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Background The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in late 2019 and spread globally, prompting an international effort to accelerate development of a vaccine. The candidate vaccine mRNA-1273 encodes the stabilized prefusion SARS-CoV-2 spike protein. Methods We conducted a phase 1, dose-escalation, open-label trial including 45 healthy adults, 18 to 55 years of age, who received two vaccinations, 28 days apart, with mRNA-1273 in a dose of 25 μg, 100 μg, or 250 μg. There were 15 participants in each dose group. Results After the first vaccination, antibody responses were higher with higher dose (day 29 enzyme-linked immunosorbent assay anti–S-2P antibody geometric mean titer [GMT], 40,227 in the 25-μg group, 109,209 in the 100-μg group, and 213,526 in the 250-μg group). After the second vaccination, the titers increased (day 57 GMT, 299,751, 782,719, and 1,192,154, respectively). After the second vaccination, serum-neutralizing activity was detected by two methods in all participants evaluated, with values generally similar to those in the upper half of the distribution of a panel of control convalescent serum specimens. Solicited adverse events that occurred in more than half the participants included fatigue, chills, headache, myalgia, and pain at the injection site. Systemic adverse events were more common after the second vaccination, particularly with the highest dose, and three participants (21%) in the 250-μg dose group reported one or more severe adverse events. Conclusions The mRNA-1273 vaccine induced anti–SARS-CoV-2 immune responses in all participants, and no trial-limiting safety concerns were identified. These findings support further development of this vaccine. (Funded by the National Institute of Allergy and Infectious Diseases and others; mRNA-1273 ClinicalTrials.gov number, NCT04283461).

Highlights • Coronaviruses (CoV) represent current and future risk for pandemic zoonotic infections. • Nucleoside analogues are highly active across multiple virus families. • CoVs encode a proofreading exoribonuclease that opposes inhibition by many nucleoside analogues. • Remdesivir is an adenosine analogue that acts against a broad spectrum of CoVs. • Other nucleoside analogues show promise against CoVs., Recent outbreaks of SARS-Coronavirus and MERS-Coronavirus (CoV) have heightened awareness about the lack of vaccines or antiviral compounds approved for prevention or treatment of human or potential zoonotic CoVs. Anti-CoV drug development has long been challenged by the activity of a 3′ to 5′ proofreading exoribonuclease unique to CoVs. Recently, a promising nucleoside analogue with broad-spectrum activity against CoVs has been identified. This review will discuss progress made in the development of antiviral nucleoside and nucleotide analogues targeting viral RNA synthesis as effective therapeutics against CoV infections and propose promising strategies for combination therapy.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in 2019 as the causative agent of the novel pandemic viral disease COVID-19. With no approved therapies, this pandemic illustrates the urgent need for safe, broad-spectrum antiviral countermeasures against SARS-CoV-2 and future emerging CoVs. We report that remdesivir (RDV), a monophosphoramidate prodrug of an adenosine analog, potently inhibits SARS-CoV-2 replication in human lung cells and primary human airway epithelial cultures (EC50 = 0.01 µM). Weaker activity was observed in Vero E6 cells (EC50 = 1.65 µM) due to their low capacity to metabolize RDV. To rapidly evaluate in vivo efficacy, we engineered a chimeric SARS-CoV encoding the viral target of RDV, the RNA-dependent RNA polymerase, of SARS-CoV-2. In mice infected with chimeric virus, therapeutic RDV administration diminished lung viral load and improved pulmonary function as compared to vehicle treated animals. These data provide evidence that RDV is potently active against SARS-CoV-2 in vitro and in vivo, supporting its further clinical testing for treatment of COVID-19. Funding: This project was funded in part by the National Institute of Allergy and Infectious Diseases, National 284 Institutes of Health, Department of Health and Human Service awards: 1U19AI142759 (Antiviral Drug 285 Discovery and Development Center awarded to M.R.D. and R.S.B); 5R01AI132178 awarded to T.P.S. 286 and R.S.B.; and 5R01AI108197 awarded to M.R.D. and R.S.B. D.R.M was funded by T32 AI007151 and 287 a Burroughs Wellcome Fund Postdoctoral Enrichment Program Award. The Marsico Lung Institute 288 Tissue Procurement and Cell Culture Core is supported by NIH grant DK065988 and Cystic Fibrosis 289 Foundation grant BOUCHE15RO. We also are grateful for support from the Dolly Parton COVID-19 290 Research Fund, the VUMC Office of Research, and the Elizabeth B. Lamb Center for Pediatric Research 291 at Vanderbilt University. Conflict of Interest: The authors affiliated with Gilead Sciences, Inc. are employees of the company and own company stock. The other authors have no conflict of interest to report. Ethical Approval: Human tracheobronchial epithelial cells provided by Dr. Scott Randell were obtained from airway specimens resected from patients undergoing surgery under University of North Carolina Institutional Review Board-approved protocols (#03-1396) by the Cystic Fibrosis Center Tissue Culture Core.

