• Signed Informed Consent Form (ICF) prior to any study-mandated procedure.

• Diagnosis of Systemic Lupus Erythematosus (SLE) made at least 6 months prior to Screening, according to 2019 European League Against Rheumatism / American College of Rheumatology Criteria.

• A modified Systemic Lupus Erythematosus Disease Activity Index-2000 (mSLEDAI-2K) score ≥ 6 and clinical mSLEDAI-2K score ≥ 4 with at least 2 points for musculoskeletal or mucocutaneous manifestations (i.e., myositis, arthritis, rash, alopecia, mucosal ulcers). The mSLEDAI-2K score does not include leukopenia.

• British Isles Lupus Assessment Group-2004 (BILAG) Grade B in ≥ 2 organ systems or a BILAG Grade A in ≥ 1 organ system.

• Physician's Global Assessment (PGA) score ≥ 1.0 on a 0 to 3 visual analog scale.

• Currently treated with one or more of the following SLE background medications:

‣ Anti-malarials (≤ 400 mg/day hydroxychloroquine, ≤ 500 mg/day chloroquine, ≤ 100 mg/day quinacrine).

⁃ Mycophenolate mofetil (≤ 2 g/day) / mycophenolic acid (≤1.44 g/day).

⁃ Azathioprine (≤ 2 mg/kg/day).

⁃ Methotrexate (≤ 25 mg/week).

⁃ Oral Corticosteroids (OCS):

• if OCS is the only SLE background medication: ≥ 7.5 mg/day and ≤ 30 mg/day prednisone or equivalent.

∙ if OCS is not the only SLE background medication: ≤ 30 mg/day prednisone or equivalent.

⁃ Belimumab (≤10 mg/kg every 4 weeks intravenously \[i.v.\], or 200 mg/week subcutaneously \[s.c.\]).

⁃ Treatment with antimalarials, mycophenolate mofetil, mycophenolic acid, azathioprine, methotrexate or belimumab must have been started at least 90 days prior to Screening. Treatment with OCS must have been started at least 30 days prior to Screening.

⁃ • For women of childbearing potential (WoCBP):

• Negative serum pregnancy test at Screening.

• Agreement to undertake monthly urine pregnancy tests from Randomization up to 6 months after study treatment discontinuation.

• Agreement to use a highly effective method of contraception from Screening (Visit 1) up to 6 months after study treatment discontinuation.

• A clinical mSLEDAI-2K score ≥ 4 with at least 2 points for musculoskeletal or mucocutaneous manifestations (i.e., myositis, arthritis, rash, alopecia, mucosal ulcers).

• BILAG Grade B in 2 or more organ systems or a BILAG Grade A in 1 or more organ system.

• PGA score ≥ 1.0 on a 0 to 3 visual analog scale.

• Presence of at least one of the following biomarkers of serological evidence of active SLE (in a Screening sample as measured by central laboratory):

‣ Anti-dsDNA antibodies elevated above normal,

⁃ Antinuclear antibodies with a titer of at least 1:160,

⁃ Anti-Smith antibody elevated above normal.

• Currently treated with one or more of the following SLE background medications that must be stable for at least 30 days prior to Randomization (except OCS, which must be stable for at least 15 days prior to Randomization):

‣ Antimalarials (≤ 400 mg/day hydroxychloroquine, ≤ 500 mg/day chloroquine, ≤ 100 mg/day quinacrine);

⁃ Mycophenolate mofetil (≤ 2 g/day) / mycophenolic acid (≤ 1.44g/day);

⁃ Azathioprine (≤ 2 mg/kg/day);

⁃ Methotrexate (≤ 25 mg/week);

⁃ OCS:

• if OCS is the only SLE background medication: ≥ 7.5 mg/day and ≤ 30 mg/day prednisone or equivalent.

∙ if OCS is not the only SLE background medication: ≤ 30 mg/day prednisone or equivalent.

⁃ Belimumab (≤ 10 mg/kg every 4 weeks i.v. or ≤ 200 mg/week s.c.).

• WoCBP must have a negative urine pregnancy test at Randomization.