Human Ebola virus infection results in substantial immune activation

Reduced Plasmodium Parasite Burden Associates with CD38+ CD4+ T Cells Displaying Cytolytic Potential and Impaired IFN-γ Production

Using a unique resource of samples from a controlled human malaria infection (CHMI) study, we identified a novel population of CD4+ T cells whose frequency in the peripheral blood was inversely correlated with parasite burden following P. falciparum infection. These CD4+ T cells expressed the multifunctional ectoenzyme CD38 and had unique features that distinguished them from other CD4+ T cells. Specifically, their phenotype was associated with proliferation, activation and cytotoxic potential as well as significantly impaired production of IFN-γ and other cytokines and reduced basal levels of activated STAT1. A CD38+ CD4+ T cell population with similar features was identified in healthy uninfected individuals, at lower frequency. CD38+ CD4+ T cells could be generated in vitro from CD38- CD4+ T cells after antigenic or mitogenic stimulation. This is the first report of a population of CD38+ CD4+ T cells with a cytotoxic phenotype and markedly impaired IFN-γ capacity in humans. The expansion of this CD38+ CD4+ T population following infection and its significant association with reduced blood-stage parasite burden is consistent with an important functional role for these cells in protective immunity to malaria in humans. Their ubiquitous presence in humans suggests that they may have a broad role in host-pathogen defense.

TRIAL REGISTRATION

ClinicalTrials.gov clinical trial numbers ACTRN12612000814875, ACTRN12613000565741 and ACTRN12613001040752.

Ebola vaccine R&D: Filling the knowledge gaps

With an emphasis on systems analyses, the VSV-EBOVAC project harnesses state-of-the-art technologies that illuminate mechanisms behind the observed immunogenicity and reactogenicity of the rVSV-ZEBOV vaccine and ensures that such information is shared among stakeholders.

Defining antigen-specific plasmablast and memory B cell subsets in human blood after viral infection or vaccination

Antigen-specific B cells bifurcate into antibody secreting cells (ASC) and memory B cells after infection or vaccination. ASCs or plasmablasts have been extensively studied in humans but less is known about B cells that get activated but do not differentiate into early plasmablasts. Here, we define the phenotype and transcriptional program of an antigen-specific B cell subset, referred to as activated B cells (ABC), that is distinct from ASCs and is committed to the memory B cell lineage. ABCs were detected in humans after infection with Ebola virus or influenza virus and also after vaccination. By simultaneously analyzing antigen-specific ASCs and ABCs in human blood after influenza vaccination we interrogated the clonal overlap and extent of somatic hypermutation (SHM) in the ASC (effector) and ABC (memory) lineages. Longitudinal tracking of vaccination-induced HA-specific clones revealed minimal increase in SHM over time suggesting that repeated annual immunization may have limitations in enhancing the quality of influenza-specific antibody.

Human Survivors of Disease Outbreaks Caused by Ebola or Marburg Virus Exhibit Cross-Reactive and Long-Lived Antibody Responses

A detailed understanding of serological immune responses to Ebola and Marburg virus infections will facilitate the development of effective diagnostic methods, therapeutics, and vaccines. We examined antibodies from Ebola or Marburg survivors 1 to 14 years after recovery from disease, by using a microarray that displayed recombinant nucleoprotein (NP), viral protein 40 (VP40), envelope glycoprotein (GP), and inactivated whole virions from six species of filoviruses. All three outbreak cohorts exhibited significant antibody responses to antigens from the original infecting species and a pattern of additional filoviruses that varied by outbreak. NP was the most cross-reactive antigen, while GP was the most specific. Antibodies from survivors of infections by Marburg marburgvirus (MARV) species were least cross-reactive, while those from survivors of infections by Sudan virus (SUDV) species exhibited the highest cross-reactivity. Based on results revealed by the protein microarray, persistent levels of antibodies to GP, NP, and VP40 were maintained for up to 14 years after infection, and survival of infection caused by one species imparted cross-reactive antibody responses to other filoviruses.

