Pathogen Heterogeneity Research Articles

Zinc-limited Mycobacterium tuberculosis stimulate distinct responses in macrophages compared with standard zinc-replete bacteria.

Tuberculosis (TB) is notoriously difficult to treat, likely due to the complex host-pathogen interactions driven by pathogen heterogeneity. An understudied area of TB pathogenesis is host responses to Mycobacterium tuberculosis bacteria (Mtb) that are limited in zinc ions. This distinct population resides in necrotic granulomas and sputum and could be the key player in tuberculosis pathogenicity. In this study, we tested the hypothesis that macrophages differentiate between Mtb grown under zinc limitation or in the standard zinc-replete medium. Using several macrophage infection models, such as murine RAW 264.7 and murine bone marrow-derived macrophages (BMDMs), as well as human THP-1-derived macrophages, we show that macrophages infected with zinc-limited Mtb have increased bacterial burden compared with macrophages infected with zinc-replete Mtb. We further demonstrate that macrophage infection with zinc-limited Mtb trigger higher production of reactive oxygen species (ROS) and cause more macrophage death. Furthermore, the increased ROS production is linked to the increased phagocytosis of zinc-limited Mtb, whereas cell death is not. Finally, transcriptional analysis of RAW 264.7 macrophages demonstrates that macrophages have more robust pro-inflammatory responses when infected with zinc-limited Mtb than zinc-replete Mtb. Together, our findings suggest that Mtb's access to zinc affects their interaction with macrophages and that zinc-limited Mtb may be influencing TB progression. Therefore, zinc availability in bacterial growth medium should be considered in TB drug and vaccine developments.

All the single cells: if you like it then you should put some virus on it.

Across a rich 70-year history, single-cell virology has revealed the impact of host and pathogen heterogeneity during virus infections. Recent technological innovations have enabled higher-resolution analyses of cellular and viral heterogeneity. Furthermore, single-cell analysis has revealed extreme phenotypes and provided additional insights into host-pathogen dynamics. Using a single-cell approach to explore fundamental virology questions, contemporary researchers have contributed to a revival of interest in single-cell virology with increased insights and enthusiasm.

History of tuberculosis disease is associated with genetic regulatory variation in Peruvians.

A quarter of humanity is estimated to have been exposed to Mycobacterium tuberculosis (Mtb) with a 5-10% risk of developing tuberculosis (TB) disease. Variability in responses to Mtb infection could be due to host or pathogen heterogeneity. Here, we focused on host genetic variation in a Peruvian population and its associations with gene regulation in monocyte-derived macrophages and dendritic cells (DCs). We recruited former household contacts of TB patients who previously progressed to TB (cases, n = 63) or did not progress to TB (controls, n = 63). Transcriptomic profiling of monocyte-derived DCs and macrophages measured the impact of genetic variants on gene expression by identifying expression quantitative trait loci (eQTL). We identified 330 and 257 eQTL genes in DCs and macrophages (False Discovery Rate (FDR) < 0.05), respectively. Four genes in DCs showed interaction between eQTL variants and TB progression status. The top eQTL interaction for a protein-coding gene was with FAH, the gene encoding fumarylacetoacetate hydrolase, which mediates the last step in mammalian tyrosine catabolism. FAH expression was associated with genetic regulatory variation in cases but not controls. Using public transcriptomic and epigenomic data of Mtb-infected monocyte-derived dendritic cells, we found that Mtb infection results in FAH downregulation and DNA methylation changes in the locus. Overall, this study demonstrates effects of genetic variation on gene expression levels that are dependent on history of infectious disease and highlights a candidate pathogenic mechanism through pathogen-response genes. Furthermore, our results point to tyrosine metabolism and related candidate TB progression pathways for further investigation.

Deciphering the pathogen heterogeneity for precise diagnosis and personalized therapeutics of infections after kidney transplantation: insights from metagenomic next-generation sequencing.

