EASL 2018 SAT-429
Cytokine-dependent activation of MAIT cells by the TLR8 agonist
GS-9688 but not the TLR7 agonist GS-9620
S. Daffis, M. Morar, D. Pattabiraman, C. Voitenleitner, S. Fletcher,
H. Javanbakht. Gilead Sciences, Biology, Foster City, United States
Email: [email protected]
Background and Aims: GS-9688 is a selective small molecule agonist
of toll-like receptor 8 (TLR8) in clinical development for the
treatment of chronic hepatitis B (CHB). GS-9620 is an oral small
molecule TLR7 agonist which has recently completed phase 2 studies
in CHB patients. Oral GS-9688 and GS-9620 induce an immune
response by pre-systemic activation of gut-associated and intrahepatic
immune cells. Mucosal associated invariant T (MAIT) cells are
innate-like Tcells enriched in the gut and liver that likely play a role in
host antiviral defense. Here we characterized in vitro activation of
MAIT cells in human peripheral blood mononuclear cells (PBMCs)
fromhealthy donors (HD) and CHB patients by GS-9688 and GS-9620.
Method: PBMCs obtained from HDs and age-matched CHB patients
(n = 8) were treated for 18 hours with GS-9688 (156nM) or GS-9620
(10nM) and cytokineswere analyzed by Luminex® assay. Intracellular
levels of IFN-γ and TNF-α (antiviral cytokines), and granzyme B (a
marker of cytotoxic function) in MAIT cells (CD3+TCRγδ−CD161+
Vα7.2+) were evaluated by flow cytometry.
Results: Consistent with previous studies, GS-9688 strongly induced
IL-12p70 and IL-18, but had minimal effect on IFN-α (a TLR7-induced
cytokine) in HD PBMCs. GS-9688 also strongly induced intracellular
IFN-γ (38-fold increase), granzyme B (17-fold increase) and TNF-α
(4-fold increase) levels in MAIT cells. Cytokine neutralization studies
demonstrated that GS-9688 indirectly activates MAIT cells, predominantly
via production of IL-12p70 and IL-18. The frequency of MAIT
cells and activation by GS-9688 were comparable in PBMCs from HDs
and CHB patients. GS-9620 induced dose-dependent IFN-α, but little
to no IL-12p70 and IL-18 in PBMCs. Consistent with this cytokine
profile, GS-9620 onlyweakly induced intracellular IFN-γ, granzyme B
and TNF-α levels in MAIT cells.
Conclusion: In line with previous studies with prototypic TLR
agonists, GS-9688 –but not GS-9620– strongly induced cytolytic
and non-cytolytic functions of human MAIT cells in vitro. These data
confirm that these innate-like T cells are indirectly activated by TLR8
but not TLR7 agonists, suggesting there are important immunological
differences in the intrahepatic response induced by GS-9688 and
GS-9620.