Ebola Virus Makona Shows Reduced Lethality in an Immune-deficient Mouse Model

Ebola virus Makona (EBOV-Makona; from the 2013-2016 West Africa outbreak) shows decreased virulence in an immune-deficient mouse model, compared with a strain from 1976. Unlike other filoviruses tested, EBOV-Makona may be slightly more virulent by the aerosol route than by the injected route, as 2 mice died following aerosol exposure, compared with no mortality among mice that received intraperitoneal injection of equivalent or higher doses. Although most mice did not succumb to infection, the detection of an immunoglobulin G antibody response along with observed clinical signs suggest that the mice were infected but able to clear the infection and recover. We hypothesize that this may be due to the growth rates and kinetics of the virus, which appear slower than that for other filoviruses and consequently give more time for an immune response that results in clearance of the virus. In this instance, the immune-deficient mouse model is unlikely to be appropriate for testing medical countermeasures against this EBOV-Makona stock but may provide insight into pathogenesis and the immune response to virus.

Kinetic Analysis of Biomarkers in a Cohort of US Patients With Ebola Virus Disease

BACKGROUND

Ebola virus (EBOV) infection causes a severe and often fatal disease. Despite the fact that more than 30 000 individuals have acquired Ebola virus disease (EVD), the medical and scientific community still does not have a clear understanding of the mechanisms by which EBOV causes such severe disease.

METHODS

In this study, 54 biomarkers in plasma samples serially collected from 7 patients with EVD were analyzed in an attempt to define the kinetics of inflammatory modulators. Two clinical disease groups were defined (moderate and severe) based on the need for clinical support. Biomarkers were evaluated for correlation with viremia and clinical disease in an effort to identify pathways that could be useful targets of therapeutic intervention.

RESULTS

Patients with severe disease had higher viremia than those with moderate disease. Several biomarkers of immune activation and control were significantly elevated in patients with moderate disease. A series of pro-inflammatory cytokines and chemokines were significantly elevated in patients with severe disease.

CONCLUSIONS

Biomarkers that were associated with severe EVD were proinflammatory and indicative of endothelial or coagulation cascade dysfunction, as has been seen historically in patients with fatal outcomes. In contrast, biomarkers that were associated with moderate EVD were suggestive of a strong interferon response and control of both innate and adaptive responses. Therefore, clinical interventions that modulate the phenotype and magnitude of immune activation may be beneficial in treating EVD.

Treating Ebola patients: a 'bottom up' approach using generic statins and angiotensin receptor blockers

The international community has responded to the Ebola outbreak in West Africa with a 'top down' approach. This has contributed to outbreak control, but has done much less to reduce the high mortality rate in individual patients. Ebola patients experience a breakdown in endothelial barrier integrity that leads to massive fluid losses and vascular collapse. Statins and angiotensin receptor blockers (ARBs) maintain or restore endothelial barrier integrity. Local physicians in Sierra Leone have treated approximately 100 consecutive Ebola patients with atorvastatin and irbesartan, and all but two inadequately treated patients have survived. The results of this experience have not been released and they need to be reviewed and validated. Unlike other treatments that target the Ebola virus itself, this 'bottom up' approach to treatment represents a paradigm shift by targeting the host response to infection. Treatment with these safe, inexpensive generic agents could be implemented readily throughout West Africa.

Protection against malaria at 1 year and immune correlates following PfSPZ vaccination

An attenuated Plasmodium falciparum (Pf) sporozoite (SPZ) vaccine, PfSPZ Vaccine, is highly protective against controlled human malaria infection (CHMI) 3 weeks after immunization, but the durability of protection is unknown. We assessed how vaccine dosage, regimen, and route of administration affected durable protection in malaria-naive adults. After four intravenous immunizations with 2.7 × 10(5) PfSPZ, 6/11 (55%) vaccinated subjects remained without parasitemia following CHMI 21 weeks after immunization. Five non-parasitemic subjects from this dosage group underwent repeat CHMI at 59 weeks, and none developed parasitemia. Although Pf-specific serum antibody levels correlated with protection up to 21-25 weeks after immunization, antibody levels waned substantially by 59 weeks. Pf-specific T cell responses also declined in blood by 59 weeks. To determine whether T cell responses in blood reflected responses in liver, we vaccinated nonhuman primates with PfSPZ Vaccine. Pf-specific interferon-γ-producing CD8 T cells were present at ∼100-fold higher frequencies in liver than in blood. Our findings suggest that PfSPZ Vaccine conferred durable protection to malaria through long-lived tissue-resident T cells and that administration of higher doses may further enhance protection.