The aim of this study was to compare the detection performance of mNGS against that of conventional tests (CT) in patients suffering from infection after kidney transplantation. A total of 138 samples from 85 kidney transplant patients with acute or chronic infections were simultaneously analyzed using mNGS and CT from July 2021 to August 2023. Compared with CT, mNGS demonstrated a higher sensitivity (95.96% vs. 27.27%) but lower specificity (48.72% vs. 84.62%) in pathogen detection. Moreover, mNGS exhibited significant advantages in detecting mixed and rare infections. The pathogens commonly identified in kidney transplant patients were severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), followed by Pneumocystis jirovecii and Cytomegalovirus (CMV). mNGS guided the precise clinical diagnosis in 89.13% of cases and assisted in altering therapeutics from empirical antibiotic approaches to personalized plans in 56.10% of cases, including treatment escalation (40.65%), initiation (11.38%), drug adjustment (3.25%), and de-escalation (0.81%). Our study demonstrated the superior detection performance of mNGS and its significant clinical value. This reflected the great potential of mNGS as a complementary clinical detection technology for kidney transplant patients.

The tempo and mode of gene regulatory programs during bacterial infection.

Innate immune recognition of bacterial pathogens is a key determinant of the ensuing systemic response, and host or pathogen heterogeneity in this early interaction can impact the course of infection. To gain insight into host response heterogeneity, we investigate macrophage inflammatory dynamics using primary human macrophages infected with Group B Streptococcus. Transcriptomic analysis reveals discrete cellular states within responding macrophages, one of which consists of four sub-states, reflecting inflammatory activation. Infection with six additional bacterial species-Staphylococcus aureus, Listeria monocytogenes, Enterococcus faecalis, Yersinia pseudotuberculosis, Shigella flexneri, and Salmonella enterica-recapitulates these states, though at different frequencies. We show that modulating the duration of infection and the presence of a toxin impacts inflammatory trajectory dynamics. We provide evidence for this trajectory in infected macrophages in an invivo model of Staphylococcus aureus infection. Our cell-state analysis defines a framework for understanding inflammatory activation dynamics in response to bacterial infection.

Commercial Vaccines Do Not Confer Protection against Two Genogroups of Piscirickettsia salmonis, LF-89 and EM-90, in Atlantic Salmon.

Simple SummaryVaccination represents one of the most relevant strategies to prevent and control infectious diseases in aquaculture. However, vaccines have failed to control and prevent Piscirickettsia salmonis, a bacterium that causes large economic losses to the industry. Therefore, we evaluated the performance of two commercial vaccines in Atlantic salmon through a cohabitation challenge (healthy fish were challenged by cohabitation with infected fish) of the two most prevalent and ubiquitous Piscirickettsia genetic variants in Chile. We found no evidence that vaccines confer protection against the LF-89 or EM-90 genogroups in Atlantic salmon.In Atlantic salmon, vaccines have failed to control and prevent Piscirickettsiosis, for reasons that remain elusive. In this study, we report the efficacy of two commercial vaccines developed with the Piscirickettsia salmonis isolates AL100005 and AL 20542 against another two genogroups which are considered highly and ubiquitously prevalent in Chile: LF-89 and EM-90. Two cohabitation trials were performed to mimic field conditions and vaccine performance: (1) post-smolt fish were challenged with a single infection of LF-89, (2) adults were coinfected with EM-90, and a low level coinfection of sea lice. In the first trial, the vaccine delayed smolt mortalities by two days; however, unvaccinated and vaccinated fish did not show significant differences in survival (unvaccinated: 60.3%, vaccinated: 56.7%; p = 0.28). In the second trial, mortality started three days later for vaccinated fish than unvaccinated fish. However, unvaccinated and vaccinated fish did not show significant differences in survival (unvaccinated: 64.6%, vaccinated: 60.2%, p = 0.58). Thus, we found no evidence that the evaluated vaccines confer effective protection against the genogroups LF-89 and EM-90 of P. salmonis with estimated relative survival proportions (RPSs) of −9% and −12%, respectively. More studies are necessary to evaluate whether pathogen heterogeneity is a key determinant of the lack of vaccine efficacy against P. salmonis.

Lečenje najčešćih respiratornih infekcija kod dece

Acute respiratory infections are the most common group of infective diseases in the pediatric population. Although the improvement of health care and vaccination program has led to a significant reduction in the incidence of certain respiratory infections, the combination of a high prevalence in vulnerable pediatric categories and uncritical prescription of antibiotics, due to the inability to adequately distinguish between viruses and bacterial etiology, still represents a significant challenge for the public health system. In order to promote rational antibiotic therapy with an overall improvement of both diagnostic and therapeutic principles, acute respiratory diseases have been the subject of consideration in numerous publications and national guidelines. Nonspecific clinical manifestations with pathogen heterogeneity and both anatomical and physiological characteristics of the child's respiratory system during growth and development have created the need for individualized therapy. Since the guidelines emphasize the undoubtful and crucial benefits of symptomatic therapy (e.g. analgesics in acute otitis media, supplemental oxygen in lower respiratory tract infections with hypoxemia), the use of antibiotics and corticosteroids is indicated in selected cases with a severe clinical picture. The choice of antibiotic depends on the clinical condition, presumed causative agent, and local epidemiologic circumstances. Respiratory support (oxygen therapy and/or artificial ventilation) is reserved for inpatient treatment of cases with a particularly severe clinical picture and associated complications.

