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DOI: 10.30906/2073-8099-2020-12-6-15-23 The possibility of producing a new form of tularemia vaccine — freeze-dried in vials — was experimentally substantiated. A new composition of the medium for drying tularemia microbe cells of the vaccine strain 15 NIIEG was developed. Optimal freeze-drying parameters were determined. The specification characteristics of tularemia vaccine were investigated. It was established that experimentally based methodological procedures for freeze-drying made it possible to obtain a finished dosage form of tularemia vaccine that meets the requirements of normative documentation.

Objective: to study the possibility of applying electro-optical analysis for the assessment of cell viability of tularemia microbe vaccine strain at different stages of experimental live tularemia vaccine production.Materials and methods. The research object was a cell culture of Francisella tularensis 15 NIIEG. Investigations were carried out at all stages of experimental live tularemia vaccine (ELTV) manufacturing according to an advanced technology: cultivation, concentrating, diafiltration, mixing with drying media, stabilization, and storage (two-year period of observation). Electro-optical analysis by the parameter “polarizability anisotropy” of bacterial cell was conducted with the help of EloTrace (EloSystems, Germany). Total concentration of cells was evaluated using density metering at 590 nm and spectrometry – at 650 nm. Viability was assessed through inoculation of plates with FT-agar.Results and discussion. The experiment has demonstrated that the change in polarizability anisotropy of the cell at the frequencies of 900 kHz and 2100 kHz, reflecting the state of cytoplasm and cytoplasmic membrane, respectively, is the earliest response to changes in vital indicators of bacterial culture in the process of cultivation. Thereby, the decrease in viability of F. tularensis cells occurrs well before the decrease in cell concentration. We have shown the preservation of viability of F. tularensis 15 NIIEG cells at all stages of experimental live tularemia vaccine production. Electro-optical analysis allows for registering the changes in vital parameters of microorganism cells in real-time mode, while the assessment of viability applying bacteriological method takes up to 5 days. Different stages of tularemia vaccine manufacturing have impact on the vital indicators of F. tularensis cells, and electro-optical analysis is a prospect method of control of such parameter as “Specific activity (the number of live microbial cells)”.

There is a need for development of an effective vaccine against Francisella tularensis, as this potential bioweapon has a high mortality rate and low infectious dose when delivered via the aerosol route. Moreover, this Tier 1 agent has a history of weaponization. We engineered targeted mutations in the Type A strain F. tularensis subspecies tularensis Schu S4 in aro genes encoding critical enzymes in aromatic amino acid biosynthesis. F. tularensis Schu S4ΔaroC, Schu S4ΔaroD, and Schu S4ΔaroCΔaroD mutant strains were attenuated for intracellular growth in vitro and for virulence in vivo and, conferred protection against pulmonary wild-type (WT) F. tularensis Schu S4 challenge in the C57BL/6 mouse model. F. tularensis Schu S4ΔaroD was identified as the most promising vaccine candidate, demonstrating protection against high-dose intranasal challenge; it protected against 1,000 CFU Schu S4, the highest level of protection tested to date. It also provided complete protection against challenge with 92 CFU of a F. tularensis subspecies holarctica strain (Type B). Mice responded to vaccination with Schu S4ΔaroD with systemic IgM and IgG2c, as well as the production of a functional T cell response as measured in the splenocyte-macrophage co-culture assay. This vaccine was further characterized for dissemination, histopathology, and cytokine/chemokine gene induction at defined time points following intranasal vaccination which confirmed its attenuation compared to WT Schu S4. Cytokine, chemokine, and antibody induction patterns compared to wild-type Schu S4 distinguish protective vs. pathogenic responses to F. tularensis and elucidate correlates of protection associated with vaccination against this agent.

Francisella tularensisis one of several biothreat agents for which a licensed vaccine is needed to protect against this pathogen. To aid in the development of a vaccine protective against pneumonic tularemia, we generated and characterized a panel ofF. tularensisisolates that can be used as challenge strains to assess vaccine efficacy. Our panel consists of both historical and contemporary isolates derived from clinical and environmental sources, including human, tick, and rabbit isolates. Whole genome sequencing was performed to assess the genetic diversity in comparison to the reference genomeF. tularensisSchu S4. Average nucleotide identity analysis showed >99% genomic similarity across the strains in our panel, and pan-genome analysis revealed a core genome of 1,707 genes, and an accessory genome of 233 genes. Three of the strains in our panel, FRAN254 (tick-derived), FRAN255 (a type B strain), and FRAN256 (a human isolate) exhibited variation from the other strains. Moreover, we identified several unique mutations within theFrancisellaPathogenicity Island across multiple strains in our panel, revealing unexpected diversity in this region. Notably, FRAN031 (Scherm) completely lacked the second pathogenicity island but retained virulence in mice. In contrast, FRAN037 (Coll) was attenuated in a murine pneumonic tularemia model and had mutations inpdpBandiglAwhich likely led to attenuation. All of the strains, except FRAN037, retained full virulence, indicating their effectiveness as challenge strains for future vaccine testing. Overall, we provide a well-characterized panel of virulentF. tularensisstrains that can be utilized in ongoing efforts to develop an effective vaccine against pneumonic tularemia to ensure protection is achieved across a rangeF. tularensisstrains.

