Background/Purpose: Human plasmacytoid dendritic cells (pDCs) have been implicated in the pathogenesis of Systemic Sclerosis (SSc) through their ability to infiltrate the skin and secrete interferons (IFN), interleukin-6 (IL-6) and other proinflammatory chemokines directly, or through type-I IFN response of resident cells. Blood dendritic cell antigen 2 (BDCA-2) is a human-specific pDC-type II C-type lectin that potently inhibits IFN secretion. Here we determined the effects of CBS004, a novel monoclonal antibody against BDCA-2, on Toll-like receptor (TLR)-induced transcriptome and IFN secretion in pDCs from healthy volunteers (HV) or patients with SSc in vitro, and developed a xeno-transplant mouse model of human pDC activation.

Methods:

Peripheral blood mononuclear cells (PBMCs) were collected from 16 SSc patients and 12 HV. IFN and CXCL-4 secretion were evaluated by ELISA. TLR7-9 stimulation was induced by Imiquimod or CpG-oligodeoxynucleotides. pDCs were isolated by magnetic cell sorting. Full transcriptome was analysed by RNA-sequencing. For the xeno-transplant model, NOD/SCID mice were injected in the tail vein with 25×10⁴human pDCs, 12 h after topical application of Imiquimod with or without intra-peritoneal (IP) injection of CBS004 (5 mg/kg). Harvested skin was analysed by FACS for human pDC infiltration and by real-time PCR using a mouse type-I IFN response array (Qiagen).

Results:

PBMCs from SSc patients spontaneously produced higher levels of IFN-I and CXCL-4 compared to HV ex vivo (206.7±23.4 vs. 43.4±6.8 pg/ml, P<0.0001 and 216.6±36.6 vs 8.6±0.3 ng/ml, P<0.05, respectively). CBS004 significantly inhibited basal levels of IFN-I in 83% of SSc samples. TLR7 or 9 stimulation showed only modest induction of CXCL-4 in both HV and SSc PBMC. TLR9 stimulation of SSc PBMCs induced >30-fold increase in IFN-I secretion (7167±4377 pg/ml), which was completely abrogated by treatment with CBS004 (209±40.5 pg/ml, P<0.001). RNA-seq analysis of human pDCs (Lineage^–HLA-DR⁺CD123⁺CD304⁺) stimulated with TLR-9 agonist revealed 168 Differentially Expressed Genes (DEGs, FDR <1%) mapping to IFN, JAK/STAT, IL-6, NF-kB and angiogenesis pathways. Pre-treatment with CBS004 prevented upregulation of most DEGs, which drove an expression profile similar to non-stimulated pDCs.

In the xeno-transplant model, Tail vein injection of pDC in resulted in detection of human CD123⁺CD304⁺cells in the skin (0.3%) with at least 2-fold upregulation of 35/74 mouse type-I IFN response genes including Ccl2, 4, 5 and Cxcl10, Ifit1, 2 and 3, Mx1 and 2, Oas1, Tlr7, 8 and 9 compared to imiquimod treatment alone (P<0.005). Mice receiving IP injection of CBS004 had a 3-fold reduction in infiltrating pDCs (0.1%) and suppression of 85% of the type-I IFN response genes upregulated by pDC injection and Imiquimod treatment (Anova P<0.01).

Conclusion:

Our study demonstrates that pDCs from SSc patients are in active status in the blood and can be functionally inhibited by BDCA-2 targeting with CBS004 mAb. Further, we show for the first time that TLR stimulation and BDCA-2 inhibitory effects go beyond IFN secretion including proinflammatory and proangiogenic response and we develop a novel xeno-transplant mouse model for studying human pDC function in vivo.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/cbs004-a-novel-monoclonal-antibody-against-bdca-2-inhibits-tlr-induced-activation-of-human-pdc-in-vitro-and-in-vivo-a-novel-therapeutic-target-for-systemic-sclerosis/