Gary Wong

Successful Treatment of Ebola Virus–Infected Cynomolgus Macaques with Monoclonal Antibodies

Macaques survived infection with Ebola virus when treated starting at 24 hours after infection with mix of three neutralizing monoclonal antibodies. A Race Against Time Although rare, Ebola infection figures prominently in the public’s fear of an infectious disease outbreak because of its marked, rapid, and fatal manifestation. This fear is fueled by our complete helplessness when it comes to fighting Ebola—there’s no vaccine, and any treatment options we do have only work if administered within minutes—or at most hours—after infection. Qiu et al. address this impotence head-on by demonstrating that administration of a three-antibody cocktail to macaques within 24 hours of infection yields 100% survival. The authors treated the macaques 24 or 48 hours after Ebola virus challenge with a virus-neutralizing antibody cocktail (ZMab). The three antibodies in the mix each bind to distinct regions of the Ebola envelop glycoprotein (GP) and show efficacy in small-animal models. When the cocktail was given at 24 hours after infection, 100% of the monkeys survived; if the same dose of the cocktail was administered 48 hours after infection, the survival rate was 50%. Surviving macaques developed both Ebola-specific antibodies and T cell responses, which suggests that the passive neutralizing antibody transfer may keep the virus in check long enough for endogenous immunity to take over. Timing, dose, and composition must be optimized before this therapy moves into humans, but the new findings add sand to the hourglass and provide hope for an expanded treatment window for Ebola virus infection. Ebola virus (EBOV) is considered one of the most aggressive infectious agents and is capable of causing death in humans and nonhuman primates (NHPs) within days of exposure. Recent strategies have succeeded in preventing acquisition of infection in NHPs after treatment; however, these strategies are only successful when administered before or minutes after infection. The present work shows that a combination of three neutralizing monoclonal antibodies (mAbs) directed against the Ebola envelope glycoprotein (GP) resulted in complete survival (four of four cynomolgus macaques) with no apparent side effects when three doses were administered 3 days apart beginning at 24 hours after a lethal challenge with EBOV. The same treatment initiated 48 hours after lethal challenge with EBOV resulted in two of four cynomolgus macaques fully recovering. The survivors demonstrated an EBOV-GP–specific humoral and cell-mediated immune response. These data highlight the important role of antibodies to control EBOV replication in vivo, and support the use of mAbs against a severe filovirus infection.

Immune Parameters Correlate with Protection Against Ebola Virus Infection in Rodents and Nonhuman Primates

Levels of specific antibodies induced by vaccination correlate with survival in Ebola-infected animals. Protecting Against the Zombie Apocalypse Halloween can wreak havoc on the imagination. The advent of seasonal symptoms—spontaneous moaning, slow jerky movements, and the desire to eat the brains of your co-workers—can convince you that you’re turning into a zombie. While there are no treatments for the prevention of zombieism, when the holiday passes, symptoms of this fictional disease fade. But dire diseases—real ones—with equally horrific symptoms persist after trick-or-treat, because there are no corresponding vaccines or drug treatments. Now, Wong et al. show that for ebolavirus infections, which can cause a nightmarish fever frightening enough to be Halloween-worthy, researchers are making progress. There are currently no licensed vaccines or treatments that prevent or cure infection with Zaire ebolavirus (ZEBOV) in human patients. Experimental vaccines have been successful in animal models of hemorrhagic fever. But how can one test the efficacy of these vaccines in people without exposing them to a potentially fatal disease? Wong et al. report on an important translational step toward vaccine testing. The authors detected specific antibody responses to ZEBOV that correlate with survival in multiple animal models (mouse, guinea pig, and nonhuman primates). Much work remains to be done to determine whether these observations hold true in people. But if they do, these immune responses may be used as surrogates for testing a successful vaccine. Ebola virus causes severe hemorrhagic fever in susceptible hosts. Currently, no licensed vaccines or treatments are available; however, several experimental vaccines have been successful in protecting rodents and nonhuman primates (NHPs) from the lethal Zaire ebolavirus (ZEBOV) infection. The objective of this study was to evaluate immune responses correlating with survival in these animals after lethal challenge with ZEBOV. Knockout mice with impaired ability to generate normal T and/or B cell responses were vaccinated and challenged with ZEBOV. Vaccine-induced protection in mice was mainly mediated by B cells and CD4+ T cells. Vaccinated, outbred guinea pigs and NHPs demonstrated the highest correlation between survival and levels of total immunoglobulin G (IgG) specific to the ZEBOV glycoprotein (ZGP). These results highlight the relevance of total ZGP-specific IgG levels as a meaningful correlate of protection against ZEBOV exposure.

mAbs and Ad-Vectored IFN-α Therapy Rescue Ebola-Infected Nonhuman Primates When Administered After the Detection of Viremia and Symptoms

