#3486 CELL-FREE CIRCULATING DNA IN ANCA-ASSOCIATED VASCULITIS – A COMPARISON OF PATIENTS DURING ACTIVE DISEASE AND REMISSION

Abstract

Abstract Background and Aims Patients with ANCA-associated vasculitis (AAV) undergo immunosuppressive treatment to thwart organ failure and avoid relapse. However, the treatment is associated with risk of infections and malignancy. There are currently no reliable biomarkers which can be used in the clinic to assess disease activity. Neutrophil extracellular traps containing nuclear (n) and/or mitochondrial (mt) DNA have been implied in the pathogenesis of AAV. The aim of this study was to explore whether there is a difference in levels of circulating cell-free DNA (cfDNA) amongst AAV patients during active disease and in remission. Method Paired samples from 7 male and 9 female patients with AAV, of which 10 were diagnosed with GPA, were obtained during both active disease and clinical remission as part of an ongoing observational prospective study. Participants’ ages ranged from 21.8 to 80.0 years (median = 64.9), and 11 participants had a history of kidney engagement. After DNA-extraction digital droplet PCR was performed to obtain levels of mtDNA and nDNA. Clinical diagnosis (GPA or MPA), ANCA-positivity, kidney involvement, and Birmingham vasculitis activity score (BVAS) were also assessed. Results There were no significant differences in levels of mtDNA or nDNA in patients with active disease compared to remission; mtDNA (median = 14 520 and 11 985 copies/µL respectively, p = .379) and nDNA (median = 4.45 and 4.70 copies/µL, p = .569). The ratio between mtDNA and nDNA did not differ either (median 2100 and 2400, p = .679). A strong correlation between mtDNA- and nDNA levels (r = .920, p < .001) was found, whereas no correlations were found between cfDNA and age, sex, clinical phenotype, ANCA positivity, kidney engagement or BVAS (Tables 1 and 2). Conclusion This study provides additional information regarding levels of mtDNA and nDNA comparing AAV patients during active disease and in clinical remission. The lack of association with disease activity and the correlation between nDNA and mtDNA may indicate cell damage as a source of cfDNA. To further delineate the contribution of NETs to the levels of cfDNA, and the mechanisms behind cellular injury and inflammation, studies with larger samples with longitudinal follow-up and healthy controls are needed.