THU0311 IL3R-Alpha as A Novel Therapeutic Target in Systemic Lupus Erythematosus
Authors: S. Oon, H. Huynh, T.Y. Tai, M. Ng, K. Monaghan, M. Biondo, G. Vairo, E. Maraskovsky, A.D. Nash, N.J. Wilson, I.P. Wicks
Journal: Annals of the Rheumatic Diseases (2016)

<h3>Background</h3> Despite currently available therapies, a significant morbidity, and mortality remains in SLE. Major therapeutic targets have been the auto-antibody producing B cell, and more recently, type I IFN, which is produced by pDCs activated via TLR7 and TLR9 stimulation by SLE immune complexes. Alternate ways of reducing type I IFN, such as by modulating pDCs, are now emerging (1, 2). We have developed a novel mAb targeting the IL-3Rα, CSL362, which both depletes IL-3Rα expressing cells, and neutralizes signaling through IL-3. <h3>Objectives</h3> Our objective was to explore the potential utility of CSL362 as a therapeutic in SLE, via its effects on multiple pathogenic cell types and cytokines. <h3>Methods</h3> <i>In vitro</i> studies were undertaken in a heterogenous population of SLE donors, and healthy and autoimmune disease controls, and major findings confirmed <i>in vivo</i> in cynomolgus macaques. The effect of CSL362 on peripheral blood mononuclear cell types was evaluated by flow cytometry, on cytokine production by ELISA or Luminex assays, and on gene expression by qRT-PCR. <h3>Results</h3> CSL362 potently and specifically depleted CD123<sup>hi</sup> pDCs and basophils (average depletion 86.07%±2.07 (SEM), p&lt;0.05, n=72 for pDCs, and 59.39%±3.57, p&lt;0.05, n=71 for basophils). This occurred mainly through antibody-dependent cell-mediated cytotoxicity, although neutralization of IL-3 alone with the Fab fragment of CSL362 resulted in pDC, but not basophil, depletion at higher doses. Through pDC depletion, TLR7-, TLR9- and SLE serum- stimulated IFNα production, and IFN-inducible gene expression was markedly reduced (average reduction in TLR9-stimulated IFNα production 99.36%±0.39, p&lt;0.05, n=29). Additionally, TLR7- and TLR9-induced plasmablast expansion was inhibited by CSL362. This depended upon depletion of pDCs by CSL362, which decreased not only IFNα, but IL-6, production that was required for plasmablast expansion. Importantly, we found that IFN-inducible gene expression and plasmablast expansion were more effectively inhibited by CSL362 than by IFNα blocking mAbs. This may be because pDC depletion by CSL362 reduced production of cytokines other than IFNα, such as IL-6, and interferon types other than type I. Indeed, CSL362 reduced production of type III IFN, a cytokine which has been postulated as a cause of ongoing disease activity despite type I IFN blockade (3). Administration of a single subcutaneous dose of CSL362 to cynomolgus macaques confirmed pDC and basophil depletion, correlating with a decrease in IFN-inducible gene expression, that lasted several weeks post dose, with no major adverse events observed. <h3>Conclusions</h3> The unique ability of CSL362 to affect the major pathogenic targets of type I IFN and the B cell, and newer targets such as the basophil (4), IL-3 (5) and type III IFN, presents a strong rationale for its therapeutic evaluation in SLE. <h3>References</h3> Pellerin A et al, EMBO Mol Med, 2015;7:464–476 Zhan Y et al, Arthritis Rheumatol, 2015;67:797–808 Amezcua-Guerra LM et al, Rheumatology (Oxford), 2015;54:203–205 Charles N et al, Nat Med, 2010;16:701–707 Renner K et al, Kidney Int, 2015;88:1088–1098 <h3>Disclosure of Interest</h3> S. Oon Grant/research support from: CSL Limited, H. Huynh Employee of: CSL Limited, T. Y. Tai Employee of: CSL Limited, M. Ng Employee of: CSL Limited, K. Monaghan Shareholder of: CSL Limited, Employee of: CSL Limited, M. Biondo Employee of: CSL Limited, G. Vairo Shareholder of: CSL Limited, Employee of: CSL Limited, E. Maraskovsky Shareholder of: CSL Limited, Employee of: CSL Limited, A. Nash Shareholder of: CSL Limited, Employee of: CSL Limited, N. Wilson Shareholder of: CSL Limited, Employee of: CSL Limited, I. Wicks Grant/research support from: CSL Limited