Monoclonal antibodies and adenovirus-vectored IFN-α extend the treatment window for Zaire ebolavirus in macaques. Every Day Counts Ebola virus (EBOV) infections cause a deadly hemorrhagic disease for which there are no currently licensed vaccines or treatments. Recent studies have demonstrated the potential of antibody therapy cocktails (ZMAb) for treating EBOV infections; however, there is a limited time window for these therapies to be effective. Because early clinical symptoms of EBOV infection resemble other common pathogens, it is critical to extend this treatment window until positive cases can be confirmed. Now, Qui et al. combine ZMAb therapy with adenovirally delivered interferon-α (Ad-IFN) to extend the EBOV treatment window in nonhuman primates. The authors dosed macaques that had received a lethal dose of EBOV with a combination of ZMAb and Ad-IFN. Combination therapy with Ad-IFN and ZMAb was 75 and 100% protective in cynomolgus and rhesus macaques, respectively, when administered together at 3 days post-infection. Fifty percent of cynomolgus macaques were protected at 4 days post-infection when Ad-IFN was administered 1 day post-infection. These results suggest that the Ad-IFN and ZMAb combination treatment could be effective after confirmation of EBOV infection as well as could substantially reduce mortality rates of cases diagnosed early after symptom onset. ZMAb is a promising treatment against Ebola virus (EBOV) disease that has been shown to protect 50% (two of four) of nonhuman primates (NHPs) when administered 2 days post-infection (dpi). To extend the treatment window and improve protection, we combined ZMAb with adenovirus-vectored interferon-α (Ad-IFN) and evaluated efficacy in EBOV-infected NHPs. Seventy-five percent (three of four) and 100% (four of four) of cynomolgus and rhesus macaques survived, respectively, when treatment was initiated after detection of viremia at 3 dpi. Fifty percent (two of four) of the cynomolgus macaques survived when Ad-IFN was given at 1 dpi, followed by ZMAb starting at 4 dpi, after positive diagnosis. The treatment was able to suppress viremia reaching ~105 TCID50 (median tissue culture infectious dose) per milliliter, leading to survival and robust specific immune responses. This study describes conditions capable of saving 100% of EBOV-infected NHPs when initiated after the presence of detectable viremia along with symptoms.

Transmission of Ebola Viruses: What We Know and What We Do Not Know

ABSTRACT Available evidence demonstrates that direct patient contact and contact with infectious body fluids are the primary modes for Ebola virus transmission, but this is based on a limited number of studies. Key areas requiring further study include (i) the role of aerosol transmission (either via large droplets or small particles in the vicinity of source patients), (ii) the role of environmental contamination and fomite transmission, (iii) the degree to which minimally or mildly ill persons transmit infection, (iv) how long clinically relevant infectiousness persists, (v) the role that “superspreading events” may play in driving transmission dynamics, (vi) whether strain differences or repeated serial passage in outbreak settings can impact virus transmission, and (vii) what role sylvatic or domestic animals could play in outbreak propagation, particularly during major epidemics such as the 2013–2015 West Africa situation. In this review, we address what we know and what we do not know about Ebola virus transmission. We also hypothesize that Ebola viruses have the potential to be respiratory pathogens with primary respiratory spread.

Sustained protection against Ebola virus infection following treatment of infected nonhuman primates with ZMAb

Ebola virus (EBOV) is one of the most lethal filoviruses, with mortality rates of up to 90% in humans. Previously, we demonstrated 100% and 50% survival of EBOV-infected cynomologus macaques with a combination of 3 EBOV-GP-specific monoclonal antibodies (ZMAb) administered at 24 or 48 hours post-exposure, respectively. The survivors demonstrated EBOV-GP–specific humoral and cell-mediated immune responses. In order to evaluate whether the immune response induced in NHPs during the ZMAb treatment and EBOV challenge is sufficient to protect survivors against a subsequent exposure, animals that survived the initial challenge were rechallenged at 10 or 13 weeks after the initial challenge. The animals rechallenged at 10 weeks all survived whereas 4 of 6 animals survived a rechallenge at 13 weeks. The data indicate that a robust immune response was generated during the successful treatment of EBOV-infected NHPs with EBOV, which resulted in sustained protection against a second lethal exposure.

