Ebola vaccine–induced protection in nonhuman primates correlates with antibody specificity and Fc-mediated effects.

Correlates of protection: Vaccines against Ebola virus (EBOV) are difficult to test in humans due to the sporadic nature of EBOV outbreaks, so understanding correlates of protection in preclinical models is necessary. To this end, Meyer et al. tested five candidate mucosal EBOV vaccines in cynomolgus macaques and showed that, despite sharing the EBOV glycoprotein as an antigen, they varied in their ability to protect animals from the EBOV challenge. The authors interrogated correlates of protection and found that functional qualities of the antibody response, such as Fc-mediated effects, were associated with protection. In contrast, neutralizing antibody titers did not correlate with survival. Thus, looking beyond the presence of neutralizing antibodies may be necessary to understand the protective effect of EBOV vaccines. Although substantial progress has been made with Ebola virus (EBOV) vaccine measures, the immune correlates of vaccine-mediated protection remain uncertain. Here, five mucosal vaccine vectors based on human and avian paramyxoviruses provided nonhuman primates with varying degrees of protection, despite expressing the same EBOV glycoprotein (GP) immunogen. Each vaccine produced antibody responses that differed in Fc-mediated functions and isotype composition, as well as in magnitude and coverage toward GP and its conformational and linear epitopes. Differences in the degree of protection and comprehensive characterization of the response afforded the opportunity to identify which features and functions were elevated in survivors and could therefore serve as vaccine correlates of protection. Pairwise network correlation analysis of 139 immune- and vaccine-related parameters was performed to demonstrate relationships with survival. Total GP-specific antibodies, as measured by biolayer interferometry, but not neutralizing IgG or IgA titers, correlated with survival. Fc-mediated functions and the amount of receptor binding domain antibodies were associated with improved survival outcomes, alluding to the protective mechanisms of these vaccines. Therefore, functional qualities of the antibody response, particularly Fc-mediated effects and GP specificity, rather than simply magnitude of the response, appear central to vaccine-induced protection against EBOV. The heterogeneity of the response profile between the vaccines indicates that each vaccine likely exhibits its own protective signature and the requirements for an efficacious EBOV vaccine are complex. [ABSTRACT FROM AUTHOR]