The purpose of this study is to assess whether co-administration of belimumab and a single cycle of rituximab will optimize treatment with belimumab, which will result in improvements of clinical status with a favorable safety profile, by comparing subjects randomized to belimumab plus rituximab versus belimumab plus rituximab-placebo. Approximately 292 subjects will be randomized in a 1:2:1 ratio to 1 of 3 treatment arms; belimumab plus rituximab-placebo (Arm A, control), belimumab plus rituximab (Arm B, combination), or belimumab plus standard therapy (Arm C, reference). Belimumab will be administered as subcutaneous (SC) and rituximab-placebo or rituximab will be administered by intravenous (IV) infusions. The total duration of the study is for 104 weeks.
Belimumab will be administered as SC injection once weekly via autoinjector in thigh or abdomen
Rituximab will be administered as IV infusion of 1000mg at Week 4 and Week 6
Saline will be administered as IV infusions at Week 4 and Week 6
Standard therapy will contain stable SLE medications including immunosuppressant to be administered from baseline through Week 104.
Standard therapy excluding Immunosuppressant will contain anti-malarials, NSAIDs, and/or corticosteroids with prednisone dose equivalent to \<= 5 mg/day will administered through Week 104.
Steroid taper will include prednisone doses equivalent to =\< 5 mg/day in all Arms through Week 104.
Ciudad Autonoma de Buenos Aires, Buenos Aires, Argentina
La Plata, Buenos Aires, Argentina
San Miguel de Tucumán, Tucumán Province, Argentina