Study of Subcutaneous (SC) Belimumab in Pediatric Participants With Systemic Lupus Erythematosus (SLE)

The purpose of this study is to evaluate the pharmacokinetics (PK), safety, and pharmacodynamics (PD) of repeat doses of 200 milligrams per milliliter (mg/mL) belimumab administered via SC injection in pediatric participants 5 to 17 years of age with SLE on a background of standard of care therapy. This bridging PK study is part of an extrapolation strategy to support the use of SC belimumab in pediatric SLE participants, based on the completed adult SLE study with SC belimumab and the pediatric SLE study with intravenous (IV) belimumab. Part A is an open label 12-week treatment phase where participants will be enrolled and allocated to treatment cohorts based on their body weight at baseline. The dose and dosing regimens selected for SC administration in this pediatric population are intended to achieve a similar average exposure as observed with the weekly 200 mg SC dosing regimen in adult SLE patients. Part B is an optional 40-week open-label continuation phase, open to all participants who have completed Part A. Dosing of SC belimumab may continue at the same frequency in Part B or may require a change in frequency according to changes in participant body weight. The total duration of the study will be 68 weeks including a 12-Week open label treatment phase (Part A), an optional 40-week open-label continuation phase (Part B) and 16-week follow-up.