Pneumonic Plague Protection Induced by a Monophosphoryl Lipid A Decorated Yersinia Outer-Membrane-Vesicle Vaccine

A new Yersinia pseudotuberculosis mutant strain, YptbS46, carrying the lpxE insertion and pmrF-J deletion is constructed and shown to exclusively produce monophosphoryl lipid A (MPLA) having adjuvant properties. Outer membrane vesicles (OMVs) isolated from YptbS46 harboring an lcrV expression plasmid, pSMV13, are designated OMV46-LcrV, which contained MPLA and high amounts of LcrV (Low Calcium response V) and displayed low activation of Toll-like receptor 4 (TLR4). Intramuscular prime-boost immunization with 30 µg of of OMV46-LcrV exhibited substantially reduced reactogenicity than the parent OMV44-LcrV and conferred complete protection to mice against a high-dose of respiratory Y. pestis challenge. OMV46-LcrV immunization induced robust adaptive responses in both lung mucosal and systemic compartments and orchestrated innate immunity in the lung, which are correlated with rapid bacterial clearance and unremarkable lung damage during Y. pestis challenge. Additionally, OMV46-LcrV immunization conferred long-term protection. Moreover, immunization with reduced doses of OMV46-LcrV exhibited further lower reactogenicity and still provided great protection against pneumonic plague. The studies strongly demonstrate the feasibility of OMV46-LcrV as a new type of plague vaccine candidate.

Co-formulation of the rF1V plague vaccine with depot-formulated cytokines enhances immunogenicity and efficacy to elicit protective responses against aerosol challenge in mice

This study evaluated a depot-formulated cytokine-based adjuvant to improve the efficacy of the recombinant F1V (rF1V) plague vaccine and examined the protective response following aerosol challenge in a murine model. The results of this study showed that co-formulation of the Alhydrogel-adsorbed rF1V plague fusion vaccine with the depot-formulated cytokines recombinant human interleukin 2 (rhuIL-2) and/or recombinant murine granulocyte macrophage colony-stimulating factor (rmGM-CSF) significantly enhances immunogenicity and significant protection at lower antigen doses against a lethal aerosol challenge. These results provide additional support for the co-application of the depot-formulated IL-2 and/or GM-CSF cytokines to enhance vaccine efficacy.

Dynamics of Changes in the cAMP/cGMP Concentration Ratio in the Thymus and Spleen of Laboratory Mice during Vaccination against Plague and Tularemia against the Background of Immunomodulation

Vaccine strains Yersinia pestis EV NIIEG at a dose of 103 CFU and Francisella tularensis 15 NIIEG at a dose of 102 CFU induced changes in the concentration of cyclic nucleotides in the thymus and spleen of white mice. Antigen-induced changes in the cAMP/cGMP ratio in immunocompetent organs had a phase or oscillatory character, which seems to be related to the regulation of postvaccination immunoreactivity in the body. Synthetic organoselenium compound 974zh stimulated an increase in the amplitude of cAMP/cGMP oscillations, indicating its stimulating effect on the immunogenic properties of vaccine strains at doses an order of magnitude below the standard doses.

Manganese-Based Nanoparticle Vaccine for Combating Fatal Bacterial Pneumonia

Bacterial pneumonia is the leading cause of death worldwide among all infectious diseases. However, currently available vaccines against fatal bacterial lung infections, e.g., pneumonic plague, are accompanied by limitations, including insufficient antigen-adjuvant co-delivery and inadequate immune stimulation. Therefore, there is an urgent requirement to develop next-generation vaccines to improve the interaction between antigen and adjuvant, as well as enhance the effects of immune stimulation. This study develops a novel amino-decorated mesoporous manganese silicate nanoparticle (AMMSN) loaded with rF1-V10 (rF1-V10@AMMSN) to prevent pneumonic plague. These results suggest that subcutaneous immunization with rF1-V10@AMMSN in a prime-boost strategy induces robust production of rF1-V10-specific IgG antibodies with a geometric mean titer of 315,844 at day 42 post-primary immunization, which confers complete protection to mice against 50 × LD50 of Yersinia pestis (Y. pestis) challenge via the aerosolized intratracheal route. Mechanistically, rF1-V10@AMMSN can be taken up by dendritic cells (DCs) and promote DCs maturation through activation of the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway and production of type I interferon. This process results in enhanced antigen presentation and promotes rF1-V10-mediated protection against Y. pestis infection. This manganese-based nanoparticle vaccine represents a valuable strategy for combating fatal bacterial pneumonia.

