CD8A and viral infectious disease: To determine whether the observed effect of OX40/4-1BB Abs on vaccine-induced CD8+ T cell responses at day 84 after immunization translated to improved immunity against viral infection at the same time point, Ifnar1−/− mice were immunized once with ZIKV M/E vaccine, treated with OX40/4-1BB agonist Abs 1 day later, and then challenged with ZIKV at 84 days after immunization (Figure 6A).