THU0034 IRAK4 INHIBITION SUPPRESSES TLR7, TLR9, AND SLE SERUM-INDUCED IFNα PRODUCTION IN PRIMARY HUMAN PLASMACYTOID DENDRITIC CELLS
Authors: Angie Hammond, Sean S. Parghi, Stacey Drabic, Nathan Wright, Ethan Grant, James Taylor, Matthew R. Warr
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background</h3> A hallmark of lupus is the presence of antinuclear autoantibodies, including those against RNA-protein complexes and double-stranded DNA (dsDNA).<sup>1,2</sup> FcγR-mediated internalization of these nucleic acid:autoantibody immune complexes results in endosomal activation of TLR7 and TLR9, respectively, and the production of IFNα from plasmacytoid dendritic cells (pDC).<sup>3,4</sup> The importance of this pathway is underscored by the majority of SLE patients having a peripheral interferon-stimulated gene (ISG) signature.<sup>5</sup> IRAK4 is a serine/threonine kinase at the top of the signaling cascade downstream of TLRs, including TLR7 and TLR9. As such, inhibition of IRAK4 represents a promising therapeutic target for lupus. <h3>Objectives</h3> To investigate the effect of a highly selective IRAK4 inhibitor on IFNα production from pDCs stimulated with TLR7 and TLR9 agonists, SLE serum, and nucleic acid:autoantibody immune complexes. <h3>Methods</h3> Primary human pDCs were precultured with an IRAK4 inhibitor followed by stimulation for 24 hours. Stimulation agents included TLR7 and TLR9 agonists, human SLE serum, and nucleic acid:autoantibody immune complexes. Culture supernatants were then assessed for secretion of IFNα by MSD. <h3>Results</h3> TLR7 and TLR9 stimulation of pDCs resulted in the secretion of IFNα from pDCs as expected. Treatment with an IRAK4 inhibitor resulted in dose-dependent inhibition of TLR7- and TLR9-induced IFNα with high potency. Human SLE serum was tested to extend findings to physiological SLE-relevant stimuli. Several SLE serum samples, which had positive ELISA titers to the antinuclear antibodies, stimulated production of IFNα in pDCs after 24 hours in culture. No induction of IFNα was observed with healthy volunteer serum samples. Treatment with an IRAK4 inhibitor effectively blocked secretion of IFNα from SLE serum-stimulated pDCs in a dose-dependent manner. Additional antigen (either RNP or dsDNA) was added to SLE samples that yielded titers for autoantibodies but failed to elicit IFNα production. Addition of RNP or dsDNA to anti–RNP and anti–dsDNA-positive SLE sera induced strong IFNα production, and this response was blocked with IRAK4 inhibition. No induction was seen with SLE serum that was negative for both anti–RNP and anti–dsDNA. <h3>Conclusion</h3> This work demonstrates the effects of IRAK4 inhibition on IFNα production in primary pDCs downstream of disease-relevant stimuli and highlights the potential for IRAK4 inhibition as a promising treatment for lupus. <h3>References</h3> [1] Rose T, Dorner T. Best Pract Res Clin Rheumatol. 2017;31:321-333. [2] Zharkova O, et al. Rheumatology. 2017;56:i55-i66. [3] Barrat FJ, et al. J Exp Med. 2005;202(8):1131-1139. [4] Means TK, et al. J Clin Invest. 2005;115(2):407-417. [5] Yao Y, et al. Hum Genomics Proteomics. 2009. 2009(374312):1-16. <h3>Disclosure of Interests</h3> Angie Hammond Grant/research support from: Gilead Sciences, Inc., Employee of: Gilead Sciences, Inc., Sean S. Parghi Grant/research support from: Gilead Sciences, Inc., Employee of: Gilead Sciences, Inc., Stacey Drabic Grant/research support from: Gilead Sciences, Inc., Employee of: Gilead Sciences, Inc., Nathan Wright Shareholder of: Gilead Sciences, Inc., Employee of: Gilead Sciences, Inc., Ethan Grant Shareholder of: Gilead Sciences, Inc., Employee of: Gilead Sciences, Inc., James Taylor Grant/research support from: Gilead Sciences, Inc., Employee of: Gilead Sciences, Inc., Matthew R. Warr Shareholder of: Gilead Sciences, Inc., Employee of: Gilead Sciences, Inc.