A Study of Belimumab in Chinese Pediatric Participants With Systemic Lupus Erythematosus

Inclusion Criteria: * Participants between 5 and 17 years of age inclusive, at the time of informed consent * Chinese pediatric participants with SLE, who have completed 48 weeks treatment in study 213560 and who, in the opinion of the investigator, may benefit from treatment with GSK1550188. * Body weight greater than equal to \>=15 kilograms (kg), at the time of signing the informed consent. * Male and/or female: 1. No contraceptive measures are required for male participants. 2. Female participants: A female participant is eligible to participate if she is not pregnant or breastfeeding, and one of the following conditions applies: i) Is a woman of non-childbearing potential OR ii) Is a woman of childbearing potential and using a contraceptive method that is highly effective, with a failure rate of \<1% * Participant signs and dates a written age-appropriate assent form (in accordance with applicable regulations) and the parent or legal guardian (or emancipated minor) that has the ability to understand the requirements of the study, provides written informed consent (including consent for the use and disclosure of research-related health information) that the participant will comply with the study protocol procedures (including required study visits). Exclusion Criteria: * Participants who have developed clinical evidence of significant, unstable or uncontrolled, acute or chronic diseases not due to SLE (i.e., cardiovascular, pulmonary, hematologic, gastrointestinal, hepatic, renal, neurological, malignancy or infectious diseases), or experienced an Adverse events (AE) in 213560 study that could, in the opinion of the principal investigator, put the participant at undue risk. * Have developed any other medical diseases (e.g., cardiopulmonary), laboratory abnormalities, or conditions that, in the opinion of the principal investigator, makes the participant unsuitable for the study. * Have an estimated glomerular filtration rate as calculated by Schwartz Formula of less than 30 milliliter per minute (mL/min). * Have an Immunoglobulin A (IgA) deficiency (IgA level \<10 milli gram per deciliter \[mg/dL\]). * Have a Grade 3 or greater laboratory abnormality based on the protocol toxicity scale except for the following that are allowed: 1. Stable Grade 3 hypoalbuminemia due to lupus nephritis and not related to liver disease or malnutrition. 2. Any grade proteinuria 3. Stable Grade 3 gamma glutamyl transferase (GGT) elevation due to lupus hepatitis and not related to alcoholic liver disease, uncontrolled diabetes or viral hepatitis. If present, any abnormalities in the alanine transaminase (ALT) and/or aspartate aminotransferase (AST) must be \<= Grade 2. 4. Stable Grade 3 neutropenia; or stable Grade 3 lymphopenia; or stable Grade 3 leukopenia, due to SLE. * Developing a positive test for Human immunodeficiency virus (HIV) antibody after inclusion into 213560, per investigator's discretion according to clinical need. * Developing hepatitis B: Serologic evidence of Hepatitis B (HB) infection defined as Hepatitis B surface antigen positive (HBsAg+) OR Hepatitis B core antibody positive (HBcAb+) after inclusion into 213560, per investigator's discretion according to clinical need. * Developing a positive test for Hepatitis C antibody after inclusion into 213560, per investigator's discretion according to clinical need. * Have received a live or live-attenuated vaccine within 30 Days of Day 1. * Are unable or unlikely, in the opinion of the investigator, to administer belimumab by SC injection and have no reliable source to administer the injection.