Recombinant Receptor Binding Domain Protein Induces Partial Protective Immunity in Rhesus Macaques Against Middle East Respiratory Syndrome Coronavirus Challenge()

Lan, Jiaming; Yao, Yanfeng; Deng, Yao; Chen, Hong; Lu, Guangwen; Wang, Wen; Bao, Linlin; Deng, Wei; Wei, Qiang; Gao, George F.; Qin, Chuan; Tan, Wenjie

Circulating neutralising antibody titres were monitored simultaneously in a pseudovirus system. Neutralisation antibodies were detected only after the second vaccination. When the pseudovirus inhibition rate was at 50% (PI 50 ), the neutralisation antibody titres of sera 2 weeks after the second vaccination were 1:800 and 1:1600, in the low-and high-dose groups, respectively (Fig. 2b) . Non-specific neutralisation antibody titres in the mock group were at 1:300. Detection of neutralisation antibodies in rRBD immunised monkeys persisted for at least 17 weeks. Neutralisation antibody titres (PI 50 ) of the sera were at 1:400 and 1:700 in the low-and high-dose groups, respectively (Fig. 2c) . Encouragingly, following the next boost, immunisation neutralisation antibody titres (PI 50 ) were as high as 1:800 and 1:1200 Fig. 2 . Humoral and cellular immune responses induced by rRBD vaccination. a. RBD-specific IgG antibody titres at the indicated time points after vaccine inoculation were monitored by ELISA. b-d. Neutralisation antibody titres in the sera of immunised rhesus macaques 2 weeks after the second vaccination; long-term observation (17-weeks) and the subsequent (i.e. third) vaccination booster were detected using a pseudovirus neutralisation system. e. Sera neutralisation antibodies were detected on Vero cells. f. ELISpot analysis of rhesus macaques PBMCs derived at the indicated time points after rRBD immunisation. All of the detections were replicated for three times. *p b 0.01 and **p b 0.01. (Fig. 2d) which were almost identical to those 2 weeks after the second vaccination at week 10. At all detection time points, high-dose rRBD induced higher neutralisation antibody titres in the pseudovirus system. Neutralisation antibody titres in sera following rRBD vaccination were also detected in Vero cells by the hCoV-EMC strain of MERS-CoV. Neutralisation antibody titres in the sera of rRBD immunised monkeys at week 10 were at 1:269 and 1:363 in the low-and high-dose groups, respectively (Fig. 2e) . After 17 weeks, neutralisation antibody titres decreased slightly. Following a subsequent immunisation boost, neutralisation antibodies 1 day pre-MERS-CoV challenge were almost as high as at week 10. At all detection time points, non-specific neutralisation antibody titres in the mock group were lower or equal to 1:10.