Robust Th1 cellular and humoral responses generated by the Yersinia pestis rF1-V subunit vaccine formulated to contain an agonist of the CD137 pathway do not translate into increased protection against pneumonic plague

Microneedle array delivery of Yersinia pestis recapitulates bubonic plague

Fleas transmit Yersinia pestis directly within the dermis of mammals to cause bubonic plague. Syringe-mediated inoculation is widely used to recapitulate bubonic plague and study Y. pestis pathogenesis. However, intradermal needle inoculation is tedious, error prone, and poses a significant safety risk for laboratorians. Microneedle arrays (MNAs) are micron-scale polymeric structures that deliver materials to the dermis, while minimizing the risk of needle sticks. We demonstrated that MNA inoculation is a viable strategy to recapitulate bubonic plague and study bacterial virulence by defining the parameters needed to establish a lethal infection in the mouse model and characterizing the course of infection using live-animal optical imaging. Using MNAs, we also demonstrated that Y. pestis must overcome calprotectin-mediated zinc restriction within the dermis and dermal delivery of an attenuated mutant has vaccine potential. Together, these data demonstrate that MNAs are a safe alternative to study Y. pestis pathogenesis in the laboratory.

Droplet Tn-Seq identifies the primary secretion mechanism for yersiniabactin in Yersinia pestis

Nutritional immunity includes sequestration of transition metals from invading pathogens. Yersinia pestis overcomes nutritional immunity by secreting yersiniabactin to acquire iron and zinc during infection. While the mechanisms for yersiniabactin synthesis and import are well-defined, those responsible for yersiniabactin secretion are unknown. Identification of this mechanism has been difficult because conventional mutagenesis approaches are unable to inhibit trans-complementation by secreted factors between mutants. To overcome this obstacle, we utilized a technique called droplet Tn-seq (dTn-seq), which uses microfluidics to isolate individual transposon mutants in oil droplets, eliminating trans-complementation between bacteria. Using this approach, we first demonstrated the applicability of dTn-seq to identify genes with secreted functions. We then applied dTn-seq to identify an AcrAB efflux system as required for growth in metal-limited conditions. Finally, we showed this efflux system is the primary yersiniabactin secretion mechanism and required for virulence during bubonic and pneumonic plague. Together, these studies have revealed the yersiniabactin secretion mechanism that has eluded researchers for over 30 years and identified a potential therapeutic target for bacteria that use yersiniabactin for metal acquisition.

Recent Advancements and Novel Approaches Contributing to the Present Arsenal of Prophylaxis and Treatment Strategies Against Category A Bacterial Biothreat Agents

Bacterial pathogens have always been a part of the ecosystem in which we thrive. Some pathogens have caused deadly outbreaks in the past and have been exploited as an agent of threat. Natural hotspots for these biological pathogens are widely distributed throughout the world and hence they remain clinically important. Technological advancement and change in general lifestyle has driven the evolution of these pathogens into more virulent and resistant variants. There has been a growing concern over the development of multidrug-resistant bacterial strains that could be used as bioweapons. This rapid change in pathogens also propels the field of science to develop and innovate new strategies and methodologies which are superior and safer to the existing ones. Some bacterial agents like-Bacillus anthracis, Yersinia pestis, Francisella tularensis and toxins produced by strains of Clostridium botulinum, have been segregated as Category A substances as they pose imminent threat to public health with a history of life threatening and catastrophic disease. This review highlights some encouraging developments and value additions in the current plan of action for protection against these select biothreat bacterial pathogens.

Detoxified synthetic bacterial membrane vesicles as a vaccine platform against bacteria and SARS-CoV-2

