A Study to Test the Safety, Tolerability, and Efficacy of an Antibody, REGN7999, Injected Under the Skin for the Treatment of Iron Overload in Adult Participants With Non-Transfusion Dependent β-thalassemia, Using MRI Scans to Measure Iron Levels in the Body

A PHASE 2, TWO-PART, RANDOMIZED, DOUBLE-BLIND, PLACEBO-CONTROLLED, MULTICENTER STUDY TO EVALUATE THE EFFICACY, SAFETY, AND TOLERABILITY OF SUBCUTANEOUSLY ADMINISTERED REGN7999 (AN INHIBITOR OF TMPRSS6) IN PARTICIPANTS WITH IRON OVERLOAD DUE TO NON-TRANSFUSION DEPENDENT β-THALASSEMIA

This study is researching an experimental drug called REGN7999 (called "study drug"). The study is focused on patients with non-transfusion dependent beta-thalassemia. The aim of the study is to see how safe and effective the study drug is.

The study is looking at several other research questions, including:

• Whether the study drug lowers extra iron levels in the body
• What side effects may happen from taking the study drug
• How much study drug is in the blood at different times
• Whether the body makes antibodies against the study drug (which could make the drug less effective or could lead to side effects)

Key Inclusion Criteria:

1. Clinical diagnosis of NTDT as described in the protocol
2. IOL, defined as LIC ≥ 5 mg Fe/g DW as measured by R2* MRI at screening
3. Serum ferritin ≥ 300 ng/mL as described in the protocol

Key Exclusion Criteria:

1. Hemoglobin ≤ 8 g/dL at screening
2. Any RBC transfusion within 12 weeks of visit 3
3. For Part A only: Any Iron Chelation Therapy (ICT) use in approximately 12 weeks prior to screening as described in the protocol
4. For Part B only: If on ICT, any change in ICT dose in approximately 12 weeks prior to screening as described in the protocol
5. Any use of luspatercept or mitapivat in 6 months prior to screening as described in the protocol
6. Absolute contraindication to MRI
7. Diagnosis of cirrhosis of the liver
8. Diagnosis of Chronic kidney disease (CKD) stage 4 or higher

Note: Other protocol-defined Inclusion/ Exclusion Criteria apply