RNA-Sequencing to Predict Response to TNF-α inhibitors Reveals Possible Mechanism for Non-response in Smokers

<b>Background</b>: Several studies have employed microarray-based profiling to predict response to tumor necrosis factor-alpha inhibitors (TNFi) in rheumatoid arthritis (RA); yet efforts to validate these targets have failed to show predictive abilities acceptable for clinical practice. <b>Methods</b>: The eighty most extreme responders and non-responders to TNFi therapy were selected from the observational BiOCURA cohort. RNA-sequencing was performed on mRNA from peripheral blood mononuclear cells (PBMCs) collected before initiation of treatment. The expression of pathways as well as individual gene transcripts between responders and non-responders was investigated. Promising targets were technically replicated and validated in n=40 new patients using qPCR-assays. <b>Results</b>: Before therapy-initiation, non-responders had lower expression of pathways related to interferon and cytokine signaling, while also showing higher levels of two genes, GPR15 and SEMA6B (p=0.02). The two targets could be validated, however, additional analyses revealed that GPR15 and SEMA6B did not independently predict response, but were rather dose-dependent markers of smoking (p&lt;0.0001). <b>Conclusions</b>: The study did not identify new transcripts ready to use in clinical practice, yet GPR15 and SEMA6B were recognized as candidate explanatory markers for the reduced treatment success in RA smokers.