Oxidative DNA Damage of Peripheral Blood Cells and Blood Plasma Сell-Free DNA as an Indicator of the Oxidative Stress Level in Children with Autism Spectrum Disorders and Schizophrenia

Background: pathogen heterogeneity and complexity are the main obstacles for schizophrenia and autism spectrum disorders (ASD) differential diagnosis in children. The role of oxidative stress in the molecular mechanisms of schizophrenia and autism pathogenesis is beyond doubt. Free radicals that accumulate during stress can cause oxidative modifications and the formation of breaks in the сell-free DNA (cfDNA) and nuclear DNA of blood cells. To date, it has been proven that 8-hydroxy-2’- deoxyguanosine (8-OHdG) can be considered as an oxidative stress biomarker. However, it is still unclear how pronounced the genotoxic consequences of oxidative stress are in ASD of varying severity and in childhood onset schizophrenia (COS). Objective: to study the relationship between the oxidative DNA damage level in peripheral blood cells and the circulating cell-free DNA characteristics with the severity of COS and the course of ASD in children. Patients and methods: blood samples of 96 patients with childhood autism (CA — F84.0 according to ICD-10), atypical autism (AA — F84.1 according to ICD-10) and with childhood onset schizophrenia (COS — F20.8 according to ICD-10) were obtained from the Child Psychiatry Department of the Mental health research center. Blood samples of the control group (34 people) — from the collection of samples of the Research Centre for medical Genetics. The selection of patients was carried out using the clinical and psychopathological method. Cell-free DNA was isolated by extraction with organic solvents. The concentration of cfDNA was determined fluorimetrically. The level of 8-OHdG in cell-free DNA was determined by binding of the corresponding antibodies on membrane filters, endonuclease activity was determined by radial diffusion in a gel. G0-peripheral blood lymphocytes were isolated by gradient centrifugation. The level of 8-OHdG and the level of the phosphorylated form of histone H2AX (yH2AX) in G0-peripheral blood lymphocytes were analyzed in fixed cells by flow cytofluorometry using appropriate antibodies. Statistical processing was carried out using Microsoft Office Excel, Statistica 6.0, StatGraph. Results and conclusions: oxidative stress has different severity in ASD, occurring in severe form (AA) and mild/moderate form (CA). In CA, the level of oxidative damage to the DNA of lymphocytes tends to increase, but does not reach statistically significant level; the level of oxidative damage to cfDNA does not differ from the control. In AA and, to an even stronger extent, in COS, the level of oxidative damage to the DNA of cells and cfDNA is significantly increased, which indicates the development of systemic oxidative stress, which is not compensated by the body’s antioxidant system. The level of 8-OHdG in the composition of the cfDNA and DNA of the nuclei of peripheral blood cells can be a marker of oxidative stress, which is important not only for diagnosing the severity of the pathological process, but also for treatment regimens development for COS and ASD in children.

Multiepitope Fusion Antigen: MEFA, an Epitope- and Structure-Based Vaccinology Platform for Multivalent Vaccine Development.

Vaccines are regarded as the most cost-effective countermeasure against infectious diseases. One challenge often affecting vaccine development is antigenic diversity or pathogen heterogeneity. Different strains produce immunologically heterogeneous virulence factors, therefore an effective vaccine needs to induce broad-spectrum host immunity to provide cross-protection. Recent advances in genomics and proteomics, particularly computational biology and structural biology, establishes structural vaccinology and highlights the feasibility of developing effective and precision vaccines. Here, we introduce the epitope- and structure-based vaccinology platform multiepitope-fusion-antigen (MEFA), and provide instructions to generate polyvalent MEFA immunogens for vaccine development. Conceptually, MEFA combines epitope vaccinology and structural vaccinology to enable a protein immunogen to present heterogeneous antigenic domains (epitopes) and to induce broadly protective immunity against different virulence factors, strains or diseases. Methodologically, the MEFA platform first identifies a safe, structurally stable and strongly immunogenic backbone protein and immunodominant (ideally neutralizing or protective) epitopes from heterogeneous strains or virulence factors of interest. Then, assisted with protein modeling and molecule dynamic simulation, MEFA integrates heterogeneous epitopes into a backbone protein via epitope substitution for a polyvalentMEFA protein and mimics epitope native antigenicity. Finally, the MEFA protein is examined for broad immunogenicity in animal immunization, and assessed for potential application for multivalent vaccine development in preclinical studies.