Plague vaccines: new developments in an ongoing search

As the reality of pandemic threats challenges humanity, exemplified during the ongoing SARS-CoV-2 infections, the development of vaccines targeting these etiological agents of disease has become increasingly critical. Of paramount concern are novel and reemerging pathogens that could trigger such events, including the plague bacterium Yersinia pestis. Y. pestis is responsible for more human deaths than any other known pathogen and exists globally in endemic regions of the world, including the four corners region and Northern California in the USA. Recent cases have been scattered throughout the world, including China and the USA, with serious outbreaks in Madagascar during 2008, 2013-2014, and, most recently, 2017-2018. This review will focus on recent advances in plague vaccine development, a seemingly necessary endeavor, as there is no Food and Drug Administration-licensed vaccine available for human distribution in western nations, and that antibiotic-resistant strains are recovered clinically or intentionally developed. Progress and recent development involving subunit, live-attenuated, and nucleic acid-based plague vaccine candidates will be discussed in this review. KEY POINTS: • Plague vaccine development remains elusive yet critical. • DNA, animal, and live-attenuated vaccine candidates gain traction.

Plague Vaccines: Status and Future

Three major plague pandemics caused by the gram-negative bacterium Yersinia pestis have killed nearly 200 million people in human history. Due to its extreme virulence and the ease of its transmission, Y. pestis has been used purposefully for biowarfare in the past. Currently, plague epidemics are still breaking out sporadically in most of parts of the world, including the United States. Approximately 2000 cases of plague are reported each year to the World Health Organization. However, the potential use of the bacteria in modern times as an agent of bioterrorism and the emergence of a Y. pestis strain resistant to eight antibiotics bring out severe public health concerns. Therefore, prophylactic vaccination against this disease holds the brightest prospect for its long-term prevention. Here, we summarize the progress of the current vaccine development for counteracting plague.

Further characterization of a highly attenuated Yersinia pestis CO92 mutant deleted for the genes encoding Braun lipoprotein and plasminogen activator protease in murine alveolar and primary human macrophages

We recently characterized the Δlpp Δpla double in-frame deletion mutant of Yersinia pestis CO92 molecularly, biologically, and immunologically. While Braun lipoprotein (Lpp) activates toll-like receptor-2 to initiate an inflammatory cascade, plasminogen activator (Pla) protease facilitates bacterial dissemination in the host. The Δlpp Δpla double mutant was highly attenuated in evoking bubonic and pneumonic plague, was rapidly cleared from mouse organs, and generated humoral and cell-mediated immune responses to provide subsequent protection to mice against a lethal challenge dose of wild-type (WT) CO92. Here, we further characterized the Δlpp Δpla double mutant in two murine macrophage cell lines as well as in primary human monocyte-derived macrophages to gauge its potential as a live-attenuated vaccine candidate. We first demonstrated that the Δpla single and the Δlpp Δpla double mutant were unable to survive efficiently in murine and human macrophages, unlike WT CO92. We observed that the levels of Pla and its associated protease activity were not affected in the Δlpp single mutant, and, likewise, deletion of the pla gene from WT CO92 did not alter Lpp levels. Further, our study revealed that both Lpp and Pla contributed to the intracellular survival of WT CO92 via different mechanisms. Importantly, the ability of the Δlpp Δpla double mutant to be phagocytized by macrophages, to stimulate production of tumor necrosis factor-α and interleukin-6, and to activate the nitric oxide killing pathways of the host cells remained unaltered when compared to the WT CO92-infected macrophages. Finally, macrophages infected with either the WT CO92 or the Δlpp Δpla double mutant were equally efficient in their uptake of zymosan particles as determined by flow cytometric analysis. Overall, our data indicated that although the Δlpp Δpla double mutant of Y. pestis CO92 was highly attenuated, it retained the ability to elicit innate and subsequent acquired immune responses in the host similar to that of WT CO92, which are highly desirable in a live-attenuated vaccine candidate.

Plague

Bubonic plague is an often fulminant systemic zoonosis, caused by Yersinia pestis. Conventional microbiology, bacterial population genetics, and genome sequence data, all suggest that Y pestis is a recently evolved clone of the enteric pathogen Yersinia pseudotuberculosis. The genetic basis of this organism's rapid adaptation to its insect vector (the flea) with transmission between mammalian hosts by novel subcutaneous and pneumonic routes of infection is becoming clearer. This transition provides a paradigm for the way in which new pathogens could emerge. Plague in humans is controlled by suppression of rodent reservoir hosts and their fleas and by early detection and treatment of cases of disease. Detection systems for plague in non-endemic regions might now be needed because of a bioterrorism threat. Rapid diagnostic tests are available and a subunit vaccine is in clinical trials.