The development of vaccines based on outer membrane vesicles (OMV) that naturally bud off from bacteria is an evolving field in infectious diseases. However, the inherent inflammatory nature of OMV limits their use as human vaccines. This study employed an engineered vesicle technology to develop synthetic bacterial vesicles (SyBV) that activate the immune system without the severe immunotoxicity of OMV. SyBV were generated from bacterial membranes through treatment with detergent and ionic stress. SyBV induced less inflammatory responses in macrophages and in mice compared to natural OMV. Immunization with SyBV or OMV induced comparable antigen-specific adaptive immunity. Specifically, immunization with Pseudomonas aeruginosa-derived SyBV protected mice against bacterial challenge, and this was accompanied by significant reduction in lung cell infiltration and inflammatory cytokines. Further, immunization with Escherichia coli-derived SyBV protected mice against E. coli sepsis, comparable to OMV-immunized group. The protective activity of SyBV was driven by the stimulation of B-cell and T-cell immunity. Also, SyBV were engineered to display the SARS-CoV-2 S1 protein on their surface, and these vesicles induced specific S1 protein antibody and T-cell responses. Collectively, these results demonstrate that SyBV may be a safe and efficient vaccine platform for the prevention of bacterial and viral infections.

The magnitude of the germinal center B cell and T follicular helper cell response predicts long-lasting antibody titers to plague vaccination

The development of a safe and effective vaccine against Yersinia pestis, the causative organism for plague disease, remains an important global health priority. Studies have demonstrated effective immune-based protection against plague challenge that is induced by plague antigen subunit vaccination in an aqueous alhydrogel formulation; however, whether these candidate vaccines in this formulation and presentation, induce long-lasting immunological memory in the form of durable cellular and antibody recall responses has not been fully demonstrated. In this study, we analyzed germinal center T follicular helper and germinal center B cell responses following F1V and F1 + V plague subunit immunization of mice with vaccines formulated in various adjuvants. Our data demonstrate that recombinant plague protein immunization formulated with IL-2/GM-CSF cytokines bound to alhydrogel adjuvant drive an increase in the magnitude of the germinal center T follicular helper and germinal center B cell responses following primary immunization, compared to vaccines formulated with Alhydrogel adjuvant alone. In contrast, plague protein subunit immunization combined with CpG ODN bound to alhydrogel increased the magnitude and duration of the germinal center Tfh and B cell responses following booster immunization. Importantly, enhanced germinal center Tfh and B cell responses correlated with long-lasting and high F1V-specific antibody titers and more robust antibody recall responses to F1V re-exposure. These findings indicate that vaccine formulations that drive enhancement of the germinal center Tfh and B cell responses are critical for inducing durable plague-specific humoral immunity.

BAP31 affects macrophage polarization through regulating helper T cells activation

Previously, we reported that B cell receptor associated protein 31 (BAP31) is a positive regulator on T-cells activation. Helper T cells [cluster of differentiation 4⁺ (CD4⁺) T cells] can regulate macrophage activation in adaptive immune response against pathogens. In this study, we elucidate that M1 and M2 macrophages polarization is significantly suppressed in Lck Cre-BAP31^flox/flox mice or the co-culture system of CD4⁺ T cells from Lck Cre-BAP31^flox/flox mice and macrophages from WT mice. It means that BAP31 may affect the regulation of CD4⁺ T cells on macrophages. Further studies suggest that BAP31 deficiency significantly reduce the expressions of T helper 1 (Th1)/ Th2/ Th17/ Th9/ Th22/ Treg cells-related cytokines and transcription factors. The inhibition of macrophages activation caused by BAP31 knockdown is due to the reduction of IFN-γ and IL-4 secreted by Th1 and Th2 cells. BAP31 also affects the levels of early activation markers (CD69 and CD25) of CD4⁺ T cells. Moreover, BAP31 deficiency downregulates the expression of TCRαβ-CD3 complex, and the adaptor proteins p-Zap70, p-Lck, and p-Lat in TCR signaling pathway. These results demonstrate that BAP31 deficiency inhibits TCR/CD3-mediated activation in CD4⁺ T cells and adversely affects macrophages polarization. These findings establish a theoretical foundation for the study of BAP31 in immunotherapy.

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.