Molecular Dynamics Study of Lipid and Cholesterol Reorganization Due to Membrane Binding and Pore Formation by Listeriolysin O.

Pore-forming toxins are proteinsexpressed by bacteria to primarily cause infections in the host cell. Cholesterol-dependent cytolysins (CDCs) are a class of proteins whose pore-forming ability requires the presence of cholesterol in the membrane. Upon binding to the target cell, cholesterol-recognizing residues in the membrane binding D4 subdomain assist in stabilizing both the pre-pore and pore states which occur during protein oligomerization on the cell membrane. Super resolution-stimulated emission depletion (STED) microscopy experiments (Sarangi et al. in Langmuir, 32:9649-9657, 2016) on supported lipid bilayers have shown that listeriolysin (LLO), a CDC expressed by Listeria monocytogenes, a food-borne pathogen, induces both spatial and dynamic heterogeneity in bilayer membranes. Here, we use all-atom molecular dynamics simulations to explore molecular details of the induced membrane reorganization by considering two distinct states of the oligomerized LLO protein in a 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC): cholesterol membrane. In the membrane bound (MB) state, four D4 subunits are placed at the bilayer interface in a pre-pore configuration and the membrane-inserted (MI) state consists of a tetrameric arc-like pore configuration. By analyzing lipid-order parameters, mobilities, and diffusion coefficients, we examine the induced spatial heterogeneity that occurs in both the MB and MI states. This heterogeneity is primarily driven by the local density enhancement of cholesterol in the vicinity of the MB, D4 subunits leading to distinct differences in lipid and cholesterol mobility across the two leaflets as well as enhanced lipid mobilities in regions where cholesterol is depleted. The leaflet-induced heterogeneity is greater for the MB state when compared with the MI state and the dynamic variations are more pronounced in the extracellular leaflet when compared with the cytosolic leaflet. Our study provides molecular-level insights into the inhomogeneity and perturbation induced in bilayer membranes upon LLO binding and pore formation and is expected to represent trends across PFTs in the broad CDC subclass of proteins.

Limited available evidence supports theoretical predictions of reduced vaccine efficacy at higher exposure dose

Understanding the causes of vaccine failure is important for predicting disease dynamics in vaccinated populations and planning disease interventions. Pathogen exposure dose and heterogeneity in host susceptibility have both been implicated as important factors that may reduce overall vaccine efficacy and cause vaccine failure. Here, we explore the effect of pathogen dose and heterogeneity in host susceptibility in reducing efficacy of vaccines. Using simulation-based methods, we find that increases in pathogen exposure dose decrease vaccine efficacy, but this effect is modified by heterogeneity in host susceptibility. In populations where the mode of vaccine action is highly polarized, vaccine efficacy decreases more slowly with exposure dose than in populations with less variable protection. We compared these theoretical results to empirical estimates from a systematic literature review of vaccines tested over multiple exposure doses. We found that few studies (nine of 5,389) tested vaccine protection against infection over multiple pathogen challenge doses, with seven studies demonstrating a decrease in vaccine efficacy with increasing exposure dose. Our research demonstrates that pathogen dose has potential to be an important determinant of vaccine failure, although the limited empirical data highlight a need for additional studies to test theoretical predictions on the plausibility of reduced host susceptibility and high pathogen dose as mechanisms responsible for reduced vaccine efficacy in high transmission settings.

Linking social and spatial networks to viral community phylogenetics reveals subtype-specific transmission dynamics in African lions.