Tularemia is an anthropozoonotic infection caused by Francisella tularensis. In clinical and sanitary-epidemiological practice, traditional diagnostics methods in tularemia are based on serological assays for detecting specific antibodies, allowing to diagnose it and estimate durability of patients’ immunity after vaccination. Previously, it was shown that specific serum antibodies in patients recovered after tularemia, unlike to those vaccinated with the live tularemia vaccine F. tularensis 15 NIIEG, can interact with specific epitopes on lipopolysaccharides isolated from strains of various subspecies — F. tularensis (Ft) and F. novicida (LPS Fn), while LPS Fn-specific immunoglobulins are lacked in the blood of vaccinated individuals. A set of experiments on identifying antibodies with similar specificity in laboratory animals of various species — mice, guinea pigs and rats with differed sensitivity to tularemia, administered with live tularemia vaccine strain as well as virulent F. tularensis strains to simulate vaccine-mediated and infectious processes, respectively was conducted. A methodical approach has been developed that allows to analyze humoral response in modelled infectious process in animals highly sensitive to tularemia such as BALB/c mice and guinea pigs that consisted of preliminary immunization with live tularemia vaccine followed by infection with virulent F. tularensis strains. It was shown that induction of specific anti-LPS Ft antibodies occured in these animal species, both after vaccination and infection with virulent strains. It was noted that, unlike guinea pigs and rats, mice both during vaccination and infection were characterized by significantly lower titers of LPS Ft-specific antibodies. However, no specific interaction between mouse serum and LPS Fn might be detected. Moreover, two types of immunoglobulins with different antigen specificities to the LPS Ft and LPS Fn epitopes were detected by dot-blot analysis in guinea pigs immunized with live tularemia vaccine, followed by infection with a virulent strain. In addition, antibodies to LPS Fn were also detected in the serum of rats infected with virulent, but not vaccine-based, F. tularensis strains. Thus, previous experimental data on the production of immunoglobulins with different antigenic specificity were confirmed in an experimental tularemia modelled in rats and guinea pigs that demonstrated a diagnostic significance and feasibility of using LPS Fn to confirm tularemia infection in humans.

An inexpensive readily manufactured COVID-19 vaccine that protects against severe disease is needed to combat the pandemic. We have employed the LVS ΔcapB vector platform, previously used successfully to generate potent vaccines against the Select Agents of tularemia, anthrax, plague, and melioidosis, to generate a COVID-19 vaccine. The LVS ΔcapB vector, a replicating intracellular bacterium, is a highly attenuated derivative of a tularemia vaccine (LVS) previously administered to millions of people. We generated vaccines expressing SARS-CoV-2 structural proteins and evaluated them for efficacy in the golden Syrian hamster, which develops severe COVID-19 disease. Hamsters immunized intradermally or intranasally with a vaccine co-expressing the Membrane (M) and Nucleocapsid (N) proteins, then challenged 5-weeks later with a high dose of SARS-CoV-2, were protected against severe weight loss and lung pathology and had reduced viral loads in the oropharynx and lungs. Protection by the vaccine, which induces murine N-specific interferon-gamma secreting T cells, was highly correlated with pre-challenge serum anti-N TH1-biased IgG. This potent vaccine against severe COVID-19 should be safe and easily manufactured, stored, and distributed, and given the high homology between MN proteins of SARS-CoV and SARS-CoV-2, has potential as a universal vaccine against the SARS subset of pandemic causing β-coronaviruses.

Francisella tularensis (F. tularensis) is an intracellular pathogen that causes a potentially debilitating febrile illness known as tularemia. F. tularensis can be spread by aerosol transmission and cause fatal pneumonic tularemia. If untreated, mortality rates can be as high as 30%. To study the host responses to a live-attenuated tularemia vaccine, peripheral blood mononuclear cell (PBMC) samples were assayed from 10 subjects collected pre- and post-vaccination, using both the 2D-DIGE/MALDI-MS/MS and LC-MS/MS approaches. Protein expression related to antigen processing and presentation, inflammation (PPAR&gamma, nuclear receptor), phagocytosis, and gram-negative bacterial infection was enriched at Day 7 and/or Day 14. Protein candidates that could be used to predict human immune responses were identified by evaluating the correlation between proteome changes and humoral and cellular immune responses. Consistent with the proteomics data, parallel transcriptomics data showed that MHC class I and class II-related signals important for protein processing and antigen presentation were up-regulated, further confirming the proteomic results. These findings provide new biological insights that can be built upon in future clinical studies, using live attenuated strains as immunogens, including their potential use as surrogates of protection.

The immune response to live-attenuated Francisella tularensis vaccine and its host evasion mechanisms are incompletely understood. Using RNA-Seq and LC&ndash, MS on samples collected pre-vaccination and at days 1, 2, 7, and 14 post-vaccination, we identified differentially expressed genes in PBMCs, metabolites in serum, enriched pathways, and metabolites that correlated with T cell and B cell responses, or gene expression modules. While an early activation of interferon &alpha, /&beta, signaling was observed, several innate immune signaling pathways including TLR, TNF, NF-&kappa, B, and NOD-like receptor signaling and key inflammatory cytokines such as Il-1&alpha, Il-1&beta, and TNF typically activated following infection were suppressed. The NF-&kappa, B pathway was the most impacted and the likely route of attack. Plasma cells, immunoglobulin, and B cell signatures were evident by day 7. MHC I antigen presentation was more actively up-regulated first followed by MHC II which coincided with the emergence of humoral immune signatures. Metabolomics analysis showed that glycolysis and TCA cycle-related metabolites were perturbed including a decline in pyruvate. Correlation networks that provide hypotheses on the interplay between changes in innate immune, T cell, and B cell gene expression signatures and metabolites are provided. Results demonstrate the utility of transcriptomics and metabolomics for better understanding molecular mechanisms of vaccine response and potential host&ndash, pathogen interactions.

