| Middle East Respiratory Syndrome Coronavirus(MERS-CoV)is a novel pathogen that causes acute respiratory illness in humans and animals,mainly in the form of fever and cough,and sometimes pneumonia and gastrointestinal symptoms including diarrhoea,which can be fatal in severe cases.Middle East Respiratory Syndrome(MERS)was first identified in Saudi Arabia in 2012,with a 34.5% mortality rate.To date,there is no specific treatment strategy against the MERS-CoV virus and no vaccine is available.The spread of MERS coincided with the global spread of coronavirus disease 2019(COVID-19)caused by SARS coronavirus type 2(SARS-CoV-2)in late 2019.Due to its highly infectious nature,COVID-19 has infected hundreds of millions of people,of which millions have died,with a huge global political and economic impact.During the COVID-19 outbreak,unprecedented advances in research on coronavirus structure and antiviral strategies were achieved.At the same time,there has been increased interest in the development of a MERS-CoV vaccine and its neutralising antibodies.The coronavirus spike protein(S)is hydrolysed by host proteases into two subunits,S1,which mediates cell attachment,and S2,which mediates virus-cell membrane fusion,both of which are critical in mediating viral invasion and inducing the production of neutralizing antibodies in the body.Our previous study found that antibodies reactive to the MERS-CoV S protein in healthy populations accounted for <8% of total antibodies,yet over 60% of serum antibodies from COVID-19 convalescents were reactive to the MERS-CoV S protein;this finding suggests that SARS-CoV-2 infection promotes antibody responses to MRES-CoV,suggesting the potential to isolate and characterise antibodies against MRES-CoV from COVID-19 convalescents.sera to isolate and characterize cross-reactive,or even broadly neutralizing,antibodies against MERS-CoV and SARS-CoV-1 and SARS-CoV-2viruses.In this study,collected 60 peripheral blood from COVID-19 convalescents and used 165 blood from healthy individuals prior to the COVID-19 epidemic as controls for our experiments.Firstly,the positive antibody binding reactions and antibody titer levels of these two groups of sera against MRES-CoV S1 and S2 were analysed by ELISA.The results showed the presence of antibodies targeting mainly the MRES-CoV S2 subunit in the sera of recovered COVID-19 convalescents with high antibody titres(median,1:12800 dilution;[log10 =4.11;interquartile range [IQR] = 3.81-4.71).To test whether the serum antibodies could neutralise MERS-CoV,constructed MRES-CoV pseudoviruses and performed antibody neutralisation experiments on the pseudoviruses,which revealed that 21.67% of COVID-19 convalescents had serum Ig G antibodies that neutralised MRES-CoV pseudoviruses.Subsequently,constructed and expressed 38 fully humanized monoclonal antibodies from peripheral blood B cells of COVID-19 convalescents by single B cell isolation and antibody gene cloning strategy.11 monoclonal antibodies were confirmed by ELISA to bind MRES-CoV S2,two of which only bind MRES-CoV S2,a MERS-CoV specific antibody,and the other nine The other nine monoclonal antibodies showed significant cross-reactivity with six other coronaviruses infecting humans(SARS-CoV,SARS-CoV-2,HCoV-OC43,HKU1-CoV,HCoV-229 E and HCoV-NL63);in addition,pseudovirus neutralization assays showed that five monoclonal antibodies were weakly neutralizing to MERS pseudoviruses.In conclusion,in this study,humanized MERS-CoV-specific monoclonal antibodies were identified and constructed from COVID-19 survivors.Nine antibodies showed broad-spectrum cross-reactivity to seven coronaviruses infecting humans,suggesting that broad-spectrum reactive antibodies as well as potentially broad-spectrum neutralizing antibodies can be isolated from coronavirus-infected individuals,providing a scientific reference for the study of immunity to multiple coronaviruses and the development of a universal vaccine for coronaviruses. |
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