Summary Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of the novel viral disease COVID-19. With no approved therapies, this pandemic illustrates the urgent need for broad-spectrum antiviral countermeasures against SARS-CoV-2 and future emerging CoVs. We report that remdesivir (RDV) potently inhibits SARS-CoV-2 replication in human lung cells and primary human airway epithelial cultures (EC50 = 0.01 μM). Weaker activity is observed in Vero E6 cells (EC50 = 1.65 μM) due to their low capacity to metabolize RDV. To rapidly evaluate in vivo efficacy, we engineered a chimeric SARS-CoV encoding the viral target of RDV, the RNA-dependent RNA polymerase, of SARS-CoV-2. In mice infected with chimeric virus, therapeutic RDV administration diminishes lung viral load and improves pulmonary function compared to vehicle treated animals. These data demonstrate that RDV is potently active against SARS-CoV-2 in vitro and in vivo, supporting its further clinical testing for treatment of COVID-19., Graphical Abstract, Highlights • Remdesivir binding of active site of polymerase is conserved across all human CoVs • Remdesivir inhibits SARS-CoV-2 in primary and continuous human lung cell cultures • Remdesivir potency depends on cell-type specific metabolism to its active form • Therapeutic remdesivir reduces viral loads and improves outcomes in mice, SARS-CoV-2 causes severe lung disease (COVID-19) in humans. Pruijssers et al. demonstrate that the antiviral drug remdesivir potently inhibits SARS-CoV-2 in human lung cell cultures. Therapeutic treatment of infected mice with remdesivir reduces viral loads and improves clinical outcomes, further supporting use of remdesivir for the treatment of COVID-19.

Coronaviruses (CoVs) traffic frequently between species resulting in novel disease outbreaks, most recently exemplified by the newly emerged SARS-CoV-2. Herein, we show that the ribonucleoside analog β-D-N4-hydroxycytidine (NHC, EIDD-1931) has broad spectrum antiviral activity against SARS-CoV 2, MERS-CoV, SARS-CoV, and related zoonotic group 2b or 2c Bat-CoVs, as well as increased potency against a coronavirus bearing resistance mutations to another nucleoside analog inhibitor. In mice infected with SARS-CoV or MERS-CoV, both prophylactic and therapeutic administration of EIDD-2801, an orally bioavailable NHC-prodrug (b-D-N4-hydroxycytidine-5’-isopropyl ester), improved pulmonary function, and reduced virus titer and body weight loss. Decreased MERS-CoV yields in vitro and in vivo were associated with increased transition mutation frequency in viral but not host cell RNA, supporting a mechanism of lethal mutagenesis. The potency of NHC/EIDD-2801 against multiple coronaviruses, its therapeutic efficacy, and oral bioavailability in vivo, all highlight its potential utility as an effective antiviral against SARS-CoV-2 and other future zoonotic coronaviruses.

BackgroundInfants and young children are particularly susceptible to viral encephalitis; however, the mechanisms are unknown. We determined the age-dependent contribution of innate and adaptive immune functions to reovirus-induced encephalitis in mice.MethodsNewborn wild-type mice, 2-20 days of age, were inoculated with reovirus or diluent and monitored for mortality, weight gain, and viral load. Four- and fifteen-day-old IFNAR-/- and RAG2-/- mice were inoculated with reovirus and similarly monitored.ResultsWeight gain was impaired in mice inoculated with reovirus at 8 days of age or less. Clinical signs of encephalitis were detected in mice inoculated at 10 days of age or less. Mortality decreased when mice were inoculated after 6 days of age. Survival was ≤15% in wild type (WT), RAG2-/-, and IFNAR-/- mice inoculated at 4 days of age. All WT mice, 92% of RAG2-/- mice, and only 48% of IFNAR-/- mice survived following inoculation at 15 days of age.ConclusionsSusceptibility of mice to reovirus-induced disease decreases between 6 and 8 days of age. Enhanced reovirus virulence in IFNAR-/- mice relative to WT and RAG2-/- mice inoculated at 15 days of age suggests that maturation of the type-I interferon response contributes to age-related mortality following reovirus infection.