Heterogeneity within pathogen species can have important consequences for how pathogens transmit across landscapes; however, discerning different transmission routes is challenging. Here, we apply both phylodynamic and phylogenetic community ecology techniques to examine the consequences of pathogen heterogeneity on transmission by assessing subtype-specific transmission pathways in a social carnivore. We use comprehensive social and spatial network data to examine transmission pathways for three subtypes of feline immunodeficiency virus (FIVPle ) in African lions (Panthera leo) at multiple scales in the Serengeti National Park, Tanzania. We used FIVPle molecular data to examine the role of social organization and lion density in shaping transmission pathways and tested to what extent vertical (i.e., father- and/or mother-offspring relationships) or horizontal (between unrelated individuals) transmission underpinned these patterns for each subtype. Using the same data, we constructed subtype-specific FIVPle co-occurrence networks and assessed what combination of social networks, spatial networks or co-infection best structured the FIVPle network. While social organization (i.e., pride) was an important component of FIVPle transmission pathways at all scales, we find that FIVPle subtypes exhibited different transmission pathways at within- and between-pride scales. A combination of social and spatial networks, coupled with consideration of subtype co-infection, was likely to be important for FIVPle transmission for the two major subtypes, but the relative contribution of each factor was strongly subtype-specific. Our study provides evidence that pathogen heterogeneity is important in understanding pathogen transmission, which could have consequences for how endemic pathogens are managed. Furthermore, we demonstrate that community phylogenetic ecology coupled with phylodynamic techniques can reveal insights into the differential evolutionary pressures acting on virus subtypes, which can manifest into landscape-level effects.

Targeted Next-Generation Sequencing for Diagnostics and Forensics.

Pathogen-specific, targeted assays such as real-time PCR are generally used for clinical diagnosis of infectious and biothreat diseases as highlighted in the recent West African Ebola virus outbreak where real-time PCR was the primary diagnostic for critical treatment decisions. However, current diagnostic algorithms rarely require determination of a single etiologic agent outside the context of an outbreak response but rather involve interrogation across a spectrum of pathogens with similar pathology and/or epidemiology. The necessity for multiple pathogen interrogation exposes the critical gap in availability of higher-multiplex diagnostics. This caveat is exacerbated with biothreat agents where initial symptoms of an infection are often similar to a myriad of less consequential pathogens. Development of diagnostic platforms is a daunting challenge given the plethora of human pathogens spanning both infectious and biothreat diseases. In general, infectious disease diagnostics must meet defined metrics for performance in clinical matrices as well as show validated efficacy for use in an actionable context to impact patient care. Detection of virulence markers to discriminate microbiota from pathogenic events and the ability to detect the spectrum of pathogen heterogeneity are critical aspects to an ideal diagnostic platform. Biothreat diagnostics include all of these requirements in addition to the need for microbial forensics/attribution. The detection of a biothreat incident (e.g., Bacillus anthracis ), environmental or clinical, has substantial consequences including public angst as well as mobilization of military, public health, and law enforcement responses, the latter of these responses requiring forensic attribution. Detection of both clinical and environmental biothreat incidents remains a perennial issue that requires some level of preparedness to mitigate situations proactively. Next-generation sequencing (NGS)2 offers a potential solution to challenges for both diagnostic and environmental detection of infectious disease and biothreats. Specifically, NGS has the potential to sequence all nucleic acids within a sample, allowing for near …

Products of Compartmental Models in Epidemiology.

We show that many structured epidemic models may be described using a straightforward product structure in this paper. Such products, derived from products of directed graphs, may represent useful refinements including geographic and demographic structure, age structure, gender, risk groups, or immunity status. Extension to multistrain dynamics, that is, pathogen heterogeneity, is also shown to be feasible in this framework. Systematic use of such products may aid in model development and exploration, can yield insight, and could form the basis of a systematic approach to numerical structural sensitivity analysis.

VALUATION OF RESISTANCE TO PLASMODIOPHORA BRASSICAE OF HYBRID COMBINATIONS OF WHITE HEAD CABBAGE DEVELOPED BASED ON DOUBLED HAPLOID LINES

