OP0041 JNJ-473 Potently and Specifically Depletes PDCS In SLE Patient Blood In Vitro and Ablates TLR9-Induced Interferon Alpha Responses

Background Plasmacytoid dendritic cells (pDCs) are potent producers of IFNα and are thought to have a pathogenic role in Systemic Lupus Erythematosus (SLE). JNJ-473, previously known as CSL362, is an Fc engineered, neutralising anti-IL-3Rα (CD123) monoclonal antibody that depletes CD123 expressing cells, such as pDCs. CSL362 has recently completed a phase I clinical trial in acute myeloid leukemia. Objectives To investigate the in vitro depletion of pDCs with JNJ-473 in SLE patient blood and evaluate novel biomarkers of JNJ-473 efficacy. Methods Blood samples from 34 SLE patients (31 female and 3 male; mean age = 44.5; mean SLEDAI = 4, range 0–21) and 34 healthy controls (HC), matched for age and gender, were obtained. Whole blood (WB) was analysed by flow cytometry (FACS) for absolute cell counts of various cell subsets (pDC, myeloid DC, basophils, monocytes, T-cell subsets, B-cell subsets, neutrophils, eosinophils and natural killer (NK) cells) and for CD123 expression. Peripheral blood mononuclear cells (PBMC) from SLE patients and HC were cultured with JNJ-473 (0, 0.0041, 0.0123 or 1 μg/ml) for 20 h and depletion of cell subsets analysed by FACS. Serum was assayed for 117 analytes by Luminex and RNA was extracted for RNAseq. PBMC from 9 SLE patients and 9 HC were cultured with 1 μg/ml JNJ-473 or isotype control for 20 h before stimulation with 0.5 μM CpG for 24 h and culture supernatant analysed by Luminex for 87 analytes. Results pDCs expressed the highest level of CD123 and SLE patients had significantly higher CD123 expression than HC (49325 vs 44152 receptors per cell). JNJ-473 induced potent and specific in vitro depletion of pDCs via NK cell mediated ADCC in PBMC from SLE patients (mean 85.80% depleted) and HC (mean 93.79% depleted). Basophils, which also express high levels of CD123, were partially depleted in SLE (mean 33.07% depleted) and HC (mean 66.64% depleted). NK cells were functional as demonstrated by up-regulation of the degranulation marker CD107a, and down-regulation of CD16 after JNJ-473 treatment and by effective depletion of pDCs. In SLE sera, 27 analytes were significantly increased compared to HC, including IFN inducible proteins IP-10 and ITAC. RNAseq analysis showed that SLE patient samples had 605 up-regulated and 498 down-regulated transcripts when compared to HC. These included many secreted proteins, some of which (IP-10, ITAC, IGFBP2, MCP-2 and BAFF) were upregulated at both the RNA and protein level in SLE. Depletion of pDCs with JNJ-473 prevented TLR9 agonist (CpG)-induced production of IFNα and other proteins including IP-10, ITAC and MCP-2. Conclusions JNJ-473 potently and specifically depletes SLE patient peripheral blood pDCs in vitro . JNJ-473–mediated depletion of pDCs resulted in reduced TLR9-induced IFNα and IFN-regulated protein production. These JNJ-473 modulated proteins were significantly elevated at both the protein and RNA level in our SLE patient cohort. These findings suggest JNJ-473 could effectively deplete pDCs and inhibit TLR9-induced proteins in SLE. Disclosure of Interest K. Monaghan Shareholder of: CSL limited, Employee of: CSL limited, T. Tai Employee of: CSL limited, J. Benson Shareholder of: Janssen, Employee of: Janssen, B. Linggi Employee of: Janssen, S. Oon Grant/research support from: CSL Limited, M. Ng Employee of: CSL Limited, A. Hoi Grant/research support from: CSL Limited, E. Morand Grant/research support from: CSL Limited, N. Wilson Shareholder of: CSL limited, Employee of: CSL limited