Gene Expression Profiling in PBMCs as a Tool for Prediction of Infliximab Responsiveness in Rheumatoid Arthritis

The objective of the study is to identify and validate predictive markers of infliximab responsiveness in RA patients by 2 approaches: i) measuring biochemical, immunological and bone markers in sera because of their involvement in pathogenic mechanisms; ii) identifying gene-expression signatures in PBMCs by the transcriptomic analysis. Patients with active RA (ACR criteria) were given i.v. 3 mg/kg infliximab associated with metotrexate at weeks 0, 2, 6, and every 8th week. Infliximab efficacy was evaluated at week 14, using the EULAR response criteria. 1. Just before the starting of infliximab treatment, the following parameters were measured in the sera: i) immunological tests: rheumatoid factor (IgA, IgG, IgM), anti-CCP, autoAb recognizing the 27 C-terminal fragment (ACAST-C27) and domain I (ACAST-DI) of calpastatin, anti-G6PI, anti a-enolase, anti-keratin and anti-perinuclear factor; ii) biochemical markers: CRP, MMP-1, MMP-3, TIMP-1, TIMP-2; markers of bone resorption: pyridinolin, deoxypyridinolin, osteoprotegerin, sRANKL, COMP. The predictive value of each parameter for a response/non-response to infliximab was analysed using Fischer's exact, Mann-Whitney and Chi2 tests. 2. A blood sample was collected just before the onset of infliximab treatment and total RNAs were extracted from the peripheral blood mononuclear cells. The \[33P\] radiolabeled mRNAs were hybridized (duplicate or triplicate) over a set of 10.000 human cDNA probes spotted at a high density on nylon membranes. Data were normalized and filtered to allow the comparison between RNA samples. Statistical analyses were performed with the R software and hierarchical clustering was performed with the Cluster and Tree View softwares.