Plasmodiophora brassicae Wor. is the one of the causative agent of disease of the family of Brassicaceae, that results in decrease of white head cabbage yield up to 10-60%. The aim of the work was the study of genetic variability of doubled haploid lines of white head cabbage obtained by the isolated microspore culture in vitro aimed at selection of the lines resistant to P. Brassicae and development of resistant hybrids. The doubled haploid lines of white head cabbage were evaluated for resistance to Plasmodiophora brassicae using the method of inoculation of seedlings by pathogen in the control condition of the chamber room. As a result of assessment, the high disease distribution among doubled haploid lines was found (25- 100%), but disease development was not higher than 68%. The score of infestation was 0.5-3.3, that was comparable with the standard (3.5). The plants of the lines 3-3-3 did not exhibit any symptoms of disease that can indicate of efficiency of its gene resistance or pathogen heterogeneity. The lines with high resistance to P. brassicae were used as a parental lines for development of F1 hybrids. Using the top-crossing method the forty-two hybrid combinations were developed based on self-incompatibility. These hybrid combinations were analyzed for clubroot resistance in the field conditions on an artificial infectious background in Moscow region. Based on the data of two-year experiments, all tested hybrid combinations were divided into the groups of relatively tolerant (52.4%) and susceptible (45.2%) genotypes. Only one hybrid combination developed with line 3-3-3 has proved to be tolerant. The score of infestation of hybrid combinations varied from 0 to 1.8. The score of infestation of the standard was 2.5. The disease distribution reached 80% but disease development varied from 0 to 25%.

Gene flow in environmental Legionella pneumophila leads to genetic and pathogenic heterogeneity within a Legionnaires’ disease outbreak

BackgroundLegionnaires’ disease is a severe form of pneumonia caused by the environmental bacterium Legionella pneumophila. Outbreaks commonly affect people with known risk factors, but the genetic and pathogenic complexity of L. pneumophila within an outbreak is not well understood. Here, we investigate the etiology of the major Legionnaires’ disease outbreak that occurred in Edinburgh, UK, in 2012, by examining the evolutionary history, genome content, and virulence of L. pneumophila clinical isolates.ResultsOur high resolution genomic approach reveals that the outbreak was caused by multiple genetic subtypes of L. pneumophila, the majority of which had diversified from a single progenitor through mutation, recombination, and horizontal gene transfer within an environmental reservoir prior to release. In addition, we discover that some patients were infected with multiple L. pneumophila subtypes, a finding which can affect the certainty of source attribution. Importantly, variation in the complement of type IV secretion systems encoded by different genetic subtypes correlates with virulence in a Galleria mellonella model of infection, revealing variation in pathogenic potential among the outbreak source population of L. pneumophila.ConclusionsTaken together, our study indicates previously cryptic levels of pathogen heterogeneity within a Legionnaires’ disease outbreak, a discovery that impacts on source attribution for future outbreak investigations. Furthermore, our data suggest that in addition to host immune status, pathogen diversity may be an important influence on the clinical outcome of individual outbreak infections.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-014-0504-1) contains supplementary material, which is available to authorized users.

Gene flow in environmental Legionella pneumophila leads to genetic and pathogenic heterogeneity within a Legionnaires' disease outbreak.

Legionnaires' disease is a severe form of pneumonia caused by the environmental bacterium Legionella pneumophila. Outbreaks commonly affect people with known risk factors, but the genetic and pathogenic complexity of L. pneumophila within an outbreak is not well understood. Here, we investigate the etiology of the major Legionnaires' disease outbreak that occurred in Edinburgh, UK, in 2012, by examining the evolutionary history, genome content, and virulence of L. pneumophila clinical isolates. Our high resolution genomic approach reveals that the outbreak was caused by multiple genetic subtypes of L. pneumophila, the majority of which had diversified from a single progenitor through mutation, recombination, and horizontal gene transfer within an environmental reservoir prior to release. In addition, we discover that some patients were infected with multiple L. pneumophila subtypes, a finding which can affect the certainty of source attribution. Importantly, variation in the complement of type IV secretion systems encoded by different genetic subtypes correlates with virulence in a Galleria mellonella model of infection, revealing variation in pathogenic potential among the outbreak source population of L. pneumophila. Taken together, our study indicates previously cryptic levels of pathogen heterogeneity within a Legionnaires' disease outbreak, a discovery that impacts on source attribution for future outbreak investigations. Furthermore, our data suggest that in addition to host immune status, pathogen diversity may be an important influence on the clinical outcome of individual outbreak infections.