Targeted Prostaglandin E2 Inhibition Enhances Antiviral Immunity through Induction of Type I Interferon and Apoptosis in Macrophages

Aspirin gained tremendous popularity during the 1918 Spanish Influenza virus pandemic, 50 years prior to the demonstration of their inhibitory action on prostaglandins. Here, we show that during influenza A virus (IAV) infection, prostaglandin E2 (PGE2) was upregulated, which led to the inhibition of type I interferon (IFN) production and apoptosis in macrophages, thereby causing an increase in virus replication. This inhibitory role of PGE2 was not limited to innate immunity, because both antigen presentation and T cell mediated immunity were also suppressed. Targeted PGE2 suppression via genetic ablation of microsomal prostaglandin E-synthase 1 (mPGES-1) or by the pharmacological inhibition of PGE2 receptors EP2 and EP4 substantially improved survival against lethal IAV infection whereas PGE2 administration reversed this phenotype. These data demonstrate that the mPGES-1-PGE2 pathway is targeted by IAV to evade host type I IFN-dependent antiviral immunity. We propose that specific inhibition of PGE2 signaling might serve as a treatment for IAV.

Characterization of host immune responses in Ebola virus infections

Ebola causes highly lethal hemorrhagic fever in humans with no licensed countermeasures. Its virulence can be attributed to several immunoevasion mechanisms: an early inhibition of innate immunity started by the downregulation of type I interferon, epitope masking and subversion of the adaptive humoural immunity by secreting a truncated form of the viral glycoprotein. Deficiencies in specific and non-specific antiviral responses result in unrestricted viral replication and dissemination in the host, causing death typically within 10 days after the appearance of symptoms. This review summarizes the host immune response to Ebola infection, and highlights the short- and long-term immune responses crucial for protection, which holds implications for the design of future vaccines and therapeutics.

Molecular Characterization of the Monoclonal Antibodies Composing ZMAb: A Protective Cocktail Against Ebola Virus

Ebola virus (EBOV) causes severe viral hemorrhagic fever in humans and non-human primates, with a case fatality rate of up to 88% in human outbreaks. Over the past 3 years, monoclonal antibody (mAb) cocktails have demonstrated high efficacy as treatments against EBOV infection. One such cocktail is ZMAb, which consists of three mouse antibodies, 1H3, 2G4, and 4G7. Here, we present the epitope binding properties of mAbs 1H3, 2G4, and 4G7. We showed that these antibodies have different variable region sequences, suggesting that the individual mAbs are not clonally related. All three antibodies were found to neutralize EBOV variant Mayinga. Additionally, 2G4 and 4G7 were shown to cross-inhibit each other in vitro and select for an escape mutation at the same position on the EBOV glycoprotein (GP), at amino acid 508. 1H3 selects an escape mutant at amino acid 273 on EBOV GP. Surface plasmon resonance studies showed that all three antibodies have dissociation constants on the order of 10−7. In combination with previous studies evaluating the binding sites of other protective antibodies, our results suggest that antibodies targeting the GP1-GP2 interface and the glycan cap are often selected as efficacious antibodies for post-exposure interventions against EBOV.

Stimulation of Ebola virus production from persistent infection through activation of the Ras/MAPK pathway

Human infections with Ebola virus (EBOV) result in a deadly viral disease known as Ebola hemorrhagic fever. Up to 90% of infected patients die, and there is no available treatment or vaccine. The sporadic human outbreaks are believed to result when EBOV “jumps” from an infected animal to a person and is subsequently transmitted between persons by direct contact with infected blood or body fluids. This study was undertaken to investigate the mechanism by which EBOV can persistently infect and then escape from model cell and animal reservoir systems. We report a model system in which infection of mouse and bat cell lines with EBOV leads to persistence, which can be broken with low levels of lipopolysaccharide or phorbol-12-myristate-13-acetate (PMA). This reactivation depends on the Ras/MAPK pathway through inhibition of RNA-dependent protein kinase and eukaryotic initiation factor 2α phosphorylation and occurs at the level of protein synthesis. EBOV also can be evoked from mice 7 days after infection by PMA treatment, indicating that a similar mechanism occurs in vivo. Our findings suggest that EBOV may persist in nature through subclinical infection of a reservoir species, such as bats, and that appropriate physiological stimulation may result in increased replication and transmission to new hosts. Identification of a presumptive mechanism responsible for EBOV emergence from its reservoir underscores the “hit-and-run” nature of the initiation of human and/or nonhuman primate EBOV outbreaks and may provide insight into possible countermeasures to interfere with transmission.

Post-exposure therapy of filovirus infections

Filovirus infections cause fatal hemorrhagic fever characterized by the initial onset of general symptoms before rapid progression to severe disease; the most virulent species can cause death to susceptible hosts within 10 days after the appearance of symptoms. Before the advent of monoclonal antibody (mAb) therapy, infection of nonhuman primates (NHPs) with the most virulent filovirus species was fatal if interventions were not administered within minutes. A novel nucleoside analogue, BCX4430, has since been shown to also demonstrate protective efficacy with a delayed treatment start. This review summarizes and evaluates the potential of current experimental candidates for treating filovirus disease with regard to their feasibility and use in the clinic, and assesses the most promising strategies towards the future development of a pan-filovirus medical countermeasure.