The continued emergence of Middle East Respiratory Syndrome (MERS) cases with a high case fatality rate stresses the need for the availability of effective antiviral treatments. Remdesivir (GS-5734) effectively inhibited MERS coronavirus (MERS-CoV) replication in vitro, and showed efficacy against Severe Acute Respiratory Syndrome (SARS)-CoV in a mouse model. Here, we tested the efficacy of prophylactic and therapeutic remdesivir treatment in a nonhuman primate model of MERS-CoV infection, the rhesus macaque. Prophylactic remdesivir treatment initiated 24 h prior to inoculation completely prevented MERS-CoV−induced clinical disease, strongly inhibited MERS-CoV replication in respiratory tissues, and prevented the formation of lung lesions. Therapeutic remdesivir treatment initiated 12 h postinoculation also provided a clear clinical benefit, with a reduction in clinical signs, reduced virus replication in the lungs, and decreased presence and severity of lung lesions. The data presented here support testing of the efficacy of remdesivir treatment in the context of a MERS clinical trial. It may also be considered for a wider range of coronaviruses, including the currently emerging novel coronavirus 2019-nCoV.

The Middle East respiratory syndrome coronavirus (MERS-CoV) has killed ∼50% of individuals known to be infected, making understanding its mechanisms of transmission and pathogenesis and identifying candidate treatments a high priority. Heinz Feldmann, Vincent J. Munster and Michael G. Katze and their colleagues now report that treating MERS-CoV-infected rhesus macaques with interferon-α2b and ribavirin reduced virus replication and infection severity, suggesting the potential use of this combination for the clinical treatment of infected humans. The emergence of Middle East respiratory syndrome coronavirus (MERS-CoV) is of global concern: the virus has caused severe respiratory illness, with 111 confirmed cases and 52 deaths1 at the time of this article's publication. Therapeutic interventions have not been evaluated in vivo; thus, patient management relies exclusively on supportive care, which, given the high case-fatality rate, is not highly effective. The rhesus macaque is the only known model organism for MERS-CoV infection, developing an acute localized to widespread pneumonia with transient clinical disease2,3 that recapitulates mild to moderate human MERS-CoV cases4,5. The combination of interferon-α2b and ribavirin was effective in reducing MERS-CoV replication in vitro6; therefore, we initiated this treatment 8 h after inoculation of rhesus macaques. In contrast to untreated, infected macaques, treated animals did not develop breathing abnormalities and showed no or very mild radiographic evidence of pneumonia. Moreover, treated animals showed lower levels of systemic (serum) and local (lung) proinflammatory markers, in addition to fewer viral genome copies, distinct gene expression and less severe histopathological changes in the lungs. Taken together, these data suggest that treatment of MERS-CoV infected rhesus macaques with IFN-α2b and ribavirin reduces virus replication, moderates the host response and improves clinical outcome. As these two drugs are already used in combination in the clinic for other infections, IFN-α2b and ribavirin should be considered for the management of MERS-CoV cases.

The goal of this study was to elucidate the molecular mechanism by which type I IFN inhibits assembly and release of HIV-1 virions. Our study revealed that the IFN-induced ubiquitin-like protein ISG15 mimics the IFN effect and inhibits release of HIV-1 virions without having any effect on the synthesis of HIV-1 proteins in the cells. ISG15 expression specifically inhibited ubiquitination of Gag and Tsg101 and disrupted the interaction of the Gag L domain with Tsg101, but conjugation of ISG15 to Gag or Tsg101 was not detected. The inhibition of Gag-Tsg101 interaction was also detected in HIV-1 infected, IFN-treated cells. Elimination of ISG15 expression by small interfering RNA reversed the IFN-mediated inhibition of HIV-1 replication and release of virions. These results indicated a critical role for ISG15 in the IFN-mediated inhibition of late stages of HIV-1 assembly and release and pointed to a mechanism by which the innate antiviral response targets the cellular endosomal trafficking pathway used by HIV-1 to exit the cell. Identification of ISG15 as the critical component in IFN-mediated inhibition of HIV-1 release advances the understanding of the IFN-mediated inhibition of HIV-1 replication and uncovers a target for the anti HIV-1 therapy.

Existing mouse models of lethal Ebola virus infection do not reproduce hallmark symptoms of Ebola hemorrhagic fever, neither delayed blood coagulation and disseminated intravascular coagulation nor death from shock, thus restricting pathogenesis studies to nonhuman primates. Here we show that mice from the Collaborative Cross panel of recombinant inbred mice exhibit distinct disease phenotypes after mouse-adapted Ebola virus infection. Phenotypes range from complete resistance to lethal disease to severe hemorrhagic fever characterized by prolonged coagulation times and 100% mortality. Inflammatory signaling was associated with vascular permeability and endothelial activation, and resistance to lethal infection arose by induction of lymphocyte differentiation and cellular adhesion, probably mediated by the susceptibility allele Tek . These data indicate that genetic background determines susceptibility to Ebola hemorrhagic fever.

Significance: The Middle East respiratory syndrome coronavirus (MERS-CoV) is the latest emerged coronavirus causing severe respiratory disease with a high case fatality rate in humans. To better understand the disease caused by MERS-CoV, we developed a rhesus macaque model. Infection of rhesus macaques with MERS-CoV resulted in the rapid development of a transient pneumonia, with MERS-CoV replication largely restricted to the lower respiratory tract. This affinity of MERS-CoV for the lungs partly explains the severity of the disease observed in humans. The MERS-CoV rhesus macaque model will be instrumental in developing and testing vaccine and treatment options for an emerging viral pathogen with pandemic potential.

Ebola virus budding is mediated by the VP40 matrix protein. VP40 can bud from mammalian cells independent of other viral proteins, and efficient release of VP40 virus-like particles (VLPs) requires interactions with host proteins such as tsg101 and Nedd4, an E3 ubiquitin ligase. Ubiquitin itself is thought to be exploited by Ebola virus to facilitate efficient virus egress. Disruption of VP40 function and thus virus budding remains an attractive target for the development of novel antiviral therapies. Here, we investigate the effect of ISG15 protein on the release of Ebola VP40 VLPs. ISG15 is an IFN-inducible, ubiquitin-like protein expressed after bacterial or viral infection. Our results show that expression of free ISG15, or the ISGylation system (UbE1L and UbcH8), inhibits budding of Ebola virus VP40 VLPs. Addressing the molecular mechanism of this inhibition, we show that ISG15 interacts with Nedd4 ubiquitin ligase and inhibits ubiquitination of VP40. Furthermore, the L-domain deletion mutant of VP40 (ΔPT/PY), which does not interact with Nedd4, was insensitive to ISG15-mediated inhibition of VLP release. These data provide evidence of antiviral activity of ISG15 against Ebola virus and suggest a mechanism of action involving disruption of Nedd4 function and subsequent ubiquitination of VP40.