Fig. 3.

Nucleoside-modified RBD-mRNA induced potent and durable antibody responses with broadly neutralizing activity. Mice were immunized I.M. with LNP-encapsulated RBD-mRNA with or without the nucleoside modification (30 μg/mouse), or empty-LNP control, boosted twice at 4 weeks and around 7 months, respectively, and sera were collected for the tests described below. (A) Mouse sera from different time points were detected for IgG antibodies (Abs) by ELISA. ELISA plates were coated with MERS-CoV S1 protein, and the Ab titer was determined based on the endpoint serum dilution that remained positively detectable. (B) Mouse sera from different time points were measured for neutralizing Abs against infection of pseudotyped MERS-CoV encoding S protein of the original virus strain (EMC2012). (C) Mouse sera from the last immunization were measured for cross-neutralizing antibodies against multiple variants of pseudotyped MERS-CoV-2. NT₅₀ was calculated as 50% neutralizing Ab titer against infection of the respective MERS-CoV pseudovirus in Huh-7 cells. The data are presented as mean ± s.e.m. of duplicate wells from five mice in each group. *** (P < 0.001) indicates significant difference between RBD-mRNA-PseudoU and other groups. The experiments were repeated twice, resulting in similar results.