Adenovirus serotype 5 vaccine vectors trigger IL-27-dependent inhibitory CD4 T cell responses that impair CD8 T cell function.

Adenovirus serotype 5 (Ad5) vaccine vectors elicit robust CD8 T cell responses, but these responses typically exhibit a partially exhausted phenotype. However, the immunologic mechanism by which Ad5 vectors induce dysfunctional CD8 T cells has not previously been elucidated. Here we demonstrate that, following immunization of B6 mice, Ad5 vectors elicit antigen-specific IL-10CD4 T cells with a distinct transcriptional profile in a dose-dependent fashion. In rhesus monkeys, we similarly observed upregulated expression of IL-10 and PD-1 by CD4 T cells following Ad5 vaccination. These cells markedly suppressed vaccine-elicited CD8 T cell responses and IL-10 blockade increased the frequency and functionality of antigen-specific CD8 T cells as well as improved protective efficacy against challenge with recombinant . Moreover, induction of these inhibitory IL-10CD4 T cells correlated with IL-27 expression and IL-27 blockade substantially improved CD4 T cell functionality. These data highlight a role for IL-27 in the induction of inhibitory IL-10CD4 T cells, which suppress CD8 T cell magnitude and function following Ad5 vector immunization. A deeper understanding of the cytokine networks and transcriptional profiles induced by vaccine vectors should lead to strategies to improve the immunogenicity and protective efficacy of viral vector-based vaccines.