Background/Purpose: Endogenous DNA derived from nuclei is released into the blood circulation as cell-free DNA (cfDNA) following cell damage or death. cfDNA is associated with various pathological conditions. In patients with rheumatoid arthritis (RA), cfDNA levels in peripheral blood and synovial fluid are increased. In addition, cfDNA induces joint inflammation via Toll-like receptor 9 (TLR9) pathways both in vitro (Dong C, et al. Front Immunol 2020) and in vivo (Liang H, et al. Nat Commun 2018). We have previously reported that the amounts of cfDNA released from synovial cells in RA are significantly suppressed with tocilizumab treatment in vitro, although they remain unchanged with etanercept (Hashimoto N, et al. ACR 2016 Annual Meeting). This study aimed to evaluate the clinical significance of cfDNA in RA treated with biological disease-modifying antirheumatic drugs (bDMARDs), specifically tocilizumab and tumor necrosis factor inhibitor (TNF-I).

Methods: We enrolled 126 patients with RA who initiated treatment with bDMARDs, including 72 with tocilizumab and 54 with TNF-I (10 with etanercept, 7 with adalimumab, 22 with certolizumab pegol, and 15 with golimumab). Plasma cfDNA levels were measured at baseline, week 4, and week 12 using quantitative polymerase chain reaction (qPCR) assays. Disease activity was also evaluated at the same timepoint, using the disease activity score 28 erythrocyte sedimentation rate (DAS28ESR).

Results: The DAS28ESR at baseline was not different between those who received tocilizumab and TNF-I (median [interquartile range, IQR]: 5.22 [4.35–6.49] and 4.91 [3.92–5.79], respectively), and it was significantly improved in both biological groups at week 12 (median [IQR]: 2.86 [1.82–4.01] and 3.34 [2.74–3.67], respectively). However, cfDNA levels in plasma were significantly decreased with tocilizumab at week 12, but not with TNF-I (Figure. 1). In particular, in the biological treatment-naïve patients with tocilizumab at week 12, cfDNA levels were significantly lower in patients with DAS28ESR remission than those in others (median [IQR]: 3.37 ng/mL [2.69–7.59] and 9.18 ng/mL [5.22–20.6], p< 0.05, respectively) (Figure.2a) and correlated with the DAS28ESR (r=0.47, p< 0.05) (Figure.2b). Meanwhile, there was no difference between remission and others in the biological treatment-naïve patients with TNF-I (median [IQR]: 8.49 ng/mL [7.03–16.4] and 11.2 ng/mL [7.50–18.1], p=0.26, respectively), with no association with the DAS28ESR (r=0.15, p=0.42).

Conclusion: Tocilizumab reduced cfDNA levels in patients with RA, like that in the in vitro study. Plasma cfDNA is a possible biomarker for tocilizumab therapy in biological treatment-naïve patients. In addition, tocilizumab may suppress inflammation via the TLR9 pathway by decreasing cfDNA levels.

Figure.1 cfDNA levels at baseline and week 12 with tocilizumab therapy (a) and with TNF-I (b)

Figure 2. cfDNA levels and DASESR in the biological treatment-naïve patients with tocilizumab therapy. (a) cfDNA levels in DAS28ESR remission patients and others at week 12. (b) Correlation between cfDNA and DAS28ESR at week 12

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/plasma-cell-free-dna-is-a-useful-biomarker-for-tocilizumab-therapy-in-rheumatoid-arthritis/