Recent clinical trials suggest that etanercept is ineffective in controlling Sjögren's syndrome (SS). To address the hypothesis that tumor necrosis factor blockade can result in increased levels of interferon-alpha (IFNalpha) and BAFF, we quantified those mediators in plasma from etanercept- and placebo-treated SS patients.
We studied plasma samples from 20 patients with SS treated with etanercept (25 mg twice weekly) or placebo in a 12-week, randomized, double-blind clinical trial. In addition, we studied plasma samples from 29 healthy controls. IFNalpha activity was determined by reporter cell assay, and BAFF levels were determined by enzyme-linked immunosorbent assay.
Baseline IFNalpha plasma activity and BAFF levels were increased in SS patients compared with healthy controls (mean +/- SD IFNalpha plasma activity score 4.43 +/- 2.60 versus 2.08 +/- 0.91; P < 0.0001) (mean +/- SD BAFF level 0.83 +/- 0.27 ng/ml versus 0.60 +/- 0.15 ng/ml; P = 0.008). A significant increase in IFNalpha activity was detected after 12 weeks of treatment in the etanercept group, but not in the placebo group (P = 0.04 and P = 0.58, respectively). Furthermore, a statistically significant increase in BAFF levels was noted in patients receiving etanercept, but not in those receiving placebo (P = 0.01 and P = 0.56, respectively). In vitro culture of control peripheral blood mononuclear cells with etanercept resulted in a dose-dependent increase in the expression of IFNalpha and the IFNalpha-inducible genes IFN-induced protein with tetratricopeptide repeats 1 and BAFF.
IFNalpha activity and BAFF levels are elevated in the plasma of patients with SS compared with healthy controls. Etanercept treatment exacerbates IFNalpha and BAFF overexpression, providing a possible explanation for the lack of efficacy of this agent in SS.