Melioidosis is a particularly dangerous infection caused by Burkholderia pseudomallei , against which a vaccine has not yet been created. In this regard, the development of effective treatment regimens and emergency prevention of melioidosis is very relevant. To improve the effectiveness of emergency prophylaxis of melioidosis, synthetic peptides (bestim, imunofan) and thiopoietin preparation glutoxim were used when combined with the antibiotic doxycycline. In addition, in experiments on white mice, the ability of heterologous vaccines (plague and tularemia), used in the emergency prevention mode, to increase the resistance of animals to melioidosis infection was assessed. It was shown that the most effective was imunofan, which, when combined with doxycycline, increased by 20% the survival rate of 5LD50 Burkholderia pseudomallei infection and significantly increased the average life span of mice infected with 5-12 LD50 (p < 0.05). The efficiency of use for stimulation of non-specific resistance to melioidosis of a heterologous plague vaccine EV, once administered 1 day prior to infection, protected 90% of mice from 6 LD50 Burkholderia pseudomallei and 60% - with an increase in the infectious dose of the pathogen of melioidosis up to 15 LD50. The same level of protection from melioidosis was provided by a 3 day course of antibiotic therapy with doxycycline. It was concluded that the tularemia vaccine is not suitable for immunostimulation in melioidosis due to its high residual virulence and reactogenicity.

Francisella tularensis, which causes tularemia, is an intracellular gram-negative bacterium. F. tularensis has received significant attention in recent decades because of its history as a biological weapon. Thus, development of novel vaccines against tularemia has been an important goal. The attenuated F. tularensis strain ΔpdpC, in which the pathogenicity determinant protein C gene (pdpC) has been disrupted by TargeTron mutagenesis, was investigated as a potential vaccine candidate for tularemia in the present study. C57BL/6J mice immunized s.c. with 1 × 106 CFUs of ΔpdpC were challenged intranasally with 100× the median lethal dose (LD50 ) of a virulent SCHU P9 strain 21 days post immunization. Protection against this challenge was achieved in 38% of immunized C57BL/6J mice administered 100 LD50 of this strain. Conversely, all unimmunized mice succumbed to death 6 days post challenge. Survival rates were significantly higher in vaccinated than in unimmunized mice. In addition, ΔpdpC was passaged serially in mice to confirm its stable attenuation. Low bacterial loads persisted in mouse spleens during the first to tenth passages. No statistically significant changes in the number of CFUs were observed during in vivo passage of ΔpdpC. The inserted intron sequences for disrupting pdpC were completely maintained even after the tenth passage in mice. Considering the stable attenuation and intron sequences, it is suggested that ΔpdpC is a promising tularemia vaccine candidate.

Objective of the study is to evaluate the effect of immunomodulators on the intensity of the post-apoptotic lysis of sensitized organism leukocytes in the presence of specific antigens of tularemia microbe in vitro. Materials and methods . Flow cytometry method was used to determine the relative content of apoptotic and proliferating splenocytes obtained from mice, immunized against tularemia against the background of immunomodulation. Results and conclusions . Obtained is the evidence that is consistent with modern data on the massive leukocyte apoptosis and post-apoptotic leukocyte autolysis (secondary necrosis) in case of tularemia infection. Given the important role of secondary necrosis in the systemic inflammatory response development, the use of immunomodulators suppressing macrophage apoptosis and dead leukocyte lysis, emerging in the course of interaction with Francisella tularensis antigens, may be promising in order to reduce the live tularemia vaccine reactogenicity.

Background Tularemia is caused by Francisella tularensis , a gram-negative bacterium that has been weaponized as an aerosol. For protection of personnel conducting biodefense research, the United States Army required clinical evaluation of a new lot of tularemia live vaccine strain manufactured in accordance with Current Good Manufacturing Practices. Methods A phase 2 randomized clinical trial compared the new lot (DVC-LVS) to the existing vaccine that has been in use for decades (USAMRIID-LVS). The vaccines were delivered by scarification to 228 participants. Safety, reactogenicity, take and/or antibody levels were assessed on days 0, 1, 2, 8, 14, 28, 56, and 180. Principal Results Both vaccines were safe and had acceptable reactogenicity profiles during six months of follow-up. There were no serious or grade 3 and 4 laboratory adverse events. Moderate systemic reactogenicity (mostly headache or feeling tired) was reported by ∼23% of participants receiving either vaccine. Injection site reactogenicity was mostly mild itchiness and pain. The frequencies of vaccine take skin reactions were 73% (95% CI, 64, 81) for DVC-LVS and 80% (95% CI, 71, 87) for USAMRIID-LVS. The 90% CI for the difference in proportions was −6.9% (−16.4, 2.6). The rates of seroconversion measured by microagglutination assay on days 28 or 56 were 94% (95% CI, 88, 98; n = 98/104) for DVC-LVS and 94% (95% CI, 87, 97; n = 103/110) for USAMRIID-LVS (p = 1.00). Day 14 sera revealed more rapid seroconversion for DVC-LVS relative to USAMRIID-LVS: 82% (95% CI, 73, 89) versus 55% (95% CI, 45, 65), respectively (p Major conclusions The DVC-LVS vaccine had similar safety, reactogenicity, take and antibody responses compared to the older USAMRIID vaccine, and was superior for early (day 14) antibody production. Vaccination take was not a sensitive surrogate for seroconversion in a multi-center study where personnel at five research clinics performed assessments. ClinicalTrials.gov identifier NCT01150695

