Objective: A proportion of patients with rheumatoid arthritis (RA) have disease that fails to respond to an initial cycle of rituximab. Using highly sensitive flow cytometry (HSFC), it has been shown that most patients who do not exhibit a response, as measured using the European League Against Rheumatism (EULAR) criteria, have persistent circulating B cell levels at week 2 after initial treatment with rituximab. This study was undertaken to examine whether an additional cycle of rituximab would improve B cell depletion and clinical response in patients whose disease did not respond to the initial cycle.
Methods: Patients with RA (n = 158) were treated with a first cycle of rituximab (2 infusions of 1 gm each). Clinical responses were assessed using EULAR criteria, and patients were categorized as either first-cycle responders or first-cycle nonresponders. Baseline characteristics of first-cycle nonresponders (n = 38) and first-cycle responders (n = 65) with complete data were compared. First-cycle nonresponders (n = 25) were treated with a second cycle of rituximab at least 6 months after the first cycle. HSFC was performed at baseline, immediately prior to the second infusion (week 2), 1 month after the second infusion (week 6), and then every 3 months for each cycle of rituximab. Complete B cell depletion was defined as being <0.0001 x 10(9) cells/liter.
Results: At baseline, the number of preplasma cells was significantly higher in first-cycle nonresponders than in first-cycle responders (P = 0.003). Following the first infusion of the first cycle of rituximab, only 9% of first-cycle nonresponders (3 of 34) exhibited complete depletion of B-lineage cells, compared with 37% of first-cycle responders (22 of 59) (P = 0.007). Following the first infusion of the second cycle of rituximab, 38% of first-cycle nonresponders exhibited complete depletion. Twenty-six weeks after the second cycle, there was a significant improvement in the Disease Activity Score in 28 joints, with 72% of patients exhibiting a EULAR response.
Conclusion: RA patients whose disease did not respond to an initial cycle of rituximab have higher circulating preplasma cell numbers at baseline and incomplete depletion. Our findings indicate that an additional cycle of rituximab administered prior to total B cell repopulation enhances B cell depletion and clinical responses.