Many animal models of disease are suboptimal in their representation of human diseases and lack of predictive power in the success of pivotal human trials. In the context of repurposing drugs with known human safety, it is sometimes appropriate to conduct the “last experiment first,” that is, progressing directly to human investigations. However, there are not accepted criteria for when to proceed straight to humans to test a new indication. We propose a specific set of criteria to guide the decision-making around when to initiate human proof of principle without preclinical efficacy studies in animal models. This approach could accelerate the transition of novel therapeutic approaches to human applications.

Viral infections have been proposed to elicit pathological processes leading to the initiation of T helper 1 (TH1) immunity against dietary gluten and celiac disease (CeD). To test this hypothesis and gain insights into mechanisms underlying virus-induced loss of tolerance to dietary antigens, we developed a viral infection model that makes use of two reovirus strains that infect the intestine but differ in their immunopathological outcomes. Reovirus is an avirulent pathogen that elicits protective immunity, but we discovered that it can nonetheless disrupt intestinal immune homeostasis at inductive and effector sites of oral tolerance by suppressing peripheral regulatory T cell (pTreg) conversion and promoting TH1 immunity to dietary antigen. Initiation of TH1 immunity to dietary antigen was dependent on interferon regulatory factor 1 and dissociated from suppression of pTreg conversion, which was mediated by type-1 interferon. Last, our study in humans supports a role for infection with reovirus, a seemingly innocuous virus, in triggering the development of CeD.

Coagulation and inflammation are interconnected, suggesting that coagulation plays a key role in the inflammatory response to pathogens. A phenome-wide association study (PheWAS) was used to identify clinical phenotypes of patients with a polymorphism in coagulation factor X. Patients with this single nucleotide polymorphism (SNP) were more likely to be hospitalized with hemostatic and infection-related disorders, suggesting that factor X contributes to the immune response to infection. To investigate this, we modeled infections by human pathogens in a mouse model of factor X deficiency. Factor X-deficient mice were protected from systemic Acinetobacter baumannii infection, suggesting that factor X plays a role in the immune response to A. baumannii. Factor X deficiency was associated with reduced cytokine and chemokine production and alterations in immune cell population during infection: factor X-deficient mice demonstrated increased abundance of neutrophils, macrophages, and effector T cells. Together, these results suggest that factor X activity is associated with an inefficient immune response and contributes to the pathology of A. baumannii infection.

Various sensors that detect double-stranded RNA, presumably of viral origin, exist in eukaryotic cells and induce IFN-responses. Ongoing IFN-responses have also been documented in a variety of human autoimmune diseases including relapsing-remitting multiple sclerosis (RRMS) but their origins remain obscure. We find increased IFN-responses in leukocytes in relapsing-remitting multiple sclerosis at distinct stages of disease. Moreover, endogenous RNAs isolated from blood cells of these same patients recapitulate this IFN-response if transfected into naive cells. These endogenous RNAs are double-stranded RNAs, contain Alu and Line elements and are transcribed from leukocyte transcriptional enhancers. Thus, transcribed endogenous retrotransposon elements can co-opt pattern recognition sensors to induce IFN-responses in RRMS.

Rotavirus (RV) encounters intestinal epithelial cells amidst diverse microbiota, opening possibilities of microbes influencing RV infection. Although RV clearance typically requires adaptive immunity, we unintentionally generated RV-resistant immunodeficient mice, which, we hypothesized, reflected select microbes protecting against RV. Accordingly, such RV resistance was transferred by co-housing and fecal transplant. RV-protecting microbiota were interrogated by heat, filtration, and antimicrobial agents, followed by limiting dilution transplant to germ-free mice and microbiome analysis. This approach revealed that segmented filamentous bacteria (SFB) were sufficient to protect mice against RV infection and associated diarrhea. Such protection was independent of previously defined RV-impeding factors, including interferon, IL-17, and IL-22. Colonization of the ileum by SFB induced changes in host gene expression and accelerated epithelial cell turnover. Incubation of RV with SFB-containing feces reduced infectivity in vitro, suggesting direct neutralization of RV. Thus, independent of immune cells, SFB confer protection against certain enteric viral infections and associated diarrheal disease.

