Hybridoma-derived neutralizing monoclonal antibodies against Beta and Delta variants of SARS-CoV-2 in vivo.

Neutralizing monoclonal antibodies (mAb) are a major therapeutic strategy for the treatment of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection. The continuous emergence of new SARS-CoV-2 variants worldwide has increased the urgency for the development of new mAbs. In this study, we immunized mice with the receptor-binding domain (RBD) of the SARS-CoV-2 prototypic strain (WIV04) and screened 35 RBD-specific mAbs using hybridoma technology. Results of the plaque reduction neutralization test showed that 25 of the mAbs neutralized authentic WIV04 strain infection. The 25 mAbs were divided into three categories based on the competitive enzyme-linked immunosorbent assay results. A representative mAb was selected from each category (RD4, RD10, and RD14) to determine the binding kinetics and median inhibitory concentration (IC) of WIV04 and two variants of concern (VOC): B.1.351 (Beta) and B.1.617.2 (Delta). RD4 neutralized the B.1.617.2 variant with an IC of 2.67 ​ng/mL; however, it completely lost neutralizing activity against the B.1.351 variant. RD10 neutralized both variants with an IC exceeding 100 ​ng/mL; whereas RD14 neutralized two variants with a higher IC (>1 ​mg/mL). Animal experiments were performed to evaluate the protective effects of RD4 and RD10 against various VOC infections. RD4 could protect Adv-hACE2 transduced mice from B.1.617.2 infection at an antibody concentration of 25 ​mg/kg, while RD10 could protect mice from B.1.351 infection at an antibody concentration of 75 ​mg/kg. These results highlight the potential for future modifications of the mAbs for practical use.