Researchers Validate REPS Assay to Predict TNFi Response in Patients With RA

An assay termed the “reversal of PTPN22 gene signature” (REPS) predicted response to etanercept and adalimumab in patients with rheumatoid arthritis (RA), according to study results published in Arthritis & Rheumatology.

The study included 39 patients who were enrolled in an ongoing trial (TARGET) who had RA and inadequate responses to methotrexate (MTX). Investigators randomly assigned patients to either 40 mg adalimumab every 2 weeks (n=18) or weekly 50 mg etanercept (n=21) in addition to baseline treatment with MTX.

The researchers used change in Clinical Disease Activity Index (CDAI) from baseline to week 12 to assess treatment response. They defined response as a decrease of CDAI ≥12 U in patients with a baseline CDAI >22 U or a decrease of CDAI ≥6 U in patients with baseline CDAI of 10 U to 22 U. According to these criteria, they found a total of 17 responders in the etanercept arm vs 11 in the adalimumab group.

The investigators obtained peripheral blood mononuclear cells (PBMCs) from each patient before initiation of the assigned treatments. They stimulated these cells with anti-cluster of differentiation (CD) 3 for 24 hours in the presence of the assigned TNF inhibitors (TNFis) and used quantitative polymerase chain reaction to quantity the level of PTPN22 in stimulated PBMCs, which was normalized against actin.

The mean fold-change by the therapies, when analyzed together, was significantly higher in patients classified as TNFi responders vs nonresponders (1.36 vs 1.04, respectively; P =.0094). According to the analysis, the area under the receiver operating characteristic curve was 0.75 (95% CI, 0.57-0.92); P =.02, which the researchers said was comparable with other published predictors of TNFi response. The difference in the fold change in PTPN22 between patients classified as responders vs nonresponders was largely driven by the etanercept arm.

Limitations of this study included its small sample size as well as the reported suboptimal quality of the PBMCs.

The investigators concluded that “the REPS assay is the first in vitro test that can assess dynamic interactions between drugs and blood cells” and can possibly “be used to simultaneously test multiple drugs” while offering “the potential to predict response in a drug-specific manner.”

Reference

Ho CH, Silva AA, Giles JT, et al. Validation of a bioassay for predicting response to TNFα inhibitors in rheumatoid arthritis. Arthritis Rheumatol. Published online January 10, 2021. doi: 10.1002/art.41645