Session Type: Abstract Submissions (ACR)
Plasmacytoid dendritic cells (pDCs) contribute to systemic lupus erythematosus (SLE) pathogenesis by producing Type 1 interferon (IFN), most likely induced by endosomal Toll like receptor (TLR) activation by immune complexes. In healthy donors, pDCs are known to express high levels of CD123, the IL3 receptor alpha chain. CSL362 is a novel monoclonal antibody (mAb) that binds to CD123, neutralizing IL3 signaling and causing antibody dependent cell mediated cytotoxicity (ADCC) of CD123 bearing cells. This study of SLE and healthy donors evaluates – 1) CD123 expression on pDCs and other cell types, 2) CSL362 mediated depletion of pDCs, and 3) the effect of CSL362 on IFNα production and IFNα-inducible gene expression from peripheral blood mononuclear cells (PBMCs) in vitro.
Quantitative flow cytometry with Quantibrite PE beads and an anti-CD123-PE antibody was used to assess CD123 expression on cell types from peripheral blood of SLE and healthy donors (n=15). PBMCs from SLE (n=13) and healthy (n=10) donors were isolated by Ficoll gradient centrifugation and incubated for 24 hours in vitro with CSL362, the Fab portion of CSL362 (Fab’, which neutralizes IL3 signaling, but does not effect ADCC), or an isotype control mAb. The percentage of viable pDCs was enumerated by flow cytometry. PBMCs from SLE (n=7) and healthy (n=6) donors were pretreated with CSL362, Fab’ or isotype control mAb for 24 hours, then stimulated with CpG, a TLR9 agonist, for 18 hours. IFNα production from culture supernatant was assessed by ELISA. A novel ‘IFN gene score’, based on 11 IFNα-inducible genes, was incorporated into a customized gene array, to serve as a ‘gene signature’ to stratify patients and assess drug efficacy. This score was evaluated by performing quantitative PCR on RNA extracted from SLE (n=17) and healthy (n=9) donor whole blood. The average of the log2 fold change for the 11 genes in the SLE patients was compared to healthy donors. This score was also evaluated in PBMCs (n=2 SLE, n=2 healthy) after CSL362 pretreatment followed by CpG stimulation. The average of the log2 fold change for the 11 genes of the treated samples was compared to the untreated samples.
CD123 expression levels were highest on pDCs compared to other cell types. pDCs were depleted after in vitro culture with CSL362 (8.3 ± 2.4% [mean ± SEM], p < 0.0001) compared to isotype control but were not depleted by Fab’ (96.8 ± 5.5%, p = 0.17) . In addition, CpG-induced IFNα production from PBMC was inhibited by CSL362 pretreatment (1.1 ± 0.8%, p < 0.0001) compared to isotype control, but was not inhibited by pretreatment with Fab’ (122.3 ± 27.7%, p = 0.78). The IFN gene score was elevated in SLE (3.31 ± 0.46) compared to healthy (1.49 ± 1.1, p = 0.07) donors. CpG-induced upregulation of the IFN gene score (3.9 ± 0.9) was reduced by pretreatment of PBMC with CSL362 (-0.9 ± 1.9, p = 0.12).
A mAb targeting CD123 (CSL362) depletes pDCs and decreases CpG-induced IFNα production and IFNα-inducible gene expression from SLE and healthy donor PBMCs. These effects were not seen with IL3 blockade alone or isotype control mAb. Cytoreductive therapy with CSL362 may therefore represent a novel treatment strategy in SLE.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/an-anti-cd123-monoclonal-antibody-csl362-depletes-plasmacytoid-dendritic-cells-and-inhibits-cpg-upregulated-ifn%ce%b1-production-and-ifn%ce%b1-inducible-gene-expression-in-peripheral-blood-mono/