Tularemia natural foci were investigated in the 15 districts of the Voronezh region. 1533 small mammals of 11 species were captured in 2011, 2014 and 2015 to identify antigen and/or DNA of tularemia pathogen. In all the studied areas there are continuous epizootic of tularemia among small mammals. In the region there are permanent natural meadow-field, floodplain- swamp and forest foci. We can assume the existence of another focus, it is a steppe type. The most active foci observed in Kashirsky, Novokhopyorsky, Petropavlosky and Ramonsky districts. The stability and activity of natural foci is maintained by alternating different biocenoses with different animals and complex pathogen exchange between foci. The most active is meadow-field and floodplain-swamp foci. Common vole is the primary carrier of the infection in the meadow-field foci during the year. In the near-water habitats of the epizootic process in strong support of field mouse and common voles. Varied species composition of small mammals provides a long time functioning and epizootic activity of natural tularemia foci. The epidemiological situation is rather calm and stable for tularemia natural foci in the Voronezh region. In the region registered a low incidence of tularemia population. There has been an increase in the incidence of the urban population. Permanent vaccination and revaccination of the population remains the main preventive anti-epidemic measures against tularemia. The results indicate the functioning and epizootic activity of tularemia natural foci in Voronezh region. It requires constant monitoring of the territory and preventive interventions, primarily vaccination of people live tularemia vaccine.

Background: Tularemia is a potential biological weapon due to its high infectivity and ease of dissemination. This study aimed to characterize the innate and adaptive responses induced by two different lots of a live attenuated tularemia vaccine and compare them to other well-characterized viral vaccine immune responses. Methods: Microarray analyses were performed on human peripheral blood mononuclear cells (PBMCs) to determine changes in transcriptional activity that correlated with changes detected by cellular phenotyping, cytokine signaling, and serological assays. Transcriptional profiles after tularemia vaccination were compared with yellow fever [YF-17D], inactivated [TIV], and live attenuated [LAIV] influenza. Results: Tularemia vaccine lots produced strong innate immune responses by Day 2 after vaccination, with an increase in monocytes, NK cells, and cytokine signaling. T cell responses peaked at Day 14. Changes in gene expression, including upregulation of STAT1, GBP1, and IFIT2, predicted tularemia-specific antibody responses. Changes in CCL20 expression positively correlated with peak CD8+ T cell responses, but negatively correlated with peak CD4+ T cell activation. Tularemia vaccines elicited gene expression signatures similar to other replicating vaccines, inducing early upregulation of interferon-inducible genes. Conclusions: A systems vaccinology approach identified that tularemia vaccines induce a strong innate immune response early after vaccination, similar to the response seen after well-studied viral vaccines, and produce unique transcriptional signatures that are strongly correlated to the induction of T cell and antibody responses.

The study of the humoral immune response to infectious and chronic diseases is important for understanding the disease progression, identification of protective antigens, vaccine development, and discovery of biomarkers for early diagnosis. Proteomic approaches, including serological proteome analysis (SERPA), have been used to identify the repertoire of immunoreactive proteins in various diseases. In this chapter, we provide an outline of the SERPA approach, using the analysis of sera from mice vaccinated with a live attenuated tularemia vaccine as an example., Series: Methods in Molecular Biology

Francisella tularensis is the causative agent of tularemia and has gained recent interest as it poses a significant biothreat risk. F. novicida is commonly used as a laboratory surrogate for tularemia research due to genetic similarity and susceptibility of mice to infection. Currently, there is no FDA-approved tularemia vaccine, and identifying therapeutic targets remains a critical gap in strategies for combating this pathogen. Here, we investigate the soluble lytic transglycosylase or Slt in F. novicida, which belongs to a class of peptidoglycan-modifying enzymes known to be involved in cell division. We assess the role of Slt in biology and virulence of the organism as well as the vaccine potential of the slt mutant. We show that the F. novicida slt mutant has a significant growth defect in acidic pH conditions. Further microscopic analysis revealed significantly altered cell morphology compared to wild-type, including larger cell size, extensive membrane protrusions, and cell clumping and fusion, which was partially restored by growth in neutral pH or genetic complementation. Viability of the mutant was also significantly decreased during growth in acidic medium, but not at neutral pH. Furthermore, the slt mutant exhibited significant attenuation in a murine model of intranasal infection and virulence could be restored by genetic complementation. Moreover, we could protect mice using the slt mutant as a live vaccine strain against challenge with the parent strain; however, we were not able to protect against challenge with the fully virulent F. tularensis Schu S4 strain. These studies demonstrate a critical role for the Slt enzyme in maintaining proper cell division and morphology in acidic conditions, as well as replication and virulence in vivo. Our results suggest that although the current vaccination strategy with F. novicida slt mutant would not protect against Schu S4 challenges, the Slt enzyme could be an ideal target for future therapeutic development.

Tularemia is a severe infectious zoonotic disease caused by Francisella tularensis. Although F. tularensis is considered to be a potential biological weapon due to its high infectivity and mortality rate, no vaccine has been currently licensed. Recently, we reported that F. tularensis SCHU P9 derived ΔpdpC strain lacking the pathogenicity determinant protein C gene conferred stable and good protection in a mouse lethal model. In this study, the protective effect of ΔpdpC was evaluated using a monkey lethal model. Two cynomolgus macaques (Macaca fascicularis) intratracheally challenged with the virulent strain SCHU P9 were euthanized on 7 and 11 days post-challenge after the development of severe clinical signs. The bacterial replication in alveolar macrophages and type II epithelial cells in the lungs would cause severe pneumonia accompanied by necrosis. Conversely, two animals subcutaneously immunized with ΔpdpC survived 3 weeks after SCHU P9 challenge. Though one of the two animals developed mild symptoms of tularemia, bacterial replication was limited in the respiratory organs, which may be due to a high level of humoral and cellular immune responses against F. tularensis. These results suggest that the ΔpdpC mutant would be a safe and promising candidate as a live attenuated tularemia vaccine.

