Chemokines in rheumatic diseases: pathogenic role and therapeutic implications

Chemokines, small pro-inflammatory chemoattractant cytokines that bind to specific G-protein-coupled seven-span transmembrane receptors, are major regulators of cell trafficking and adhesion. The chemokine CXCL12 (also called stromal-derived factor-1) is an important α-chemokine that binds primarily to its cognate receptor CXCR4 and thus regulates the trafficking of normal and malignant cells. For many years, it was believed that CXCR4 was the only receptor for CXCL12. Yet, recent work has demonstrated that CXCL12 also binds to another seven-transmembrane span receptor called CXCR7. Our group and others have established critical roles for CXCR4 and CXCR7 on mediating tumor metastasis in several types of cancers, in addition to their contributions as biomarkers of tumor behavior as well as potential therapeutic targets. Here, we review the current concepts regarding the role of CXCL12 / CXCR4 / CXCR7 axis activation, which regulates the pattern of tumor growth and metastatic spread to organs expressing high levels of CXCL12 to develop secondary tumors. We also summarize recent therapeutic approaches to target these receptors and/or their ligands.

Alternative C activation is involved in the pathogenesis of ANCA-associated vasculitis. However, glucocorticoids used as treatment contribute to the morbidity and mortality of vasculitis. We determined whether avacopan (CCX168), an orally administered, selective C5a receptor inhibitor, could replace oral glucocorticoids without compromising efficacy. In this randomized, placebo-controlled trial, adults with newly diagnosed or relapsing vasculitis received placebo plus prednisone starting at 60 mg daily (control group), avacopan (30 mg, twice daily) plus reduced-dose prednisone (20 mg daily), or avacopan (30 mg, twice daily) without prednisone. All patients received cyclophosphamide or rituximab. The primary efficacy measure was the proportion of patients achieving a ≥50% reduction in Birmingham Vasculitis Activity Score by week 12 and no worsening in any body system. We enrolled 67 patients, 23 in the control and 22 in each of the avacopan groups. Clinical response at week 12 was achieved in 14 of 20 (70.0%) control patients, 19 of 22 (86.4%) patients in the avacopan plus reduced-dose prednisone group (difference from control 16.4%; two-sided 90% confidence limit, −4.3% to 37.1%; P =0.002 for noninferiority), and 17 of 21 (81.0%) patients in the avacopan without prednisone group (difference from control 11.0%; two-sided 90% confidence limit, −11.0% to 32.9%; P =0.01 for noninferiority). Adverse events occurred in 21 of 23 (91%) control patients, 19 of 22 (86%) patients in the avacopan plus reduced-dose prednisone group, and 21 of 22 (96%) patients in the avacopan without prednisone group. In conclusion, C5a receptor inhibition with avacopan was effective in replacing high-dose glucocorticoids in treating vasculitis.

Plasmacytoid dendritic cells have been implicated in the pathogenesis of systemic sclerosis through mechanisms beyond the previously suggested production of type I interferon. We isolated plasmacytoid dendritic cells from healthy persons and from patients with systemic sclerosis who had distinct clinical phenotypes. We then performed proteome-wide analysis and validated these observations in five large cohorts of patients with systemic sclerosis. Next, we compared the results with those in patients with systemic lupus erythematosus, ankylosing spondylitis, and hepatic fibrosis. We correlated plasma levels of CXCL4 protein with features of systemic sclerosis and studied the direct effects of CXCL4 in vitro and in vivo. Proteome-wide analysis and validation showed that CXCL4 is the predominant protein secreted by plasmacytoid dendritic cells in systemic sclerosis, both in circulation and in skin. The mean (±SD) level of CXCL4 in patients with systemic sclerosis was 25,624±2652 pg per milliliter, which was significantly higher than the level in controls (92.5±77.9 pg per milliliter) and than the level in patients with systemic lupus erythematosus (1346±1011 pg per milliliter), ankylosing spondylitis (1368±1162 pg per milliliter), or liver fibrosis (1668±1263 pg per milliliter). CXCL4 levels correlated with skin and lung fibrosis and with pulmonary arterial hypertension. Among chemokines, only CXCL4 predicted the risk and progression of systemic sclerosis. In vitro, CXCL4 down-regulated expression of transcription factor FLI1, induced markers of endothelial-cell activation, and potentiated responses of toll-like receptors. In vivo, CXCL4 induced the influx of inflammatory cells and skin transcriptome changes, as in systemic sclerosis. Levels of CXCL4 were elevated in patients with systemic sclerosis and correlated with the presence and progression of complications, such as lung fibrosis and pulmonary arterial hypertension. (Funded by the Dutch Arthritis Association and others.).