Expression profiling of Yersinia pestis during mouse pulmonary infection

Yersinia pestis, the causative agent of plague, can be transmitted by infected flea bite or inhaled aerosol. Both routes of infection have a high mortality rate, and pneumonic infections of Y. pestis represent a significant concern as a tool of bioterrorism. Understanding the transcriptional program of this pathogen during pulmonary infection should be valuable in understanding plague pathogenesis, as well as potentially offering insights into new vaccines and therapeutics. Toward this goal we developed a long oligonucleotide microarray to the plague bacillus and evaluated the expression profiles of Y. pestis in vitro and in the mouse pulmonary infection model in vivo. The in vitro analysis compared expression patterns at 27 versus 37 degrees C, as a surrogate of the transition from the flea to the mammalian host. The in vivo analysis used intranasal challenge to the mouse lung. By amplifying the Y. pestis RNA from individual mouse lungs we were able to map the transcriptional profile of plague at postinfection days 1 to 3. Our data present a very different transcriptional profile between in vivo and in vitro expression, suggesting Y. pestis responds to a variety of host signals during infection. Of note was the number of genes found in genomic regions with altered %GC content that are upregulated within the mouse lung environment. These data suggest these regions may provide particularly promising targets for both vaccines and therapeutics.

Achievements of the Soviet biological weapons programme and implications for the future

The military-biological complex of the former Union of Soviet Socialist Republics was a true Frankenstein's Monster, with a powerful scientific potential--or good and for ill. This article examines both the direct scientific results of the twin biological weapons (BWs) programmes run by the 'civilian' Biopreparat and by the Ministry of Defence (MoD) and the public health benefits that sprang, despite the original intent, out of those programmes. The authors will also explore the potential for both crop and livestock destruction and for enhanced agricultural methods growing out of the parallel Soviet programme under the management of the Special Directorate of the Ministry of Agriculture. In the last section of the article the authors discuss the situation in the military-biological complex that arose after former President Boris Yeltsin's 1992 decree abolishing all research and development on offensive BWs. The possibility is considered that expertise, technologies and materials from the former Soviet BWs programme have leaked out of Russia, because the living standards in Russia remain low and the overwhelming majority of scientists have a miserable existence.

Intraspecific diversity of Yersinia pestis

Increased interest in the pathogenic potential of Yersinia pestis has emerged because of the potential threats from bioterrorism. Pathogenic potential is based on genetic factors present in a population of microbes, yet most studies evaluating the role of specific genes in virulence have used a limited number of strains. For Y. pestis this issue is complicated by the fact that most strains available for study in the Americas are clonally derived and thus genetically restricted, emanating from a strain of Y. pestis introduced into the United States in 1902 via marine shipping and subsequent spread of this strain throughout North and South America. In countries from the former Soviet Union (FSU), Mongolia, and China there are large areas of enzootic foci of Y. pestis infection containing genetically diverse strains that have been intensely studied by scientists in these countries. However, the results of these investigations are not generally known outside of these countries. Here we describe the variety of methods used in the FSU to classify Y. pestis strains based on genetic and phenotypic variation and show that there is a high level of diversity in these strains not reflected by ones obtained from sylvatic areas and patients in the Americas.

[Evaluation of outcomes of combined specific prophylaxis with the antibiotic resistant immunogenic plague pathogen strain and emergency prophylaxis with aminoglycosides in the experimental plague model in white mice]

It was shown that aminoglycosides (streptomycin, kanamycin, gentamicin, sisomicin, tobramycin, amikacin) prevented manifestation of postvaccine immunity in albino mice immunized by vaccine strain Yersinia pestis EV. Avirulent strain Y. pestis 363 Monr with chromosome resistance to aminoglycosides of the 1st, 2nd and 3rd generations provided manifestation of antiplague immunity when streptomycin, kanamycin, gentamicin and amikacin were administered for prophylaxis. ED50 achieved 1.0-1.2 x 10(3) CFU and in control group (without treatment) 9.3 x 10(2) CFU. Gentamicin and amikacin were highly effective for experimental plague prophylaxis (90-100% animal survival), but inhibited development of postinfective immunity. Protective index (PI) value was 1.1 x 10(2). It was demonstrated that combination of specific prophylaxis (Y. pestis 363 Monr) and emergency prophylaxis with aminoglycosides in albino mice infected with approximately 1000 LD50 of virulent strain Y. pestis 358 (5 hours after infection) was highly effective and provided protective effect against subsequent infection with plague pathogen. Value of PI was 1.1 x 10(5) and practically did not differ from PI (1.7 x 10(5)) in control group (intact mice, immunized with strains EV [symbol: see text] 363 Monr).

