Abstract

Background: Janus kinase inhibitors (JAK inhibitors) have expanded therapeutic options for rheumatoid arthritis (RA), although factors associated with treatment response in routine clinical practice remain incompletely defined. Objectives: This study aimed to evaluate clinical, treatment-related and pharmacogenetic factors associated with response to different JAK inhibitors in patients with RA. Methods: An ambispective observational real-world cohort study was conducted in patients with RA treated with tofacitinib, baricitinib, filgotinib, or upadacitinib. Disease activity was assessed at 3 and 6 months using the Disease Activity Score in 28 joints based on C-reactive protein (DAS28-CRP). Clinical response was evaluated according to European Alliance of Associations for Rheumatology (EULAR) response criteria, low disease activity (LDA), and remission thresholds. Clinical, laboratory, and treatment-related variables were collected, and selected single-nucleotide polymorphisms (SNPs) in JAK1, JAK2, and JAK3 genes were genotyped. Bivariate and multivariable analyses were performed to identify variables associated with treatment outcomes. Results: Lower baseline inflammatory burden and lower disease activity were consistently associated with higher probabilities of EULAR response, LDA, and remission across JAK inhibitors. Treatment-related factors were also associated with improved outcomes. Pharmacogenetic associations were heterogeneous and drug-specific, with the most recurrent exploratory signals involving JAK2 variants. However, these genetic findings showed variability across outcomes and time points. Conclusions: In this real-world RA cohort, clinical and treatment-related factors were the most consistent variables associated with response to JAK inhibitors. Pharmacogenetic variation within the JAK pathway, particularly involving JAK2, may contribute to drug-specific variability in response, but these findings should be considered exploratory because of the limited sample size, multiple comparisons, and sparse genotype subgroups. Larger independent studies are required before JAK genotyping can be incorporated into individualized treatment strategies.

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