Age-Specific Adjuvant Synergy: Dual TLR7/8 and Mincle Activation of Human Newborn Dendritic Cells Enables Th1 Polarization

<jats:title>Abstract</jats:title> <jats:p>Due to functionally distinct cell-mediated immunity, newborns and infants are highly susceptible to infection with intracellular pathogens. Indeed, neonatal Ag-presenting dendritic cells (DCs) demonstrate impaired Th1 responses to many candidate adjuvants, including most TLR agonists (TLRAs). Combination adjuvantation systems may provide enhanced immune activation but have typically been developed without regard to the age of the target population. We posited that distinct combinations of TLRAs and C-type lectin receptor agonists may enhance Th1 responses of newborn DCs. TLRA/C-type lectin receptor agonist combinations were screened for enhancement of TNF production by human newborn and adult monocyte-derived DCs cultured in 10% autologous plasma or in newborn cord, infant, adult, and elderly whole blood. Monocyte-derived DC activation was characterized by targeted gene expression analysis, caspase-1 and NF-κB studies, cytokine multiplex and naive autologous CD4+ T cell activation. Dual activation of newborn DCs via the C-type lectin receptor, macrophage-inducible C-type lectin (trehalose-6,6-dibehenate), and TLR7/8 (R848) greatly enhanced caspase-1 and NF-κB activation, Th1 polarizing cytokine production and autologous Th1 polarization. Combined activation via TLR4 (glycopyranosyl lipid adjuvant aqueous formulation) and Dectin-1 (β-glucan peptide) acted synergistically in newborns and adults, but to a lesser extent. The degree of synergy varied dramatically with age, and was the greatest in newborns and infants with less synergy in adults and elders. Overall, combination adjuvant systems demonstrate markedly different immune activation with age, with combined DC activation via Macrophage-inducible C-type lectin and TLR7/8 representing a novel approach to enhance the efficacy of early-life vaccines.</jats:p>