SARS-CoV-2 has observably higher propensity to accept uracil as nucleotide substitution: Prevalence of amino acid substitutions and their predicted functional implications in circulating SARS-CoV-2 in India up to July, 2020 (preprint)

SARS-CoV-2 has emerged as pandemic all over the world since late 2019. In this study, we investigated the diversity of the virus in the context of SARS-CoV-2 spread in India. Full-length SARS-CoV-2 genome sequences of the circulating viruses from all over India were collected from GISAID, an open data repository, until 25thJuly, 2020. We have focused on the non-synonymous changes across the genome that resulted in amino acid substitutions. Analysis of the genomic signatures of the non-synonymous mutations demonstrated a strong association between the time of sample collection and the accumulation of genetic diversity. Most of these isolates from India belonged to the A2a clade (63.4%) which has overcome the selective pressure and is spreading rapidly across several continents. Interestingly a new clade I/A3i has emerged as the second-highest prevalent type among the Indian isolates, comprising 25.5% of the Indian sequences. Emergence of new mutations in the S protein was observed. Major SARS-CoV-2 clades in India have defining mutations in the RdRp. Maximum accumulation of mutations was observed in ORF1a. Other than the clade-defining mutations, few representative non-synonymous mutations were checked against the available crystal structures of the SARS-CoV-2 proteins in the DynaMut server to assess their thermodynamic stability. We have observed that SARS-CoV-2 genomes contain more uracil than any other nucleotide. Furthermore, substitution of nucleotides to uracil was highest among the non-synonymous mutations observed. The A+U content in SARS-CoV-2 genome is much higher compared to other RNA viruses, suggesting that the virus RdRp has a propensity towards uracil incorporation in the genome. This implies that thymidine analogues may have a better chance to competitively inhibit SARS-CoV-2 RNA replication than other nucleotide analogues.

Extremely potent human monoclonal antibodies from convalescent Covid-19 patients (preprint)

Human monoclonal antibodies are safe, preventive and therapeutic tools, that can be rapidly developed to help restore the massive health and economic disruption caused by the Covid-19 pandemic. By single cell sorting 4277 SARS-CoV-2 spike protein specific memory B cells from 14 Covid-19 survivors, 453 neutralizing antibodies were identified and 220 of them were expressed as IgG. Up to 65,9% of monoclonals neutralized the wild type virus at a concentration of >500 ng/mL, 23,6% neutralized the virus in the range of 100 - 500 ng/mL and 9,1% had a neutralization potency in the range of 10 - 100 ng/mL. Only 1,4% neutralized the authentic virus with a potency of 1-10 ng/mL. We found that the most potent neutralizing antibodies are extremely rare and recognize the RBD, followed in potency by antibodies that recognize the S1 domain, the S-protein trimeric structure and the S2 subunit. The three most potent monoclonal antibodies identified were able to neutralize the wild type and D614G mutant viruses with less than 10 ng/mL and are good candidates for the development of prophylactic and therapeutic tools against SARS-CoV-2. One Sentence SummaryExtremely potent neutralizing human monoclonal antibodies isolated from Covid-19 convalescent patients for prophylactic and therapeutic interventions.

Clinical and molecular characterization of COVID-19 hospitalized patients (preprint)

Clinical and molecular characterization by Whole Exome Sequencing (WES) is reported in 35 COVID-19 patients attending the University Hospital in Siena, Italy, from April 7 to May 7, 2020. Eighty percent of patients required respiratory assistance, half of them being on mechanical ventilation. Fiftyone percent had hepatic involvement and hyposmia was ascertained in 3 patients. Searching for common genes by collapsing methods against 150 WES of controls of the Italian population failed to give straightforward statistically significant results with the exception of two genes. This result is not unexpected since we are facing the most challenging common disorder triggered by environmental factors with a strong underlying heritability (50%). The lesson learned from Autism-Spectrum-Disorders prompted us to re-analyse the cohort treating each patient as an independent case, following a Mendelian-like model. We identified for each patient an average of 2.5 pathogenic mutations involved in virus infection susceptibility and pinpointing to one or more rare disorder(s). To our knowledge, this is the first report on WES and COVID-19. Our results suggest a combined model for COVID-19 susceptibility with a number of common susceptibility genes which represent the favorite background in which additional host private mutations may determine disease progression.

Identification of neutralizing human monoclonal antibodies from Italian Covid-19 convalescent patients (preprint)

In the absence of approved drugs or vaccines, there is a pressing need to develop tools for therapy and prevention of Covid-19. Human monoclonal antibodies have very good probability of being safe and effective tools for therapy and prevention of SARS-CoV-2 infection and disease. Here we describe the screening of PBMCs from seven people who survived Covid-19 infection to isolate human monoclonal antibodies against SARS-CoV-2. Over 1,100 memory B cells were single-cell sorted using the stabilized prefusion form of the spike protein and incubated for two weeks to allow natural production of antibodies. Supernatants from each cell were tested by ELISA for spike protein binding, and positive antibodies were further tested for neutralization of spike binding to receptor(s) on Vero E6 cells and for virus neutralization in vitro. From the 1,167 memory B specific for SARS-CoV-2, we recovered 318 B lymphocytes expressing human monoclonals recognizing the spike protein and 74 of these were able to inhibit the binding of the spike protein to the receptor. Finally, 17 mAbs were able to neutralize the virus when assessed for neutralization in vitro. Lead candidates to progress into the drug development pipeline will be selected from the panel of neutralizing antibodies identified with the procedure described in this study. One Sentence SummaryNeutralizing human monoclonal antibodies isolated from Covid-19 convalescent patients for therapeutic and prophylactic interventions.