Innate and Cellular Immune Response to the Ebola Vaccine Ad26.ZEBOV, MVA-BN-Filo: An Ancillary Study of the EBL2001 Phase 2 Trial

Background: The EBL2001 phase 2 trial tested the 2-dose Ad26.ZEBOV, MVA-BN-Filo Ebola vaccine in Europe. Safety and humoral immunogenicity assessments led to European Union market authorization in 2020. Complementary analyses of immune responses are warranted to better characterize vaccine effects.

Methods: We conducted an ancillary study to analyze changes in the serum and cellular responses. Serum biomarkers of activation/inflammation were evaluated using a Luminex assay. Vaccine-elicited T-cell responses and functions were evaluated by assessing their phenotype, cytokine production, proliferation, and cytotoxic potential. Integrated data analysis was performed through correlation and principal component analysis of serum biomarkers and cellular immune responses.

Results: Forty-eight volunteers were included. The Ad26.ZEBOV, MVA-BN-Filo vaccine elicited (1) serum increase of inflammatory/activation markers mainly at 1 day after the Ad26.ZEBOV vaccine; and (2) durable EBOV-specific T-cell proliferation and CD8+ T cells exhibiting a cytotoxic phenotype after Ad26.ZEBOV prime, after MVA-BN-Filo boost, and 6 months postvaccination. Integrated analysis revealed correlations between (1) EBOV-specific CD8+ T-cell proliferation and cytotoxic phenotype; and (2) high EBOV-specific CD8+ T-cell cytotoxic phenotype and low inflammatory marker IL-8 at day 1 postvaccination.

Discussion: This study provides unique insights into the in vivo contribution of proliferation/cytotoxic CD8+ T cells and inflammation to the Ad26.ZEBOV, MVA-BN-Filo vaccine-induced potency. Clinical Trials Registration. NCT02416453.