COVID-19 Research: Scientist Discover Unique Epitope At SARS-CoV-2 Spike Furin Cleavage Site And Also A New Corresponding Monoclonal Antibody

COVID-19 Research: Researchers from China and the United States have discovered a novel epitope at the SARS-CoV-2 spike’s Furin cleavage site and also a new corresponding monoclonal antibody that can target this immunogenic epitope to prevent or treat COVID-19 infections.


 
The COVID-19 Research team was led by scientists from the Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing-China, Hubei University of Medicine-China, University of Texas Medical Branch, Galveston-USA, Beijing Institute of Microbiology and Epidemiology, AMMS-China, Suzhou Func Biotech Inc-China and the University of California, Los Angeles-USA.
 
SARS-CoV-2 coronavirus, the causative agent of the global COVID-19 pandemic, contains a unique, four amino acid (aa) “PRRA” insertion in the spike (S) protein that creates a transmembrane protease serine 2 (TMPRSS2)/furin cleavage site and enhances viral infectivity.
 
To date, there is not much detailed research done into the immunogenic epitopes and protective antibodies against this SARS-CoV-2 furin cleavage site.
 
The study team by combining computational and experimental methods, identified and characterized an immunogenic epitope overlapping the furin cleavage site that detects antibodies in COVID-19 patients and elicits strong antibody responses in immunized mice.
 
The study team also identified a high-affinity monoclonal antibody from COVID-19 patient peripheral blood mononuclear cells; the antibody directly binds the furin cleavage site and protects against SARS-CoV-2 infection in a mouse model.
 
Importantly, the presence of “PRRA” amino acids in the S protein of SARS-CoV-2 not only creates a furin cleavage site but also generates an immunogenic epitope that elicits an antibody response in COVID-19 patients.
 
The study team identified an antibody against this epitope protected against SARS-CoV-2 infection in mice.
The study findings involving the newly identified immunogenic epitope and a corresponding antibody may augment a new strategy in handling COVID-19 epidemic. (Perhaps for at least a while, as Thailand Medical News warns that the virus will also eventually evolved and create the necessary mutations to evade even this eventually as we have always been against antibody-based therapeutics to deal with the novel coronavirus based on past data we have seen with regards to the initial SARS virus.
 
The study findings were published in the peer reviewed journal: eBioMedicine (Lancet)
https://www.thelancet.com/journals/ebiom/article/PIIS2352-3964(22)00583-7/fulltext
 
The discovery of this immunogenic epitope at the furin cleavage site of the SARS-CoV-2 virus that induces robust antibody responses in COVID-19) patients along with the identification of a new monoclonal antibody that binds to this epitope and  as seen in animal studies involving mice that it protects against SARS-CoV-2 infection, is causing a new stir in the medical and research community after literally every monoclonal therapeutic that was approve d for use is no longer effective against any of the new emerging SARS-CoV-2 variants and sub-lineages that are in circulation globally at the moment.
https://www.thailandmedical.news/news/covid-19-news-u-s-fda-halts-usage-of-bebtelovimab-to-treat-covid-19-as-drug-is-not-able-to-neutralize-new-sars-cov-2-variants-and-sub-lineages
 
The SARS-CoV-2 contains a unique four-amino acid insertion (PRRA) between the S1 and S2 subunits of the spike protein. This unique insertion creates a transmembrane protease serine 2 (TMPRSS2)/furin cleavage site in the spike protein, which increases the infectivity of SARS-CoV-2. The sequential cleavage of the spike protein at S1/S2 and S2’ cleavage sites by furin and TMPRSS2 is essential for viral entry and infectivity.
 
The COVID-19 Research team identified an immunogenic epitope at the furin cleavage site that specifically recognizes immunoglobulin G (IgG) and IgM antibodies in COVID-19 patients.
 
The researchers then screened spike epitopes using the immune epitope database and analysis resource prediction, ultimately identifying seven peptides.
 
Subsequently, the structural models of these proteins were then constructed using a computer-guided homology modeling approach.
 
The study team also chemically synthesized these peptides and subjected them to the enzyme-linked immunosorbent assay (ELISA) to identify peptide-specific antibodies in COVID-19 patients and healthy individuals.
 
Interestingly, the most potent antibody response was detected against the peptide at the 672-691 spike position, indicating that this peptide contains an immunogenic epitope.
 
A detailed comparison of the peptide sequence with other human coronaviruses revealed that the peptide contains a PRRA between the S1 and S2 subunits absent in other coronaviruses.
 
Subsequent ELISA findings revealed that both IgG and IgM antibodies targeting the spike peptide 672-691 are present in COVID-19 patients and suspected patients at significantly higher concentrations than healthy individuals.
 
The COVID-19 research team further tested the applicability of the spike peptide as an immunogenic antigen for the diagnosis of COVID-19.
 
Importantly, these experiments revealed that the serum titers of peptide-specific IgG antibodies could serve as potential biomarkers for diagnostic purposes.
 
The research team next developed a synthetic version of the spike peptide 672-691 to determine its ability to prevent SARS-CoV-2 infection in cultured cells. To this end, 672-691 was found to block wild-type SARS-CoV-2 and the Omicron variant from infecting the cells.
 
Animal models involving mice were then treated with the peptide, followed by the collection of serum samples to determine its virus-neutralizing efficiency.
 
Importantly, the findings showed that serum samples obtained from 672-691-treated mice could prevent SARS-CoV-2 infection.
 
The study team also introduced deletion mutations within the spike peptide to isolate a specific antibody-binding region.
 
Interestingly, the identified immunogenic epitope of 672-691 was found to overlap with the PRRA, which is unique to SARS-CoV-2.
 
Next, peripheral blood mononuclear cells derived from COVID-19 patients were screened for spike peptide-specific human monoclonal antibodies. Multiple phage clones were obtained, following which sequence analysis was performed to identify two independent clones.
 
Surprisingly, a monoclonal antibody generated from one of these clones exhibited a strong binding affinity for the spike peptide derived from wild-type SARS-CoV-2 and the Omicron variant.
 
Further analysis with mutant viral strains however revealed that the spike peptide lacking the PRRA insertion does not bind to this monoclonal antibody, thus indicating that the monoclonal antibody directly binds to the furin cleavage site of the spike protein!
 
In terms of antiviral efficacy, it was found that the new monoclonal antibody significantly reduced viral ribonucleic acid (RNA) titers in the lungs of SARS-CoV-2-infected mice.
 
In summary, the COVID-19 research findings reveal an immunogenic epitope at the furin cleavage site of the SARS-CoV-2 spike protein. This epitope induces a robust antibody response in COVID-19 patients. The study also identified a human monoclonal antibody that targets this epitope and protects mice from developing SARS-CoV-2 infection.
 
The research findings highlight that, apart from creating a furin cleavage site between the S1 and S2 subunits, the PRRA in the spike protein generates a highly immunogenic epitope. Thus, antibodies binding to the spike protein outside of the well-established receptor-binding domain (RBD) may also have potent antiviral activity.
 
The study was funded by the National Natural Science Foundation of China, the Chinese Academy of Medical Sciences Initiative for Innovative Medicine, the Non-profit Central Research Institute Fund of the Chinese Academy of Medical Sciences, the National Key Research and Development Project of China, US National Institute of Health (NIH) funds grant AI158154, University of California Los Angeles (UCLA) AI and Charity Treks, and UCLA DGSOM BSCRC COVID-19 Award Program. H.Y. is supported by Natural Science Foundation of Jiangsu Province.
 
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