Overview

This study is researching an experimental drug called REGN7257 (called "study drug"). The study is focused on patients who have severe aplastic anemia (SAA), a disease of the bone marrow resulting in an impairment of the production of blood cells.

The main purpose of this two-part study (Part A and Part B) is to test how safe and tolerable REGN7257 is in patients with SAA in which other Immunosuppressive therapies (ISTs) have not worked well.

The study is looking at several other research questions to better understand the following properties of REGN7257:

• Side effects that may be experienced by participants taking REGN7257
• How REGN7257 works in the body
• How much REGN7257 is present in blood after dosing
• If REGN7257 works to raise levels of certain blood counts after treatment
• How quickly REGN7257 works to raise levels of certain blood counts
• In patients for whom REGN7257 works to raise levels of certain blood counts after treatment, how many continue to show such a response throughout the study
• If REGN7257 works to lower the number of platelet and red blood cell transfusions needed
• How REGN7257 changes immune cell counts and composition
• How the body reacts to REGN7257 and if it produces proteins that bind to REGN7257 (this would be called the formation of anti-drug antibodies [ADA])

Eligibility

Key Inclusion Criteria:

1. Part A: SAA that is IST-refractory or IST-relapsed, as defined in the protocol
2. Part B: SAA that is IST-relapsed, as defined in the protocol
3. Hematopoietic stem cell transplantation (HSCT) is not available or suitable as a treatment option or has been refused by the patient
4. Adequate hepatic and renal function as defined in the protocol

Key Exclusion Criteria:

1. Diagnosis of Fanconi anemia or other congenital bone marrow failure syndrome as defined in the protocol
2. Evidence of myelodysplastic syndrome as defined in the protocol
3. Paroxysmal nocturnal hemoglobinuria (PNH) with evidence of clinically significant hemolysis (eg, treatment indicated) or history of PNH-associated thrombosis
4. Treatment with a T cell-depleting agent (eg, ATG or alemtuzumab) within 6 months prior to dosing
5. Treatment with a calcineurin inhibitor (eg, cyclosporine) within 4 weeks prior to dosing for patients enrolled in Part A
6. Treatment with eltrombopag or investigational thrombopoietin receptor agonist, Granulocyte Colony-Stimulating Factor (G-CSF), or an androgen (eg, danazol), within 2 weeks prior to dosing
7. HIV, hepatitis B or hepatitis C positive by serological testing at the screening visit as defined in the protocol
8. Active tuberculosis, latent tuberculosis infection (LTBI) or history incompletely-treated tuberculosis or LTBI
9. Active infection as defined in the protocol

Note: Other protocol-defined inclusion/ exclusion criteria apply