Coverage of Related Pathogenic Species by Multivalent and Cross-Protective Vaccine Design: Arenaviruses as a Model System

The arenaviruses are a family of negative-sense RNA viruses that cause severe human disease ranging from aseptic meningitis to hemorrhagic fever syndromes. There are currently no FDA-approved vaccines for the prevention of arenavirus disease, and therapeutic treatment is limited to the use of ribavirin and/or immune plasma for a subset of the pathogenic arenaviruses. The considerable genetic variability observed among the seven arenaviruses that are pathogenic for humans illustrates one of the major challenges for vaccine development today, namely, to overcome pathogen heterogeneity. Over the past 5 years, our group has tested several strategies to overcome pathogen heterogeneity, utilizing the pathogenic arenaviruses as a model system. Because T cells play a prominent role in protective immunity following arenavirus infection, we specifically focused on the development of human vaccines that would induce multivalent and cross-protective cell-mediated immune responses. To facilitate our vaccine development and testing, we conducted large-scale major histocompatibility complex (MHC) class I and class II epitope discovery on murine, nonhuman primate, and human backgrounds for each of the pathogenic arenaviruses, including the identification of protective HLA-restricted epitopes. Finally, using the murine model of lymphocytic choriomeningitis virus infection, we studied the phenotypic characteristics associated with immunodominant and protective T cell epitopes. This review summarizes the findings from our studies and discusses their application to future vaccine design.

Polyfunctional CD4+ T cell responses to a set of pathogenic arenaviruses provide broad population coverage

BackgroundSeveral arenaviruses cause severe hemorrhagic fever and aseptic meningitis in humans for which no licensed vaccines are available. A major obstacle for vaccine development is pathogen heterogeneity within the Arenaviridae family. Evidence in animal models and humans indicate that T cell and antibody-mediated immunity play important roles in controlling arenavirus infection and replication. Because CD4+ T cells are needed for optimal CD8+ T cell responses and to provide cognate help for B cells, knowledge of epitopes recognized by CD4+ T cells is critical to the development of an effective vaccine strategy against arenaviruses. Thus, the goal of the present study was to define and characterize CD4+ T cell responses from a broad repertoire of pathogenic arenaviruses (including lymphocytic choriomeningitis, Lassa, Guanarito, Junin, Machupo, Sabia, and Whitewater Arroyo viruses) and to provide determinants with the potential to be incorporated into a multivalent vaccine strategy.ResultsBy inoculating HLA-DRB1*0101 transgenic mice with a panel of recombinant vaccinia viruses, each expressing a single arenavirus antigen, we identified 37 human HLA-DRB1*0101-restricted CD4+ T cell epitopes from the 7 antigenically distinct arenaviruses. We showed that the arenavirus-specific CD4+ T cell epitopes are capable of eliciting T cells with a propensity to provide help and protection through CD40L and polyfunctional cytokine expression. Importantly, we demonstrated that the set of identified CD4+ T cell epitopes provides broad, non-ethnically biased population coverage of all 7 arenavirus species targeted by our studies.ConclusionsThe identification of CD4+ T cell epitopes, with promiscuous binding properties, derived from 7 different arenavirus species will aid in the development of a T cell-based vaccine strategy with the potential to target a broad range of ethnicities within the general population and to protect against both Old and New World arenavirus infection.

A Multivalent and Cross-Protective Vaccine Strategy against Arenaviruses Associated with Human Disease

Arenaviruses are the causative pathogens of severe hemorrhagic fever and aseptic meningitis in humans, for which no licensed vaccines are currently available. Pathogen heterogeneity within the Arenaviridae family poses a significant challenge for vaccine development. The main hypothesis we tested in the present study was whether it is possible to design a universal vaccine strategy capable of inducing simultaneous HLA-restricted CD8+ T cell responses against 7 pathogenic arenaviruses (including the lymphocytic choriomeningitis, Lassa, Guanarito, Junin, Machupo, Sabia, and Whitewater Arroyo viruses), either through the identification of widely conserved epitopes, or by the identification of a collection of epitopes derived from multiple arenavirus species. By inoculating HLA transgenic mice with a panel of recombinant vaccinia viruses (rVACVs) expressing the different arenavirus proteins, we identified 10 HLA-A02 and 10 HLA-A03-restricted epitopes that are naturally processed in human antigen-presenting cells. For some of these epitopes we were able to demonstrate cross-reactive CD8+ T cell responses, further increasing the coverage afforded by the epitope set against each different arenavirus species. Importantly, we showed that immunization of HLA transgenic mice with an epitope cocktail generated simultaneous CD8+ T cell responses against all 7 arenaviruses, and protected mice against challenge with rVACVs expressing either Old or New World arenavirus glycoproteins. In conclusion, the set of identified epitopes allows broad, non-ethnically biased coverage of all 7 viral species targeted by our studies.