Inclusion Criteria:  Diagnosis of SLE according to the 2019 European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) Classification Criteria >=12 weeks prior to screening Anti-nuclear antibody (ANA) >=1:80, or anti-dsDNA and/or anti-Sm antibodies above the upper limit of normal (ULN), as determined by the central laboratory at screening Low C3, C4, and/or CH50 as determined by the central laboratory at screening High disease activity at screening, based on; BILAG-2004 (level A disease in >=1 organ system and/or Level B disease in >=2 organ systems), Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) (score >=8) and Physician's Global Assessment (PGA) (score >=1.0 on a 0 to 3 visual analogue scale [VAS]) High disease activity on Day 1, based on; SLEDAI-2K (score >=8) and PGA (score >=1.0 on a 0 to 3 VAS) Current receipt of >=1 of the following classes of standard therapies for the treatment of SLE at stable doses: oral corticosteroid (OCS), antimalarials, conventional immunosuppressants Other inclusion criteria may apply  Exclusion Criteria:  Pregnancy or breastfeeding Presence of significant lupus-associated renal disease and/or renal impairment Receipt of an excluded therapy, including any anti-CD20, anti-CD19 therapy less than 9 months prior to screening or during screening; or cyclophosphamide, tacrolimus, ciclosporin, or voclosporin during the 2 months prior to screening or during screening Significant or uncontrolled medical disease which, in the investigator's opinion, would preclude patient participation Known active infection of any kind or recent major episode of infection Intolerance or contraindication to study therapies Other exclusion criteria may apply