Preparing for Serious Communicable Diseases in the United States: What the Ebola Virus Epidemic Has Taught Us

Ending the West Africa Ebola virus disease (EVD) outbreak required an unprecedented international response. For the United States, participation in the international response to the West Africa EVD outbreak provided an opportunity to learn important lessons in four key domains critical to preparing for future outbreaks of EVD and other serious communicable diseases: (i) safe and effective patient care, (ii) the role of experimental therapeutics and vaccines, (iii) infection control, and (iv) hospital and community preparedness.

Correspondence of Neutralizing Humoral Immunity and CD4 T Cell Responses in Long Recovered Sudan Virus Survivors

Robust humoral and cellular immunity are critical for survival in humans during an ebolavirus infection. However, the interplay between these two arms of immunity is poorly understood. To address this, we examined residual immune responses in survivors of the Sudan virus (SUDV) outbreak in Gulu, Uganda (2000–2001). Cytokine and chemokine expression levels in SUDV stimulated whole blood cultures were assessed by multiplex ELISA and flow cytometry. Antibody and corresponding neutralization titers were also determined. Flow cytometry and multiplex ELISA results demonstrated significantly higher levels of cytokine and chemokine responses in survivors with serological neutralizing activity. This correspondence was not detected in survivors with serum reactivity to SUDV but without neutralization activity. This previously undefined relationship between memory CD4 T cell responses and serological neutralizing capacity in SUDV survivors is key for understanding long lasting immunity in survivors of filovirus infections.

Unique human immune signature of Ebola virus disease in Guinea

Despite the magnitude of the Ebola virus disease (EVD) outbreak in West Africa, there is still a fundamental lack of knowledge about the pathophysiology of EVD. In particular, very little is known about human immune responses to Ebola virus. Here we evaluate the physiology of the human T cell immune response in EVD patients at the time of admission to the Ebola Treatment Center in Guinea, and longitudinally until discharge or death. Through the use of multiparametric flow cytometry established by the European Mobile Laboratory in the field, we identify an immune signature that is unique in EVD fatalities. Fatal EVD was characterized by a high percentage of CD4(+) and CD8(+) T cells expressing the inhibitory molecules CTLA-4 and PD-1, which correlated with elevated inflammatory markers and high virus load. Conversely, surviving individuals showed significantly lower expression of CTLA-4 and PD-1 as well as lower inflammation, despite comparable overall T cell activation. Concomitant with virus clearance, survivors mounted a robust Ebola-virus-specific T cell response. Our findings suggest that dysregulation of the T cell response is a key component of EVD pathophysiology.

[Emerging viral infections and hepatotropic virus]

Environmental degradation, population movements and urban agglomerations have broken down the borders for infectious diseases. The expansion of microorganisms has entered an increasing area of transmission vectors. The lack of immunity of the population leads to an increased risk of spreading infectious diseases. Furthermore, the decline in vaccination rates in developed countries and socio-economic difficulties in large regions has meant that diseases in the process of eradication have re-emerged. That is why health care workers must be trained to avoid delaying in diagnosis and to accelerate the implementation of public health measures. A great deal of education and health prevention should fall under the responsibilities of travellers who move around different regions.

