ABSTRACT
@#Abstract: Objective To construct SARS-CoV-2 receptor binding domain molecular probe for monoclonal memory B cell sorting and obtain RBD specific neutralizing antibodies from peripheral blood mononuclear cells (PBMCs) of COVID-19 convalescents by single-cell sorting. Methods The SARS-CoV-2 RBD sequence was downloaded from GenBank, and the Avi tag and 6-histidine tags were added at the C-terminal. After codon optimization, it was chemically synthesized, cloned into the pDRVI1.0 vector, expressed after transfection of 293F cells, and biotinylated consequently. RBD-specific B cells were sorted out with this probe1 from the PBMCs of convalescents recovered from COVID-19. After B cells were lysed, the variable regions of heavy chain and light chain were amplified, cloned into the antibody expression vector, and transfected into 293F cells to express the antibody. Then the antibody was purified from the supernatant using protein A column and SARS-CoV-2 pseudovirus was used to test their neutralizing activity. Results RBD-Avi probe was produced and successfully biotinylated sequentially with an efficiency of 30%-50%. Western blot analysis revealed that the biotinylated probe was recognized by the antibodies purified from COVID-19 convalescent plasma. Using this probe, 7 and 16 RBD-specific memory B cells were successfully isolated from the PBMCs of two convalescent individuals, accounting for 0.24% and 0.17% of the total cell population, respectively. After amplifying the variable regions of antibody heavy and light chains from the lysed B cells, 7 and 12 pairs of antibody heavy-light chains were obtained. A total of 16 antibodies were expressed in the convalescent individuals, and most of the purified antibodies showed neutralizing activity against the pseudovirus, with IC50 values of 6 antibodies below 1 μg/mL. The IC50 values of XJ-A9 and SCF-F1 against the wild-type pseudovirus were 0.07 μg/mL and 0.35 μg/mL, respectively. Conclusion The SARS-CoV-2 RBD molecular probe constructed in this study has good antigenicity, and the isolated antibodies present neutralizing activity against wild-type SARS-CoV-2 pseudovirus.