Imidazoquinoline Toll-like receptor 8 agonists activate human newborn monocytes and dendritic cells through adenosine-refractory and caspase-1–dependent pathways

Abstract

Background Newborns suffer frequent infection and manifest impaired vaccine responses, motivating a search for neonatal vaccine adjuvants. Alum is a neonatal adjuvant, but may confer a Th2 bias. Toll-like receptor (TLR) agonists are candidate adjuvants, but human neonatal cord blood monocytes (Mos) demonstrate impaired Th1-polarizing responses to many TLR agonists due to plasma adenosine acting via cAMP. TLR8 agonists, including imidazoquinolines (IMQs) such as the small synthetic 3M-002, induce adult-level TNF from neonatal Mos, but the scope and mechanisms of IMQ-induced activation of neonatal Mos and Mo-derived dendritic cells (MoDCs) have not been reported. Objectives To characterize IMQ-induced activation of neonatal Mos and MoDCs. Methods Neonatal cord and adult peripheral blood Mos and MoDCs were cultured in autologous plasma; Alum- and TLR agonist-induced cytokines and co-stimulatory molecules were measured. TLR8 and inflammasome function were assayed using siRNA and western blotting/caspase-1 inhibitory peptide, respectively. The ontogeny of TLR8 agonist–induced cytokine responses was defined in Rhesus macaque whole blood ex vivo. Results IMQs were more potent and effective than Alum at inducing TNF and IL-1β from Mos. 3M-002 induced robust TLR pathway transcriptome activation and Th1-polarizing cytokine production in neonatal and adult Mos and MoDCs, signaling via TLR8 in an adenosine/cAMP- refractory manner. Newborn MoDCs displayed impaired LPS/ATP-induced caspase-1-mediated IL-1β production, but robust 3M-002-induced caspase-1-mediated inflammasome activation independent of exogenous ATP. TLR8-IMQs induced robust TNF and IL-1β in whole blood of Rhesus macaques at birth and infancy. Conclusions IMQ TLR8 agonists engage adenosine-refractory TLR8 and inflammasome pathways to induce robust Mo and MoDC activation and represent promising neonatal adjuvants.

Balancing Trained Immunity with Persistent Immune Activation and the Risk of Simian Immunodeficiency Virus Infection in Infant Macaques Vaccinated with Attenuated Mycobacterium tuberculosis or Mycobacterium bovis BCG Vaccine

“…As mycobacteria infect not only monocytes/macrophages but also dendritic cells (DC), we tested both monocytes/macrophages and myeloid DC (mDC) for their ability to produce cytokines in response to Toll-like receptor (TLR) ligation. Although mycobacteria are not known to signal through Toll-like receptor 7 (TLR7) or TLR8, we chose the TLR7/8 agonist R848 because monocytes/macrophages and myeloid dendritic cells from infants show reduced function compared to those from adults, and R848 has been demonstrated to potently activate infant cell populations (33,34). At 16 to 18 weeks after vaccination, in vitro R848 stimulation of PBMC resulted in higher frequencies of interleukin 12 (IL-12)-producing monocytes/macrophages (Fig.…”

Use of the Microparticle Nanoscale Silicon Dioxide as an Adjuvant To Boost Vaccine Immune Responses against Influenza Virus in Neonatal Mice

“…A recent study using a polysaccharide microparticle adjuvant (Advax) also demonstrated protection against influenza virus challenge (31); likewise, an alphavirus-based adjuvant improved protection compared to antigen alone (32). It is of note that all these formulations are microparticle based, though it is not clear how the particles are being recognized by the immune system as studies have suggested that IL-1␤ responses in early life are deficient (33); however, this may be dependent upon the agonist used (34).…”

An Immunological Perspective on Neonatal Sepsis

“…By comparison, PRR activity in mononuclear cells increases until about 33 weeks of gestation, with the earliest activity detected in endosomal (TLR7, 8 and 9) and intracellular (e.g. NLRs), followed by extracellular PRRs such as the TLR1, 2, 4 and 5 and the dectin-1 receptor [9,16].…”