Broadly neutralizing monoclonal antibodies derived from mRNA LNP immunization exhibit potent neutralizing ability...

Since the emergence of severe acute respiratory syndrome coronavirus 2 Omicron, dramatic changes in the receptor-binding domain have allowed for virus escape from many therapeutic antibodies. Development of antibodies effective against current viral strains is, therefore, necessary to provide useful clinical treatments and can also yield fundamental information about viral neutralization. Here, we utilized single B-cell antibody technology to isolate and characterize neutralizing antibodies from splenocytes of mice immunized with mRNA-LNPs. With this approach, we identified five BA.5 and four XBB.1.5 neutralizing chimeric antibodies (ChAbs). The identified ChAbs, BA.5-ChAb-41, XBB.1.5-ChAb-17 and XBB.1.5-ChAb-26, each potently neutralized BA.5, XBB.1.5 and JN.1 pseudotype viruses with low IC₅₀ (1.9, 2.3 and 10.93 ng ml^-1). Furthermore, XBB.1.5-ChAb-26 showed neutralizing capability against the current JN.1-related variants, KP.3.1.1 and XEC. By performing single amino acid substitution of the receptor-binding motif (RBM), we observed that the epitopes of BA.5-ChAb-41 and XBB.1.5-ChAb-17 include Y453 and R498 in the RBM. Moreover, XBB.1.5-ChAb-26 epitope includes Y453 and T500, which may contribute to its ability to neutralize JN.1, KP.3.1.1 and XEC variants. In summary, our approach allowed us to efficiently screen for highly functional antibodies, and we further identified critical residues in the epitopes to aid in the design of therapeutic virus-neutralizing antibodies.