25 Recently a novel coronavirus (2019-nCoV) has emerged from Wuhan, China, 26 causing symptoms in humans similar to those caused by SARS coronavirus (SARS-27 CoV). Since SARS-CoV outbreak in 2002, extensive structural analyses have revealed 28 key atomic-level interactions between SARS-CoV spike protein receptor-binding domain 29 (RBD) and its host receptor angiotensin-converting enzyme 2 (ACE2), which regulate 30 both the cross-species and human-to-human transmissions of SARS-CoV. Here we 31 analyzed the potential receptor usage by 2019-nCoV, based on the rich knowledge about 32 SARS-CoV and the newly released sequence of 2019-nCoV. First, the sequence of 2019-33 nCoV RBD, including its receptor-binding motif (RBM) that directly contacts ACE2, is 34 similar to that of SARS-CoV, strongly suggesting that 2019-nCoV uses ACE2 as its 35 receptor. Second, several critical residues in 2019-nCoV RBM (particularly Gln493) 36 provide favorable interactions with human ACE2, consistent with 2019-nCoV's capacity 37 for human cell infection. Third, several other critical residues in 2019-nCoV RBM 38 (particularly Asn501) are compatible with, but not ideal for, binding human ACE2, 39 suggesting that 2019-nCoV has acquired some capacity for human-to-human 40 transmission. Last, while phylogenetic analysis indicates a bat origin of 2019-nCoV, 41 2019-nCoV also potentially recognizes ACE2 from a diversity of animal species (except 42 mice and rats), implicating these animal species as possible intermediate hosts or animal 43 models for 2019-nCoV infections. These analyses provide insights into the receptor 44 usage, cell entry, host cell infectivity and animal origin of 2019-nCoV, and may help 45 epidemic surveillance and preventive measures against 2019-nCoV. 46 47 on March 16, 2020 by guest http://jvi.asm.org/ Downloaded from Significance 48 The recent emergence of Wuhan coronavirus (2019-nCoV) puts the world on 49 alert. 2019-nCoV is reminiscent of the SARS-CoV outbreak in 2002-2003. Our decade-50 long structural studies on the receptor recognition by SARS-CoV have identified key 51 interactions between SARS-CoV spike protein and its host receptor angiotensin-52 converting enzyme 2 (ACE2), which regulate both the cross-species and human-to-53 human transmissions of SARS-CoV. One of the goals of SARS-CoV research was to 54 build an atomic-level iterative framework of virus-receptor interactions to facilitate 55 epidemic surveillance, predict species-specific receptor usage, and identify potential 56 animal hosts and animal models of viruses. Based on the sequence of 2019-nCoV spike 57 protein, we apply this predictive framework to provide novel insights into the receptor 58 usage and likely host range of 2019-nCoV. This study provides a robust test of this 59 reiterative framework, providing the basic, translational and public health research 60 communities with predictive insights that may help study and battle this novel 2019-61 nCoV. 62 63 on March 16, 2020 by guest

The present outbreak of a coronavirus-associated acute respiratory disease called coronavirus disease 19 (COVID-19) is the third documented spillover of an animal coronavirus to humans in only two decades that has resulted in a major epidemic. The Coronaviridae Study Group (CSG) of the International Committee on Taxonomy of Viruses, which is responsible for developing the classification of viruses and taxon nomenclature of the family Coronaviridae, has assessed the placement of the human pathogen, tentatively named 2019-nCoV, within the Coronaviridae. Based on phylogeny, taxonomy and established practice, the CSG recognizes this virus as forming a sister clade to the prototype human and bat severe acute respiratory syndrome corona- viruses (SARS-CoVs) of the species Severe acute respiratory syndrome-related coronavirus, and designates it as SARS-CoV-2. In order to facilitate communication, the CSG proposes to use the following naming convention for individual isolates: SARS-CoV-2/host/location/isolate/date. While the full spectrum of clinical manifestations associated with SARS-CoV-2 infections in humans remains to be determined, the independent zoonotic transmission of SARS-CoV and SARS-CoV-2 highlights the need for studying viruses at the species level to complement research focused on individual pathogenic viruses of immediatesignificance. This will improve our understanding of virus-host interactions in an ever-changing environment and enhance our preparedness for future outbreaks.

Highlights d A SARS-CoV-2 infectious cDNA clone and reporter viruses are generated d SARS-CoV-2 and SARS-CoV neutralization assays show limited cross neutralization d SARS-CoV-2 shows a gradient infectivity from the proximal to distal respiratory tract d Ciliated airway cells and AT-2 cells are primary targets for SARS-CoV-2 infection

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.

Limited knowledge is available on the relationship between antigen-specific immune responses and COVID-19 disease severity. We completed a combined examination of all three branches of adaptive immunity at the level of SARS-CoV-2-specific CD4 + and CD8 + T cell and neutralizing antibody responses in acute and convalescent subjects. SARS-CoV-2-specific CD4 + and CD8 + T cells were each associated with milder disease. Coordinated SARS-CoV-2-specific adaptive immune responses were associated with milder disease, suggesting roles for both CD4 + and CD8 + T cells in protective immunity in COVID-19. Notably, coordination of SARS-CoV-2 antigen-specific responses was disrupted in individuals > 65 years old. Scarcity of naive T cells was also associated with ageing and poor disease outcomes. A parsimonious explanation is that coordinated CD4 + T cell, CD8 + T cell, and antibody responses are protective, but uncoordinated responses frequently fail to control disease, with a connection between ageing and impaired adaptive immune responses to SARS-CoV-2.