Emerging viral infections are difficult to control as heterogeneous members periodically cycle in and out of humans and zoonotic hosts, complicating the development of specific antiviral therapies and vaccines. Coronaviruses (CoVs) have a proclivity to spread rapidly into new host species causing severe disease. SARS-CoV and MERS-CoV successively emerged causing severe epidemic respiratory disease in immunologically naïve human populations throughout the globe. Broad-spectrum therapies capable of inhibiting CoV infections would address an immediate unmet medical need and could be invaluable in the treatment of emerging and endemic CoV infections. Here we show that a nucleotide prodrug GS-5734, currently in clinical development for treatment of Ebola virus disease, can inhibit SARS-CoV and MERS-CoV replication in multiple in vitro systems including primary human airway epithelial cell cultures with submicromolar IC50 values. GS-5734 was also effective against bat-CoVs, prepandemic bat-CoVs and circulating contemporary human CoV in primary human lung cells, thus demonstrating broad-spectrum anti-CoV activity. In a mouse model of SARS-CoV pathogenesis, prophylactic and early therapeutic administration of GS-5734 significantly reduced lung viral load and improved clinical signs of disease as well as respiratory functions. These data provide substantive evidence that GS-5734 may prove effective against endemic MERS-CoV in the Middle East, circulating human CoV, and possibly most importantly, emerging CoV of the future.

Three human coronaviruses are known to exist: human coronavirus 229E (HCoV-229E), HCoV-OC43 and severe acute respiratory syndrome (SARS)-associated coronavirus (SARS-CoV). Here we report the identification of a fourth human coronavirus, HCoV-NL63, using a new method of virus discovery. The virus was isolated from a 7-month-old child suffering from bronchiolitis and conjunctivitis. The complete genome sequence indicates that this virus is not a recombinant, but rather a new group 1 coronavirus. The in vitro host cell range of HCoV-NL63 is notable because it replicates on tertiary monkey kidney cells and the monkey kidney LLC-MK2 cell line. The viral genome contains distinctive features, including a unique N-terminal fragment within the spike protein. Screening of clinical specimens from individuals suffering from respiratory illness identified seven additional HCoV-NL63-infected individuals, indicating that the virus was widely spread within the human population.

Coronavirus (CoV) infection of humans is usually not associated with severe disease. However, discovery of the severe acute respiratory syndrome (SARS) CoV revealed that highly pathogenic human CoVs (HCoVs) can evolve. The identification and characterization of new HCoVs is, therefore, an important task. Recently, a HCoV termed NL63 was discovered in patients with respiratory tract illness. Here, cell tropism and receptor usage of HCoV-NL63 were analyzed. The NL63 spike (S) protein mediated infection of different target cells compared with the closely related 229E-S protein but facilitated entry into cells known to be permissive to SARS-CoV-S-driven infection. An analysis of receptor engagement revealed that NL63-S binds angiotensin-converting enzyme (ACE) 2, the receptor for SARS-CoV, and HCoV-NL63 uses ACE2 as a receptor for infection of target cells. Potent neutralizing activity directed against NL63-but not 229E-S protein was detected in virtually all sera from patients 8 years of age or older, suggesting that HCoV-NL63 infection of humans is common and usually acquired during childhood. Here, we show that SARS-CoV shares its receptor ACE2 with HCoV-NL63. Because the two viruses differ dramatically in their ability to induce disease, analysis of HCoV-NL63 might unravel pathogenicity factors in SARS-CoV. The frequent HCoV-NL63 infection of humans suggests that highly pathogenic variants have ample opportunity to evolve, underlining the need for vaccines against HCoVs.C oronaviruses (CoVs) are enveloped RNA viruses that are grouped according to genome sequence and serology (1). Human CoVs (HCoVs) 229E and OC43 are members of groups I and II, respectively, and infection with these viruses is thought to be responsible for Ϸ30% of common-cold cases (1). In contrast, infection with severe acute respiratory syndrome (SARS)-CoV causes a severe respiratory tract illness (RTI) that is fatal in Ϸ10% of infected individuals (2, 3). The factors that determine the pathogenicity of CoVs are incompletely understood; however, a role for the spike (S) protein has been suggested (4). The S proteins of CoVs, which provide virions with a corona-like appearance, mediate infection of target cells and play a central role in viral replication (4). The interaction of CoV S proteins with specific cellular receptors determines, to a large extent, which cells can be infected (5), and the entry process is an attractive target for antiviral therapy (6).Recently, a HCoV termed NL63 was discovered in infants and immunocompromised adults with RTI (7, 8). HCoV-NL63 is a group I CoV and is most closely related to HCoV-229E (7-9). HCoV-229E employs CD13 (aminopeptidase N) as a receptor for infection of target cells (10,11). Because the NL63-and 229E-S proteins share 56% amino acid identity (7), it is conceivable that HCoV-NL63 also engages CD13 for infectious cellular entry. However, the HCoV-NL63-S protein contains a unique, 179-aa sequence at its N terminus that does not share homology with other known CoV proteins and that might alter the re...