Objectives: The inflammatory cytokine interleukin-6 (IL-6) directly stimulates C-reactive protein (CRP) expression. The present study aimed to examine how clinical treatment outcomes of rheumatoid arthritis (RA) with tocilizumab (TCZ), a humanised monoclonal anti-IL-6 receptor antibody, are related to CRP levels monitored for 52 weeks.
Methods: One hundred and twenty-two RA patients who underwent TCZ treatment between May 2008 and September 2009 were registered in the Tsurumai Biologics Communication Registry. Data were collected at initiation of treatment (baseline) and over 52 weeks for Disease Activity Score 28-ESR (DAS28-ESR), Boolean core measurements, serum CRP levels and matrix metalloproteinase-3 levels. To compare clinical results, patients were divided into three groups based on treatment time required to achieve normal CRP levels.
Results: Multivariate analysis using the Cox proportional-hazards regression model found that higher CRP levels at baseline was a significant and independent factor in predicting normal CRP levels over 52 weeks (hazard ratio 0.86 per 1 mg/dL). In contrast, disease duration, concomitant methotrexate use and previous tumour necrosis factor inhibitor failure were not significant factors. Patients with normal CRP levels at 12 weeks of TCZ treatment achieved better clinical outcomes, including remission based on DAS28-ESR criteria, compared to patients with elevated CRP levels at 12 weeks.
Conclusions: Adequate suppression of pathological IL-6 signalling during TCZ treatment improves clinical outcomes and can be monitored with serum CRP levels, a readily available biomarker in clinical practice.