This study is testing a new treatment called **dapirolizumab pegol (DZP)** for people with **moderately to severely active Systemic Lupus Erythematosus (SLE)**. SLE is a disease where the immune system attacks the body's own tissues, causing inflammation and damage. The study aims to see if adding DZP to the regular treatment helps improve symptoms. Participants must be at least 16 years old and already diagnosed with SLE with certain symptoms and lab results to join. **Key Points to Consider:** - The study involves multiple visits and medical tests to check the drug's effects. - Participants will continue their current medications alongside the study drug. - Risks include potential side effects and reactions to the study drug. People with serious health issues, certain infections, or specific medical histories may not qualify. The study excludes those with other immune system diseases or who have participated in similar studies recently. Participants must be stable on their current SLE treatment. The study does not allow certain medications and vaccines during participation.