Comprehensive Overview of Broadly Neutralizing Antibodies against SARS-COV-2 Variants (preprint)

Currently, SARS-CoV-2 has evolved into various variants, including the numerous highly mutated Omicron sub-lineages, significantly increasing immune evasion ability. The development raises concerns about possibly diminished effectiveness of available vaccines and antibody-based therapeutics. Here, we describe those representative categories of broadly neutralizing antibodies (bnAbs) that retain prominent effectiveness against emerging variants including Omicron sub-lineages. The molecular characteristics, epitope conservation, and resistance mechanisms of these antibodies are further detailed, aiming to offer suggestion or direction for the development of therapeutic antibodies, and facilitate the vaccine design with broad-spectrum potential.

Change in Japanese children's 24-hour movement guidelines and mental health during the COVID-19 pandemic.

Specialized guidelines are required for the health behaviors of vulnerable populations such as children. This is especially true during the COVID-19 pandemic, wherein major lifestyle changes have occurred, especially among young children. The present study aims to use longitudinal data to understand changes in the physical activity, screen time, sleep, and mental health of preschoolers in Japan during the COVID-19 pandemic, compared to pre-pandemic period. Subjective and objective measures were used to assess the variables of interest longitudinally. It was found that physical activity, adherence to WHO-recommended screen time, and prosocial behaviors decreased significantly. On the other hand, sedentary time and hyperactivity increased. Our results are consistent with findings from other countries. The implications with respect to outdoor playtime, screen-time in the context of online learning during the pandemic, and the effects of parents' mental health on preschool-aged children are discussed.

Changes in Physical Activity, Screen Time, Sleep, and Mental Health of Japanese Young Children: A Longitudinal Study Pre- and During-COVID-19 (preprint)

Specialized guidelines are required for the health behaviors of vulnerable populations such as children. This is especially true during the COVID-19 pandemic, wherein major lifestyle changes have occurred, especially among young children. The present study aims to use longitudinal data to understand changes in the physical activity, screen time, sleep, and mental health of preschool-aged children in Japan during the COVID-19 pandemic, compared to pre-pandemic periods. Subjective and objective measures were used to assess the variables of interest longitudinally. It was found that physical activity, adherence to WHO-recommended screen time, and prosocial behaviors decreased significantly. On the other hand, sedentary time and hyperactivity increased. Our results are consistent with findings from other countries. The implications with respect to outdoor playtime, screen-time in the context of online learning during the pandemic, and the effects of parents’ mental health on preschool-aged children are discussed.

Cross-neutralizing antibodies bind a SARS-CoV-2 cryptic site and resist to circulating variants (preprint)

The emergence of numerous variants of SARS-CoV-2, the causative agent of COVID-19, has presented new challenges to the global efforts to control the still ravaging COVID-19 pandemic. Here, we obtain two cross-neutralizing antibodies (7D6 and 6D6) that target Sarbecoviruses’ receptor binding domain (RBD) with sub-picomolar affinities and potently neutralize authentic SARS-CoV-2. Crystal structures show that both antibodies bind a cryptic site different from that recognized by existing antibodies and highly conserved across Sarbecovirus isolates. Binding of these two antibodies to the RBD clashes with the adjacent N-terminal domain and disrupts the viral spike. Significantly, both antibodies confer good mutation resistance to the currently circulating SARS-CoV-2 variants. Thus, our results have direct relevance to public health as options for passive antibody therapeutics and even active prophylactics, and can also inform the design of pan-sarbecovirus vaccines.

Landscapes and dynamic diversifications of B-cell receptor repertoires in COVID-19 patients (preprint)

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused the pandemic of coronavirus disease 2019 (COVID-19). Great international efforts have been put into the development of prophylactic vaccines and neutralizing antibodies. However,the knowledge about the B cell immune response induced by the SARS-CoV-2 virus is still limited. Here,we report a comprehensive characterization of the dynamics of immunoglobin heavy chain (IGH) repertoire in COVID-19 patients. By using next-generation sequencing technology, we examined the temporal changes in the landscape of the patient's immunological status, and found dramatic changes in the IGH within the patient's immune system after the onset of COVID-19 symptoms. Although different patients have distinct immune responses to SARS-CoV-2 infection, by employing clonotype overlap, lineage expansion and clonotype network analyses, we observed a higher clonotype overlap and substantial lineage expansion of B cell clones during 2-3 weeks of illness, which is of great importance to B-cell immune responses. Meanwhile, for preferences of V gene usage during SARS-CoV-2 infection, IGHV3-74 and IGHV4-34 and IGHV4-39 in COVID-19 patients were more abundant than that of healthy controls. Overall, we present an immunological resource for SARS-CoV-2 that could promote both therapeutic development as well as mechanistic research.

