Comparison of immunological responses of plague vaccines F1+rV270 and EV76 in Chinese-origin rhesus macaque, Macaca mulatta

The subunit vaccine SV1 (20 μg F1+10 μg rV270) has been identified as the optimal formulation in mice, which provided a good protection against plague in mice, guinea pigs and rabbits. To compare SV1 and SV2 (200 μg F1+100 μg rV270) with live attenuated vaccine EV76, antibody responses, protective efficacy, cytokines (IFN-γ, TNF-α, IL-2, IL-4, IL-10 and IL-12) production, CD4/CD8 ratio and CD69(+) T-cell activation marker were determined in sera of the immunized Chinese-origin rhesus macaques, Macaca mulatta. The immunized animals with SV1 or SV2 developed higher anti-rV270 IgG titre, while those immunized with EV76 elicited a negligible IgG to V antigen, indicating that subunit vaccine (SV) had an advantage over EV76 in terms of the indispensable role of anti-V antibody against Yersinia pestis. There was no significant antibody titre difference between SV1 and SV2, suggesting that the immune response may have been saturated at the dose level of SV1. There were no statistical changes for CD4/CD8 ratios, IL-4 and CD69 levels between the three-vaccine immunized groups. However, a significant higher level of IL-12 was observed in the EV76 immunized animals, indicating that EV76 had an advantage over SV in respect of cellular immunity. Complete protection was observed for the immunized animals with SV and EV76, revealing that SV has a similar protective efficacy with EV76 against 6×10⁶ CFU of Y. pestis challenge by subcutaneous route in Chinese-origin rhesus macaques.