SARS-CoV-2 manipulates the SR-B1-mediated HDL uptake pathway for its entry (preprint)

The recently emerged pathogenic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread rapidly, leading to a global COVID-19 pandemic. Binding of the viral spike protein (SARS-2-S) to cell surface receptor angiotensin-converting enzyme 2 (ACE2) mediates host cell infection. In the present study, we demonstrate that in addition to ACE2, the S1 subunit of SARS-2-S binds to HDL and that SARS-CoV-2 hijacks the SR-B1-mediated HDL uptake pathway to facilitate its entry. SR-B1 facilitates SARS-CoV-2 entry into permissive cells by augmenting virus attachment. MAb (monoclonal antibody)-mediated blocking of SARS-2-S-HDL binding and SR-B1 antagonists strongly inhibit HDL-enhanced SARS-CoV-2 infection. Notably, SR-B1 is co-expressed with ACE2 in human pulmonary and extrapulmonary tissues. These findings revealed a novel mechanism for SARS-CoV-2 entry and could provide a new target to treat SARS-CoV-2 infection.

A single dose of an adenovirus-vectored vaccine provides complete protection of the upper and lower respiratory tracts against SARS-CoV-2 challenge (preprint)

The unprecedented coronavirus disease 2019 (COVID-19) epidemic has created a worldwide public health emergency, and there is an urgent need to develop an effective vaccine to control this severe infectious disease. Here, we found that a single vaccination with a replication-defective human type 5 adenovirus encoding the SARS-CoV-2 spike protein (Ad5-nCoV) protected mice completely against SARS-CoV-2 infection in the upper and lower respiratory tracts. Additionally, a single vaccination with Ad5-nCoV protected ferrets from SARS-CoV-2 infection in the upper respiratory tract. This study suggested that a combination of intramuscular and mucosal vaccination maybe provide a desirable protective efficacy and different Ad5-nCoV delivery modes are worth further investigation in human clinical trials.

A potent neutralizing human antibody reveals the N-terminal domain of the Spike protein of SARS-CoV-2 as a site of vulnerability (preprint)

The pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) presents a global public health threat. Most research on therapeutics against SARS-CoV-2 focused on the receptor binding domain (RBD) of the Spike (S) protein, whereas the vulnerable epitopes and functional mechanism of non-RBD regions are poorly understood. Here we isolated and characterized monoclonal antibodies (mAbs) derived from convalescent COVID-19 patients. An mAb targeting the N-terminal domain (NTD) of the SARS-CoV-2 S protein, named 4A8, exhibits high neutralization potency against both authentic and pseudotyped SARS-CoV-2, although it does not block the interaction between angiotensin-converting enzyme 2 (ACE2) receptor and S protein. The cryo-EM structure of the SARS-CoV-2 S protein in complex with 4A8 has been determined to an overall resolution of 3.1 Angstrom and local resolution of 3.4 Angstrom for the 4A8-NTD interface, revealing detailed interactions between the NTD and 4A8. Our functional and structural characterizations discover a new vulnerable epitope of the S protein and identify promising neutralizing mAbs as potential clinical therapy for COVID-19.

Immune Cell Profiling of COVID-19 Patients in the Recovery Stage by Single-Cell Sequencing (preprint)

COVID-19 caused by SARS-CoV-2 has recently affected over 200,000 people and killed more than 8000. Immune system dysregulation such as lymphopenia and inflammatory cytokine storm has been observed in COVID-19 patients, but it remains unclear for the change of key immune cell subsets and their states during COVID-19. Here, we applied single-cell technology to comprehensively characterize transcriptional changes of peripheral blood mononuclear cells in ten patients recovered from COVID-19. Compared with healthy control, COVID-19 induced a unique signature of immune cells in humans, especially in the early recovery stage (ERS). In ERS patients, T cells were decreased remarkably, while monocytes were increased. A detailed analysis of monocytes showed that there was an increased ratio of classical CD14++ monocytes with highly inflammatory genes expression, as well as a greater abundance of CD14++IL1B+ monocytes. For nature killer (NK) cells and T cells, CD4+ T cells were significantly decreased and expressed high level of inflammatory markers, while NK cells were increased. In addition, T cells were highly expanded clone, especially in CD4+ T memory cells and CD8+ T cells. Among B cells, plasma cells were increased remarkably, and naive B cells were reduced. Our study also identified several novel B cell receptor (BCR) changes (such as IGHV1-8 and IGHV3-7), and confirmed isotypes (IGKV3-11 and IGHV3-21) previously used for virus vaccine development. The strongest pairing frequencies, IGHV3-23+IGHJ4, indicated a monoclonal state associated with SARS-CoV-2 specificity. Furthermore, integrated analysis predicated that IL-1B and M-CSF may be novel candidate target gene for inflammatory storm, and TNFSF13, IL-18 and IL-4 may be benefit for the recovery of COVID-19 patients. Our study provides the first evidence of inflammatory immune signature in early recovery stage, suggesting that the COVID-19 patients are still vulnerable after hospital discharge. Our identification of novel BCR signaling may lead to the development of vaccine and antibodies for the treatment of COVID-19.