Objective: Rituximab displays therapeutic benefits in the treatment of rheumatoid arthritis (RA) patients resistant to TNF blockade. However, the precise role of B cells in the pathogenesis of RA is still unknown. In this study we investigated the global molecular effects of rituximab in synovial biopsies obtained from anti-TNF resistant RA patients before and after administration of the drug.
Methods: Paired synovial biopsies were obtained from the affected knee of anti-TNF resistant RA patients before (T0) and 12 weeks after initiation of rituximab therapy (T12). Total RNA was extracted, labeled according to standard Affymetrix procedures and hybridized on GeneChip HGU133 Plus 2.0 slides. Immunohistochemistry and quantitative real-time PCR experiments were performed to confirm the differential expression of selected transcripts.
Results: According to paired Student’s t-tests, 549 out of 54,675 investigated probe sets were differentially expressed between T0 and T12. Pathway analysis revealed that genes down-regulated between T0 and T12 were significantly enriched in immunoglobulin genes, and genes involved in chemotaxis, leucocyte activation and immune responses (Gene Ontology annotations). By contrast, genes up-regulated between T0 and T12 were significantly enriched in transcripts involved in cell development (Gene Ontology annotation) and wound healing (GSEA). At baseline, higher synovial expression of immunoglobulin genes was associated with response to therapy.
Conclusion: Rituximab displays unique effects on global gene expression profiles in synovial tissue of RA patients. These observations open new perspectives in the understanding of the biological effects of the drug and in the selection of patients likely to benefit from this therapy.
Overall design: Twenty patients with RA (17 women and 3 men, average age +/- SEM: 52,6+/-3,8 years) were included in the study. All patients met the American College of Rheumatology classification criteria for the diagnosis of RA. All patients had active disease at the time of tissue sampling and were resistant to TNF blockade. They all had erosive changes imaged on conventional x-rays of the hands and/or feet. All of them had a swollen knee at inclusion. Rituximab therapy was administrated at a dose of 1,000 mg IV at baseline (T0) and at week 2, together with 125 mg IV Methylprednisolone. Clinical parameters at baseline (T0) and 12 weeks after the initiation of therapy (T12) was evaluated using DAS(28)-CRP scores and clinical responses were assessed using EULAR response criteria. Synovial biopsies were obtained by needle-arthroscopy of an affected knee from all patients at T0 and T12. For each procedure, 4 to 8 synovial samples were kept overnight at 4°C in a RNA stabilizing solution (RNALater, Ambion, Applied Biosystems, TX, USA) and then stored at –80°C for later RNA extraction. The same amount of tissue was snap-frozen in liquid nitrogen and kept at –80°C for immunostaining experiments on frozen sections. The remaining material was fixed in 10% formaldehyde and paraffin embedded for conventional optical evaluation and immunostaining of selected markers. All the experiments (RNA extraction, histology, immunohistochemistry) were performed on at least 4 biopsies harvested during every procedure in order to correct for variations related to the potential heterogeneous distribution of synovial inflammation. The study was approved by the ethics committee of the Université catholique de Louvain and informed consent was obtained from all patients.
At least 1 µg total RNA could be extracted from 12 paired samples at T0 and T12 for further processing.
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