High dose versus low dose fludarabine in the treatment of patients with severe refractory rheumatoid arthritis

Objective: Fludarabine, a nucleoside analog that targets both resting and proliferating lymphocytes, is a promising drug for the treatment of autoimmune diseases. We conducted a 2 dose, open label clinical trial to evaluate the toxicity/safety of the fludarabine treatment and its clinical and immunological effects. Methods. Twenty-six patients with severe rheumatoid arthritis (RA) refractory to treatment with at least one slow acting antirheumatic drug were treated with intravenous fludarabine [20 mg/m₂ body surface area (n = 12) or 30 mg/m₂ body surface area (n = 14) per day for 3 consecutive days] given monthly for 6 months. Second line agents with the exception of glucocorticoids were discontinued at least 4 weeks before study entry. Measurements included toxicity and tolerability monitored at monthly intervals; efficacy, by both a 50% reduction in tender or swollen joint count and American College of Rheumatology (ACR) criteria for 20% response; and phenotypic analysis of peripheral blood mononuclear cells and T cell functional assays. Results. Using intention-to-treat analysis, 2 of 12 (17%) patients in the low dose and 7 of 14 (50%) in the high dose groups had 50% or grater reduction in tender and/or swollen joint count after 6 months of therapy compared to baseline (p = 0.09). Two of 12 (17%) on the low dose group and 5 of 14 (36%) in the high dose group met ACR criteria for 20% improvement (p = 0.28). No immediate toxicity was observed. Several infections occurred, including 4 episodes of limited Herpes zoster, which responded to standard therapy. Significant lymphopenia involving T and B cells was observed in all patients. Both naive (CD4+CD45RA+) and memory CD4+ T cells (CD4+CD45RO+) were reduced (naive > memory). No significant regeneration of naive T cells was observed, which may suggest limited thymic regenerative capacity. Fludarabine decreased the proliferative response of peripheral blood lymphocytes to mitogens, as well as the production of T cell (interleukin 2 and interferon-γ) and monocyte derived (tumor necrosis factor-α and Il-10) cytokines. Conclusion. Fludarabine treatment of patients with severe, refractory RA resulted in significant lymphopenia, suppression of lymphocyte function, and clinical improvement in the high dose group. There was no immediate toxicity; however, several infections occurred. Controlled trials are needed to substantiate the clinical improvement observed in this open label trial.