A replication defective recombinant Ad5 vaccine expressing Ebola virus GP is safe and immunogenic in healthy adults

Engineered Viruses as Vaccine Platforms

Many viruses have been investigated for the development of genetic vaccines and the ideal ones must be endowed with many properties, such as the quality and the quantity of the immunological response induced against the encoded antigens, safety and production on a large scale basis. Viral based vaccines must also deal with the potential problem of the pre-existing antivector immunity. Several viral vaccine vectors have emerged to date, all of them having relative advantages and limits depending on the proposed application. Recent successes reflect diverse improvements such as development of new adenovirus serotypes and prime-boost regimes. This chapter describes the features of four viral vector systems based on poxviruses, adenoviruses, alphaviruses and lentiviruses and recent results following their use with a particular emphasis on clinical research, highlighting the challenges and successes.

Protective role of cytotoxic T lymphocytes in filovirus hemorrhagic fever

Infection with many emerging viruses, such as the hemorrhagic fever disease caused by the filoviruses, Marburg (MARV), and Ebola virus (EBOV), leaves the host with a short timeframe in which to mouse a protective immune response. In lethal cases, uncontrolled viral replication and virus-induced immune dysregulation are too severe to overcome, and mortality is generally associated with a lack of notable immune responses. Vaccination studies in animals have demonstrated an association of IgG and neutralizing antibody responses against the protective glycoprotein antigen with survival from lethal challenge. More recently, studies in animal models of filovirus hemorrhagic fever have established that induction of a strong filovirus-specific cytotoxic T lymphocyte (CTL) response can facilitate complete viral clearance. In this review, we describe assays used to discover CTL responses after vaccination or live filovirus infection in both animal models and human clinical trials. Unfortunately, little data regarding CTL responses have been collected from infected human survivors, primarily due to the low frequency of disease and the inability to perform these studies in the field. Advancements in assays and technologies may allow these studies to occur during future outbreaks.

Prevention of influenza virus shedding and protection from lethal H1N1 challenge using a consensus 2009 H1N1 HA and NA adenovirus vector vaccine

Vaccines against emerging pathogens such as the 2009 H1N1 pandemic virus can benefit from current technologies such as rapid genomic sequencing to construct the most biologically relevant vaccine. A novel platform (Ad5 [E1-, E2b-]) has been utilized to induce immune responses to various antigenic targets. We employed this vector platform to express hemagglutinin (HA) and neuraminidase (NA) genes from 2009 H1N1 pandemic viruses. Inserts were consensuses sequences designed from viral isolate sequences and the vaccine was rapidly constructed and produced. Vaccination induced H1N1 immune responses in mice, which afforded protection from lethal virus challenge. In ferrets, vaccination protected from disease development and significantly reduced viral titers in nasal washes. H1N1 cell mediated immunity as well as antibody induction correlated with the prevention of disease symptoms and reduction of virus replication. The Ad5 [E1-, E2b-] should be evaluated for the rapid development of effective vaccines against infectious diseases.

Functional genomics reveals the induction of inflammatory response and metalloproteinase gene expression during lethal Ebola virus infection

Ebola virus is the etiologic agent of a lethal hemorrhagic fever in humans and nonhuman primates with mortality rates of up to 90%. Previous studies with Zaire Ebola virus (ZEBOV), mouse-adapted virus (MA-ZEBOV), and mutant viruses (ZEBOV-NP(ma), ZEBOV-VP24(ma), and ZEBOV-NP/VP24(ma)) allowed us to identify the mutations in viral protein 24 (VP24) and nucleoprotein (NP) responsible for acquisition of high virulence in mice. To elucidate specific molecular signatures associated with lethality, we compared global gene expression profiles in spleen samples from mice infected with these viruses and performed an extensive functional analysis. Our analysis showed that the lethal viruses (MA-ZEBOV and ZEBOV-NP/VP24(ma)) elicited a strong expression of genes 72 h after infection. In addition, we found that although the host transcriptional response to ZEBOV-VP24(ma) was nearly the same as that to ZEBOV-NP/VP24(ma), the contribution of a mutation in the NP gene was required for a lethal phenotype. Further analysis indicated that one of the most relevant biological functions differentially regulated by the lethal viruses was the inflammatory response, as was the induction of specific metalloproteinases, which were present in our newly identify functional network that was associated with Ebola virus lethality. Our results suggest that this dysregulated proinflammatory response increased the severity of disease. Consequently, the newly discovered molecular signature could be used as the starting point for the development of new drugs and therapeutics. To our knowledge, this is the first study that clearly defines unique molecular signatures associated with Ebola virus lethality.

