AB0337 Blood b cell counts as predictor of early clinical response after rituximab in patients with rheumatoid arthritis

Background B cell depletion with rituximab is effective for reducing the symptoms and inhibiting the progression of joint damage in patients with rheumatoid arthritis (RA). However, the use of peripheral B cell counts as a predictive factor of clinical response is limited. Objectives We aimed to investigate the potential value of measurement of peripheral blood B cell counts after rituximab therapy in patients with active RA refractory to anti-tumor necrosis factor inhibitors. Methods A total of twenty-seven RA patients whom received more than 1 cycle (two 1-gram infusion) of rituximab were included in this study. Absolute B cell counts on day 1 and 15 before each rituximab infusion was measured by conventional flow cytometry. On day 15, peripheral B cell levels below 2.5 X 106 cells/liter was defined as B cell depletion and the clinical response was analyzed between the 2 groups; depletion vs. non-depletion. Clinical response at 18 weeks after 1st infusion of rituximab was measured by Disease Activity Score in 28 joints (DAS28) using the erythrocyte sedimentation rate. The analysis of B cell depletion with regard to DAS28 and continuous variables were performed using Mann-Whitney test. Results The mean age at rituximab treatment was 55 ± 13.8 (25-83) years and the baseline DAS28 was 6.6 ± 0.9 (4.4-8.1). The positive rate of RF and ACPA was 90% (27/30) and 72.2% (13/18), respectively. B cells on day 15 was depleted in 17 (56.7%) patients with median value of B cell counts as 1.2 X 106 cells/liter [range 0.0∼2.5 X 106/liter]). Patients in whom B cell depletion was not achieved showed persistently high DAS28 (4.7 ± 0.6 versus 3.3 ± 1.0 [p = 0.007]) by 18 weeks and significant short duration of B cell depletion time (4.0 ± 2.3 versus 8.2 ± 4.3, months [p = 0.008]) than those in depletions. Conclusions Data derived from B cell depletion with rituximab in active RA patients suggest that measurement of peripheral B cell counts on 15th day might provide clinical information on early response and non-depletion of B cells can be used as a predictive factor of poor response. References Efficacy of B-cell-targeted therapy with rituximab in patients with rheumatoid arthritis. NEJM (2004) 350(25). 2572-81 Disclosure of Interest None Declared