Studies On Monoclonal Antibodies Of SARS-CoV-2 And ASFV

African swine fever(ASF)and COVID-19 are emerging and re-emerging infectious diseases that seriously endanger global public health and cause huge economic losses.Monoclonal antibodies play an important role in the diagnosis,prevention and treatment of infectious diseases.The emergence of variant has a huge impact on the protective efficacy of existing vaccines and monoclonal antibodies.In this paper,based on the interaction between antibodies and viral immunogens,severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)and African Swine fever virus(ASFV)have carried out a series of studies related to monoclonal antibodies,which will provide important theoretical reference for understanding the immune escape mechanism of viruses and developing the next generation of vaccines and antibody drugs.First,this study focused on immune escape of SARS-CoV-2 Omicron variant against existing monoclonal antibodies.SARS-CoV-2,the pathogen of COVID-19,has infected more than 500 million people and killed more than 6 million people worldwide.At present,neutralizing antibodies against SARS-CoV-2 mainly target the receptor-binding domain(RBD)of Spike protein(S),which can be divided into seven categories according to epitopes.Omicron RBD with a large number of amino acid mutations has presented a major challenge to the existing antibodies.In this study,we systematically evaluated the immune escape of Omicron BA.1,BA.1.1,BA.2 and BA.3 sub-variant against 50 human monoclonal antibodies covering 7 RBD epitopes by combination assay and pseudovirus neutralization assay.It was found that 37 of the 50 antibodies completely lost their neutralizing activity against the four Omicron sub-variant,and the neutralizing activity of the remaining antibodies against the four Omicron sub-variants also showed varying degrees of reduction,indicating that the four Omicron sub-variants widely escaped the existing antibodies,and there were similar antibody escape patterns among the sub-variants.At the same time,it was found that BA.2 sub-variant was more sensitive to RBD-5 epitope antibodies than other sub-variants.In this study,we further analyzed the electron microscopy structure of the complex of three antibodies with different neutralizing effects on Omicron BA.1 RBD,which provided a basis for understanding the molecular mechanism of immune escape of Omicron variant.We also found that G446S mutation could affect the neutralizing effect of RBD-5 epitope antibodies.This study provides guidance for the application of existing monoclonal antibodies and the development of universal therapeutic antibodies and vaccines against COVID-19.Secondly,this study focused on the screening of monoclonal neutralizing antibodies against the structural proteins CD2v(pEP402R)and p54(pE183L)of ASFV.ASFV is the pathogen of ASF.The virulent strain can cause acute hemorrhagic fever and rapid death in infected domestic pigs or wild boars,with a fatality rate of about 100%.There are no safe,effective,broad-spectrum vaccines and drugs to prevent and treat ASF.ASFV is a large double-stranded DNA virus with a five-layer membrane structure and a regular icosahedron.CD2v and p54,which are respectively located in the outer and inner membranes of ASFV particles,play an important role in the life cycle of viral particles and immune escape,and are known to be important immunogens.In this study,the extracellular segment of CD2v and p54 were used as " bait " to isolate antigen-recognizing B cells from peripheral blood of recovered pigs infected with ASFV.By single-cell sequencing,SPR affinity assay and live virus neutralization assay at the cellular level,eight monoclonal antibodies binding to CD2v protein and blocking CD2v-dependent cell invasion and one monoclonal antibody binding to p54 protein and partially neutralizing ASFV-AMGF strain were screened.These results indicate that CD2v and p54 extracellular proteins have the ability to induce neutralizing antibodies.This study initially revealed the immunogenicity of CD2v and p54 extracellular protein,and provided potential candidate antibodies for the detection and prevention of ASF.In summary,this study systematically compared the efficacy of 50 human monoclonal antibodies,neutralizing SARS-CoV-2,against Omicron sub-variants BA.1,BA.1.1,BA.2,and BA.3 and analyzed the molecular mechanism of the immune evasion of Omicron sub-variants.Eight antibodies binding to extracellular segment of CD2v and one binding to extracellular segment of p54 were screened.These antibodies could partially inhibit the infection of ASFV-ΔMGF strain to host cells,which proved that CD2v and p54 extracellular protein have good immunogenicity.These studies have improved our understanding of viral infection and immune escape,and contributed to epidemic prevention and control as well as the development of therapeutic antibodies and vaccines.