Highly Pathogenic Avian Influenza Virus Infection of Mallards with Homo- and Heterosubtypic Immunity Induced by Low Pathogenic Avian Influenza Viruses

The potential role of wild birds as carriers of highly pathogenic avian influenza virus (HPAIV) subtype H5N1 is still a matter of debate. Consecutive or simultaneous infections with different subtypes of influenza viruses of low pathogenicity (LPAIV) are very common in wild duck populations. To better understand the epidemiology and pathogenesis of HPAIV H5N1 infections in natural ecosystems, we investigated the influence of prior infection of mallards with homo- (H5N2) and heterosubtypic (H4N6) LPAIV on exposure to HPAIV H5N1. In mallards with homosubtypic immunity induced by LPAIV infection, clinical disease was absent and shedding of HPAIV from respiratory and intestinal tracts was grossly reduced compared to the heterosubtypic and control groups (mean GEC/100 µl at 3 dpi: 3.0×10² vs. 2.3×10⁴ vs. 8.7×10⁴; p<0.05). Heterosubtypic immunity induced by an H4N6 infection mediated a similar but less pronounced effect. We conclude that the epidemiology of HPAIV H5N1 in mallards and probably other aquatic wild bird species is massively influenced by interfering immunity induced by prior homo- and heterosubtypic LPAIV infections.     

Structural and Functional Characterization of a Cross-Reactive Dengue Virus Neutralizing Antibody that Recognizes a Cryptic Epitope

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Chikungunya Virus Infection Results in Higher and Persistent Viral Replication in Aged Rhesus Macaques Due to Defects in Anti-Viral Immunity

Chikungunya virus (CHIKV) is a re-emerging mosquito-borne Alphavirus that causes a clinical disease involving fever, myalgia, nausea and rash. The distinguishing feature of CHIKV infection is the severe debilitating poly-arthralgia that may persist for several months after viral clearance. Since its re-emergence in 2004, CHIKV has spread from the Indian Ocean region to new locations including metropolitan Europe, Japan, and even the United States. The risk of importing CHIKV to new areas of the world is increasing due to high levels of viremia in infected individuals as well as the recent adaptation of the virus to the mosquito species Aedes albopictus. CHIKV re-emergence is also associated with new clinical complications including severe morbidity and, for the first time, mortality. In this study, we characterized disease progression and host immune responses in adult and aged Rhesus macaques infected with either the recent CHIKV outbreak strain La Reunion (LR) or the West African strain 37997. Our results indicate that following intravenous infection and regardless of the virus used, Rhesus macaques become viremic between days 1–5 post infection. While adult animals are able to control viral infection, aged animals show persistent virus in the spleen. Virus-specific T cell responses in the aged animals were reduced compared to adult animals and the B cell responses were also delayed and reduced in aged animals. Interestingly, regardless of age, T cell and antibody responses were more robust in animals infected with LR compared to 37997 CHIKV strain. Taken together these data suggest that the reduced immune responses in the aged animals promotes long-term virus persistence in CHIKV-LR infected Rhesus monkeys.     

DNA Vaccine Encoding Hemagglutinin Provides Protective Immunity against H5N1 Influenza Virus Infection in Mice

