Krzysztof Pyrć

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 function. 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.

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.

UNLABELLED: Human coronavirus NL63 (HCoV-NL63) is an alphacoronavirus that was first identified in 2004 in the nasopharyngeal aspirate from a 7-month-old patient with a respiratory tract infection. Previous studies showed that HCoV-NL63 and the genetically distant severe acute respiratory syndrome (SARS)-CoV employ the same receptor for host cell entry, angiotensin-converting enzyme 2 (ACE2), but it is largely unclear whether ACE2 interactions are sufficient to allow HCoV-NL63 binding to cells. The present study showed that directed expression of angiotensin-converting enzyme 2 (ACE2) on cells previously resistant to HCoV-NL63 renders them susceptible, showing that ACE2 protein acts as a functional receptor and that its expression is required for infection. However, comparative analysis showed that directed expression or selective scission of the ACE2 protein had no measurable effect on virus adhesion. In contrast, binding of HCoV-NL63 to heparan sulfates was required for viral attachment and infection of target cells, showing that these molecules serve as attachment receptors for HCoV-NL63. IMPORTANCE: ACE2 protein was proposed as a receptor for HCoV-NL63 already in 2005, but an in-depth analysis of early events during virus infection had not been performed thus far. Here, we show that the ACE2 protein is required for viral entry but that it is not the primary binding site on the cell surface. Conducted research showed that heparan sulfate proteoglycans function as adhesion molecules, increasing the virus density on cell surface and possibly facilitating the interaction between HCoV-NL63 and its receptor. Obtained results show that the initial events during HCoV-NL63 infection are more complex than anticipated and that a newly described interaction may be essential for understanding the infection process and, possibly, also assist in drug design.

BACKGROUND: The clinical relevance of infections with the novel human coronavirus NL63 (HCoV-NL63) has not been investigated systematically. We therefore determined its association with disease in young children with lower respiratory tract infection (LRTI). METHODS AND FINDINGS: Nine hundred forty-nine samples of nasopharyngeal secretions from children under 3 y of age with LRTIs were analysed by a quantitative HCoV-NL63-specific real-time PCR. The samples had been collected from hospitalised patients and outpatients from December 1999 to October 2001 in four different regions in Germany as part of the prospective population-based PRI.DE study and analysed for RNA from respiratory viruses. Forty-nine samples (5.2%), mainly derived from the winter season, were positive for HCoV-NL63 RNA. The viral RNA was more prevalent in samples from outpatients (7.9%) than from hospitalised patients (3.2%, p = 0.003), and co-infection with either respiratory syncytial virus or parainfluenza virus 3 was observed frequently. Samples in which only HCoV-NL63 RNA could be detected had a significantly higher viral load than samples containing additional respiratory viruses (median 2.1 x 10(6) versus 2.7 x 10(2) copies/ml, p = 0.0006). A strong association with croup was apparent: 43% of the HCoV-NL63-positive patients with high HCoV-NL63 load and absence of co-infection suffered from croup, compared to 6% in the HCoV-NL63-negative group, p < 0.0001. A significantly higher fraction (17.4%) of samples from croup patients than from non-croup patients (4.2%) contained HCoV-NL63 RNA. CONCLUSION: HCoV-NL63 infections occur frequently in young children with LRTI and show a strong association with croup, suggesting a causal relationship.