Longitudinal characterization of dysfunctional T cell-activation during human acute Ebola infection

Data on immune responses during human Ebola virus disease (EVD) are scanty, due to limitations imposed by biosafety requirements and logistics. A sustained activation of T-cells was recently described but functional studies during the acute phase of human EVD are still missing. Aim of this work was to evaluate the kinetics and functionality of T-cell subsets, as well as the expression of activation, autophagy, apoptosis and exhaustion markers during the acute phase of EVD until recovery. Two EVD patients admitted to the Italian National Institute for Infectious Diseases, Lazzaro Spallanzani, were sampled sequentially from soon after symptom onset until recovery and analyzed by flow cytometry and ELISpot assay. An early and sustained decrease of CD4 T-cells was seen in both patients, with an inversion of the CD4/CD8 ratio that was reverted during the recovery period. In parallel with the CD4 T-cell depletion, a massive T-cell activation occurred and was associated with autophagic/apoptotic phenotype, enhanced expression of the exhaustion marker PD-1 and impaired IFN-gamma production. The immunological impairment was accompanied by EBV reactivation. The association of an early and sustained dysfunctional T-cell activation in parallel to an overall CD4 T-cell decline may represent a previously unknown critical point of Ebola virus (EBOV)-induced immune subversion. The recent observation of late occurrence of EBOV-associated neurological disease highlights the importance to monitor the immuno-competence recovery at discharge as a tool to evaluate the risk of late sequelae associated with resumption of EBOV replication. Further studies are required to define the molecular mechanisms of EVD-driven activation/exhaustion and depletion of T-cells.

Sequelae of Ebola virus disease: the emergency within the emergency

As the massive outbreak of Ebola virus disease (EVD) in west Africa wanes, it has become increasingly clear that thousands of survivors have many sequelae, some of which might be very severe, such as arthritis and vision-threatening uveitis. The mental health effects of EVD on survivors and other family and community members is similarly profound. Furthermore, it is increasingly being recognised that Ebola virus might persist for weeks or months in selected body compartments of survivors, most notably in the semen of men, bringing risk of renewed transmission where it has previously been eliminated. These challenges to EVD survivors constitute a new emergency in terms of addressing individual patient need and to control the disease spread. In this Review, we assess what is known regarding the sequelae of EVD, including possible delayed virus clearance. We discuss some of the key challenges regarding the provision of care to survivors and implementation of necessary future research.

Presence and Persistence of Ebola or Marburg Virus in Patients and Survivors: A Rapid Systematic Review

BACKGROUND

The 2013-15 Ebola outbreak was unprecedented due to sustained transmission within urban environments and thousands of survivors. In 2014 the World Health Organization stated that there was insufficient evidence to give definitive guidance about which body fluids are infectious and when they pose a risk to humans. We report a rapid systematic review of published evidence on the presence of filoviruses in body fluids of infected people and survivors.

METHODS

Scientific articles were screened for information about filovirus in human body fluids. The aim was to find primary data that suggested high likelihood of actively infectious filovirus in human body fluids (viral RNA). Eligible infections were from Marburg virus (MARV or RAVV) and Zaire, Sudan, Taï Forest and Bundibugyo species of Ebola. Cause of infection had to be laboratory confirmed (in practice either tissue culture or RT-PCR tests), or evidenced by compatible clinical history with subsequent positivity for filovirus antibodies or inflammatory factors. Data were extracted and summarized narratively.

RESULTS

6831 unique articles were found, and after screening, 33 studies were eligible. For most body fluid types there were insufficient patients to draw strong conclusions, and prevalence of positivity was highly variable. Body fluids taken >16 days after onset were usually negative. In the six studies that used both assay methods RT-PCR tests for filovirus RNA gave positive results about 4 times more often than tissue culture.

CONCLUSIONS

Filovirus was reported in most types of body fluid, but not in every sample from every otherwise confirmed patient. Apart from semen, most non-blood, RT-PCR positive samples are likely to be culture negative and so possibly of low infectious risk. Nevertheless, it is not apparent how relatively infectious many body fluids are during or after illness, even when culture-positive, not least because most test results come from more severe cases. Contact with blood and blood-stained body fluids remains the major risk for disease transmission because of the known high viral loads in blood.