In Hong Kong in 1997, a highly lethal H5N1 avian influenza virus was apparently transmitted directly from chickens to humans with no intermediate mammalian host and caused 18 confirmed infections and six deaths. Strategies must be developed to deal with this virus if it should reappear, and prospective vaccines must be developed to anticipate a future pandemic. We have determined that unadapted H5N1 viruses are pathogenic in mice, which provides a well-defined mammalian system for immunological studies of lethal avian influenza virus infection. We report that a DNA vaccine encoding hemagglutinin from the index human influenza isolate A/HK/156/97 provides immunity against H5N1 infection of mice. This immunity was induced against both the homologous A/HK/156/97 (H5N1) virus, which has no glycosylation site at residue 154, and chicken isolate A/Ck/HK/258/97 (H5N1), which does have a glycosylation site at residue 154. The mouse model system should allow rapid evaluation of the vaccine’s protective efficacy in a mammalian host. In our previous study using an avian model, DNA encoding hemagglutinin conferred protection against challenge with antigenic variants that differed from the primary antigen by 11 to 13% in the HA1 region. However, in our current study we found that a DNA vaccine encoding the hemagglutinin from A/Ty/Ir/1/83 (H5N8), which differs from A/HK/156/97 (H5N1) by 12% in HA1, prevented death but not H5N1 infection in mice. Therefore, a DNA vaccine made with a heterologous H5 strain did not prevent infection by H5N1 avian influenza viruses in mice but was useful in preventing death.     

Genotype-Specific vs. Cross-Reactive Host Immunity against a Macroparasite

Vertebrate hosts often defend themselves against several co-infecting parasite genotypes simultaneously. This has important implications for the ecological dynamics and the evolution of host defence systems and parasite strategies. For example, it can drive the specificity of the adaptive immune system towards high genotype-specificity or cross-reactivity against several parasite genotypes depending on the sequence and probability of re-infections. However, to date, there is very little evidence on these interactions outside mammalian disease literature. In this study we asked whether genotype-specific or cross-reactive responses dominate in the adaptive immune system of a fish host towards a common macroparasite. In other words, we investigated if the infection success of a parasite genotype is influenced by the immunization genotype. We reciprocally immunized and re-exposed rainbow trout (Oncorhynchus mykiss) to a range of genotypes of the trematode eye fluke Diplostomum pseudospathaceum, and measured infection success of the parasite. We found that the infection success of the parasite genotypes in the re-exposure did not depend on the immunization genotype. While immunization reduced average infection success by 31%, the reduction was not larger against the initial immunization genotype. Our results suggest significant cross-reactivity, which may be advantageous for the host in genetically diverse re-exposures and have significant evolutionary implications for parasite strategies. Overall, our study is among the first to demonstrate cross-reactivity of adaptive immunity against genetically diverse macroparasites with complex life cycles.     

Loss of Effector and Anti-Inflammatory Natural Killer T Lymphocyte Function in Pathogenic Simian Immunodeficiency Virus Infection

Chronic immune activation is a key determinant of AIDS progression in HIV-infected humans and simian immunodeficiency virus (SIV)-infected macaques but is singularly absent in SIV-infected natural hosts. To investigate whether natural killer T (NKT) lymphocytes contribute to the differential modulation of immune activation in AIDS-susceptible and AIDS-resistant hosts, we compared NKT function in macaques and sooty mangabeys in the absence and presence of SIV infection. Cynomolgus macaques had significantly higher frequencies of circulating invariant NKT lymphocytes compared to both rhesus macaques and AIDS-resistant sooty mangabeys. Despite this difference, mangabey NKT lymphocytes were functionally distinct from both macaque species in their ability to secrete significantly more IFN-γ, IL-13, and IL-17 in response to CD1d/α-galactosylceramide stimulation. While NKT number and function remained intact in SIV-infected mangabeys, there was a profound reduction in NKT activation-induced, but not mitogen-induced, secretion of IFN-γ, IL-2, IL-10, and TGF-β in SIV-infected macaques. SIV-infected macaques also showed a selective decline in CD4⁺ NKT lymphocytes which correlated significantly with an increase in circulating activated memory CD4⁺ T lymphocytes. Macaques with lower pre-infection NKT frequencies showed a significantly greater CD4⁺ T lymphocyte decline post SIV infection. The disparate effect of SIV infection on NKT function in mangabeys and macaques could be a manifestation of their differential susceptibility to AIDS. Alternately, these data also raise the possibility that loss of anti-inflammatory NKT function promotes chronic immune activation in pathogenic SIV infection, while intact NKT function helps to protect natural hosts from developing immunodeficiency and aberrant immune activation.     

