ZIKV and DENV2 adenoviral vectors priming and FliC-DIII booster immunizations using ij loop glycan masking mutations to minimize cross-reactive ADE effects. (A) Glycan-masking mutation on the ZIKV E protein ij loop (E-248NHT). Immunizations with two doses of Ad-ZprME-248, the Ad-ZprME-248 priming and FliC-ZDIII booster immunization (Ad-ZprME-248+FliC-ZDIII), and the PBS-immunized control group. Antisera were measured for the titers of ZDIII-specific total IgG and neutralizing antibodies. (B) Glycan-masking mutation on the DENV2 E protein ij loop (E-242NHT). Immunizations with two doses of Ad-D2prME-242, the Ad-D2prME-242 priming and FliC-D2DIII booster immunization (Ad-D2prME-242+FliC-D2DIII), and the PBS-immunized control group. Antisera were measured for the titers of D2DIII-specific total IgG and neutralizing antibodies (***, p <0.001). (C) ADE activity of DENV or ZIKV infection mediated by Ad-ZprME-248 and Ad-ZprME-248+FliC-ZDIII antisera. (D) ADE activity of DENV or ZIKV infection mediated by Ad-D2prME-242 and Ad-D2prME-242+FliC-D2DIII antisera.