To assess the efficacy/safety of the B-lymphocyte stimulator inhibitor belimumab/standard-of-care (SOC) versus placebo/SOC in active systemic lupus erythematosus (SLE).
In a multicenter, randomized, controlled, phase 3 trial, 819 antinuclear antibody- or anti-dsDNA-positive SLE patients with Safety of Estrogens in Lupus Erythematosus National Assessment–SLE Disease Activity Index (SELENA-SLEDAI) ≥ 6 were randomized (1:1:1 ratio) to receive intravenous belimumab 1 or 10 mg/kg, or placebo on days 0, 14, and 28, and then every 28 days for 72 weeks. Primary efficacy analyses: SLE Responder Index (SRI) at week 52 (≥ 4-point reduction in SELENA-SLEDAI; no new British Isles Lupus Assessment Group A and < 2 new B organ domain scores; no worsening in Physician’s Global Assessment).
Belimumab 10 mg/kg plus SOC met the primary efficacy endpoint: significantly greater SRI response at week 52 than placebo (43.2% versus 33.5%; P = 0.017); the rate with belimumab 1 mg/kg was 40.6% (P = 0.089). Week-76 response rates: 32.4%, 39.1%, and 38.5% with placebo, and belimumab 1 and 10 mg/kg, respectively. In post-hoc sensitivity analyses evaluating higher SELENA-SLEDAI thresholds, belimumab 10 mg/kg achieved better discrimination at weeks 52/76. Risk of severe SELENA-SLEDAI flares over 76 weeks was reduced with belimumab 1 mg/kg (34%; P = 0.023) and 10 mg/kg (23%; P = 0.13). Serious and severe adverse events including infections, laboratory abnormalities, malignancies, and deaths, were comparable across groups.
Belimumab plus SOC significantly improved SRI response rate, reduced SLE disease activity and severe flares, and was generally well-tolerated in SLE.