Yersiniabactin contributes to overcoming zinc restriction during Yersinia pestis infection of mammalian and insect hosts

Yersinia pestis causes human plague and colonizes both a mammalian host and a flea vector during its transmission cycle. A key barrier to bacterial infection is the host's ability to actively sequester key biometals (e.g., iron, zinc, and manganese) required for bacterial growth. This is referred to as nutritional immunity. Mechanisms to overcome nutritional immunity are essential virulence factors for bacterial pathogens. Y. pestis produces an iron-scavenging siderophore called yersiniabactin (Ybt) that is required to overcome iron-mediated nutritional immunity and cause lethal infection. Recently, Ybt has been shown to bind to zinc, and in the absence of the zinc transporter ZnuABC, Ybt improves Y. pestis growth in zinc-limited medium. These data suggest that, in addition to iron acquisition, Ybt may also contribute to overcoming zinc-mediated nutritional immunity. To test this hypothesis, we used a mouse model defective in iron-mediated nutritional immunity to demonstrate that Ybt contributes to virulence in an iron-independent manner. Furthermore, using a combination of bacterial mutants and mice defective in zinc-mediated nutritional immunity, we identified calprotectin as the primary barrier for Y. pestis to acquire zinc during infection and that Y. pestis uses Ybt to compete with calprotectin for zinc. Finally, we discovered that Y. pestis encounters zinc limitation within the flea midgut, and Ybt contributes to overcoming this limitation. Together, these results demonstrate that Ybt is a bona fide zinc acquisition mechanism used by Y. pestis to surmount zinc limitation during the infection of both the mammalian and insect hosts.

Impact of Toll-Like Receptor-Specific Agonists on the Host Immune Response to the Yersinia pestis Plague rF1V Vaccine

Relatively recent advances in plague vaccinology have produced the recombinant fusion protein F1-V plague vaccine. This vaccine has been shown to readily protect mice from both bubonic and pneumonic plague. The protection afforded by this vaccine is solely based upon the immune response elicited by the F1 or V epitopes expressed on the F1-V fusion protein. Accordingly, questions remain surrounding its efficacy against infection with non-encapsulated (F1-negative) strains. In an attempt to further optimize the F1-V elicited immune response and address efficacy concerns, we examined the inclusion of multiple toll-like receptor agonists into vaccine regimens. We examined the resulting immune responses and also any protection afforded to mice that were exposed to aerosolized Yersinia pestis. Our data demonstrate that it is possible to further augment the F1-V vaccine strategy in order to optimize and augment vaccine efficacy.

Single-dose intranasal subunit vaccine rapidly clears secondary sepsis in a high-dose pneumonic plague infection

Yersinia pestis, the causative agent of plague, has killed millions throughout human history. Though public health initiatives have reduced the number of plague cases, it remains endemic in many areas of the world. It also remains a significant threat for use as a biological weapon. Naturally occurring multi-drug antibiotic resistance has been observed in Y. pestis, and resistant strains have been engineered for use as a biological weapon. Vaccines represent our best means of protection against the threat of antibiotic resistant plague. We have developed a vaccine consisting of two Y. pestis virulence factors, LcrV (V) and F1, conjugated to Tobacco Mosaic Virus (TMV), a safe, non-replicating plant virus that can be administered mucosally, providing complete protection against pneumonic plague, the deadliest form of the disease and the one most likely to be seen in a biological attack. A single intranasal (i.n.) dose of TMV-F1 + TMV-V (TMV-F1/V) protected 88% of mice against lethal challenge with 100 LD₅₀ of Y. pestis CO92pgm-, while immunization with rF1 + rV without TMV was not protective. Serum and tissues were collected at various timepoints after challenge to assess bacterial clearance, histopathology, cytokine production, and antibody production. Overall, TMV-F1/V immunized mice showed a significant reduction in histopathology, bacterial burden, and inflammatory cytokine production following challenge compared to rF1 + rV vaccinated and unvaccinated mice. Pneumonic challenge resulted in systemic dissemination of the bacteria in all groups, but only TMV-F1/V immunized mice rapidly cleared bacteria from the spleen and liver. There was a direct correlation between pre-challenge serum F1 titers and recovery in all immunized mice, strongly suggesting a role for antibody in the neutralization and/or opsonization of Y. pestis in this model. Mucosal administration of a single dose of a Y. pestis TMV-based subunit vaccine, without any additional adjuvant, can effectively protect mice from lethal infection.

