Most human coronaviruses cause mild upper respiratory tract disease but may be associated with more severe pulmonary disease in immunocompromised individuals. However, SARS coronavirus caused severe lower respiratory disease with nearly 10% mortality and evidence of systemic spread. Recently, another coronavirus (human coronavirus-Erasmus Medical Center (hCoV-EMC)) was identified in patients with severe and sometimes lethal lower respiratory tract infection. Viral genome analysis revealed close relatedness to coronaviruses found in bats. Here we identify dipeptidyl peptidase 4 (DPP4; also known as CD26) as a functional receptor for hCoV-EMC. DPP4 specifically co-purified with the receptor-binding S1 domain of the hCoV-EMC spike protein from lysates of susceptible Huh-7 cells. Antibodies directed against DPP4 inhibited hCoV-EMC infection of primary human bronchial epithelial cells and Huh-7 cells. Expression of human and bat (Pipistrellus pipistrellus) DPP4 in non-susceptible COS-7 cells enabled infection by hCoV-EMC. The use of the evolutionarily conserved DPP4 protein from different species as a functional receptor provides clues about the host range potential of hCoV-EMC. In addition, it will contribute critically to our understanding of the pathogenesis and epidemiology of this emerging human coronavirus, and may facilitate the development of intervention strategies.

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S evere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the third highly pathogenic human coronavirus to cross the species barrier into the human population during the past 20 years (1-3). SARS-CoV-2 infection is associated with coronavirus disease (COVID-19), which is characterized by severe respiratory distress, fever, and cough and high rates of mortality, especially in older persons and those with underlying health conditions (3). The World Health Organization (WHO) declared SARS-CoV-2 a pandemic on March 11, 2020 (4), and by April 8, a total of 1,447,466 confirmed cases and 83,471 deaths from SARS-CoV-2 had been reported worldwide (5). Human-to-human transmission of SARS-CoV-2 is efficient, and infected persons can transmit the virus even when they have no, or only mild, symptoms (3). Because no antiviral drugs or vaccines are available, virus containment and prevention of infection are the current highest priorities. To limit virus spread, effective hand hygiene is crucial. Therefore, easily available but efficient disinfectants are needed. WHO's guidelines for hand hygiene in healthcare suggest 2 alcohol-based formulations for hand sanitization to reduce the infectivity and spread of pathogens (6). WHO's recommendations are based on fastacting, broad-spectrum microbicidal activity, along with accessibility and safety. The original WHO formulations failed to meet the efficacy requirements of European Norm 1500 in previous tests (7). However, Suchomel et al. (8) suggested modified versions with increased concentrations of ethanol: 80% (wt/ wt) (85.5% [vol/vol]; formulation I), or isopropanol, 75% (wt/wt) (81.3% [vol/vol]; formulations II). Later, they complemented these by reducing the glycerol concentrations (9). We previously showed that these modified WHO formulations were able to inactivate severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV; 10), which are related to SARS-CoV-2. Current recommendations to inactivate SARS-CoV-2 were translated from findings of other coronaviruses (11). To evaluate whether these alcohol-based disinfectants also effectively inactivate SARS-CoV-2, we tested different concentrations of the original and modified WHO formulations I and II (6,9), ethanol, and 2-propanol for virucidal activity.

e Infection with human coronavirus 229E (HCoV-229E) is associated with the common cold and may result in pneumonia in immunocompromised patients. The viral spike (S) protein is incorporated into the viral envelope and mediates infectious entry of HCoV-229E into host cells, a process that depends on the activation of the S-protein by host cell proteases. However, the proteases responsible for HCoV-229E activation are incompletely defined. Here we show that the type II transmembrane serine proteases TMPRSS2 and HAT cleave the HCoV-229E S-protein (229E-S) and augment 229E-S-driven cell-cell fusion, suggesting that TMPRSS2 and HAT can activate 229E-S. Indeed, engineered expression of TMPRSS2 and HAT rendered 229E-S-driven virus-cell fusion insensitive to an inhibitor of cathepsin L, a protease previously shown to facilitate HCoV-229E infection. Inhibition of endogenous cathepsin L or TMPRSS2 demonstrated that both proteases can activate 229E-S for entry into cells that are naturally susceptible to infection. In addition, evidence was obtained that activation by TMPRSS2 rescues 229E-S-dependent cell entry from inhibition by IFITM proteins. Finally, immunohistochemistry revealed that TMPRSS2 is coexpressed with CD13, the HCoV-229E receptor, in human airway epithelial (HAE) cells, and that CD13 ؉ TMPRSS2 ؉ cells are preferentially targeted by HCoV-229E, suggesting that TMPRSS2 can activate HCoV-229E in infected humans. In sum, our results indicate that HCoV-229E can employ redundant proteolytic pathways to ensure its activation in host cells. In addition, our observations and previous work suggest that diverse human respiratory viruses are activated by TMPRSS2, which may constitute a target for antiviral intervention.

