This study aims to test how well and safely ianalumab works for people with systemic lupus erythematosus (SLE), a disease where the immune system attacks healthy tissues in the body. Participants will receive ianalumab through a shot under the skin (subcutaneous injection) either every month or every three months, alongside their usual treatment. A placebo, which looks like the medicine but doesn't have the active ingredient, will also be used for comparison. Participants must be 12 years or older and have been diagnosed with SLE for at least 6 months. They need to be on certain medications already, like corticosteroids (CS), which help reduce inflammation, or other drugs that modify the disease.

• Study duration may vary; injections are monthly or quarterly.
• Participants will receive either the study drug or a placebo.
• Potential risks include reactions to the injections and other side effects.