Study On Application Of Pseudoviruses In The Assessment Of Neutralization Ability Of COVID-19 Vaccines

SARS-CoV-2 is an enveloped,positive-sense single-stranded RNA virus,which belongs to the Betacoronavirus（βCoV）,the highly contagious disease caused by SARS-CoV-2 is COVID-19,which has been spreading around the world for more than two years and remains severe today.At present,there is no specific drug for this disease,so the development and vaccination of safe and effective vaccine is still the main method to deal with the epidemic situation,the experimental research on SARS-CoV-2,a highly pathogenic virus,needs to be conducted in biosafety level 3 laboratories（BSL3）,the pseudoviruses basically does not contain virulent virus components,and only replicate intracellularly for a single round.So SARS-COV-2 pseudovirus has become a safe and effective evaluation tool.Therefore,in this study,produce SARS-CoV-2 pseudoviruses and investigate the protective capacity of neutralizing antibody from Convidecia（the Ad5-vectored novel coronovirus vaccine from Cansino Bio）.In this study,the expression plasmids of spike protein from SARS-CoV-2 Delta strain（p HDM-SARS-CoV-2-Δ18re）was constructed by site-directed mutation of seven discontinuous amino acid sites of the expression plasmids of spike protein from SARS-CoV-2 Wuhan strain（p HDM-SARS-CoV-2-Δ18）.p HDM-SARS-CoV-2-Δ18 and p HDM-SARS-CoV-2-Δ18re were transfected into HEK293FT cells by liposome transfection system respectively,which would be used for pseudovirus production with VSV packaging system.The Wuhan strain and Delta strain pseudovirus neutralization tests（p VNT）were developed and validated by assessing the repeatability、intermediate precision、robustness and linearity.The serum samples from monkeys immunized with Convidecia were collected to determine the neutralization antibody titers to SARS-Cov-2 Wuhan strain and Delta strain with the verified p VNT methods.The results are as follows:SARS-CoV-2 pseudovirus of both Wuhan strain and Delta strain were produced,with the titres of 1.86×10⁵CCID₅₀/m L and 4.31×10⁵CCID₅₀/m L respectively.The repeatability,intermediate precision,robustness and linearity tests had qualified the performance of p VNT methods for SARS-CoV-2 Wuhan strain and Delta strain.The results showed that neutralization antibody was detected in all the experimental groups,although the protective capacity against the Delta strain was lower than that against the wuhan strain,the adenovirus vector COVID-19 vaccines remain 68.9%protective against the Delta strain pseudovirus.The adenovirus vector COVID-19 vaccines can effectively induce the production of neutralizing antibodies and it has cross neutralization effect on mutated strains,and can protect Delta strain.