Antiviral Vaccines: Challenges and Advances

Vaccination is the most effective means of preventing and controlling viral infections. The eradication of smallpox and the significant progress made toward polio eradication are clear examples of the great impact of antiviral vaccines. However, viral infections remain a major public health threat and a significant cause of death. Most of the antiviral vaccines introduced over the past century were empirically developed. Poliomyelitis, measles, mumps, and rubella are examples of diseases that are now largely controlled thanks to these empirically developed vaccines. However, there is a growing list of viral pathogens against which effective vaccines are yet to be developed. Recent technological advances will potentially provide us with new platforms that could be harnessed to develop vaccines against emerging and reemerging viral pathogens.

Specific neutralizing response in plasma from convalescent patients of Ebola Virus Disease against the West Africa Makona variant of Ebola virus

BACKGROUND

The current outbreak of Ebola Virus Disease in West Africa is caused by a new variant of Ebola virus (EBOV) named Makona 2014, whose sequence differs 3% from isolates from Central Africa such as Mayinga 1976 EBOV. The specificity and kinetics of the neutralizing antibody response induced by the circulating Makona EBOV has not been thoroughly studied.

METHODS

We have used a lentiviral EBOV-glycoprotein (GP)-pseudotyped infection assay to measure Makona-GP and Mayinga-GP specific neutralizing activity of plasma from three convalescent Ebola Virus Disease patients from the current EBOV outbreak at 2, 3, 4 and 9 months post-infection. Total anti-EBOV GP IgG was measured by a commercial ELISA assay.

FINDINGS

In convalescent Ebola Virus Disease patients, Makona-GP-specific neutralizing titers increased from 2 months (mean IC50 1/59), 3 months (IC50 1/212), 4 months (IC50 1/239) and up to 9 months (IC50 1/268) post-infection. Neutralizing activity of plasma from the three convalescent Ebola Virus Disease patients was more vigorous against the current Makona-GP pseudotyped EBOV variant than against Mayinga-GP pseudotyped EBOV and this difference was observed at each time point tested: Mayinga vs Makona mean IC50 fold=4.92 at 2 months post-infection, 2.89 fold at 3 months post-infection, 2.23 at 4 months post-infection and 2.98 at 9 months post-infection (all differences p<0.01). Total level of IgG against EBOV-GP did not evolve significantly during the follow up.

DISCUSSION

In convalescent Ebola Virus Disease patients, EBOV-GP specific neutralizing activity increases over time, at least up to 9 months post-infection, which suggests that active affinity maturation of antibodies takes place long after clinical recovery. EBOV-GP specific neutralizing response is significantly higher against Makona EBOV circulating in West Africa than against the variants included in the currently approved vaccines. Correlates of protection for EBOV vaccines have not been completely established and the relevance of a lower neutralizing activity in convalescent plasma from the current outbreak against one of the EBOV-GPs contained in the vaccines in terms of its potential efficacy does not necessarily preclude its efficacy. However, this observation highlights the concern regarding the natural diversity of EBOV and its subsequent challenge for diagnosis, therapy and vaccine design. EBOV-GP neutralizing activity varies considerably over time in convalescent Ebola Virus Disease patients. Titering of convalescent blood products would be desirable to standardize and evaluate their potential therapeutic value.

Early clinical sequelae of Ebola virus disease in Sierra Leone: a cross-sectional study

BACKGROUND

Limited data are available on the prevalence and predictors of clinical sequelae in survivors of Ebola virus disease (EVD). The EVD Survivor Clinic in Port Loko, Sierra Leone, has provided clinical care for 603 of 661 survivors living in the district. We did a cross-sectional study to describe the prevalence, nature, and predictors of three key EVD sequelae (ocular, auditory, and articular) in this cohort of EVD survivors.

METHODS

We reviewed available clinical and laboratory records of consecutive patients assessed in the clinic between March 7, 2015, and April 24, 2015. We used univariate and multiple logistic regression to examine clinical and laboratory features of acute EVD with the following outcomes in convalescence: new ocular symptoms, uveitis, auditory symptoms, and arthralgias.

