title: Imidazoquinoline Toll-like receptor 8 agonists activate human newborn monocytes and dendritic cells through adenosine-refractory and caspase-1-dependent pathways.
abstract: BACKGROUND
  Newborns have frequent infections and manifest impaired vaccine responses, motivating a search for neonatal vaccine adjuvants. Alum is a neonatal adjuvant but might confer a T(H)2 bias. Toll-like receptor (TLR) agonists are candidate adjuvants, but human neonatal cord blood monocytes demonstrate impaired T(H)1-polarizing responses to many TLR agonists caused by plasma adenosine acting through cyclic AMP. TLR8 agonists, including imidazoquinolines (IMQs), such as the small synthetic 3M-002, induce adult-level TNF from neonatal monocytes, but the scope and mechanisms of IMQ-induced activation of neonatal monocytes and monocyte-derived dendritic cells (MoDCs) have not been reported.
  
  
  OBJECTIVE
  We sought to characterize IMQ-induced activation of neonatal monocytes and MoDCs.
  
  
  METHODS
  Neonatal cord and adult peripheral blood monocytes and MoDCs were cultured in autologous plasma; levels of alum- and TLR agonist-induced cytokines and costimulatory molecules were measured. TLR8 and inflammasome function were assayed by using small interfering RNA 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 monocytes. 3M-002 induced robust TLR pathway transcriptome activation and T(H)1-polarizing cytokine production in neonatal and adult monocytes and MoDCs, signaling through TLR8 in an adenosine/cyclic AMP-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 monocyte and MoDC activation and represent promising neonatal adjuvants.
authors.affiliation: Department of Medicine, Division of Infectious Diseases, Children's Hospital Boston, Boston, Mass; Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Victoria J
authors.initials: VJ
authors.lastname: Philbin
authors.forename: David J
authors.initials: DJ
authors.lastname: Dowling
authors.forename: Leighanne C
authors.initials: LC
authors.lastname: Gallington
authors.forename: Guadalupe
authors.initials: G
authors.lastname: Cortés
authors.forename: Zhen
authors.initials: Z
authors.lastname: Tan
authors.forename: Eugénie E
authors.initials: EE
authors.lastname: Suter
authors.forename: Kevin W
authors.initials: KW
authors.lastname: Chi
authors.forename: Ariel
authors.initials: A
authors.lastname: Shuckett
authors.forename: Liat
authors.initials: L
authors.lastname: Stoler-Barak
authors.forename: Mark
authors.initials: M
authors.lastname: Tomai
authors.forename: Richard L
authors.initials: RL
authors.lastname: Miller
authors.forename: Keith
authors.initials: K
authors.lastname: Mansfield
authors.forename: Ofer
authors.initials: O
authors.lastname: Levy
mesh_terms: D000241:Adenosine / Q000378:metabolism*; D000276:Adjuvants, Immunologic; D000328:Adult; D000534:Alum Compounds; D000818:Animals; D020170:Caspase 1 / Q000378:metabolism*; D016207:Cytokines / Q000276:immunology / Q000378:metabolism; D003713:Dendritic Cells / Q000276:immunology*; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology*; D007231:Infant, Newborn; D008253:Macaca mulatta; D009000:Monocytes / Q000276:immunology*; D011804:Quinolines / Q000494:pharmacology*; D051200:Toll-Like Receptor 8 / Q000819:agonists*
chemical_list: C526117:3M 002; D000276:Adjuvants, Immunologic; D000534:Alum Compounds; D016207:Cytokines; D007093:Imidazoles; D011804:Quinolines; C495349:TLR8 protein, human; D051200:Toll-Like Receptor 8; C041524:aluminum sulfate; C037219:quinoline; D020170:Caspase 1; D000241:Adenosine