A new generation needle- and adjuvant-free trivalent plague vaccine utilizing adenovirus-5 nanoparticle platform

A plague vaccine with a fusion cassette of YscF, F1, and LcrV encoding genes in an adenovirus-5 vector (rAd5-YFV) is evaluated for efficacy and immune responses in mice. Two doses of the vaccine provides 100% protection when administered intranasally against challenge with Yersinia pestis CO92 or its isogenic F1 mutant in short- or long- term immunization in pneumonic/bubonic plague models. The corresponding protection rates drop in rAd5-LcrV monovalent vaccinated mice in plague models. The rAd5-YFV vaccine induces superior humoral, mucosal and cell-mediated immunity, with clearance of the pathogen. Immunization of mice with rAd5-YFV followed by CO92 infection dampens proinflammatory cytokines and neutrophil chemoattractant production, while increasing Th1- and Th2-cytokine responses as well as macrophage/monocyte chemo-attractants when compared to the challenge control animals. This is a first study showing complete protection of mice from pneumonic/bubonic plague with a viral vector-based vaccine without the use of needles and the adjuvant.

Yersinia Outer Membrane Vesicles as Potential Vaccine Candidates in Protecting against Plague

Despite the relatively low incidence of plague, its etiological agent, Yersinia pestis, is an exceptional epidemic danger due to the high infectivity and mortality of this infectious disease. Reports on the isolation of drug-resistant Y. pestis strains indicate the advisability of using asymmetric responses, such as phage therapy and vaccine prophylaxis in the fight against this problem. The current relatively effective live plague vaccine is not approved for use in most countries because of its ability to cause heavy local and system reactions and even a generalized infectious process in people with a repressed immune status or metabolic disorders, as well as lethal infection in some species of nonhuman primates. Therefore, developing alternative vaccines is of high priority and importance. However, until now, work on the development of plague vaccines has mainly focused on screening for the potential immunogens. Several investigators have identified the protective potency of bacterial outer membrane vesicles (OMVs) as a promising basis for bacterial vaccine candidates. This review is aimed at presenting these candidates of plague vaccine and the results of their analysis in animal models.

Insights of Novel Coronavirus (SARS-CoV-2) disease outbreak, management and treatment

Emerging and re-emerging viral diseases poses a threat to living organisms, and led to serious concern to humankind and public health. The last two decades, viral epidemics such as the severe acute respiratory syndrome (SARS-CoV) reported in the years 2002-2003, and H1N1 influenza (Swine flu) in 2009, middle east respiratory syndrome (MERS-CoV) from Saudi Arabia in 2012, Ebola virus in 2014-2016, and Zika virus in 2015. The recent outbreak of 2019-CoV-2 or severe acute respiratory syndrome-2 (SARS-CoV-2), novel coronavirus (2019-nCoV, or 2019 disease, COVID-19) in Dec 2019, from, Wuhan city of China, has severe implications of health concerns to the whole world, due to global spread and high health risk. More than 423349 deaths had occurred globally and is still increasing every day. The whole world is under a health emergency, and people are advised to stay at their homes to avoid the spread of person-to-person infection, and advised to maintain social distancing. The advancement in clinical diagnosis techniques like Real-Time PCR (RT-PCR), immunological, microscopy, and geographic information system (GIS) mapping technology helped in tacking the rapid diagnosis and tracking viral infection in a short period. In the same way, artificial intelligence (AI), combinatorial chemistry, and deep learning approaches help to find novel therapeutics in less time and wide applicability in biomedical research. National Institute of Allergy and Infectious Diseases (NIAID) has started the clinical trials of investigation COVID-19 vaccine. Therefore, we can expect vaccines to be available for this deadly disease in the coming few months.

Vaccine Potential of a Recombinant Bivalent Fusion Protein LcrV-HSP70 Against Plague and Yersiniosis

