Different response to rituximab in tumor necrosis factor blocker-naive patients with active ankylosing spondylitis and in patients in whom tumor necrosis factor blockers have failed: a twenty-four-week clinical trial

Objective: Histologic studies have shown B cell clusters in the subchondral bone marrow of the spine of patients with ankylosing spondylitis (AS). An immunotherapy targeting B cells in AS is therefore of interest. We undertook this study to examine the efficacy and safety of rituximab in patients with AS refractory to nonsteroidal antiinflammatory drugs in whom previous treatment with tumor necrosis factor alpha (TNFalpha) blockers either had not been tried or had failed.

Methods: In this phase II clinical trial, 1,000 mg rituximab was administered intravenously at baseline and at week 2 in 20 patients with active AS. Ten of these patients had never received TNF blockers, and treatment with TNF blockers had failed in the other 10 patients. The primary end point was a 20% improvement in disease activity at week 24 according to the criteria of the Assessment of SpondyloArthritis international Society (an ASAS20 response).

Results: Seventy-five percent of the patients were male, 90% were HLA-B27 positive, their mean age was 39.7 years, and their mean disease duration was 16.8 years. Patients had active disease, defined as a Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) score >or=4. While there was no clear response at week 24 in the group in whom TNF blockers had failed (30% had achieved an ASAS20 response, 10% had achieved an ASAS40 response, none had achieved partial remission according to the ASAS criteria, and none had achieved 50% improvement on the BASDAI [a BASDAI50 response] beyond an expected placebo response), we observed a good improvement in the TNF blocker-naive group at week 24 (50% had achieved an ASAS20 response, 40% had achieved an ASAS40 response, 30% had achieved partial remission according to the ASAS criteria, and 50% had achieved a BASDAI50 response).

Conclusion: Although rituximab does not seem to be effective in patients with AS that does not respond to TNF blockers, it had significant efficacy in TNF blocker-naive patients. Therefore, further controlled trials with B cell-directed therapies should be performed in TNF blocker-naive AS patients in the future.