The Imidazoquinoline Toll-Like Receptor-7/8 Agonist Hybrid-2 Potently Induces Cytokine Production by Human Newborn and Adult Leukocytes

• Published in: PloS one 2015-08, Vol.10 (8), p.e0134640
• Main Authors: Ganapathi, Lakshmi, Van Haren, Simon, Dowling, David J, Bergelson, Ilana, Shukla, Nikunj M, Malladi, Subbalakshmi S, Balakrishna, Rajalakshmi, Tanji, Hiromi, Ohto, Umeharu, Shimizu, Toshiyuki, David, Sunil A, Levy, Ofer
• Format: Article
• Language: English
• Subjects: Adenosine; Adjuvants; Adult; Adults; Age; Blood; Carbonyl compounds; Carbonyls; Congeners; Cord blood; Crystallography; Cytokines; Cytokines - metabolism; Dendritic cells; Dendritic Cells - drug effects; Dendritic Cells - metabolism; Electrostatic properties; Enzyme-linked immunosorbent assay; Ethics; Female; Fetal Blood - cytology; Fetal Blood - drug effects; Fetal Blood - metabolism; Health risks; HEK293 Cells; Hospitals; Humans; IL-1β; Imidazoles - pharmacology; Immune system; Immunization; Immunomodulation; Immunomodulators; Immunosuppressive Agents - pharmacology; Infant, Newborn; Infants; Infectious diseases; Leukocytes; Leukocytes - drug effects; Leukocytes - metabolism; Lymphocytes T; Medical schools; Monocytes; Neonates; Newborn babies; NF-κB protein; Oxygen; Peripheral blood; Pharmaceutical sciences; Pregnancy; Proteins; Quinolines - pharmacology; Recombinant Fusion Proteins - pharmacology; TLR7 protein; Toll-Like Receptor 7 - agonists; Toll-Like Receptor 8 - agonists; Toll-like receptors; Tumor necrosis factor-TNF; Tumor necrosis factor-α; Up-Regulation - drug effects; Vaccines; White blood cells; X-ray crystallography
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0134640

Newborns and young infants are at higher risk for infections than adults, and manifest suboptimal vaccine responses, motivating a search for novel immunomodulators and/or vaccine adjuvants effective in early life. In contrast to most TLR agonists (TLRA), TLR8 agonists such as imidazoquinolines (IMQs) induce adult-level Th1-polarizing cytokine production from human neonatal cord blood monocytes and are candidate early life adjuvants. We assessed whether TLR8-activating IMQ congeners may differ in potency and efficacy in inducing neonatal cytokine production in vitro, comparing the novel TLR7/8-activating IMQ analogues Hybrid-2, Meta-amine, and Para-amine to the benchmark IMQ resiquimod (R848). TLRA-induced NF-κB activation was measured in TLR-transfected HEK cells. Cytokine production in human newborn cord and adult peripheral blood and in monocyte-derived dendritic cell cultures were measured by ELISA and multiplex assays. X-ray crystallography characterized the interaction of human TLR8 with Hybrid-2. Hybrid-2 selectively activated both TLR7 and 8 and was more potent than R848 in inducing adult-like levels of TNF-α, and IL-1β. Consistent with its relatively high in vitro activity, crystallographic studies suggest that absence in Hybrid-2 of an ether oxygen of the C2-ethoxymethyl substituent, which can engage in unfavorable electrostatic and/or dipolar interactions with the carbonyl oxygen of Gly572 in human TLR8, may confer greater efficacy and potency compared to R848. Hybrid-2 is a selective and potent TLR7/8 agonist that is a candidate adjuvant for early life immunization.