The Capacity To Induce Cross-Presentation Dictates the Success of a TLR7 Agonist-Conjugate Vaccine for Eliciting Cellular Immunity

Abstract

Covalent conjugation of TLR agonists to protein Ags often facilitates the generation of a CD8+ T cell response. However, mechanisms underlying the efficacy of the conjugate over its unconjugated counterpart have been largely uninvestigated. In this study, we show that conjugation of a TLR7 agonist enhances CD8+ T cell responses without affecting Ag persistence and with minimal impact on cellular uptake of the Ag in vivo. Instead, the conjugated form induced a robust accumulation of dendritic cells (DCs) in regional lymph nodes. Perhaps more importantly, cross-presentation in DCs was detected only when the Ag was delivered in the conjugated form with the TLR7 agonist. Collectively, these data represent the first demonstration that a TLR agonist–Ag conjugate elicits CD8+ T cell responses based not on its capacity to induce DC maturation or Ag persistence and uptake, but on the engagement of DC cross-presentation pathways.