T cells are the immunological cornerstone in host defense against infections by intracellular bacterial pathogens, such as virulent Francisella tularensis spp. tularensis (Ftt). The general paucity of novel vaccines for Ftt during the past 60 y can, in part, be attributed to the poor understanding of immune parameters required to survive infection. Thus, we developed a strategy utilizing classical immunological tools to elucidate requirements for effective adaptive immune responses directed against Ftt. Following generation of various Francisella strains expressing well-characterized lymphocytic choriomeningitis virus epitopes, we found that survival correlated with persistence of Ag-specific CD4+ T cells. Function of these cells was confirmed in their ability to more effectively control Ftt replication in vitro. The importance of understanding the Ag-specific response was underscored by our observation that inclusion of an epitope that elicits high-avidity CD4+ T cells converted a poorly protective vaccine to one that engenders 100% protection. Taken together, these data suggest that improved efficacy of current tularemia vaccine platforms will require targeting appropriate Ag-specific CD4+ T cell responses and that elucidation of Francisella epitopes that elicit high-avidity CD4+ T cell responses, specifically in humans, will be required for successful vaccine development.

Objective of the study was to develop and test new biotechnological approaches for live tularemia vaccine production. Materials and methods: Francisella tularensis 15 NIIEG strain was used as producer-strain; Francisella tularensis 503 strain – as test infecting one. Producer strain was cultivated on solid and liquid nutrient media. Tangential ultrafiltration was performed with the help of microfiltration module “Viva-flow”. Lyophilization was conducted using drying installation – Free Zone 2.5 L. Results and discussion: Application of the designed liquid nutrient medium on the basis of enzymatic fibrin hydrolysate and submerged cultivation of the producer-strain has allowed for a significant biomass yield increment. At the stage of tularemia microbe culture concentration via microfiltration through filtering membranes with pore size of 0.2 μm, in the mode of tangential liquid flow, increased has been the content of microbe cells; the nutrient media residues – removed. Comparative analysis of the obtained in accordance with experimental technique laboratory series of the vaccine and commercial preparation of live tularemia vaccine has demonstrated their conformity with the specific normative properties. It is established that application of modified liquid nutrient medium, submerged cultivation conditions, methods of biomass concentration and separation has no negative influence on the main properties of live tularemia vaccine and will provide for considerable produce-ability increase in the future.

Francisella tularensis (Ft) is a Category A biothreat agent for which there currently is no FDA-approved vaccine. Thus, there is a substantial effort underway to develop an effective tularemia vaccine. While it is well established that gender can significantly impact susceptibility to primary infection, the impact of gender on vaccine efficacy is not well established. Thus, development of a successful vaccine against tularemia will require an understanding of the impact gender has on vaccine-induced protection against this organism. In this study, a role for gender in vaccine-induced protection following Ft challenge is identified for the first time. In the present study, mucosal vaccination with inactivated Ft (iFt) LVS elicited gender-based protection in C57BL/6Tac mice against respiratory challenge with Ft LVS. Specifically, vaccinated male mice were more susceptible to subsequent Ft LVS challenge. This increased susceptibility in male mice correlated with increased bacterial burden, increased tissue inflammation, and increased proinflammatory cytokine production late in post-challenge infection. In contrast, improved survival of iFt-vaccinated female mice correlated with reduced bacterial burden and enhanced levels of Ft-specific Abs in serum and broncho-alveolar lavage (BAL) fluid post-challenge. Furthermore, vaccination with a live attenuated vaccine consisting of an Ft LVS superoxide dismutase (SodB) mutant, which has proven efficacious against the highly virulent Ft SchuS4 strain, demonstrated similar gender bias in protection post-Ft SchuS4 challenge. Of particular significance is the fact that these are the first studies to demonstrate that gender differences impact disease outcome in the case of lethal respiratory tularemia following mucosal vaccination. In addition, these studies further emphasize the fact that gender differences must be a serious consideration in any future tularemia vaccine development studies.

Tularemia is a highly infectious and contagious disease caused by the bacterium Francisella tularensis. To better understand human response to a live-attenuated tularemia vaccine and the biological pathways altered post-vaccination, healthy adults were vaccinated, and plasma was collected pre- and post-vaccination for longitudinal lipidomics studies. Using tandem mass spectrometry, we fully characterized individual lipid species within predominant lipid classes to identify changes in the plasma lipidome during the vaccine response. Separately, we targeted oxylipins, a subset of lipid mediators involved in inflammatory pathways. We identified 14 differentially abundant lipid species from eight lipid classes. These included 5-hydroxyeicosatetraenoic acid (5-HETE) which is indicative of lipoxygenase activity and, subsequently, inflammation. Results suggest that 5-HETE was metabolized to a dihydroxyeicosatrienoic acid (DHET) by day 7 post-vaccination, shedding light on the kinetics of the 5-HETE-mediated inflammatory response. In addition to 5-HETE and DHET, we observed pronounced changes in 34:1 phosphatidylinositol, anandamide, oleamide, ceramides, 16:1 cholesteryl ester, and other glycerophospholipids, several of these changes in abundance were correlated with serum cytokines and T cell activation. These data provide new insights into alterations in plasma lipidome post-tularemia vaccination, potentially identifying key mediators and pathways involved in vaccine response and efficacy.