FINDINGS

Among 277 survivors (59% female), median age was 29 years (IQR 20-36) and median time from discharge from an EVD treatment facility to first survivor clinic visit was 121 days (82-151). Clinical sequelae were common, including arthralgias (n=210, 76%), new ocular symptoms (n=167, 60%), uveitis (n=50, 18%), and auditory symptoms (n=67, 24%). Higher Ebola viral load at acute EVD presentation (as shown by lower cycle thresholds on real-time RT-PCR testing) was independently associated with uveitis (adjusted odds ratio [aOR] 3·33, 95% CI 1·87-5·91, for every five-point decrease in cycle threshold) and with new ocular symptoms or ocular diagnoses (aOR 3·04, 95% CI 1·87-4·94).

INTERPRETATION

Clinical sequelae during early EVD convalescence are common and sometimes sight threatening. These findings underscore the need for early clinical follow-up of survivors of EVD and urgent provision of ocular care as part of health systems strengthening in EVD-affected west African countries.

FUNDING

Canadian Institutes of Health Research.

Humanized Mouse Model of Ebola Virus Disease Mimics the Immune Responses in Human Disease

Animal models recapitulating human Ebola virus disease (EVD) are critical for insights into virus pathogenesis. Ebola virus (EBOV) isolates derived directly from human specimens do not, without adaptation, cause disease in immunocompetent adult rodents. Here, we describe EVD in mice engrafted with human immune cells (hu-BLT). hu-BLT mice developed EVD following wild-type EBOV infection. Infection with high-dose EBOV resulted in rapid, lethal EVD with high viral loads, alterations in key human antiviral immune cytokines and chemokines, and severe histopathologic findings similar to those shown in the limited human postmortem data available. A dose- and donor-dependent clinical course was observed in hu-BLT mice infected with lower doses of either Mayinga (1976) or Makona (2014) isolates derived from human EBOV cases. Engraftment of the human cellular immune system appeared to be essential for the observed virulence, as nonengrafted mice did not support productive EBOV replication or develop lethal disease. hu-BLT mice offer a unique model for investigating the human immune response in EVD and an alternative animal model for EVD pathogenesis studies and therapeutic screening.

Blood kinetics of Ebola virus in survivors and nonsurvivors

BACKGROUND

Infection with Ebola virus (EBOV) results in a life-threatening disease, with reported mortality rates between 50%-70%. The factors that determine patient survival are poorly understood; however, clinical observations indicate that EBOV viremia may be associated with fatal outcome. We conducted a study of the kinetics of Zaire EBOV viremia in patients with EBOV disease (EVD) who were managed at an Ebola Treatment Centre in Sierra Leone during the recent West African outbreak.

METHODS

Data from 84 EVD patients (38 survivors, 46 nonsurvivors) were analyzed, and EBOV viremia was quantified between 2 and 13 days after symptom onset. Time since symptom onset and clinical outcome were used as independent variables to compare EBOV viral kinetics in survivors and nonsurvivors.

RESULTS

In all patients, EBOV viremia kinetics was a quadratic function of time; however, EBOV viremia was 0.94 logarithm (log) copies per ml (cp/ml) (P = 0.011) higher in nonsurvivors than in survivors from day 2 after the onset of symptoms. Survivors reached peak viremia levels at an earlier time after symptom onset than nonsurvivors (day 5 versus day 7) and had lower mean peak viremia levels compared with nonsurvivors (7.46 log cp/ml; 95% CI, 7.17-7.76 vs. 8.60 log cp/ml; 95% CI, 8.27-8.93). Before reaching peak values, EBOV viremia similarly increased both in survivors and nonsurvivors; however, the decay of viremia after the peak was much stronger in survivors than in nonsurvivors.

CONCLUSION

Our results demonstrate that plasma concentrations of EBOV are markedly different between survivors and nonsurvivors at very early time points after symptom onset and may be predicative of outcome. Further studies focused on the early phase of the disease will be required to identify the causal and prognostic factors that determine patient outcome.

FUNDING

Italian Ministry of Health; Italian Ministry of Foreign Affairs; EMERGENCY's private donations; and Royal Engineers for DFID-UK.

Convalescent plasma: new evidence for an old therapeutic tool?

