Induced pluripotent stem cells as a tool for comparative physiology: lessons from the thirteen-lined ground squirrel.

Comparative physiologists are often interested in adaptive physiological phenomena found in unconventional model organisms; however, research on these species is frequently constrained by the limited availability of investigative tools. Here, we propose that induced pluripotent stem cells (iPSCs) from unconventional model organisms may retain certain species-specific features that can consequently be investigated in depth in vitro; we use hibernating mammals as an example. Many species (including ground squirrels, bats and bears) can enter a prolonged state of physiological dormancy known as hibernation to survive unfavorable seasonal conditions. Our understanding of the mechanisms underpinning the rapid transition and adaptation to a hypothermic, metabolically suppressed winter torpor state remains limited partially because of the lack of an easily accessible model. To address the fascinating unanswered questions underlying hibernation biology, we have developed a powerful model system: iPSCs from a hibernating species, the thirteen-lined ground squirrel (Ictidomys tridecemlineatus). These stem cells can potentially be differentiated into any cell type, and can be used for the analysis of cell-autonomous mechanisms that facilitate adaptation to hibernation and for comparisons with non-hibernators. Furthermore, we can manipulate candidate molecular and cellular pathways underlying relevant physiological phenomena by pharmacological or RNAi-based methods, and CRISPR/Cas9 gene editing. Moreover, iPSC strategies can be applied to other species (e.g. seals, naked mole rats, humming birds) for in vitro studies on adaptation to extreme physiological conditions. In this Commentary, we discuss factors to consider when attempting to generate iPSCs from unconventional model organisms, based on our experience with the thirteen-lined ground squirrel.

PiggyMac, a domesticated piggyBac transposase involved in programmed genome rearrangements in the ciliate Paramecium tetraurelia.

Programmed genome rearrangements drive functional gene assembly in ciliates during the development of the somatic macronucleus. The elimination of germline sequences is directed by noncoding RNAs and is initiated by DNA double-strand breaks, but the enzymes responsible for DNA cleavage have not been identified. We show here that PiggyMac (Pgm), a domesticated piggyBac transposase, is required for these rearrangements in Paramecium tetraurelia. A GFP-Pgm fusion localizes in developing macronuclei, where rearrangements take place, and RNAi-mediated silencing of PGM abolishes DNA cleavage. This is the first in vivo evidence suggesting an essential endonucleolytic function of a domesticated piggyBac transposase.

The Syk-binding ubiquitin ligase c-Cbl mediates signaling-dependent B cell receptor ubiquitination and B cell receptor-mediated antigen processing and presentation.

B cell receptor (BCR)-mediated antigen (Ag) processing and presentation lead to B cell-T cell interactions, which support affinity maturation and immunoglobulin class switching. These interactions are supported by generation of peptide-MHC class II complexes in multivesicular body-like MIIC compartments of B cells. Previous studies have shown that trafficking of Ag·BCR complexes to MVB-like MIIC occurs via an ubiquitin-dependent pathway and that ubiquitination of Ag·BCR complexes occurs by an Src family kinase signaling-dependent mechanism that is restricted to lipid raft-resident Ag·BCR complexes. This study establishes that downstream Syk-dependent BCR signaling is also required for BCR ubiquitination and BCR-mediated antigen processing and presentation. Knockdown studies reveal that of the two known Syk-binding E3 ubiquitin ligases c-Cbl and Cbl-b, only c-Cbl appears to have a central role in BCR ubiquitination, trafficking to MIIC, and ubiquitin-dependent BCR-mediated antigen processing and presentation. These results establish the novel role for Syk signaling and the Syk-binding ubiquitin ligase c-Cbl in the BCR-mediated processing and presentation of cognate antigen and define one mechanism by which antigen-induced BCR ubiquitination is modulated to impact the initiation and maturation of the humoral immune response.

Physiological-range temperature changes modulate cognate antigen processing and presentation mediated by lipid raft-restricted ubiquitinated B cell receptor molecules.