Alphavirus-Specific Cytotoxic T Lymphocytes Recognize a Cross-Reactive Epitope from the Capsid Protein and Can Eliminate Virus from Persistently Infected Macrophages

Persistent alphavirus infections in synovial and neural tissues are believed to be associated with chronic arthritis and encephalitis, respectively, and represent likely targets for CD8⁺ αβ cytotoxic T lymphocytes (CTL). Here we show that the capsid protein is a dominant target for alphavirus-specific CTL in BALB/c mice and that capsid-specific CTL from these mice recognize an H-2K^d restricted epitope, QYSGGRFTI. This epitope lies in the highly conserved region of the capsid protein, and QYSGGRFTI-specific CTL were cross reactive across a range of Old World alphaviruses. In vivo the acute primary viraemia of these highly cytopathic viruses was unaffected by QYSGGRFTI-specific CTL. However, in vitro these CTL were able to completely clear virus from macrophages persistently and productively infected with the arthrogenic alphavirus Ross River virus.     

Dengue and Zika Virus Cross-Reactive Human Monoclonal Antibodies Protect against Spondweni Virus Infection and Pathogenesis in Mice

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Nanodisc-Incorporated Hemagglutinin Provides Protective Immunity against Influenza Virus Infection

Every year, influenza virus infection causes significant mortality and morbidity in human populations. Although egg-based inactivated viral vaccines are available, their effectiveness depends on the correct prediction of the circulating viral strains and is limited by the time constraint of the manufacturing process. Recombinant subunit vaccines are easier to manufacture with a relatively short lead time but are limited in their efficacy partly because the purified recombinant membrane proteins in the soluble form most likely do not retain their native membrane-bound structure. Nanodisc (ND) particles are soluble, stable, and reproducibly prepared discoid shaped nanoscale structures that contain a discrete lipid bilayer bound by two amphipathic scaffold proteins. Because ND particles permit the functional reconstitution of membrane/envelope proteins, we incorporated recombinant hemagglutinin (HA) from influenza virus strain A/New Caledonia/20/99 (H1N1) into NDs and investigated their potential to elicit an immune response to HA and confer immunity to influenza virus challenge relative to the commercial vaccines Fluzone and FluMist. HA-ND vaccination induced a robust anti-HA antibody response consisting of predominantly the immunoglobulin G1 (IgG1) subclass and a high hemagglutination inhibition titer. Intranasal immunization with HA-ND induced an anti-HA IgA response in nasal passages. HA-ND vaccination conferred protection that was comparable to that of Fluzone and FluMist against challenge with influenza virus strain A/Puerto Rico/8/1934 (H1N1).The influenza A virus-type viral genome encodes 11 proteins including hemagglutinin (HA) and neuraminidase (NA). HA is important in virus transmission and is also a major determinant of host range (16). NA prevents viral aggregation and helps in the release of new viruses from the infected cell (25). These glycoproteins are the principal antigens against which humoral immune responses of the host are directed. Vaccination has been accepted as the most effective method of preventing influenza virus. Current licensed vaccines against influenza virus include conventional inactivated virus vaccine, live-attenuated vaccine, or inactivated “split-virus” vaccines, all grown in embryonated chicken eggs. Influenza virus vaccines may contain residual egg-derived antigens, which is a risk factor for persons with hypersensitivity to eggs. In the case of live-attenuated vaccines that are delivered by the mucosal route, there are several potential safety concerns including the possibility that the vaccine strain could undergo spontaneous genetic change and in a rare case of simultaneous infection with another influenza virus could undergo antigenic shift. These factors are of special concern for children and the elderly, who are the primary populations at risk for influenza virus infection (9). Therefore, there is a continuing need for developing more efficacious and safer vaccines.Apart from licensed vaccines, a number of different vaccine formulations including soluble glycoproteins, virus-like particles, and subunit vaccines (6, 9, 14) with various efficacies have been developed. Recombinant glycoprotein vaccines offer many distinct advantages, including cost, the possibility of adapting them to rapidly changing strains within a short time, and independence from egg-based formulations. In experimental setups, recombinant HA (rHA) and recombinant NA have provided protection against lethal challenge to mice (18, 27). The safety, immunogenicity, and efficacy of trivalent rHA vaccines have been established (26), and a potential trivalent HA vaccine (FluBlok; Protein Sciences Corporation) is currently in phase III clinical trials.Some rHA-based vaccines elicit high titers of anti-HA antibodies. However, these antibodies do not necessarily possess a high capacity for virus neutralization. This apparent discrepancy likely results from the use