Passive immunisation for the prevention and treatment of human infectious diseases can be traced back to the 20(th) century. The recent Ebola virus outbreak in West Africa has turned the spotlight onto the possible use of convalescent whole blood and convalescent plasma in the treatment of infectious diseases because they are the only therapeutic strategy available in some cases, given the unavailability of vaccines, drugs or other specific treatments. Convalescent blood products could be a valid option in the treatment/prophylaxis of several infectious diseases both in association with other drugs/preventive measures and as the only therapy when a specific treatment is not available. However, there are still some issues to consider in determining the advisability of implementing a large-scale convalescent plasma transfusion programme.

The Role of Cytokines and Chemokines in Filovirus Infection

Ebola- and marburgviruses are highly pathogenic filoviruses and causative agents of viral hemorrhagic fever. Filovirus disease is characterized by a dysregulated immune response, severe organ damage, and coagulation abnormalities. This includes modulation of cytokines, signaling mediators that regulate various components of the immune system as well as other biological processes. Here we examine the role of cytokines in filovirus infection, with an emphasis on understanding how these molecules affect development of the antiviral immune response and influence pathology. These proteins may present targets for immune modulation by therapeutic agents and vaccines in an effort to boost the natural immune response to infection and/or reduce immunopathology.

Computational elucidation of potential antigenic CTL epitopes in Ebola virus

Cell-mediated immunity is important for the control of Ebola virus infection. We hypothesized that those HLA A0201 and HLA B40 restricted epitopes derived from Ebola virus proteins, would mount a good antigenic response. Here we employed an immunoinformatics approach to identify specific 9mer amino acid which may be capable of inducing a robust cell-mediated immune response in humans. We identified a set of 28 epitopes that had no homologs in humans. Specifically, the epitopes derived from NP, RdRp, GP and VP40 share population coverage of 93.40%, 84.15%, 74.94% and 77.12%, respectively. Based on the other HLA binding specificity and population coverage, seven novel promiscuous epitopes were identified. These 7 promiscuous epitopes from NP, RdRp and GP were found to have world-wide population coverage of more than 95% indicating their potential significance as useful candidates for vaccine design. Epitope conservancy analysis also suggested that most of the peptides are highly conserved (100%) in other virulent Ebola strain (Mayinga-76, Kikwit-95 and Makona-G3816- 2014) and can therefore be further investigated for their immunological relevance and usefulness as vaccine candidates.

Filovirus pathogenesis and immune evasion: insights from Ebola virus and Marburg virus

Ebola viruses and Marburg viruses, members of the filovirus family, are zoonotic pathogens that cause severe disease in people, as highlighted by the latest Ebola virus epidemic in West Africa. Filovirus disease is characterized by uncontrolled virus replication and the activation of host responses that contribute to pathogenesis. Underlying these phenomena is the potent suppression of host innate antiviral responses, particularly the type I interferon response, by viral proteins, which allows high levels of viral replication. In this Review, we describe the mechanisms used by filoviruses to block host innate immunity and discuss the links between immune evasion and filovirus pathogenesis.

Clinical development of Ebola vaccines

The ongoing outbreak of Ebola virus disease in West Africa highlighted the lack of a licensed drug or vaccine to combat the disease and has renewed the urgency to develop a pipeline of Ebola vaccines. A number of different vaccine platforms are being developed by assessing preclinical efficacy in animal models and expediting clinical development. Over 15 different vaccines are in preclinical development and 8 vaccines are now in different stages of clinical evaluation. These vaccines include DNA vaccines, virus-like particles and viral vectors such as live replicating vesicular stomatitis virus (rVSV), human and chimpanzee adenovirus, and vaccinia virus. Recently, in preliminary results reported from the first phase III trial of an Ebola vaccine, the rVSV-vectored vaccine showed promising efficacy. This review charts this rapidly advancing area of research focusing on vaccines in clinical development and discusses the future opportunities and challenges faced in the licensure and deployment of Ebola vaccines.