BCR-mediated Ag processing and presentation is critical to the initiation and control of a humoral immune response. Trafficking of internalized Ag-BCR complexes to intracellular Ag processing compartments is driven by ubiquitination of the cytoplasmic domain of the BCR. Using a biochemical approach, it is here established that ubiquitinated Ag-BCR complexes are formed via a signaling-dependent mechanism and restricted to plasma membrane lipid rafts. Because the structure of lipid rafts is temperature sensitive, the impact of physiological-range temperature changes (PRTCs; 33-39°C) on lipid raft-dependent and -independent BCR functions was investigated. Whereas the kinetics of lipid raft-independent BCR internalization is unaffected by temperature changes within this range, raft-dependent BCR signaling and ubiquitination as well as BCR-mediated Ag processing are significantly affected. The extent and duration of Ag-BCR ubiquitination is increased and prolonged at 37-39°C (normal to febrile temperature) compared with that at 33°C (peripheral body temperature). As might be expected, increased temperature also accelerates the overall kinetics of Ag-BCR degradation. Notably, at 33°C the expression of peptide-MHC class II complexes derived from the BCR-mediated processing of cognate Ag is profoundly slowed, whereas the kinetics of expression of peptide-MHC class II complexes derived from fluid-phase Ag processing remains unchanged. These results establish the effect of PRTCs on multiple lipid raft-dependent BCR functions including the processing and presentation of cognate Ag, suggesting one mechanism by which PRTCs, such as fever, may impact the initiation and/or maturation of a humoral immune response.

Statistical learning in visual search reflects distractor rarity, not only attentional suppression.

In visual search tasks, salient distractors may capture attention involuntarily, but interference can be reduced when the salient distractor appears more frequently on one out of several possible positions. The reduction was attributed to attentional suppression of the high-probability position. However, all previous studies on this topic compared performance on the high-probability position to the remaining positions, which had a low probability of containing the distractor. Therefore, it is not clear whether the difference resulted from reduced interference on the high-probability position or from increased interference on the low-probability positions. To decide between these alternatives, we compared high-probability and low-probability with equal-probability positions. Consistent with attentional suppression, interference was reduced on the high-probability position compared with equal-probability positions. However, there was also an increase in interference on low-probability positions compared with equal-probability positions. The increase is in line with previous reports of boosted interference when distractors are rare. Our results show that the experimental design used in previous research is insufficient to separate effects of attentional suppression and those of distractor rarity.

Suicide Risk Among Military Veterans in the Southwestern United States Before and During the COVID-19 Pandemic.

INTRODUCTION: Military Veterans have an increased risk of suicide compared to the general population, but less is known about changes in risk with the onset of the COVID-19 pandemic, or whether any changes have been moderated by psychiatric or demographic factors. The primary objective was to test the hypothesis that the likelihood of suicide attempt or death by suicide was stable during the first year of the pandemic versus the preceding year for the full sample. A second objective was to test the hypothesis that, in contrast, risk increased for Veteran subgroups characterized by traditional risk factors (e.g., psychiatric diagnosis). MATERIALS AND METHODS: We extracted electronic health record data for 771,570 Veterans who received one or more health care visits between March 13, 2019, and March 12, 2021, at eight VA hospitals across the southwestern United States. Primary outcome measures were suicide attempts and deaths by suicide. Predictor variables included psychiatric diagnoses and demographic factors. RESULTS: Multivariable models indicated that the odds of death by suicide did not change during the first year of the COVID-19 pandemic, while the odds of making a suicide attempt declined. Veterans treated for major depression were at heightened risk for attempting suicide in both years, but the association was smaller during the pandemic than the year prior. In contrast, the relative risk of attempt for Veterans who were never married and Veterans treated for a non-alcohol, non-opioid substance-use disorder increased during the pandemic. CONCLUSIONS AND RELEVANCE: The findings suggest that the pandemic has not led to an increase in suicidal behavior, which is consistent with other studies, although the degree of decline varied across diagnostic and demographic groups. Further longitudinal research is needed to evaluate whether the prolonged nature of COVID-19 may lead to changes in risk over time.

Relationship Variables in Group Psychotherapy for Women Sexual Trauma Survivors.

This study examined relational group psychotherapy processes, including group cohesion, bond with group leaders, perceptions of shame, and posttraumatic stress disorder (PTSD) symptomatology for sexual trauma survivors. Six separate treatment groups of women who were either adult sexual assault survivors (N = 24) or adult survivors of childhood sexual abuse (N = 9) participated in the study. Participants completed the Posttraumatic Stress Disorder Checklist for DSM-5 (PCL-5) pre- and posttreatment, the Group Climate Questionnaire, Bond scale of the Working Alliance Inventory Short Form (WAI-S), and Compass of Shame Scale at four intervals. Growth curve models analyzed Engagement, Bond, and Shame Reactions over time. PCL-5 scores were compared pre- and posttreatment and examined in relationship to the process variables of Engagement and Bond. Results showed increases in group cohesion and perceptions of Bond with group leaders and decreases in PTSD symptoms and attacking self-shame reactions. Clinical implications and recommendations for this population are presented.