The cytoplasmic domain of Marburg virus GP modulates early steps of viral infection

Marburg virus infection is mediated by the only viral surface protein, GP, a trimeric type I transmembrane protein. While its ectodomain mediates receptor binding and fusion of viral and cellular membranes and its transmembrane domain is essential for the recruitment of GP into budding particles by the matrix protein VP40, the role of the short cytoplasmic domain has remained enigmatic. Here we show that a missing cytoplasmic domain did not impair trimerization, intracellular transport, or incorporation of GP into infectious Marburg virus-like particles (iVLPs) but altered the glycosylation pattern as well as the recognition of GP by neutralizing antibodies. These results suggest that subtle conformational changes took place in the ectodomain. To investigate the function of the cytoplasmic domain during viral entry, a novel entry assay was established to monitor the uptake of filamentous VLPs by measuring the occurrence of luciferase-labeled viral nucleocapsids in the cytosol of target cells. This quantitative assay showed that the entry process of VLPs incorporating GP missing its cytoplasmic domain (GPΔCD) was impaired. Supporting these results, iVLPs incorporating a mutant GP missing its cytoplasmic domain were significantly less infectious than iVLPs containing wild-type GP. Taken together, the data indicate that the absence of the short cytoplasmic domain of Marburg virus GP may induce conformational changes in the ectodomain which impact the filoviral entry process.

Filovirus vaccines

Filoviruses can cause severe and often fatal hemorrhagic fever in humans and non-human primates (NHPs). Although there are currently no clinically proven treatments for filovirus disease, much progress has been made in recent years in the discovery of therapeutics and vaccines against these viruses. A variety of vaccine platforms have been shown to be effective against filovirus infection. This review summarizes the literature in this field, focusing on vaccines that have been shown to protect NHPs from infection. Furthermore, the uses of rodent models in vaccine development, as well as correlates of immunity, are discussed.

Recombinant adenovirus serotype 26 (Ad26) and Ad35 vaccine vectors bypass immunity to Ad5 and protect nonhuman primates against ebolavirus challenge

The use of adenoviruses (Ad) as vaccine vectors against a variety of pathogens has demonstrated their capacity to elicit strong antibody and cell-mediated immune responses. Adenovirus serotype C vectors, such as Ad serotype 5 (Ad5), expressing Ebolavirus (EBOV) glycoprotein (GP), protect completely after a single inoculation at a dose of 10(10) viral particles. However, the clinical application of a vaccine based on Ad5 vectors may be hampered, since impairment of Ad5 vaccine efficacy has been demonstrated for humans and nonhuman primates with high levels of preexisting immunity to the vector. Ad26 and Ad35 segregate genetically from Ad5 and exhibit lower seroprevalence in humans, making them attractive vaccine vector alternatives. In the series of studies presented, we show that Ad26 and Ad35 vectors generate robust antigen-specific cell-mediated and humoral immune responses against EBOV GP and that Ad5 immune status does not affect the generation of GP-specific immune responses by these vaccines. We demonstrate partial protection against EBOV by a single-shot Ad26 vaccine and complete protection when this vaccine is boosted by Ad35 1 month later. Increases in efficacy are paralleled by substantial increases in T- and B-cell responses to EBOV GP. These results suggest that Ad26 and Ad35 vectors warrant further development as candidate vaccines for EBOV.

Tackling Ebola: new insights into prophylactic and therapeutic intervention strategies

Since its discovery in 1976, Ebolavirus has caused periodic outbreaks of viral hemorrhagic fever associated with severe and often fatal disease. Ebolavirus is endemic in Central Africa and the Philippines. Although there is currently no approved treatment available, the past 10 years has seen remarkable progress in our understanding of the pathogenicity of Ebolavirus and the development of prophylactic and post-exposure therapies against it. In vitro and in vivo experiments have shown that Ebolavirus pathogenicity is multifactorial, including viral and host determinants. Besides their function in the virus replication cycle, the viral glycoprotein, nucleoprotein, minor matrix protein and polymerase cofactor are viral determinants of pathogenicity, with evasion of the host innate and adaptive immune responses as the main mechanism. Although no licensed Ebolavirus vaccines are currently available, vaccine research in non-human primates, the 'gold standard' animal model for Ebolavirus, has produced several promising candidates. A combination of DNA vaccination and a recombinant adenovirus serotype 5 boost resulted in cross-protective immunity in non-human primates. A recombinant vesicular stomatitis vaccine vector protected non-human primates in pre- and post-exposure challenge studies. Several antiviral therapies are currently under investigation, but only a few of these have been tested in non-human primate models. Antisense therapies, in which oligonucleotides inhibit viral replication, have shown promising results in non-human primates following post-exposure treatment. In light of the severity of Ebolavirus disease and the observed increase in Ebolavirus outbreaks over the past decade, the expedited translation of potential candidate therapeutics and vaccines from bench to bedside is currently the most challenging task for the field. Here, we review the current state of Ebolavirus research, with emphasis on prophylactic and therapeutic intervention strategies.

Filovirus emergence and vaccine development: a perspective for health care practitioners in travel medicine

Recent case reports of viral hemorrhagic fever in Europe and the United States have raised concerns about the possibility for increased importation of filoviruses to non-endemic areas. This emerging threat is concerning because of the increase in global air travel and the rise of tourism in central and eastern Africa and the greater dispersion of military troops to areas of infectious disease outbreaks. Marburg viruses (MARV) and Ebola viruses (EBOV) have been associated with outbreaks of severe hemorrhagic fever involving high mortality (25-90% case fatality rates). First recognized in 1967 and 1976 respectively, subtypes of MARV and EBOV are the only known viruses of the Filoviridae family, and are among the world's most virulent pathogens. This article focuses on information relevant for health care practitioners in travel medicine to include, the epidemiology and clinical features of filovirus infection and efforts toward development of a filovirus vaccine.