Background Increased expression of B cell activating factor (BAFF or B lymphocyte stimulator) may explain the B cell activation characteristic of primary Sjögren's syndrome (pSS).

Objectives To evaluate the efficacy and safety of belimumab, targeting BAFF, in patients with pSS.

Methods Patients were included in this bi-centric prospective 1-year open-label trial if they fulfilled American European Consensus group criteria, were anti-Sjögren's syndrome A-positive and had current systemic complications or salivary gland enlargement, or early disease (<5 years), or biomarkers of B cell activation. They received belimumab, 10 mg/kg, at weeks 0, 2 and 4 and then every 4 weeks to week 24. The primary end-point, assessed at week 28, was improvement in two of five items: reduction in ≥30% in dryness score on a visual analogue scale (VAS), ≥30% in fatigue VAS score, ≥30% in VAS pain score, ≥30% in systemic activity VAS assessed by the physician and/or >25% improvement in any B cell activation biomarker values.

Results Among 30 patients included, the primary end-point was achieved in 18 (60%). The mean (SD) European League Against Rheumatism (EULAR) Sjögren's Syndrome Disease Activity Index decreased from 8.8 (7.4) to 6.3 (6.6) (p=0.0015) and EULAR) Sjögren's Syndrome Patient Reported Index from 6.4 (1.1) to 5.6 (2.0) (p=0.0174). The mean dryness, fatigue and pain VAS varied from 7.8 (1.8) to 6.2 (2.9) (p=0.0021), 6.9 (1.8) to 6.0 (2.2) (p=0.0606) and 4.6 (2.6) to 4.7 (2.4) (p=0.89), respectively. Salivary flow and Schirmer's test did not change.

Conclusions These encouraging results justify future randomised controlled trials of belimumab in a selected target population of pSS patients most likely to benefit from treatment.