Francisella tularensis is the causative agent of tularemia and a Tier I bioterrorism agent. In the 1900s, several vaccines were developed against tularemia including the killed "Foshay" vaccine, subunit vaccines comprising F. tularensis protein(s) or lipoproteins(s) in an adjuvant formulation, and the F. tularensis Live Vaccine Strain (LVS); none were licensed in the U.S.A. or European Union. The LVS vaccine retains toxicity in humans and animals-especially mice-but has demonstrated efficacy in humans, and thus serves as the current gold standard for vaccine efficacy studies. The U.S.A. 2001 anthrax bioterrorism attack spawned renewed interest in vaccines against potential biowarfare agents including F. tularensis. Since live attenuated-but not killed or subunit-vaccines have shown promising efficacy and since vaccine efficacy against respiratory challenge with less virulent subspecies holarctica or F. novicida, or against non-respiratory challenge with virulent subsp. tularensis (Type A) does not reliably predict vaccine efficacy against respiratory challenge with virulent subsp. tularensis, the route of transmission and species of greatest concern in a bioterrorist attack, in this review, we focus on live attenuated tularemia vaccine candidates tested against respiratory challenge with virulent Type A strains, including homologous vaccines derived from mutants of subsp. holarctica, F. novicida, and subsp. tularensis, and heterologous vaccines developed using viral or bacterial vectors to express F. tularensis immunoprotective antigens. We compare the virulence and efficacy of these vaccine candidates with that of LVS and discuss factors that can significantly impact the development and evaluation of live attenuated tularemia vaccines. Several vaccines meet what we would consider the minimum criteria for vaccines to go forward into clinical development-safety greater than LVS and efficacy at least as great as LVS, and of these, several meet the higher standard of having efficacy ≥LVS in the demanding mouse model of tularemia. These latter include LVS with deletions in purMCD, sodBFt , capB or wzy; LVS ΔcapB that also overexpresses Type VI Secretion System (T6SS) proteins; FSC200 with a deletion in clpB; the single deletional purMCD mutant of F. tularensis SCHU S4, and a heterologous prime-boost vaccine comprising LVS ΔcapB and Listeria monocytogenes expressing T6SS proteins.

Francisella tularensis is an intracellular bacterium that causes the disease tularemia. There are several subspecies of F. tularensis whose ability to cause disease varies in humans. The most virulent subspecies, tularensis, is a Tier One Select Agent and a potential bioweapon. Although considerable effort has made to generate efficacious tularemia vaccines, to date none have been licensed for use in the United States. Despite the lack of a tularemia vaccine, we have learned a great deal about the adaptive immune response the underlies protective immunity. Herein, we detail the animal models commonly used to study tularemia and their recapitulation of human disease, the field's current understanding of vaccine-mediated protection, and discuss the challenges associated with new vaccine development.

Live vaccine used in Russia against tularemia is based on Francisella tularensis subsp. holarctica NIIEG vaccine strain 15. This vaccine is highly effective, but fairly unstable. Therefore, the development of stable live tularemia vaccine with minimal side effects is rather pressing. F. tularensis iglC gene is required for intracellular production of the microbe, and recA gene is crucial for homologous recombination. Using methodology for allele removal, we deleted one copy of iglC gene and both copies of recA gene in F. tularensis vaccine strain. To achieve replacement of intact F. tularensis chromosome segments with modified segments, we constructed a novel pGM5 suicide vector based on pHV33 bireplicon plasmid. Modified chromosome segments contained a F. tularensis DNA fragment without 545 bp of iglC structural gene segment (in pGMΔiglC plasmid) and lacked a 1060-bp DNA fragment containing recA structural gene segment (pGMΔrecA plasmid). The constructed 15/23-lΔrecA mutant was capable to reproduce in macrophage-like J77A.l cell line with proliferation efficiency eight to ten times higher than parent vaccine strain 15. BALB/c mouse responded to immunization by 15/23-lΔrecA strain with a slight (about 2%) weight decrease compared to infection with strain 15 (about 14%). Bacteria of 15/23-lΔrecA strain were virtually incapable of maintaining germination in BALB/c murine spleen 14 days after invasion. In turn, bacteria of strain 15 were detected in murine spleen even after 21 days. Thus, F. tularensis 15/23-lΔrecA strain, which results in a lighter organismal reaction, can be successfully used as a basis for construction of stable live tularemia vaccines with minimal side effects.

Within the frames of the investigation on constructing of an improved live tularemia vaccine with less reactogenicity by the method of allelic replacement using a suicidal plasmid pGM5, the mutant variants have been obtained from the vaccine strain Francisella tularensis 15 NIIEG with a reduced expression of the superoxide dismutase sodB gene. This reduction was a result of the substitution of rare for frequent natural codons in the F e-superoxide dismutase (FeSOD) gene. It was shown that the decrease in the FeSOD production up to 30% of the level in the original strain had no negative effect on the rate of the tularemia cause reproduction. It was shown that the mutant strains were more sensitive to hydrogen peroxide and paraquat as compared to the vacci- he bacteria. All the strains were shown (by Q-PCR) to have at the log phase the elevated content of gene groEL mRNA encoding GroEL chaperone.

Pulmonary infection with the bacterium Francisella tularensis can lead to the serious and potentially fatal disease, tularemia, in humans. Due to the current lack of an approved tularemia vaccine for humans, research is focused on vaccine development utilizing appropriate animal models. The Fischer 344 rat has emerged as a model that reflects human susceptibility to F. tularensis infection, and thus is an attractive model for tularemia vaccine development. Intratracheal inoculation of the Fischer 344 rat with F. tularensis mimics pulmonary exposure in humans. The successful delivery into the rat trachea is critical for pulmonary delivery. A laryngoscope with illumination is used to properly intubate the tracheae of anesthetized rats; the correct placement within the trachea is determined by a simple device to detect breathing. Following intubation, the F. tularensis culture is delivered in a measured dose via syringe. This technique standardizes pulmonary delivery of F. tularensis within the rat trachea to evaluate vaccine efficacy.

