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

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.

Protecting the Newborn and Young Infant from Infectious Diseases: Lessons from Immune Ontogeny

“…Mechanisms that lead to this early life pattern of innate cytokine response include (1) high mononuclear cell levels of intracellular cyclic adenosine monophosphate (cAMP), a secondary messenger that suppresses Th1 but enhances Th2 and anti-inflammatory cytokine production (Levy et al, 2006) and (2) altered DNA binding capacity of transcription factors such as IRF3 to the promoter regions of cytokine genes secondary to age-specific chromatin remodelling (Lissner et al, 2015). Of note, simultaneous stimulation of TLR and C-type lectin receptors (CLR) reveals marked synergy in immune activation as compared to single PRR stimulation, a synergy that strongly varies with age (Lemoine et al, 2015;van Haren et al, 2016a). Specifically, coactivation of newborn DCs via the CLR agonist Dectin or macrophage-inducible C-type lectin (Mincle), and TLR7/8 potently drives caspase-1 and NF-kB activation and Th1-supporting cytokine production (including IL-12p70, overcoming the agespecific epigenetic hurdle in early life for IRF3 function) that results in autologous T cell polarization toward a Th-1 phenotype.…”

Lipid conjugation of TLR7 agonist Resiquimod ensures co-delivery with the liposomal Cationic Adjuvant Formulation 01 (CAF01) but does not enhance immunopotentiation compared to non-conjugated Resiquimod+CAF01

“…induced immune responses observed in neonates and elderly [66,67]. The potential to overcome the impaired immunity of specific age or immunocompromised risk groups is therefore also an important application for future studies of the adjuvant combination developed in the present study.…”

“…Whilst no vaccines including TLR7/8 ligands are yet licensed, studies in monkeys have shown that including a TLR7/8 agonist allows for boosting of anti-HIV Envelope IgG responses compared to when alum was used alone [64,65]. Furthermore, the capability of co-adjuvantation with TLR7 agonists to redirect the alum-induced T cell responses towards IFN-ɣ producing Th1 cells was also demonstrated in monkeys [67]. It was recently found that a TLR7/8 agonist can boost antibody titers to pneumococcal conjugate vaccine at birth [66].…”

Neonatal vaccine effectiveness and the role of adjuvants

“…Trehalose 6,6ʹ-dibehenate (TDB) is a synthetic analog of mycobacterially-expressed trehalose-6,6-dimycolate (TDM) that targets the PAMP receptor, MINCLE (macrophage inducible Ca 2+ -dependent lectin receptor). TDB was shown to activate human newborn DCs and enhanced Th1 polarizing cytokine production by DCs when given in combination with a TLR7/8-ligand [116]. TDB enhanced protection against influenza in immunized neonatal mice through the induction of Tfh cells and highaffinity plasma cells [110].…”