To counteract the deadly pathogens, i.e., Y. pestis, Y. enetrocolitica, and Y. pseudotuberculosis, we prepared a recombinant DNA construct lcrV-hsp70 encoding the bivalent fusion protein LcrV-HSP70. The lcrV gene of Y. pestis and hsp70 domain II DNA fragment of M. tuberculosis were amplified by PCR. The lcrV amplicon was first ligated in the pET vector using NcoI and BamHI restriction sites. Just downstream to the lcrV gene, the hsp70 domain II was ligated using BamHI and Hind III restriction sites. The in-frame and the orientation of cloned lcrV-hsp70 were checked by restriction analysis and nucleotide sequencing. The recombinant bivalent fusion protein LcrV-HSP70 was expressed in E. coli and purified by affinity chromatography. The vaccine potential of LcrV-HSP70 fusion protein was evaluated in formulation with alum. BALB/c mice were vaccinated, and the humoral and cellular immune responses were studied. The fusion protein LcrV-HSP70 induced a strong and significant humoral immune response in comparison to control animals. We also observed a significant difference in the expression levels of IFN-γ and TNF-α in LcrV–HSP70-immunized mice in comparison to control, HSP70, and LcrV groups. To test the protective efficacy of the LcrV–HSP70 fusion protein against plague and Yersiniosis, the vaccinated mice were challenged with Y. pestis, Y. enterocolitica, and Y. pseudotuberculosis separately. The bivalent fusion protein LcrV–HSP70 imparted 100% protection against the plague. In the case of Yersiniosis, on day 2 post challenge, there was a significant reduction in the number of CFU of Y. enterocolitica and Y. pseudotuberculosis in the blood (CFU/ml) and the spleen (CFU/g) of vaccinated animals in comparison to the LcrV, HSP70, and control group animals.

The Impact of Age and Sex on Mouse Models of Melioidosis

Mouse models have been used to generate critical data for many infectious diseases. In the case of Burkholderia pseudomallei, mouse models have been invaluable for bacterial pathogenesis studies as well as for testing novel medical countermeasures including both vaccines and therapeutics. Mouse models of melioidosis have also provided a possible way forward to better understand the chronicity associated with this infection, as it appears that BALB/c mice develop an acute infection with B. pseudomallei, whereas the C57BL/6 model is potentially more suggestive of a chronic infection. Several unanswered questions, however, persist around this model. In particular, little attention has been paid to the effect of age or sex on the disease outcome in these animal models. In this report, we determined the LD₅₀ of the B. pseudomallei K96243 strain in both female and male BALB/c and C57BL/6 mice in three distinct age groups. Our data demonstrated a modest increase in susceptibility associated with sex in this model, and we documented important histopathological differences associated with the reproductive systems of each sex. There was a statistically significant inverse correlation between age and susceptibility. The older mice, in most cases, were more susceptible to the infection. Additionally, our retrospective analyses suggested that the impact of animal supplier on disease outcome in mice may be minimal. These observations were consistent regardless of whether the mice were injected with bacteria intraperitoneally or if they were exposed to aerosolized bacteria. All of these factors should be considered when designing experiments using mouse models of melioidosis.

The Use of Analgesics during Vaccination with a Live Attenuated Yersinia pestis Vaccine Alters the Resulting Immune Response in Mice

The administration of antipyretic analgesics prior to, in conjunction with, or due to sequelae associated with vaccination is a common yet somewhat controversial practice. In the context of human vaccination, it is unclear if even short-term analgesic regimens can significantly alter the resulting immune response, as literature exists to support several scenarios including substantial immune interference. In this report, we used a live attenuated Yersinia pestis vaccine to examine the impact of analgesic administration on the immune response elicited by a single dose of a live bacterial vaccine in mice. Mice were assessed by evaluating natural and provoked behavior, as well as food and water consumption. The resulting immune responses were assessed by determining antibody titers against multiple antigens and assaying cellular responses in stimulated splenocytes collected from vaccinated animals. We observed no substantial benefit to the mice associated with the analgesic administration. Splenocytes from both C57BL/6 and BALB/c vaccinated mice receiving acetaminophen have a significantly reduced interferon-gamma (IFN-γ) recall response. Additionally, there is a significantly lower immunoglobulin (Ig)G2a/IgG1 ratio in vaccinated BALB/c mice treated with either acetaminophen or meloxicam and a significantly lower IgG2c/IgG1 ratio in vaccinated C57BL/6 mice treated with acetaminophen. Taken together, our data indicate that the use of analgesics, while possibly ethically warranted, may hinder the accurate characterization and evaluation of novel vaccine strategies with little to no appreciable benefits to the vaccinated mice.