Ebola virus glycoprotein stimulates IL-18–dependent natural killer cell responses

Abstract

BACKGROUND. NK cells are activated by innate cytokines and viral ligands to kill virus-infected cells. These functions are enhanced during secondary immune responses and after vaccination by synergy with effector T cells and virus-specific antibodies. In human Ebola virus infection, clinical outcome is strongly associated with the initial innate cytokine response, but the role of NK cells has not been thoroughly examined. METHODS.The novel 2-dose heterologous Adenovirus type 26.ZEBOV (Ad26.ZEBOV) and modified vaccinia Ankara-BN-Filo (MVA-BN-Filo) vaccine regimen is safe and provides specific immunity against Ebola glycoprotein, and is currently in phase 2 and 3 studies. Here, we analyzed NK cell phenotype and function in response to Ad26.ZEBOV, MVA-BN-Filo vaccination regimen and in response to in vitro Ebola glycoprotein stimulation of PBMCs isolated before and after vaccination. RESULTS.We show enhanced NK cell proliferation and activation after vaccination compared with baseline. Ebola glycoprotein-induced activation of NK cells was dependent on accessory cells and TLR-4-dependent innate cytokine secretion (predominantly from CD14 + monocytes) and enriched within less differentiated NK cell subsets. Optimal NK cell responses were dependent on IL-18 and IL-12, whereas IFN-γ secretion was restricted by high concentrations of IL-10. CONCLUSION.This study demonstrates the induction of NK cell effector functions early after Ad26.ZEBOV, MVA-BN-Filo vaccination and provides a mechanism for the activation and regulation of NK cells by Ebola glycoprotein. TRIAL REGISTRATION. ClinicalTrials.gov NCT02313077.

Regulation of the human NK cell compartment by pathogens and vaccines

“…Similarly, increased absolute numbers of CD56 bright and CD56 dim NK cells are observed within 3 days of immunisation with the rVSV‐ZEBOV Ebola virus vaccine; increased NK cell expression of CXCR6 is an independent correlate of rVSV‐ZEBOV vaccine responsiveness whilst reduced frequencies of NKG2D + and increased frequencies of NKp30 and KIR + NK cells are inversely correlated with plasma cytokine and chemokine concentrations, indicating likely recirculation of NK cell subsets within 72 h of vaccination 93 . The Ad26.ZEBOV Ebola virus vaccine also activates CD56 bright NK cells as assessed by the induction of CD25 and Ki67 expression up to 14 days after the second dose 70 . The extent to which different vaccine vectors, delivery platforms and adjuvating systems impact on NK cell differentiation will likely depend on their primary cellular tropism, interactions with pattern recognition receptors and downstream production of NK cell‐activating cytokines; this aspect of vaccination has as yet received very little attention.…”

“…During EVD, there is a rapid reduction in the frequency of CD56 bright NK cells, within days of infection, and a subsequent increase in the frequencies of proliferating CD56 bright and CD56 dim cells 69 . In vitro , Ebola virus glycoprotein directly induces the secretion of both pro‐inflammatory cytokines (including IL‐18 which contributes significantly to NK cell activation, degranulation and IFN‐γ production) and anti‐inflammatory IL‐10 (which restricts these responses) 70 . In this scenario, NK cell responses are dominated by CD56 bright and CD56 dim CD57 − cells, raising the possibility that these less differentiated, cytokine‐producing cells may act to further amplify the inflammatory cascade (and thus disease severity) in vivo .…”

“…69 In vitro, Ebola virus glycoprotein directly induces the secretion of both proinflammatory cytokines (including IL-18 which contributes significantly to NK cell activation, degranulation and IFN-c production) and antiinflammatory IL-10 (which restricts these responses). 70 In this scenario, NK cell responses are dominated by CD56 bright and CD56 dim CD57 À cells, raising the possibility that these less differentiated, cytokine-producing cells may act to further amplify the inflammatory cascade (and thus disease severity) in vivo. Interestingly, increases in the frequency of CD56 À CD16 + NK cells are observed up to 2 years after recovery from severe EVD, suggestive of persistent activation and/or terminal differentiation from CD56 dim CD16 + NK cells.…”

“…93 The Ad26.ZEBOV Ebola virus vaccine also activates CD56 bright NK cells as assessed by the induction of CD25 and Ki67 expression up to 14 days after the second dose. 70 The extent to which different vaccine vectors, delivery platforms and adjuvating systems impact on NK cell differentiation will likely depend on their primary cellular tropism, interactions with pattern recognition receptors and downstream production of NK cell-activating cytokines; this aspect of vaccination has as yet received very little attention.…”

NK Cell Subset Redistribution and Antibody Dependent Activation after Ebola Vaccination in Africans

“…Our previous studies show that serum collected post-dose one and post-dose two from Ad26.ZEBOV, MVA-BN-Filo vaccinated individuals induced significant NK cell degranulation (surface expression of CD107a), higher IFN-γ secretion and CD16 (FcγRIII) downregulation compared with baseline (pre-vaccination) serum [13]. These studies in European trials also demonstrate that this vaccine induces a redistribution of NK cell subsets towards less differentiated CD56 bright and CD57 − NK cells accompanied by increased frequency of CD25 + NK cells, suggesting potential for increased responsiveness to CD4 + T cell derived IL-2 (CD25 expression) and proliferation 21 days after the second vaccine dose [14]. Further, we demonstrated persistent redistribution of NK cell subsets up to 180 days post-dose 2, also involving an enrichment of CD56 bright NK cells and enhanced CD25 expression [15].…”