Several viruses induce intestinal epithelial cell death during enteric infection. However, it is unclear whether proapoptotic capacity promotes or inhibits replication in this tissue. We infected mice with two reovirus strains that infect the intestine but differ in the capacity to alter immunological tolerance to new food antigen. Infection with reovirus strain T1L, which induces an inflammatory immune response to fed antigen, is prolonged in the intestine, whereas T3D-RV, which does not induce this response, is rapidly cleared from the intestine. Compared with T1L, T3D-RV infection triggered apoptosis of intestinal epithelial cells and subsequent sloughing of dead cells into the intestinal lumen. We conclude that the infection advantage of T1L derives from its capacity to subvert host restriction by epithelial cell apoptosis, providing a possible mechanism by which T1L enhances inflammatory signals during antigen feeding. Using a panel of T1L × T3D-RV reassortant viruses, we identified the viral M1 and M2 gene segments as determinants of reovirus-induced apoptosis in the intestine. Expression of the T1L M1 and M2 genes in a T3D-RV background was sufficient to limit epithelial cell apoptosis and enhance viral infection to levels displayed by T1L. These findings define additional reovirus gene segments required for enteric infection of mice and illuminate the antiviral effect of intestinal epithelial cell apoptosis in limiting enteric viral infection. Viral strain-specific differences in the capacity to infect the intestine may be useful in identifying viruses capable of ameliorating tolerance to fed antigen in autoimmune conditions like celiac disease. IMPORTANCE Acute viral infections are thought to be cleared by the host with few lasting consequences. However, there may be much broader and long-lasting effects of viruses on immune homeostasis. Infection with reovirus, a common, nonpathogenic virus, triggers inflammation against innocuous food antigens, implicating this virus in the development of celiac disease, an autoimmune intestinal disorder triggered by exposure to dietary gluten. Using two reovirus strains that differ in the capacity to abrogate oral tolerance, we found that strain-specific differences in the capacity to replicate in the intestine inversely correlate with the capacity to induce apoptotic death of intestinal epithelial cells, providing a host-mediated process to restrict intestinal infection. This work contributes new knowledge about virus-host interactions in the intestine and establishes a foundation for future studies to define mechanisms by which viruses break oral tolerance in celiac disease.

Reovirus infection leads to apoptosis in both cultured cells and the murine central nervous system (CNS). NF-κB-driven transcription of proapoptotic cellular genes is required for the effector phase of the apoptotic response. Although both extrinsic death-receptor signaling pathways and intrinsic pathways involving mitochondrial injury are implicated in reovirus-induced apoptosis, mechanisms by which either of these pathways are activated and their relationship to NF-κB signaling following reovirus infection are unknown. The proapoptotic Bcl-2 family member, Bid, is activated by proteolytic cleavage following reovirus infection. To understand how reovirus integrates host signaling circuits to induce apoptosis, we examined proapoptotic signaling following infection of Bid-deficient cells. Although reovirus growth was not affected by the absence of Bid, cells lacking Bid failed to undergo apoptosis. Furthermore, we found that NF-κB activation is required for Bid cleavage and subsequent proapoptotic signaling. To examine the functional significance of Bid-dependent apoptosis in reovirus disease, we monitored fatal encephalitis caused by reovirus in the presence and absence of Bid. Survival of Bid-deficient mice was significantly enhanced in comparison to wild-type mice following either peroral or intracranial inoculation of reovirus. Decreased reovirus virulence in Bid-null mice was accompanied by a reduction in viral yield. These findings define a role for NF-κB-dependent cleavage of Bid in the cell death program initiated by viral infection and link Bid to viral virulence., Author Summary Viruses injure host tissues by activating signaling pathways that trigger cell death by a process called apoptosis. Hence, blockade of apoptosis may serve as a useful strategy to dampen the severity of viral disease. However, deployment of such a strategy requires identification of host signaling networks that control cell death and a detailed molecular blueprint of how these pathways are activated by a virus. In this study, we used mammalian reovirus, an important experimental model for studies of viral encephalitis, to elucidate how cell death pathways are activated following viral infection and whether these signaling cascades influence the capacity of a virus to produce lethal CNS disease. We found that Bid, a host regulator of cell death, influences apoptosis induction by reovirus. Moreover, Bid is required for efficient reovirus replication in the CNS and modulates reovirus neurological disease. These findings highlight Bid as a critical regulator of viral pathogenesis and illuminate a potential new target for development of antiviral therapeutics.