella burnetii CD8+ T-Cell Epitopes and Delivery by Attenuated Listeria monocytogenes as a Vaccine Vector in a C57BL/6 Mouse Model

Coxiella burnetii is a gram-negative bacterium that causes acute and chronic Q fever. Because of the severe adverse effect of whole-cell vaccination, identification of immunodominant antigens of C. burnetii has become a major focus of Q fever vaccine development. We hypothesized that secreted C. burnetii type IV secretion system (T4SS) effectors may represent a major class of CD8+ T-cell antigens, owing to their cytosolic localization. Twenty-nine peptides were identified that elicited robust CD8+ T-cell interferon γ (IFN-γ) recall responses from mice infected with C. burnetii. Interestingly, 22 of 29 epitopes were derived from 17 T4SS-related proteins, none of which were identified as immunodominant antigens by using previous antibody-guided approaches. These epitopes were expressed in an attenuated Listeria monocytogenes vaccine strain. Immunization with recombinant L. monocytogenes vaccines induced a robust CD8+ T-cell response and conferred measurable protection against C. burnetii infection in mice. These data suggested that T4SS effectors represent an important class of C. burnetii antigens that can induce CD8+ T-cell responses. We also showed that attenuated L. monocytogenes vaccine vectors are an efficient antigen-delivery platform that can be used to induce robust protective CD8+ T-cell immune responses against C. burnetii infection.

From Q Fever to Coxiella burnetii Infection: a Paradigm Change

Coxiella burnetii is the agent of Q fever, or "query fever," a zoonosis first described in Australia in 1937. Since this first description, knowledge about this pathogen and its associated infections has increased dramatically. We review here all the progress made over the last 20 years on this topic. C. burnetii is classically a strict intracellular, Gram-negative bacterium. However, a major step in the characterization of this pathogen was achieved by the establishment of its axenic culture. C. burnetii infects a wide range of animals, from arthropods to humans. The genetic determinants of virulence are now better known, thanks to the achievement of determining the genome sequences of several strains of this species and comparative genomic analyses. Q fever can be found worldwide, but the epidemiological features of this disease vary according to the geographic area considered, including situations where it is endemic or hyperendemic, and the occurrence of large epidemic outbreaks. In recent years, a major breakthrough in the understanding of the natural history of human infection with C. burnetii was the breaking of the old dichotomy between "acute" and "chronic" Q fever. The clinical presentation of C. burnetii infection depends on both the virulence of the infecting C. burnetii strain and specific risks factors in the infected patient. Moreover, no persistent infection can exist without a focus of infection. This paradigm change should allow better diagnosis and management of primary infection and long-term complications in patients with C. burnetii infection.

Vaccine potential of bacterial macrophage infectivity potentiator (MIP)-like peptidyl prolyl cis/trans isomerase (PPIase) proteins

Peptidyl prolyl cis/trans isomerases (PPIases) are a superfamily of proteins ubiquitously distributed among living organisms, which function primarily to assist the folding and structuring of unfolded and partially folded polypeptide chains and proteins. In this review, we focus specifically on the Macrophage Infectivity Potentiator (MIP)-like PPIases, which are members of the immunophilin family of FK506-binding proteins (FKBP). MIP-like PPIases have accessory roles in virulence and are candidates for inclusion in vaccines protective against both animal and human bacterial pathogens. A structural vaccinology approach obviates any issues over molecular mimicry and potential cross-reactivity with human FKBP proteins and studies with a representative antigen, the Neisseria meningitidis-MIP, support this strategy. Moreover, a dual approach of vaccination and drug targeting could be considered for controlling bacterial infectious diseases of humans and animals.

Vaccination against Q fever for biodefense and public health indications

Coxiella burnetii is the etiological agent of Q fever, a disease that is often spread to humans via inhalational exposure to the bacteria from contaminated agricultural sources. Outbreaks have been observed all over the world with larger foci generating interest in vaccination programs, most notably in Australia and the Netherlands. Importantly, exposure rates among military personnel deployed to the Middle East can be relatively high as measured by seroconversion to C. burnetii-specific antibodies. Q fever has been of interest to the biodefense community over the years due to its low infectious dose and environmental stability. Recent advances in cell-free growth and genetics of C. burnetii also make this organism easier to culture and manipulate. While there is a vaccine that is licensed for use in Australia, the combination of biodefense- and public health-related issues associated with Q fever warrant the development of a safer and more effective vaccine against this disease.

Dysregulated microRNA expression in serum of non-vaccinated children with varicella

Circulating microRNAs (miRNAs) may play an important role in pathogen-host interactions and can serve as molecular markers for the detection of infectious diseases. To date, the relationship between circulating miRNAs and varicella-zoster virus (VZV) caused varicella has not been reported. Using TaqMan Low-Density Array (TLDA) analysis, expression levels of miRNAs in serum samples from 29 patients with varicella and 60 patients with Bordetella pertussis (BP), measles virus (MEV) and enterovirus (EV) were analyzed. The array results showed that 247 miRNAs were differentially expressed in sera of the varicella patients compared with healthy controls (215 up-regulated and 32 down-regulated). Through the following qRT-PCR confirmation and receiver operational characteristic (ROC) curve analysis, five miRNAs (miR-197, miR-629, miR-363, miR-132 and miR-122) were shown to distinguish varicella patients from healthy controls and other microbial infections with moderate sensitivity and specificity. A number of significantly enriched pathways regulated by these circulating miRNAs were predicted, and some of them were involved in inflammatory response, nervous system and respiratory system development. Our results, for the first time, revealed that a number of miRNAs were differentially expressed during VZV infection, and these five serum miRNAs have great potential to serve as biomarkers for the diagnosis of VZV infection in varicella patients.