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The recent emergence of a novel human coronavirus (HCoV-EMC) in the Middle East raised considerable concerns, as it is associated with severe acute pneumonia, renal failure, and fatal outcome and thus resembles the clinical presentation of severe acute respiratory syndrome (SARS) observed in 2002 and 2003. Like SARS-CoV, HCoV-EMC is of zoonotic origin and closely related to bat coronaviruses. The human airway epithelium (HAE) represents the entry point and primary target tissue for respiratory viruses and is highly relevant for assessing the zoonotic potential of emerging respiratory viruses, such as HCoV-EMC. Here, we show that pseudostratified HAE cultures derived from different donors are highly permissive to HCoV-EMC infection, and by using reverse transcription (RT)-PCR and RNAseq data, we experimentally determined the identity of seven HCoV-EMC subgenomic mRNAs. Although the HAE cells were readily responsive to type I and type III interferon (IFN), we observed neither a pronounced inflammatory cytokine nor any detectable IFN responses following HCoV-EMC, SARS-CoV, or HCoV-229E infection, suggesting that innate immune evasion mechanisms and putative IFN antagonists of HCoV-EMC are operational in the new host. Importantly, however, we demonstrate that both type I and type III IFN can efficiently reduce HCoV-EMC replication in HAE cultures, providing a possible treatment option in cases of suspected HCoV-EMC infection.

The IFNL4 gene is a recently discovered type III interferon, which in a significant fraction of the human population harbours a frameshift mutation abolishing the IFNk4 ORF. The expression of IFNk4 is correlated with both poor spontaneous clearance of hepatitis C virus (HCV) and poor response to treatment with type I interferon. Here, we show that the IFNL4 gene encodes an active type III interferon, named IFNk4, which signals through the IFNkR1 and IL-10R2 receptor chains. Recombinant IFNk4 is antiviral against both HCV and coronaviruses at levels comparable to IFNk3. However, the secretion of IFNk4 is impaired compared to that of IFNk3, and this impairment is not due to a weak signal peptide, which was previously believed. We found that IFNk4 gets N-linked glycosylated and that this glycosylation is required for secretion. Nevertheless, this glycosylation is not required for activity. Together, these findings result in the paradox that IFNk4 is strongly antiviral but a disadvantage during HCV infection.

A 29 nucleotide deletion in open reading frame 8 (ORF8) is the most obvious genetic change in severe acute respiratory syndrome coronavirus (SARS-CoV) during its emergence in humans. In spite of intense study, it remains unclear whether the deletion actually reflects adaptation to humans. Here we engineered full, partially deleted (−29 nt), and fully deleted ORF8 into a SARS-CoV infectious cDNA clone, strain Frankfurt-1. Replication of the resulting viruses was compared in primate cell cultures as well as Rhinolophus bat cells made permissive for SARS-CoV replication by lentiviral transduction of the human angiotensin-converting enzyme 2 receptor. Cells from cotton rat, goat, and sheep provided control scenarios that represent host systems in which SARS-CoV is neither endemic nor epidemic. Independent of the cell system, the truncation of ORF8 (29 nt deletion) decreased replication up to 23-fold. The effect was independent of the type I interferon response. The 29 nt deletion in SARS-CoV is a deleterious mutation acquired along the initial human-to-human transmission chain. The resulting loss of fitness may be due to a founder effect, which has rarely been documented in processes of viral emergence. These results have important implications for the retrospective assessment of the threat posed by SARS.