Env-specific CD8⁺ T-cell responses are increased, but Env-specific binding antibody and CD4⁺ T-cell responses do not increase after boost immunization.

Env-specific binding IgG antibody titers (A) were determined in sera of C57BL/6 mice prime or prime boost immunized with Ad26.ZIKV.M-Env (n = 5) at the doses indicated, at 12 weeks after prime immunization by using an in-house developed ELISA assay. Dots represent individual responses of the relative potency (log10) compared to a ZIKV Env-specific monoclonal antibody ZV-67, and the mean per group is indicated with a horizontal line. Env-specific splenic CD4+ (B) and CD8+ T cells (C) secreting IFNγ were determined after overnight stimulation with Env-specific peptide pools. Dots represent percentage IFNγ+ T cells of CD3+CD4+ or CD3+CD8+ gated cells, and geometric mean responses are indicated with a horizontal line. Blue (prime only) and green (prime-boost). Asterisks indicate statistically significant trend (*p<0.05, **p<0.01 and ***p<0.001) and “ns” indicates no statistical significant trend.