Background Rituximab (RTX) is a B-cell depleting antibody widely used to treat rheumatoid arthritis (RA). Responses to RTX are in close correlation with the efficacy of B-cell depletion. Therefore the determination of residual B-cell counts is crucial for the efficacy of treatment.
Objectives Here we wished to assess the efficacy and safety of long-term RTX therapy and study correlations between B-cell depletion, clinical response and autoantibody production.
Methods Seventy-seven patients with active RA received RTX and were re-treated every six months regardless of clinical response. All patients received at least 5 cycles. We assessed DAS28, IgM rheumatoid factor (RF) and ACPA levels at baseline, after 15 days and then every 6 months for 24 months. Absolute CD19+ B-lymphocyte counts were also determined in 50 patients using high-sensitivity flow-cytometry (hsFACS).
Results After 6, 12, 18 and 24 months, 51.6%, 51.9%, 73.3% and 83.8% of patients showed good EULAR responses, respectively. Significant and sustained decreases in IgM RF and anti-CCP levels were observed as early as after 6 months and 12 months, respectively. The baseline mean absolute B-cell number was 0.234 G/l. B-cell numbers significantly dropped after the very first infusion by day 15 (0.104 G/l; p=0.007), which further decreased until 24 months (0.0013 g/l; p<0.001). One RTX infusion resulted in incomplete depletion in 76.7% of patients. B-cell numbers positively correlated with DAS28 (r=0.964; p<0.001), IgM RF (r=0.955; p<0.001) and anti-CCP (r=0.755; p<0.01). No safety issues arose.
Conclusions In RA, clinical response to RTX is associated with the extent of B-cell depletion and with autoantibody production. hsFACS may be a useful method to more accurately assess incomplete B-cell depletion and maybe, as in oncohematology, minimal residual disease.
Disclosure of Interest None Declared