This study aims to examine the efficacy and safety of obexelimab in participants with systemic lupus erythematosus (SLE).

This study consists of a 24-week treatment period followed by a 12-week follow-up period. Patients must have a clinical diagnosis of SLE at least 24 weeks prior to screening and meet the 2019 European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) Classification Criteria. To enter the Screening Period (Day -28 to Day -1) patients will have active SLE as defined by having: a) hybrid Systemic Lupus Erythematosus Disease Activity Index (hSLEDAI) ≥ 6 and clinical hSLEDAI ≥ 4, and b) British Isles Lupus Assessment Group (BILAG)-2004 Grade A or B in ≥ 1 organ system. Patients must be treated with one or more of the following background nonbiologic lupus standard of care therapies: oral corticosteroid, antimalarial, and/or immunosuppressant.

On Day 1, patients will be randomized 1:1 to obexelimab or placebo subcutaneous (SC) injection once per week (QW) for 24 weeks. All patients will return to the study site for scheduled visits at Week 2, Week 4, and then every 4 weeks thereafter until study completion. During the study, patients will undergo assessments for efficacy, safety, PK, PD, and immunogenicity.

Including screening and follow-up, the maximum duration of participation in this study for an individual patient is approximately 40 weeks (i.e., up to a 28-day Screening Period, 24-week Treatment Period, and a 12-week follow-up).

Inclusion Criteria:

1. Males and females, ≥ 18 to ≤ 70 years of age

2. Diagnosed with SLE at least 24 weeks prior to screening and meets the 2019 EULAR/ACR classification criteria.

3. Patient has all 3 of the following based on features active on the day of the visits:

   1. hSLEDAI ≥ 6 and clinical hSLEDAI ≥ 4 at screening, and clinical hSLEDAI ≥ 4 at Day 1 Note: Clinical points exclude laboratory tests, except proteinuria.
   2. BILAG-2004 Grade A or B in ≥ 1 organ system at screening and Day 1.
   3. In the opinion of the investigator and the central adjudicator, there is sufficient disease activity to warrant enrollment into a clinical study with an investigational agent.

4. Patients must be treated with one or more of the following background nonbiologic lupus standard of care therapies: oral corticosteroid, antimalarial, and/or immunosuppressant.

Exclusion Criteria:

1. Active lupus nephritis for which, in the opinion of the investigator or the central adjudicator, current medications are insufficient for patient's safety or additional therapy that is not permitted in the protocol is needed.
2. A history of thrombosis or embolism in the previous 6 months before the Screening visit, or previous 12 months associated with antiphospholipid syndrome (APS) or another relevant hypercoagulable state.
3. Any active skin conditions other than cutaneous lupus erythematosus (CLE) that may interfere with the study assessment of CLE such as, but not limited to, psoriasis, dermatomyositis, and systemic sclerosis.
4. Active severe neuropsychiatric or central nervous system SLE.
5. Current inflammatory disease other than SLE (including, but not limited to, rheumatoid arthritis, psoriatic arthritis, spondyloarthropathy, reactive arthritis, scleroderma, dermatomyositis) that may interfere with the assessment of lupus signs and symptoms in the opinion of the investigator or central adjudicator.