Study of BOS161721 in Systemic Lupus Erythematosus (SLE) Patients on a Background of Limited Standard of Care

This study will be conducted to assess the safety, tolerability, and immunogenicity of repeat doses of BOS161721 (20 milligrams \[mg\], 60 mg, and 120 mg) administered subcutaneously in adult participants with moderately to severely active Systemic Lupus Erythematosus (SLE) on limited background standard of care treatment, in order to estimate the optimal dose. BOS161721 at the chosen dose will be compared to placebo for response on the SLE Responder Index 4, with sustained reduction of oral corticosteroids, in the same participant population.