[Study of PGM mutation mechanism in Yersinia pestis (plague pathogen) vaccine strain EV76]

Yersinia pestis vaccine strain EV76 is a mutant of the virulent strain which has lost the pigmentation phenotype (Pgm+). This phenotype includes three characteristics: it absorbs pigments from agar media (Hms+), produces a siderophore yersiniabactin (Ybt+), and causes a lethal disease after subcutaneous inoculation of laboratory animals (Vir+). These characteristics are lost simultaneously after high frequency spontaneous deletion of 10 kB fragment of chromosomal DNA, termed the pgm locus. We compared the pgm locus-associated genetic and phenotypical properties of the vaccine strain with those of a typical Pgm- deletion mutant of a virulent strain. The results indicate that Pgm- phenotype of the vaccine strain results not from the deletion of the pgm locus, but from the insertion inactivation of the genes located in this locus. In contrast to the deletion mutant, the vaccine strain carries sequences detected by hybridization and PCR, which are complementary to the pgm locus genes. Moreover, the vaccine strain differed from the deletion mutant by a low level of Hms+ expression, a slower rate of cell death under iron-chelated conditions at 37 degrees C, "residual virulence" upon subcutaneous inoculation, and capacity to form revertants which restore the characteristics of Pgm+ phenotype after cell growth at 12 degrees C.

[Lipid peroxidation and the antioxidant blood system in dynamics of pestilential and choleraic intoxication]

Lipid peroxidation (LPO) and activity of antioxidant system were studied spectrophotometrically in white rats developing pestilential and choleraic intoxication achieved by intraperitoneal injection of plague autolysate of vaccine EB strain in dose equivalent to DL50, cholerain endotoxin in doses DL50 and DL25 as well as combined effect of choleraic endo- and enterotoxins. With progression of the intoxication, the levels of diene conjugates and malonic dialdehyde in blood plasma and erythrocytes rose. LPO activation in plague intoxication arose in high activity of SOD and blood catalase. In choleraic intoxication the activity of the above enzymes progressively lowered.

Plague as a biological weapon: medical and public health management. Working Group on Civilian Biodefense

OBJECTIVE

The Working Group on Civilian Biodefense has developed consensus-based recommendations for measures to be taken by medical and public health professionals following the use of plague as a biological weapon against a civilian population.

PARTICIPANTS

The working group included 25 representatives from major academic medical centers and research, government, military, public health, and emergency management institutions and agencies.

EVIDENCE

MEDLINE databases were searched from January 1966 to June 1998 for the Medical Subject Headings plague, Yersinia pestis, biological weapon, biological terrorism, biological warfare, and biowarfare. Review of the bibliographies of the references identified by this search led to subsequent identification of relevant references published prior to 1966. In addition, participants identified other unpublished references and sources. Additional MEDLINE searches were conducted through January 2000.

CONSENSUS PROCESS

The first draft of the consensus statement was a synthesis of information obtained in the formal evidence-gathering process. The working group was convened to review drafts of the document in October 1998 and May 1999. The final statement incorporates all relevant evidence obtained by the literature search in conjunction with final consensus recommendations supported by all working group members.

CONCLUSIONS

An aerosolized plague weapon could cause fever, cough, chest pain, and hemoptysis with signs consistent with severe pneumonia 1 to 6 days after exposure. Rapid evolution of disease would occur in the 2 to 4 days after symptom onset and would lead to septic shock with high mortality without early treatment. Early treatment and prophylaxis with streptomycin or gentamicin or the tetracycline or fluoroquinolone classes of antimicrobials would be advised.

[The properties of the cellular surface of Yersinia pestis strain EV and its achromogenic variants]

The comparative study of the properties of the surface of vaccine strain Y. pestis EV and its achromogenic variants (AV) differing from the initial strain by decreased immunogenicity and by the morphology of colonies, has been made. The achromogenicity of Y. pestis colonies has been shown to correlate with the loss of the outer membrane protein with a molecular weight 22 kD. The synthesis of this protein is determined by chromosomal genes. AV have been found to have different sensitivity to bacteriophages. The analysis of the electrokinetic potential of Y. pestis EV and its AV has revealed that in the latter have surface charge is considerably greater (1.4- to 1.5-fold). As shown in this study, the hemagglutinating activity of AV with respect to red blood cells of humans with blood group I (O) and guinea pigs is decreased by 1-2 orders and these strains do not agglutinate with sheep red blood cells. The low activity of the initial stage of the phagocytosis of AV by mouse macrophages has been shown. The possible role of the 22 kD proteins as an adhesion factor is discussed.

