Background Tumor necrosis alpha (TNF) blockade has been a highly successful therapeutical approach in the management of Rheumatoid Arthritis (RA). However, ∼33% of RA patients do not respond adequately to this treatment. To date, there is insufficient knowledge on the biological mechanisms that prevent an adequate clinical response when using anti-TNF agents.
Objectives We have performed a microarray gene expression analysis on synovial biopsies to identify key genes and pathways associated with the lack of response to anti-TNF therapies. We also performed immunohistochemistry in order to confirm mRNA expression data.
Methods Synovial biopsies from n=11 RA patients were obtained during active inflammation, before the initiation of an anti-TNF therapy. Samples from pathological tissue were obtained by guided arthroscopy and preserved for RNA and histological examination. RNA was extracted from all samples and analyzed using Illumina WG-6 v3.0 expression BeadChip, containing probes for the analysis of 48,000 transcripts. Gene expression data normalization and statistical analysis was performed using the Bioconductor statistical software tools. EULAR response was measured after 5 months of anti-TNF treatment. Quantification of PIK3-delta (PIK3CD) in synovial biopsies was performed using Digital Image Analysis.
Results After 5 months of therapy, 8 patients achieved an EULAR moderate or good response and 3 patients were categorized as none responders. Table 1 shows the main clinical features of the patient cohort. Differential gene expression between both groups revealed several genes significantly associated with anti-TNF response. Pathway analysis revealed an elevated expression of genes associated with CD14+ monocyte profiles in the synovial tissue of non-responder patients (P<0.05, FDR correction for multiple tests). The most significant gene having >1.5 fold change difference between the two groups was PIK3CD (P < 1x10-12), a gene recently identified as a key regulator of synoviocyte function in RA. The differential expression of PIK3CD and other highly significant genes was confirmed by RealTime-PCR. Histological analysis of synovial samples demonstrated a significant reduction in PIK3CD expression in responders (P=0.036 PIK3CD/mm2) as well as a significant reduction in CD68 expressing cells in the synovial lining (P=0.027) after 5 months of anti-TNF therapy.
Conclusions This study is in line with previous investigations that PIK3CD is crucial for RA pathophysiology. We have found, for the first time, an association of this gene with the response to anti-TNF therapy in RA.
Acknowledgements Patent pending.
Disclosure of Interest None Declared