of soluble HA protein that may not accurately mimic the native structure of the membrane-embedded glycoprotein on the viral envelope for immunization. This could result in a robust antibody response with a limited ability to react with “native epitopes.” This notion is supported by data from previously reported studies that indicated that antigens expressed in their native three-dimensional conformation can elicit a more effective antibody response than proteins in their nonnative forms (19). Therefore, we investigated whether rHA presented in a lipid-bilayer-embedded formulation would elicit a potent neutralizing antibody response.The Nanodisc (ND) system was developed as a novel method for functionally reconstituting membrane proteins into soluble nanoscale lipid bilayers (3, 4, 12, 22). NDs are robust, reproducible, and monodisperse discoidal particles 5.5 nm high and nominally 10 nm in diameter that are formed via a self-assembly process. ND particles contain two copies of an alpha-helical, amphipathic protein, termed membrane scaffold protein (MSP), which encircles a lipid bilayer in a “belt-like” fashion (Fig. ​(Fig.1a).1a). A mixture of phospholipids and MSP are placed in a nonequilibrium solubilized state, for instance, using detergent or high hydrostatic pressure, and the system is then allowed to approach equilibrium by the gentle removal of the perturbant. This initiates a process of self-assembly, wherein the phospholipids and MSP find each other and generate a discoidal phospholipid bilayer encircled by the MSP. The resulting nanostructures represent a highly stable and homogeneous population with an aqueous solubility in the millimolar range (11).Open in a separate windowFIG. 1.Construction of HA-NDs. (a) Schematic showing an ND particle that contains a phospholipid bilayer encircled by membrane scaffold proteins (left) (5) and the same ND particle with an embedded transmembrane protein (right) (17). (b) HA-ND assemblies were first purified by Ni²⁺ affinity chromatography. (Top left) Silver-stained SDS-PAGE showing flowthrough, wash, and elution of HA-ND assembly mix over a Ni-nitrilotriacetic acid column (FT1 and FT2 are flowthrough, and the eluate contains the eluted protein). Arrows show the positions of the 72-kDa HA band and the 25-kDa MSPs. (Top right) Anti-HA Western blotting of the same SDS-PAGE gel. Depending on the quality of purification, a certain fraction of full-length 72-kDa rHA (HA0) can exist as proteolytically cleaved HA1 (∼50-kDa) and HA2 (∼28-kDa) subunits. (Bottom left) Ni²⁺ column eluates were further purified by SEC. Silver-stained SDS-PAGE gel shows size-based fractionation of Ni²⁺ column eluate. The numbers at the bottom correspond to the fractions collected. The MSP amounts are largest at fractions 27 to 30, showing that empty NDs eluted at those fractions. (Bottom right) Anti-HA Western blotting of the same SDS-PAGE gel showing that HA-ND assemblies eluted mainly between fractions 18 and 26. (c) Elution profile of HA-ND following SEC separation. The elution times for protein standards used for calibration are indicated at the top. The control profile for empty NDs is superimposed. HA-ND assemblies have a shorter retention time than empty NDs. inj, injection. (d) HA-ND assemblies from different SEC fractions separate as discrete-sized molecules upon native PAGE separation. Silver staining (left) and anti-HA Western blotting (right) of native PAGE gels from size exclusion fractions show different HA polymers contained in NDs. Earlier fractions are rich in higher-polymeric forms of HA, while later fractions are richer in monomeric HA. Control HA was loaded in the last well to the right in both cases.The value of the ND self-assembly process is that one can simply and reproducibly incorporate membrane proteins into these structures. This is accomplished by including the membrane protein in the initial mixture of MSP, lipid, and detergent prior to the initiation of the self-assembly process. An incorporated membrane protein then finds itself in a native-like environment with stability and activity normally found in vivo. By using phospholipids with different chemical characteristics (charge, degree of unsaturation, and length of acyl chains), the bilayer environment can be optimized to accommodate functional requirements. Furthermore, larger scaffold proteins, which in turn create a larger-diameter particle, can be employed to incorporate multimers or membrane protein complexes. Numerous membrane proteins from the three major classes-integral, tethered, and embedded (including monomers and multimers)-in the lipid bilayer environment created by NDs have been studied (2-5, 8, 10, 13, 20, 23). Since the ND system creates a stable bilayer environment that mimics that encountered by a membrane protein in the cell membrane, membrane proteins display normal folding, native ligand binding kinetics, and intact signaling activity (1, 3, 5, 8, 10, 13, 17, 23).In this study, we successfully incorporated recombinant baculovirus-derived HA into NDs (HA-ND) and compared its efficacy to induce a relevant immune response and confer protection against influenza virus challenge with those of existing licensed vaccines by using a mouse model.     

