Rituximab levels are associated with the B cell homeostasis but not with the clinical response in patients with rheumatoid arthritis

OBJECTIVE: To study the levels of rituximab (RTX) and anti-RTX antibodies (ARAs) in patients with rheumatoid arthritis (RA) at 30, 90, and 180 days after the first infusion, in relation to clinical and serological parameters and B cell homeostasis. METHODS: Thirty-four patients with RA who failed to respond to anti-tumor necrosis factor therapy received RTX. At baseline, 4, 12, and 24 weeks after the first infusion of RTX, we performed a clinical assessment and determined the levels of RTX, ARAs, B cells, rheumatoid factors, anti-cyclic citrullinated peptide antibodies, immunoglobulins, and complements. RESULTS: RTX levels varied widely among patients. No ARAs were detected during the follow-up. Patients with lower levels of RTX presented with higher decreases in erythrocyte sedimentation rate, immunoglobulins, and complement 6 months after the first infusion. Patients with higher levels of RTX showed a higher B cell depletion at 90 days but an earlier B cell recovery than those with lower levels of RTX. No differences in clinical response were observed between the two groups at 6 months after starting the treatment. CONCLUSION: Our findings suggest that RTX levels in the serum of patients with RA are related to B cell homeostasis and the severity of immunological parameters but not to the clinical response at 6 months.