Structural dynamics of the SARS-CoV-2 frameshift-stimulatory pseudoknot reveal topologically distinct conformers (preprint)

The RNA pseudoknot that stimulates -1 programmed ribosomal frameshifting in SARS coronavirus-2 (SARS-CoV-2) is a possible drug target. To understand how this 3-stemmed pseudoknot responds to the mechanical tension applied by ribosomes during translation, which is thought to play a key role during frameshifting, we probed its structural dynamics under tension using optical tweezers. Unfolding curves revealed that the frameshift signal formed multiple different structures: at least two distinct pseudoknotted conformers with different unfolding forces and energy barriers, as well as alternative stem-loop structures. Refolding curves showed that stem 1 formed first in the pseudoknotted conformers, followed by stem 3 and then stem 2. By extending the handle holding the RNA to occlude the 5' end of stem 1, the proportion of the different pseudoknot conformers could be altered systematically, consistent with structures observed in cryo-EM images and computational simulations that had distinct topologies: the 5' end of the RNA threaded through the 3-helix junction to form a ring-knot, or unthreaded as in more standard H-type pseudoknots. These results resolve the folding mechanism of the frameshift signal in SARS-CoV-2 and highlight the dynamic conformational heterogeneity of this RNA, with important implications for structure-based drug-discovery efforts.

ACE2 peptide fragment interacts with several sites on the SARS-CoV-2 spike protein S1 (preprint)

The influence of the peptide QAKTFLDKFNHEAEDLFYQ on the kinetics of the SARS-CoV-2 spike protein S1 binding to angiotensin-converting enzyme 2(ACE2) was studied to model the interaction of the virus with its host cell. This peptide corresponds to the sequence 24-42 of the ACE2 1 domain, which is the binding site for the S1 protein. The on-rate and off-rate of S1-ACE2 complex formation were measured in the presence of various peptide concentrations using Bio-Layer Interferometry (BLI). The formation of the S1-ACE2 complex was inhibited when the S1 protein was preincubated with the peptide, however, no significant inhibitory effect was observed in the absence of preincubation. Dissociation kinetics revealed that the peptide remained bound to the S1-ACE2 complex and stabilized this complex. Computational mapping of the S1 protein surface for peptide binding revealed two additional sites, located at some distance from the receptor binding domain (RBD) of S1. These additional binding sites affect the interaction between the peptide, the S1 protein, and ACE2.

Lentiviral vector-based SARS-CoV-2 pseudovirus enables analysis of neutralizing activity in COVID-19 convalescent plasma (preprint)

As the COVID-19 pandemic caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) continues to spread around the globe, effective vaccination protocols are under deployment. Alternatively, the use of convalescent plasma (CP) therapy relies on the transfer of the immunoglobulin repertoire of a donor that has recovered from the disease as a means of passive vaccination. While the lack of an effective antiviral treatment inadvertently increases the interest in CP products, initial clinical evaluation on COVID-19 patients revealed that critical factors determining the outcome of CP therapy need to be defined clearly if clinical efficacy is to be expected. Measurement of neutralizing activity against SARS-CoV-2 using live virus presents a reliable functional assay but the availability of suitable BSL3 facilities for live virus culture restricts its applicability. Instead, the use of pseudovirus particles containing elements from the SARS-CoV-2 virus is widely applied to determine the activity of CP or other neutralizing agents such as monoclonal antibodies. In this study, we present our approach to optimize GFP-encoding lentiviral particles pseudotyped with the SARS-CoV-2 Spike and Membrane proteins for use in neutralization assays. Our results show the feasibility of pseudovirus production using a C-terminal truncated Spike protein which is greatly enhanced by the incorporation of the D614G mutation. Moreover, we report that the use of sodium butyrate during lentiviral vector production dramatically increases pseudovirus titers. Analysis of CP neutralizing activity against particles pseudotyped with wildtype or D614G mutant Spike protein in the presence or absence the M protein revealed differential activity in CP samples that did not necessarily correlate with the amount of anti-SARS-CoV-2 antibodies. Our results indicate that the extent of neutralizing activity in CP samples depends on the quality rather than the quantity of the humoral immune responses and varies greatly between donors. Functional screening of neutralizing activity using pseudovirus-based neutralization assays must be accepted as a critical tool for choosing CP donors if clinical efficacy is to be maximized.