High-Avidity and Potently Neutralizing Cross-Reactive Human Monoclonal Antibodies Derived from Secondary Dengue Virus Infection

The envelope (E) protein of dengue virus (DENV) is the major target of neutralizing antibodies (Abs) and vaccine development. Previous studies of human dengue-immune sera reported that a significant proportion of anti-E Abs, known as group-reactive (GR) Abs, were cross-reactive to all four DENV serotypes and to one or more other flaviviruses. Based on studies of mouse anti-E monoclonal antibodies (MAbs), GR MAbs were nonneutralizing or weakly neutralizing compared with type-specific MAbs; a GR response was thus not regarded as important for vaccine strategy. We investigated the epitopes, binding avidities, and neutralization potencies of 32 human GR anti-E MAbs. In addition to fusion loop (FL) residues in E protein domain II, human GR MAbs recognized an epitope involving both FL and bc loop residues in domain II. The neutralization potencies and binding avidities of GR MAbs derived from secondary DENV infection were stronger than those derived from primary infection. GR MAbs derived from primary DENV infection primarily blocked attachment, whereas those derived from secondary infection blocked DENV postattachment. Analysis of the repertoire of anti-E MAbs derived from patients with primary DENV infection revealed that the majority were GR, low-avidity, and weakly neutralizing MAbs, whereas those from secondary infection were primarily GR, high-avidity, and potently neutralizing MAbs. Our findings suggest that the weakly neutralizing GR anti-E Abs generated from primary DENV infection become potently neutralizing MAbs against the four serotypes after secondary infection. The observation that the dengue immune status of the host affects the quality of the cross-reactive Abs generated has implications for new strategies for DENV vaccination.     

HLA-Associated Clinical Progression Correlates with Epitope Reversion Rates in Early Human Immunodeficiency Virus Infection