[The effect of a modification to the lipopolysaccharide of Yersinia pestis on its neutrophilokine-inducing activity]

The ability of the isolated and modified Yersinia pestis LPS to induce the synthesis of the neutrophilokines that regulate the macrophage functional activity was studied. It is established that the Y. pestis LPS detoxication, especially by the method of deacylation, does not lead to the decrease in biological, in particular neutrophilokine-inducing activity of these preparations, but actually even increases it. These results are in agreement with many reports showing the possibility of decreasing the LPS toxicity without reducing immunostimulatory activity of this important component of the outer membrane of gram-negative bacteria.

Failure of intragastrically administered Yersinia pestis capsular antigen to protect mice against challenge with virulent plague: suppression of fraction 1-specific antibody response

We evaluated the Yersinia pestis capsular (fraction 1 [F1]) antigen as a potential oral immunogen in mice. We found that single doses of as much as 0.4 mg of F1, administered by intragastric (ig) intubation, were unprotective and did not stimulate production of detectable levels of specific antibody. Three weekly ig doses resulted in low serum antibody levels that also did not provide protection against challenge with virulent Y. pestis. Assays of type-specific antibody following intubation and subsequent challenge with a subcutaneous inoculation of F1 revealed that the quantity of antigen intubated and the secondary IgG2a antibody levels were inversely related, suggesting the induction of tolerance to intragastrically administered F1 antigen. Transfer of spleen cells from intubated mice to F1 immune recipients failed to demonstrate suppression of specific antibody, indicating that the immune tolerance observed in intubated mice was not due to a T suppressor cell-mediated effect. The results of this study indicate that Y. pestis F1 antigen is not likely to be an efficacious immunogen for oral vaccination of mice against plague.

Potency of killed plague vaccines prepared from avirulent Yersinia pestis

Killed plague vaccines prepared from avirulent strains A1122 and EV76S of Yersinia pestis were more effective in mouse potency tests than samples of Plague Vaccine, USP, prepared from killed Y. pestis of the virulent strain 195/P. Manufacture of vaccine from avirulent Y. pestis would obviate requirements for the large containment facilities that are currently needed for producing Plague Vaccine, USP.

[Electron microscopic study of dry live plague vaccine EB by the scanning method]

Dry live plague vaccine EB was examined under microscope; it appeared that in the mentioned preparation the bacterial cells were enclosed in the artificial sucrose-gelatin capsule of the stabilizer which apparently maintained the vital activity of the microorganisms in the state of anabiosis by forming a stable bond with the bacterial body.

[The effects of enzymes and secretions of the gastrointestinal tract on the EB vaccine strain]

Experiments were conducted in vitro. A study was made of the action of the enzymes and of the secretions of the gastrointestinal tract on the viability of the EB vaccine strain. Sensitivity of bacterial cells to the action of saliva, gastric juice, intestinal contents, trypsin, and bile proved to differ. Gastric juice inactivated the vaccine strain which expressed a satisfactory resistance towards the rest of the factors under study practically immediately. There were revealed no significant morphological changes in the cells subjected to the two-hour action of saliva, bile, trypsin and the intestinal content, by means of the electron microscopic examination. These studies permitted to substantiate the rational form of the preparation for oral administration.

Pathogenicity and immunogenic efficacy of a live attentuated plaque vaccine in vervet monkeys

A live attenuated Yersinia pestis (Pasteurella pestis) vaccine strain designated EV51f, which had been passaged through guinea pigs previously treated with ferrous sulfate, was shown to be pathogenic for African green vervet monkeys (Cercopithecus aethips pygerythrus), but not for guinea pigs. The bacilli multiplied in the monkeys, as shown by positive blood cultures, caused an elevation of white cell counts and rectal temperatures, and resulted in death of 26% (13/50) of animals. Postmortem findings of these animals were typical of bubonic-septicemic plague. This vaccine did not cause deaths in 50 guinea pigs even in doses up to 100 million viable bacilli inoculated subcutaneously. It is suggested that the virulence of an attenuated Y. pestis strain which does not produce pigment on a defined medium containing hemin, but possesses all other known virulence determinants, is dependent on the availability of iron in vivo. The serological response of the monkeys as determined by the hemagglutinating and mouse protective antibodies was high one month after vaccination and also in guinea pigs, as shown by virulent challenge. This antibody level declined in monkeys over a period of nearly 6 months, and a decline in immunity was confirmed by virulent challenge which resulted in the death of 30% of vaccinated monkeys. The level of immunity in monkeys did not appear to be related to the dose of vaccine.