Developmentally programmed DNA splicing in Paramecium reveals short-distance crosstalk between DNA cleavage sites.

Somatic genome assembly in the ciliate Paramecium involves the precise excision of thousands of short internal eliminated sequences (IESs) that are scattered throughout the germline genome and often interrupt open reading frames. Excision is initiated by double-strand breaks centered on the TA dinucleotides that are conserved at each IES boundary, but the factors that drive cleavage site recognition remain unknown. A degenerate consensus was identified previously at IES ends and genetic analyses confirmed the participation of their nucleotide sequence in efficient excision. Even for wild-type IESs, however, variant excision patterns (excised or nonexcised) may be inherited maternally through sexual events, in a homology-dependent manner. We show here that this maternal epigenetic control interferes with the targeting of DNA breaks at IES ends. Furthermore, we demonstrate that a mutation in the TA at one end of an IES impairs DNA cleavage not only at the mutant end but also at the wild-type end. We conclude that crosstalk between both ends takes place prior to their cleavage and propose that the ability of an IES to adopt an excision-prone conformation depends on the combination of its nucleotide sequence and of additional determinants.

Prediction of Conserved Peptides of Paracoccidioides for Interferon-γ Release Assay: The First Step in the Development of a Lab-Based Approach for Immunological Assessment during Antifungal Therapy.

Impaired antigen-specific cell-mediated immunity (CMI) is a primary immunological disturbance observed in individuals that develop paracoccidioidomycosis (PCM) after exposure to Paracoccidioides spp. Restoration of Paracoccidioides-specific CMI is crucial to stop the antifungal treatment and avoid relapses. A convenient and specific laboratory tool to assess antigen specific CMI is required for the appropriate clinical treatment of fungal infections, in order to decrease the time of antifungal therapy. We used an interferon-γ release assay strategy, used in the diagnosis of latent tuberculosis infection, to address our aims in this study. Information on proteins secreted by two well-studied representative strains-Paracoccidioides brasiliensis (Pb18) and P. lutzii (Pb-01)-were explored using PubMed or MEDLINE. From 26 publications, 252 proteins were identified, of which 203 were similar according to the Basic Local Alignment Search Tool. This enabled a selection of conserved peptides using the MEGA software. The SignalP-5.0, TMHMM, IEDB, NetMHC II, and IFNepitope algorithms were used to identify appropriate epitopes. In our study, we predicted antigenic epitopes of Paracoccidioides that could bind to MHC class II and induce IFN-γ secretion. These T cell epitopes can be used in the development of a laboratory tool to monitor the CMI of patients with PCM.

Autotransporter-Mediated Display of Complement Receptor Ligands by Gram-Negative Bacteria Increases Antibody Responses and Limits Disease Severity.

The targeting of immunogens/vaccines to specific immune cells is a promising approach for amplifying immune responses in the absence of exogenous adjuvants. However, the targeting approaches reported thus far require novel, labor-intensive reagents for each vaccine and have primarily been shown as proof-of-concept with isolated proteins and/or inactivated bacteria. We have engineered a plasmid-based, complement receptor-targeting platform that is readily applicable to live forms of multiple gram-negative bacteria, including, but not limited to, Escherichia coli, Klebsiella pneumoniae, and Francisella tularensis. Using F. tularensis as a model, we find that targeted bacteria show increased binding and uptake by macrophages, which coincides with increased p38 and p65 phosphorylation. Mice vaccinated with targeted bacteria produce higher titers of specific antibody that recognizes a greater diversity of bacterial antigens. Following challenge with homologous or heterologous isolates, these mice exhibited less weight loss and/or accelerated weight recovery as compared to counterparts vaccinated with non-targeted immunogens. Collectively, these findings provide proof-of-concept for plasmid-based, complement receptor-targeting of live gram-negative bacteria.

Correction to: BCG revaccination of health workers in Brazil to improve innate immune responses against COVID-19: A structured summary of a study protocol for a randomised controlled trial.