Human immunodeficiency virus type 1 (HIV-1) can evade immunity shortly after transmission to a new host but the clinical significance of this early viral adaptation in HIV infection is not clear. We present an analysis of sequence variation from a longitudinal cohort study of HIV adaptation in 189 acute seroconverters followed for up to 3 years. We measured the rates of variation within well-defined epitopes to determine associations with the HLA-linked hazard of disease progression. We found early reversion across both the gag and pol genes, with a 10-fold faster rate of escape in gag (2.2 versus 0.27 forward mutations/1,000 amino acid sites). For most epitopes (23/34), variation in the HLA-matched and HLA-unmatched controls was similar. For a minority of epitopes (8/34, and generally associated with HLA class I alleles that confer clinical benefit), new variants appeared early and consistently over the first 3 years of infection. Reversion occurred early at a rate which was HLA-dependent and correlated with the HLA class 1-associated relative hazard of disease progression and death (P = 0.0008), reinforcing the association between strong cytotoxic T-lymphocyte responses, viral fitness, and disease status. These data provide a comprehensive overview of viral adaptation in the first 3 years of infection. Our findings of HLA-dependent reversion suggest that costs are borne by some escape variants which may benefit the host, a finding contrary to a simple immune evasion paradigm. These epitopes, which are both strongly and frequently recognized, and for which escape involves a high cost to the virus, have the potential to optimize vaccine design.The dynamics of viral replication in acute and early human immunodeficiency virus (HIV) infection are not well understood as longitudinal data from large cohorts of seroconverters are hard to assemble. Recent studies have shown that new HIV infections may be the result of a single transmitted variant, that new env gene mutations can be detected within a few weeks (25), and that early immune escape can be detected at sites across the HIV genome (9). These data add to a body of work showing that cytotoxic T cells act early, contributing to the early reduction in viremia (8, 30).Whether early cytotoxic T-lymphocyte (CTL) immune responses influence longer-term clinical outcome is not clear. Antigen-specific CTLs capable of producing gamma interferon and other cytokines are detectable at all stages of HIV infection (1, 3, 24, 41). Much weight is placed on the macaque/simian immunodeficiency virus model in which nearly total peripheral blood CD8⁺ T-cell elimination using monoclonal antibodies results in rising viremia (42). The role of other forms of host immunity (e.g., neutralizing antibodies, natural killer cells, and macrophages) has, to some extent, been pursued with less intensity in light of persuasive evidence that CTLs can control retrovirus infection (46). The extent to which the simian model mirrors HIV infection has been questioned (5) and, despite exhaustive cellular assays of T-cell function—from gamma interferon enzyme-linked immunospot assays(1, 27, 38) to polyfunctional cytokine matrices (2, 6)—no CTL function correlates robustly with HIV plasma viral load or viral dynamics. Moreover, analyses of evolutionary data suggest that CTLs are inefficient at killing HIV-infected cells (4).However, statistical analysis of data from large cross-sectional studies link HLA class I alleles with specific genome-wide HIV polymorphisms, suggestive of a pervasive selection pressure enacted by CTLs (7, 10, 18, 36, 40). It is clear that associations between some HLA class I alleles and particular amino acid polymorphisms are robust although it is disputed whether immune escape influences disease progression. The viral fitness costs resulting from immune escape may even contribute to better clinical outcomes associated with the possession of HLA class I alleles such as B*27, B*57, and B*58 (18).Evolutionary studies of HIV require longitudinal data from large cohorts of patients sampled since seroconversion to detect adaptation in new hosts as it accrues. HIV is one of the few pathogens where it is possible to do this within individuals because of the high viral turnover and rapid intrahost evolution. Here, we investigate a cohort of 189 acute seroconverters—the largest cohort reported to date—followed for up to 3 years to study the rates of viral mutation in individual epitopes within internal HIV proteins and to determine the association between HLA class I alleles and rates of immune escape and reversion.     

Identification of a Broadly Cross-Reactive Epitope in the Inner Shell of the Norovirus Capsid

Noroviruses are major pathogens associated with acute gastroenteritis. They are diverse viruses, with at least six genogroups (GI-GVI) and multiple genotypes defined by differences in the major capsid protein, VP1. This diversity has challenged the development of broadly cross-reactive vaccines as well as efficient detection methods. Here, we report the characterization of a broadly cross-reactive monoclonal antibody (MAb) raised against the capsid protein of a GII.3 norovirus strain. The MAb reacted with VLPs and denatured VP1 protein from GI, GII, GIV and GV noroviruses, and mapped to a linear epitope located in the inner shell domain. An alignment of all available VP1 sequences showed that the putative epitope (residues 52–56) is highly conserved across the genus Norovirus. This broadly cross-reactive MAb thus constitutes a valuable reagent for the diagnosis and study of these diverse viruses.     