Single-cell transcriptome analysis of the immunosuppressive effect of differential expression of tumor PD-L1 on responding TCR-T cells (preprint)

PD-L1 expression levels in tumors do not consistently predict cancer patients’ response to PD-(L)1 inhibitors. We therefore evaluated how tumor PD-L1 levels affect the anti-PD-(L)1 efficacy and T cell function. We used MART-1-specific TCR-T cells (TCR-T MART-1 ) stimulated with MART-1 27-35 peptide-loaded MEL-526 tumor cells with different proportions of them expressing PD-L1 to perform cellular assays and high-throughput single-cell RNA sequencing. Compared to control T cells, TCR-T MART-1 were more sensitive to exhaustion and secreted lower pro-inflammatory but higher anti-inflammatory cytokines with increasing proportions of PD-L1 + tumor cells. The colocalization of T cells and tumor cells in gene clusters correlated negatively with the proportion of PD-L1 + tumor cells and positively with immune cell cytotoxicity. Moreover, elevated proportion of PD-L1 + tumor cells increased PD-L1 expression and decreased PD-1 expression on T cells and enhanced T cell death. The expression of PD-1 and PD-L1 in T cells and macrophages also correlated positively with COVID-19 severity.

Point-of-care training program on COVID-19 infection prevention and control for pediatric healthcare workers (preprint)

Background: To evaluate the effectiveness of training on knowledge and practices of infection prevention and control (IPC) among pediatric health care workers (HCW) in Shanghai, China, in the context of COVID-19 pandemic. Methods: An online training program was designed by the Shanghai Pediatric Clinical Quality Control Center (SPQCC) during the early phase of COVID-19 pandemic on disease knowledge and practice of IPC. Training took place in the 81 partner hospitals affiliated with SPQCC. A 25-item self-administered questionnaire was used to evaluate knowledge gained from the training. Stratified-random sampling was used to select HCW according to three professionals (i.e., pediatricians, nurses and administrators) within each partner hospital. Awareness and knowledge of COVID-19 and its related infection control and practice was assessed by comparing survey results between different types of hospitals, professionals and professional ranks. A higher survey score meant that the respondent was more prepared and knowledgeable about COVID-19 and its infection control measures. Results: Completed questionnaires were returned from 1,062 subjects (385 pediatricians, 410 nurses, and 267 administrators), giving a response rate of 96.5%. Overall, awareness of clinical information related to COVID-19, importance of personal hygiene and isolation policy was high among the respondents. No statistical difference of scores on knowledge of COVID-19, IPC and relevant practice between the tertiary and peripheral hospitals. Among all respondents, middle-ranked health care personnel were most knowledgeable and achieved the highest score. Conclusions: Majority of pediatric HCW showed good recognition and practice in infection protection and control measures. The online training was able to achieve its aim to enhance knowledge and awareness and could have contributed to the zero infection rate among HCW caring for confirmed COVID-19 cases in Shanghai.

Characterization of the SARS-CoV-2 Spike in an Early Prefusion Conformation (preprint)

Pandemic coronavirus disease 2019 (COVID-19) is caused by the emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), for which there are no efficacious vaccines or therapeutics that are urgently needed. We expressed three versions of spike (S) proteins--receptor binding domain (RBD), S1 subunit and S ectodomain--in insect cells. RBD appears monomer in solutions, whereas S1 and S associate into homotrimer with substantial glycosylation. The three proteins confer excellent antigenicity with six convalescent COVID-19 patient sera. Cryo-electron microscopy (cryo-EM) analyses indicate that the SARS-CoV-2 S trimer dominate in a unique conformation distinguished from the classic prefusion conformation of coronaviruses by the upper S1 region at lower position ~15 [A] proximal to viral membrane. Such conformation is proposed as an early prefusion state for the SARS-CoV-2 spike that may broaden the knowledge of coronavirus and facilitate vaccine development.