An amendment to this paper has been published and can be accessed via the original article.

BCG revaccination of health workers in Brazil to improve innate immune responses against COVID-19: A structured summary of a study protocol for a randomised controlled trial.

OBJECTIVES: The BCG vaccine, widely used in Brazil in new-borns, induces adjuvant protection for several diseases, including childhood virus infections. BCG activates monocytes and innate memory NK cells which are crucial for the antiviral immune response. Therefore, strategies to prevent COVID-19 in health workers (HW) should be carried out to prevent them becoming unwell so that they can continue to work during the pandemic. The hypothesis is that BCG will improve the innate immune response and prevent symptomatic infection or COVID-19 severity. The primary objective is to verify the effectiveness and safety of the BCG vaccine to prevent or reduce incidence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection in the city of Goiânia (Brazil) among HW previously vaccinated with BCG and also its severity and mortality during the pandemic of the disease. Secondary objectives are to estimate the incidence of COVID-19 among these professionals and the innate immune response elicited to BCG. TRIAL DESIGN: This a phase II trial for repositioning BCG as a preventive strategy against COVID-19. The trial is an open-label, parallel-group randomised clinical trial, comparing HW vaccinated with BCG and HW not vaccinated. PARTICIPANTS: The trial will recruit 800 HW of Goiânia - Goiás, Brazil to reach a total of 400 HW included after comorbidities questioning and laboratorial evaluation. Eligibility criteria: Any HW presenting BCG vaccination scar with direct contact with suspected COVID-19 patients for at least 8 hours per week, whether in hospital beds, ICU, or in transportation or admission (nurses, doctors, physiotherapists, nutritionists, receptionists, etc.) who have negative IgM and IgG COVID-19 test. Participants with any of the following characteristics will be excluded: - Have had in the last fifteen days any signs or symptoms of virus infection, including COVID-19; - Have had fever in the last fifteen days; - Have been vaccinated fifteen days before the inclusion; - Have a history or confirmation of any immunosuppressive disease such as HIV, presented solid tumour in the last two years or autoimmune diseases; - Are under preventive medication with antibiotics, steroid anti-inflammatories, or chemotherapy; - Have less than 500 neutrophils per mL of blood; - Have previously been diagnosed with tuberculosis; - Are breastfeeding or pregnant; - Are younger than 18 years old; - Are participating as an investigator in this clinical trial. INTERVENTION AND COMPARATOR: HW will be randomized into the BCG vaccinated group or the BCG unvaccinated control group. The BCG vaccinated group will receive in the right arm, intradermally, a one off dose of 0.1 mL corresponding to approximately 2 x105 to 8 x105 CFU of live, freeze-dried, attenuated BCG Moscow 361-I, Bacillus Calmette Guerin vaccine (Serum Institute of India PVT. LTD.). The unvaccinated control group will not be vaccinated. The HW allocated in both groups will be followed up at specific times points until 180 days post inclusion. The vaccinated and control groups will be compared according to COVID-19 related outcomes. MAIN OUTCOMES: The primary outcomes are the incidence coefficient of infection by SARS-CoV-2 determined by RT-PCR of naso-oropharyngeal swab specimen or rapid lateral flow IgG and IgM test, and presence of general COVID-19 symptoms, disease severity and admission to hospital during the 180 days of follow up. The secondary outcome is the innate immune response elicited 15-20 days after vaccination. RANDOMISATION: The vaccine vial contains approximately 10 doses. In order to optimize the vaccine use, the randomisation was performed in blocks of 20 participants using the platform randomization.com [ http://www.jerrydallal.com/random/permute.htm ]. The randomization was prepared before any HW inclusion. The results were printed and inserted in sealed envelopes that were numbered with BCG-001 to BCG-400. The printed results as well the envelopes had the same numbers. At the time of the randomisation, each participant that meets the inclusion criteria will receive a consecutive participant number [BCG-001-BCG-400]. The sealed envelope with the assigned number, blinded to the researchers, will be opened in front of the participant and the arm allocation will be known. BLINDING (MASKING): There is no masking for the participants or for the healthcare providers. The study will be blinded to the laboratory researchers and to those who will be evaluating the outcomes and performing the statistical analyses. In this case, only the participant identification number will be available. NUMBERS TO BE RANDOMISED (SAMPLE SIZE): Four hundred heath workers will be randomised in two groups. Two hundred participants will be vaccinated, and 200 participants will not be vaccinated. TRIAL STATUS: The protocol approved by the Brazilian Ethical Committee is the seventh version, number CAAE: 31783720.0.0000.5078. The trial has been recruiting since September 20th, 2020. The clinical trial protocol was registered on August 5th, 2020. It is estimated that recruitment will finish by March 2021. TRIAL REGISTRATION: The protocol number was registered on August 5th, 2020 at REBEC (Registro Brasileiro de Ensaios Clínicos). Register number: RBR-4kjqtg and WHO trial registration number UTN: U1111-1256-3892. FULL PROTOCOL: The full protocol is attached as an additional file, accessible from the Trials website (Additional file 1). In the interest in expediting dissemination of this material, the familiar formatting has been eliminated; this Letter serves as a summary of the key elements of the full protocol.