Interferon-Based Anti-Viral Therapy for Hepatitis C Virus Infection after Renal Transplantation: An Updated Meta-Analysis

Background

Hepatitis C virus (HCV) infection is highly prevalent in renal transplant (RT) recipients. Currently, interferon-based (IFN-based) antiviral therapies are the standard approach to control HCV infection. In a post-transplantation setting, however, IFN-based therapies appear to have limited efficacy and their use remains controversial. The present study aimed to evaluate the efficacy and safety of IFN-based therapies for HCV infection post RT.

Methods

We searched Pubmed, Embase, Web of Knowledge, and The Cochrane Library (1997–2013) for clinical trials in which transplant patients were given Interferon (IFN), pegylated interferon (PEG), interferon plus ribavirin (IFN–RIB), or pegylated interferon plus ribavirin (PEG–RIB). The Sustained Virological Response (SVR) and/or drop-out rates were the primary outcomes. Summary estimates were calculated using the random-effects model of DerSimonian and Laird, with heterogeneity and sensitivity analysis.

Results

We identified 12 clinical trials (140 patients in total). The summary estimate for SVR rate, drop-out rate and graft rejection rate was 26.6% (95%CI, 15.0–38.1%), 21.1% (95% CI, 10.9–31.2%) and 4% (95%CI: 0.8%–7.1%), respectively. The overall SVR rate in PEG-based and standard IFN-based therapy was 40.6% (24/59) and 20.9% (17/81), respectively. The most frequent side-effect requiring discontinuation of treatment was graft dysfunction (14 cases, 45.1%). Meta-regression analysis showed the covariates included contribute to the heterogeneity in the SVR logit rate, but not in the drop-out logit rate. The sensitivity analyses by the random model yielded very similar results to the fixed-effects model.

Conclusions

IFN-based therapy for HCV infection post RT has poor efficacy and limited safety. PEG-based therapy is a more effective approach for treating HCV infection post-RT than standard IFN-based therapy. Future research is required to develop novel strategies to improve therapeutic efficacy and tolerability, and reduce the liver-related morbidity and mortality in this important patient population.     

Mechanisms of Immunity in Post-Exposure Vaccination against Ebola Virus Infection

Ebolaviruses can cause severe hemorrhagic fever that is characterized by rapid viral replication, coagulopathy, inflammation, and high lethality rates. Although there is no clinically proven vaccine or treatment for Ebola virus infection, a virus-like particle (VLP) vaccine is effective in mice, guinea pigs, and non-human primates when given pre-infection. In this work, we report that VLPs protect Ebola virus-infected mice when given 24 hours post-infection. Analysis of cytokine expression in serum revealed a decrease in pro-inflammatory cytokine and chemokine levels in mice given VLPs post-exposure compared to infected, untreated mice. Using knockout mice, we show that VLP-mediated post-exposure protection requires perforin, B cells, macrophages, conventional dendritic cells (cDCs), and either CD4+ or CD8+ T cells. Protection was Ebola virus-specific, as marburgvirus VLPs did not protect Ebola virus-infected mice. Increased antibody production in VLP-treated mice correlated with protection, and macrophages were required for this increased production. However, NK cells, IFN-gamma, and TNF-alpha were not required for post-exposure-mediated protection. These data suggest that a non-replicating Ebola virus vaccine can provide post-exposure protection and that the mechanisms of immune protection in this setting require both increased antibody production and generation of cytotoxic T cells.