Global gene expression profile changes were monitored in human peripheral blood mononuclear cells (PBMCs) after challenge with the live vaccine strain (LVS) of Francisella tularensis. Because these PBMCs were from individuals previously immunized with LVS, stimulating these cells with LVS should activate memory responses. The Ingenuity Pathway Analysis tool identified pathways, functions, and networks associated with this in vitro recall response, including novel pathways triggered by the memory response. Dendritic cell (DC) maturation was the most significant among the more than 25 relevant pathways discovered. Interleukin 15, granulocyte-macrophage colony-stimulating factor, and triggering receptor expressed on myeloid cells 1 signaling pathways were also significant. Pathway analysis indicated that Class 1 antigen presentation may not be optimal with LVS vaccination. The top three biological functions were antigen presentation, cell-mediated and humoral immune responses. Network analysis revealed that the top network associated with these functions had IFNγ and TNFα in central interactive positions. Our results suggest that DC maturation is a key factor in the recall responses and that more effective antigen processing and presentation is needed for cytotoxic T lymphocyte responses. Taken together, these considerations are critical for future tularemia vaccine development studies.

Designed is an experimental preparation of a prototype chemical tularemia vaccine (PCTV). It is composed of protective antigenic complex (PAC) of tularemia microbe and S-layer protein (Slp) of plague microbe. Determined is optimum ratio of these components in the preparation and schedule of its administration. Displayed are the results of its testing as regards physical-chemical properties, reactogenicity, specific activity and impact on the immune system of laboratory animals. It is found out that preparation of the prototype is non-toxic for white mice and Guinea pigs and has no damaging effect on their immune systems. Single-stage subcutaneous immunization with PCTV induces elaboration of high-level adaptive immunity in laboratory animals within 14–21 days: specific antibody generation and stimulation of immune system cell component. PCTV protective index for white mice in case of experimental tularemia, caused by Francisella tularensis subsp. holarctica , is 87,5 % on average; in case of infecting with F. tularensis subsp. nearctica – 50 %; and high-level immunity in both cases. High potency of the experimental preparation against tularemia caused by subsp. holarctica (protective index is 75 %) and high-grade immunity persistence is verified on the model of Guinea pigs too.

Francisella tularensis (Ft) is a Category A biothreat agent for which there is no FDA-approved vaccine. Ft can survive in a variety of habitats with a remarkable ability to adapt to changing environmental conditions. Furthermore, Ft expresses distinct sets of antigens (Ags) when inside of macrophages (its in vivo host) as compared to those grown in vitro with Mueller Hinton Broth medium (MHB). However, in contrast to MHB-grown Ft, Ft grown in Brain Heart Infusion medium (BHI) more closely mimics the antigenic profile of macrophage-grown Ft. Thus, we anticipated that when used as a vaccine, BHI-grown Ft would provide better protection compared to MHB-grown Ft, due primarily to its greater antigenic similarity to Ft circulating inside the host (macrophages) during natural infection. Our investigation however revealed that inactivated Ft (iFt) grown in MHB (iFt-MHB) exhibited superior protective activity when used as a vaccine, as compared to iFt grown in BHI (iFt-BHI). The superior protection afforded by iFt-MHB compared to that of iFt-BHI was associated with significantly lower bacterial burden and inflammation in the lungs and spleens of vaccinated mice. Moreover, iFt-MHB also induced increased levels of Ft-specific IgG. Further evaluation of early immunological cues also revealed that iFt-MHB exhibits increased engagement of Ag presenting cells (APCs) including: increased iFt binding to dendritic cells (DCs), increased expression of costimulatory markers, and increased secretion of pro-inflammatory cytokines. Importantly, these studies directly demonstrate that Ft growth conditions strongly impact Ft vaccine efficacy and that the growth medium used to produce whole cell vaccines to Ft must be a key consideration in the development of a tularemia vaccine.

Francisella tularensis (Ft) is a gram-negative intercellular pathogen and category A biothreat agent. However, despite 15 years of strong government investment and intense research focused on the development of a US Food and Drug Administration-approved vaccine against Ft, the primary goal remains elusive. This article reviews research efforts focused on developing an Ft vaccine, as well as a number of important factors, some only recently recognized as such, which can significantly impact the development and evaluation of Ft vaccine efficacy. Finally, an assessment is provided as to whether a US Food and Drug Administration-approved Ft vaccine is likely to be forthcoming and the potential means by which this might be achieved.

There is very limited evidence concerning the phenotype, function, and homing characteristics of memory T (T(M)) cells elicited by vaccination against intracellular bacteria in humans. Here we studied T(M) subsets elicited by exposure to Francisella tularensis in humans as a model of immunity to intracellular bacteria. To this end, T(M) cells were evaluated in two groups: (1) subjects immunized with live attenuated tularemia vaccine by skin scarification and (2) tularemia naturally infected subjects. In both groups the immune responses were mediated by CD4(+) and CD8(+) effector T(M) cells, mostly CD45RA(-)CD62L(-) and CD45RA(+)CD62L(-). Based on the expression of CD27, integrins alpha(4)/beta(7,) and alpha(4)/beta(1), it is likely that some of these T(M) cells have lytic potential and the ability to enter both mucosal and non-mucosal sites. Thus, regardless of whether by immunization or natural exposure, tularemia antigens elicited a broad spectrum of specific T(M) subsets with diverse homing characteristics.