Differential In Vitro Cultivation of Francisella tularensis Influences Live Vaccine Protective Efficacy by Altering the Immune Response.

Francisella tularensis (Ft) is a biothreat agent for which there is no FDA-approved human vaccine. Currently, there are substantial efforts underway to develop both vaccines and improved tools to assess these vaccines. Ft expresses distinct sets of antigens (Ags) in vivo as compared to those expressed in vitro. Importantly, Ft grown in brain-heart infusion medium (BHIM) more closely mimics the antigenic profile of macrophage-grown Ft when compared to Mueller-Hinton medium (MHM)-grown Ft. Thus, we predicted that when used as a live vaccine BHIM-grown Ft (BHIM-Ft) would provide better protection, as compared to MHM-Ft. We first determined if there was a difference in growth kinetics between BHIM and MHM-Ft. We found that BHIM-Ft exhibited an initial growth advantage ex vivo that manifests as slightly hastened intracellular replication as compared to MHM-Ft. We also observed that BHIM-Ft exhibited an initial growth advantage in vivo represented by rapid bacterial expansion and systemic dissemination associated with a slightly shorter mean survival time of naive animals. Next, using two distinct strains of Ft LVS (WT and sodB), we observed that mice vaccinated with live BHIM-Ft LVS exhibited significantly better protection against Ft SchuS4 respiratory challenge compared to MHM-Ft-immunized mice. This enhanced protection correlated with lower bacterial burden, reduced tissue inflammation, and reduced pro-inflammatory cytokine production late in infection. Splenocytes from BHIM-Ft sodB-immunized mice contained more CD4+, effector, memory T-cells, and were more effective at limiting intracellular replication of Ft LVS in vitro. Concurrent with enhanced killing of Ft LVS, BHIM-Ft sodB-immune splenocytes produced significantly higher levels of IFN-γ and IL-17A cytokines than their MHM-Ft sodB-immunized counterparts indicating development of a more effective T cell memory response when immunizing mice with BHIM-Ft.

Evaluation of an outbred mouse model for Francisella tularensis vaccine development and testing.

Francisella tularensis (Ft) is a biothreat agent for which there is no FDA-approved human vaccine. Currently, there are substantial efforts underway to develop both vaccines and the tools to assess these vaccines. Tularemia laboratory research has historically relied primarily upon a small number of inbred mouse strains, but the utility of such findings to outbred animals may be limited. Specifically, C57BL/6 mice are more susceptible than BALB/c mice to Ft infection and less easily protected against challenge with highly virulent type A Ft. Thus, depending on the inbred mouse strain used, one could be misled as to which immunogen(s)/vaccine will ultimately be effective in an outbred human population. Accordingly, we evaluated an outbred Swiss Webster (SW) mouse model in direct comparison to a well-established, inbred C57BL/6 mouse model. Mucosal vaccination with the live, attenuated Ft LVS superoxide dismutase (sodB) mutant demonstrated significantly higher protection in outbred SW mice compared to inbred C57BL/6 mice against Ft SchuS4 respiratory challenge. The protection observed in vaccinated outbred mice correlated with lower bacterial density, reduced tissue inflammation, and reduced levels of pro-inflammatory cytokine production. This protection was CD4+ and CD8+ T cell-dependent and characterized by lower titers of serum antibody (Ab) that qualitatively differed from vaccinated inbred mice. Enhanced protection of vaccinated outbred mice correlated with early and robust production of IFN-γ and IL-17A. Neutralizing Ab administered at the time of challenge revealed that IFN-γ was central to this protection, while IL-17A neutralization did not alter bacterial burden or survival. The present study demonstrates the utility of the outbred mouse as an alternative vaccination model for testing tularemia vaccines. Given the limited MHC repertoire in inbred mice, this outbred model is more analogous to the human in terms of immunological diversity.

