No abstract

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.

Due to impairments in cell-mediated immunity, newborns are markedly susceptible to infection with intracellular pathogens. Impaired newborn immunity includes a reduced response to Toll-like Receptor agonists (TLRAs) by dendritic cells (DCs), placing them at risk for infection and limiting Th1-responses to many vaccines. Our hypothesis was that dual stimulation with TLRAs and C-type Lectin Receptor agonists (CLRAs) may overcome the reduced response of newborn DCs to common vaccine formulations. We screened TLRAs, CLRAs and their combinations for their ability to induce Th1-polarizing cytokine production from neonatal dendritic cells. Human adult- and cord blood monocyte-derived DCs (MoDCs) were generated in the presence of autologous plasma and stimulated for 18 hours. Cytokines and markers for cellular toxicity were measured to assess correlates of immunogenicity and reactogenicity. Dual activation of newborn DCs with a TLR8 agonist (R848) and a Mincle agonist (TDB) or with a TLR4 agonist (MPLA or GLA) and a Dectin-1 agonist (alkali-treated Zymosan) synergistically enhanced the production of the T-cell activating and -polarizing cytokines TNF-α, IL-12p70 and IL-1β. Our data suggest that targeting vaccinal antigens to the endocytic receptors Mincle or Dectin-1 is a powerful approach to induce Th1-mediated immunity in newborns. This study has the potential to inform development of novel adjuvanted neonatal vaccines and reduce infections in infants.