Addressing Therapeutic Options for Ebola Virus Infection in Current and Future Outbreaks

Ebola virus can cause severe hemorrhagic disease with high fatality rates. Currently, no specific therapeutic agent or vaccine has been approved for treatment and prevention of Ebola virus infection of humans. Although the number of Ebola cases has fallen in the last few weeks, multiple outbreaks of Ebola virus infection and the likelihood of future exposure highlight the need for development and rapid evaluation of pre- and postexposure treatments. Here, we briefly review the existing and future options for anti-Ebola therapy, based on the data coming from rare clinical reports, studies on animals, and results from in vitro models. We also project the mechanistic hypotheses of several potential drugs against Ebola virus, including small-molecule-based drugs, which are under development and being tested in animal models or in vitro using various cell types. Our paper discusses strategies toward identifying and testing anti-Ebola virus properties of known and medically approved drugs, especially those that can limit the pathological inflammatory response in Ebola patients and thereby provide protection from mortality. We underline the importance of developing combinational therapy for better treatment outcomes for Ebola patients.

Immunological features underlying viral hemorrhagic fevers

Several enveloped RNA viruses of the arenavirus, bunyavirus, filovirus and flavivirus families are associated with a syndrome known as viral hemorrhagic fever (VHF). VHF is characterized by fever, vascular leakage, coagulation defects and multi organ system failure. VHF is currently viewed as a disease precipitated by viral suppression of innate immunity, which promotes systemic virus replication and excessive proinflammatory cytokine responses that trigger the manifestations of severe disease. However, the mechanisms by which immune dysregulation contributes to disease remain poorly understood. Infection of nonhuman primates closely recapitulates human VHF, notably Ebola and yellow fever, thereby providing excellent models to better define the immunological basis for this syndrome. Here we review the current state of our knowledge and suggest future directions that will better define the immunological mechanisms underlying VHF.

Ebola Virus Disease: Experience and Decision Making for the First Patients outside of Africa

David Stephens and colleagues describe their experience of treating patients with Ebola virus disease at Emory University in the United States.

Molecular mechanisms of Ebola virus pathogenesis: focus on cell death

Ebola virus (EBOV) belongs to the Filoviridae family and is responsible for a severe disease characterized by the sudden onset of fever and malaise accompanied by other non-specific signs and symptoms; in 30–50% of cases hemorrhagic symptoms are present. Multiorgan dysfunction occurs in severe forms with a mortality up to 90%. The EBOV first attacks macrophages and dendritic immune cells. The innate immune reaction is characterized by a cytokine storm, with secretion of numerous pro-inflammatory cytokines, which induces a huge number of contradictory signals and hurts the immune cells, as well as other tissues. Other highly pathogenic viruses also trigger cytokine storms, but Filoviruses are thought to be particularly lethal because they affect a wide array of tissues. In addition to the immune system, EBOV attacks the spleen and kidneys, where it kills cells that help the body to regulate its fluid and chemical balance and that make proteins that help the blood to clot. In addition, EBOV causes liver, lungs and kidneys to shut down their functions and the blood vessels to leak fluid into surrounding tissues. In this review, we analyze the molecular mechanisms at the basis of Ebola pathogenesis with a particular focus on the cell death pathways induced by the virus. We also discuss how the treatment of the infection can benefit from the recent experience of blocking/modulating cell death in human degenerative diseases.

Relationship Between Ebola Virus Real-Time Quantitative Polymerase Chain Reaction-Based Threshold Cycle Value and Virus Isolation From Human Plasma

We performed a longitudinal analysis of plasma samples obtained from 4 patients with Ebola virus (EBOV) disease (EVD) to determine the relationship between the real-time quantitative reverse transcriptase polymerase chain reaction (qRT-PCR)-based threshold cycle (Ct) value and the presence of infectious EBOV. EBOV was not isolated from plasma samples with a Ct value of >35.5 or >12 days after onset of symptoms. EBOV was not isolated from plasma samples in which anti-EBOV nucleoprotein immunoglobulin G was detected. These data demonstrate the utility of interpreting qRT-PCR results in the context of the course of EBOV infection and associated serological responses for patient-management decisions.