This study aims to examine the efficacy and safety of obexelimab in participants with Warm Autoimmune Hemolytic Anemia (wAIHA).

This study consists of a 6-month open label Safety and Dose Confirmation Run-in Period (SRP), 6-month Randomized Control Period (RCP), and an additional 1-year open-label extension (OLE) period. To enter the Screening Period (Day -28 to Day -1) in the SRP or RCP, patients must have a clinical diagnosis of primary or secondary wAIHA due to an underlying autoimmune disorder, have failed at least 1 prior wAIHA treatment regimen, and have a Hgb level of ≥ 7 to < 10 g/dL with at least one sign or symptom of anemia. For the SRP only, patients with secondary wAIHA due to underlying lymphoproliferative disease may be eligible if they are receiving stable treatment.

All patients in the SRP or RCP are allowed to continue up to 2 failed wAIHA therapies throughout the 24-week study. On Day 1 of the SRP, patients receive obexelimab administered as subcutaneous (SC) injections. On Day 1 of the RCP, patients will be randomized in a ratio of 1:1 to receive either obexelimab or placebo administered as subcutaneous (SC) injections. Patients must return to the study site for the first 5 weeks and then every 2 weeks thereafter. Patients will undergo assessments for efficacy, safety, PK, PD, and immunogenicity during the 24-week SRP or RCP.

Following the 24-week SRP or RCP, patients will have the opportunity to receive obexelimab for up to 52 weeks in the Open Label Extension (OLE) Period.

Including screening and follow-up, the maximum duration of participation in this study for an individual patient is 81 weeks (i.e., 28-day screening, 24-week SRP or RCP, 52-week OLE, and an 8-week follow-up).

Inclusion Criteria:

1. Males and females, ≥ 18 years of age
2. Clinically diagnosed with wAIHA for at least 3 months and currently receiving treatment for wAIHA or have previously received treatment for wAIHA.
3. Diagnosis of primary or secondary wAIHA documented by a positive direct antiglobulin test specific for anti-IgG or anti-IgA.
4. Failed at least 1 prior wAIHA treatment regimen.
5. At least one sign or symptom of anemia as assessed by the investigator at screening.
6. Other inclusion criteria apply.

Exclusion Criteria:

1. Have cold antibody AIHA, cold agglutinin syndrome, mixed type (i.e., warm, and cold) AIHA, or paroxysmal cold hemoglobinuria.
2. Have any other associated cause of hereditary or acquired hemolytic anemia.
3. For the RCP only, patients with secondary wAIHA not due to autoimmune disorders, including LPDs.
4. Received a transfusion within 2 weeks prior to randomization.
5. Use of B cell-depleting, B cell-targeted, or other biologic immunomodulatory agents within the 6 months prior to randomization.
6. Received IV Ig or epoetin alfa within 6 weeks prior to randomization.
7. Receiving more than 2 concomitant medications for the treatment of wAIHA.
8. Other exclusion criteria apply.