A disadvantage of several old vaccines is that the genetic events resulting in the attenuation are often largely unknown and reversion to virulence cannot be excluded. In the 1950s, a live vaccine strain, LVS, was developed from a type B strain of Francisella tularensis , the causative agent of tularemia. LVS, which is highly attenuated for humans but still virulent for mice by some infection routes, has been extensively studied and found to protect staff from laboratory-acquired tularemia. The efforts to improve biopreparedness have identified a demand for a vaccine against tularemia. Recently the rapid progress in genomics of different Francisella strains has led to identification of several regions of differences (RDs). Two genes carried within RDs, pilA , encoding a putative type IV pilin, and FTT0918, encoding an outer membrane protein, have been linked to virulence. Interestingly, LVS has lost these two genes via direct repeat-mediated deletions. Here we show that reintroduction of the two deleted regions restores virulence of LVS in a mouse infection model to a level indistinguishable from that of virulent type B strains. The identification of the two attenuating deletion events could facilitate the licensing of LVS for use in humans.

Vaccination of mice with Francisella tularensis live vaccine strain (LVS) mutants described so far have failed to induce protection in C57BL/6 mice against challenge with the virulent strain F. tularensis SchuS4. We have previously reported that a mutant of F. tularensis LVS deficient in iron superoxide dismutase (sodB(Ft)) is hypersensitive to oxidative stress and attenuated for virulence in mice. Herein, we evaluated the efficacy of this mutant as a vaccine candidate against respiratory tularemia caused by F. tularensis SchuS4. C57BL/6 mice were vaccinated intranasally (i.n.) with the sodB(Ft) mutant and challenged i.n. with lethal doses of F. tularensis SchuS4. The level of protection against SchuS4 challenge was higher in sodB(Ft) vaccinated group as compared to the LVS vaccinated mice. sodB(Ft) vaccinated mice following SchuS4 challenge exhibited significantly reduced bacterial burden in lungs, liver and spleen, regulated production of pro-inflammatory cytokines and less severe histopathological lesions compared to the LVS vaccinated mice. The sodB(Ft) vaccination induced a potent humoral immune response and protection against SchuS4 required both CD4 and CD8 T cells in the vaccinated mice. sodB(Ft) mutants revealed upregulated levels of chaperonine proteins DnaK, GroEL and Bfr that have been shown to be important for generation of a potent immune response against Francisella infection. Collectively, this study describes an improved live vaccine candidate against respiratory tularemia that has an attenuated virulence and enhanced protective efficacy than the LVS.

Tularemia is an endemic zoonotic infection caused by Francisella tularensis, which primarily causes infection in humans who have handled contaminated animal tissue or have been bitten by infected arthropods. Because of its ease of dispersion and transmission and its high degree of infectivity, F. tularensis is also considered to be a bioterrorism agent. Consequently, there is renewed interest in the development of safe, effective measures, such as vaccines, to prevent the morbidity and mortality associated with aerosol exposure to F. tularensis. Current efforts, however, are hampered by the lack of an animal model that faithfully reproduces human infection. Employing a model of "induced human infection" with aerosol administration of F. tularensis, Dr. Theodore E. Woodward and colleagues pioneered the clinical studies of tularemia vaccines that form the basis for current tularemia vaccine research.

The T lymphocyte antigens, which may have a role in protection against tularemia, were predicted by immunoinformatics analysis of Francisella tularensis Schu4. Twenty-seven class II putative promiscuous epitopes and 125 putative class I supertype epitopes were chosen for synthesis; peptides were tested in vitro for their ability to bind HLA and to induce immune responses from PBMCs of 23 previously infected subjects. While the immune responses of individual subjects showed heterogeneity, 95% of the subjects responded strongly to a pool of 27 promiscuous peptides; 25%, 33%, and 44% of subjects responded to pools of 25 A2, A24, and B7 peptides, respectively. These data can aid in the development of novel epitope-based and subunit tularemia vaccines.

Introduction. Live vaccine strain (LVS) Francisella tularensis is a live, attenuated investigational tularemia vaccine that has been used by the US Army for decades to protect laboratory workers. Postvaccination bacterial kinetic characteristics of LVS at the inoculation site and in the blood are unknown and, therefore, were assessed in a prospective study. LVS vaccination of laboratory workers provided the opportunity to compare culture with polymerase chain reaction (PCR) for the detection of F. tularensis in human clinical samples. Methods. Blood and skin swab samples were prospectively collected from volunteers who received the LVS tularemia vaccine at baseline (negative controls) and at 5 specified time points (days 1, 2, 7 or 8, 14 or 15, and 35 after vaccination). Bacterial culture and PCR of whole blood samples (17 volunteers) and inoculation site swabs (41 volunteers) were performed. Results. The culture and PCR results of all blood samples were negative. Results of real-time PCR from the inoculation site samples were positive for 41 (100%) of 41 volunteers on day 1, for 40 (97.6%) of 41 volunteers on day 2, for 24 (58.5%) of 41 on day 7 or 8, for 6 (16.7%) of 36 on day 14 or 15, and for 0 (0%) of 9 on day 35. Positive results of bacterial cultures of the inoculation site samples occurred significantly less frequently, compared with PCR testing, with 4 (9.8%) of 41 volunteers having positive results on day 1 ( ) and 4 P ! .001 (9.8%) of 41 on day 2 ( ); all results from subsequent days were negative. P ! .001 Conclusions. F. tularensis LVS genomic DNA was detected in the majority of samples from the inoculation site up to 1 week after LVS vaccination, with real-time PCR being more sensitive than culture. Our data suggest that bacteremia does not occur after LVS vaccination in normal, healthy human volunteers.