Differential Growth of Francisella tularensis, Which Alters Expression of Virulence Factors, Dominant Antigens, and Surface-Carbohydrate Synthases, Governs the Apparent Virulence of Ft SchuS4 to Immunized Animals.

The gram-negative bacterium Francisella tularensis (Ft) is both a potential biological weapon and a naturally occurring microbe that survives in arthropods, fresh water amoeba, and mammals with distinct phenotypes in various environments. Previously, we used a number of measurements to characterize Ft grown in Brain-Heart Infusion (BHI) broth as (1) more similar to infection-derived bacteria, and (2) slightly more virulent in naïve animals, compared to Ft grown in Mueller Hinton Broth (MHB). In these studies we observed that the free amino acids in MHB repress expression of select Ft virulence factors by an unknown mechanism. Here, we tested the hypotheses that Ft grown in BHI (BHI-Ft) accurately displays a full protein composition more similar to that reported for infection-derived Ft and that this similarity would make BHI-Ft more susceptible to pre-existing, vaccine-induced immunity than MHB-Ft. We performed comprehensive proteomic analysis of Ft grown in MHB, BHI, and BHI supplemented with casamino acids (BCA) and compared our findings to published "omics" data derived from Ft grown in vivo. Based on the abundance of ~1,000 proteins, the fingerprint of BHI-Ft is one of nutrient-deprived bacteria that-through induction of a stringent-starvation-like response-have induced the FevR regulon for expression of the bacterium's virulence factors, immuno-dominant antigens, and surface-carbohydrate synthases. To test the notion that increased abundance of dominant antigens expressed by BHI-Ft would render these bacteria more susceptible to pre-existing, vaccine-induced immunity, we employed a battery of LVS-vaccination and S4-challenge protocols using MHB- and BHI-grown Ft S4. Contrary to our hypothesis, these experiments reveal that LVS-immunization provides a barrier to infection that is significantly more effective against an MHB-S4 challenge than a BHI-S4 challenge. The differences in apparent virulence to immunized mice are profoundly greater than those observed with primary infection of naïve mice. Our findings suggest that tularemia vaccination studies should be critically evaluated in regard to the growth conditions of the challenge agent.

Francisella tularensis - Immune Cell Activator, Suppressor, or Stealthy Evader: The Evolving View from the Petri Dish.

One of the hallmarks of pulmonary tularemia, which results from inhalation of Francisella tularensis - a significant bioterrorism concern, is the lack of an acute TH1-biased inflammatory response in the early phase of disease (days 1-3) despite significant bacterial loads. In an effort to understand this apparent hypo-responsiveness, many laboratories have utilized in vitro cell-based models as tools to probe the nature and consequences of host cell interactions with F. tularensis. The first uses of this model suggested that mammalian host cells recognize this bacterium principally through TLR2 to evoke a robust, classical TH1-biased cytokine response including TNF, IL-6, IL-1ß, and IFN-γ. Others used this model in concert with a variety of non-genetic perturbations of the bacterial-host cell interaction and suggested that F. tularensis actively-suppressed the cellular response. Consistent with this notion, others engaged this model to assess isogenic mutants and, in many cases, found the mutant bacteria to be more pro-inflammatory than their WT counter-parts. Frequently, these observations were interpreted as evidence for the immunosuppressive function of the gene of interest. However, recently appreciated roles of the health of the bacterium and the impact of host factors have refined this model to suggest a "stealthy" mode of bacterial-host cell interaction (rather than one involving active suppression) consistent with the observations during early phase disease.

Differential Cultivation of Francisella tularensis Induces Changes in the Immune Response to and Protective Efficacy of Whole Cell-Based Inactivated Vaccines.

Francisella tularensis (Ft) is a category A biothreat agent for which there is no Food and Drug Administration-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 (MHB). However, in contrast to MHB-grown Ft, Ft grown in Brain-Heart Infusion (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, primarily due 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 including increased iFt binding to dendritic cells, 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.