Omisirge Wins FDA Approval as First Cell Therapy for Severe Aplastic Anemia

The FDA has approved Omisirge (omidubicel-onlv) as the first hematopoietic stem cell transplant (HSCT) therapy specifically indicated for patients with severe aplastic anemia (SAA).

The approval covers adults and children aged six years and older with SAA, especially those who do not have access to a compatible donor, when provided after reduced intensity conditioning.

Omisirge was previously indicated for adults and pediatric patients 12 years and older with hematologic malignancies, but this approval now extends to younger pediatric patients with SAA.

SAA is a rare, life-threatening disorder in which the bone marrow fails to produce sufficient red blood cells, white blood cells and platelets. Patients often rely on immunosuppressive therapy or donor stem cell transplants, the latter requiring a matched sibling or related donor. For many patients without a suitable donor, options have been limited.

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Omisirge uses umbilical cord blood-derived stem cells that have been chemically enhanced with nicotinamide (a form of vitamin B₃) before transplant. This processing helps overcome some of the traditional limitations of cord blood transplants, such as slow blood cell recovery and high infection risk, giving patients access to a viable graft even without a matched donor.

“This approval is revolutionary in the therapeutic landscape and fundamentally changes how we approach treatment for SAA, where earlier treatment has potential to alter one’s life course,” Vinay Prasad, MD, MPH, chief medical and scientific officer and director of the FDA’s Center for Biologics Evaluation and Research (CBER). “Severe aplastic anemia is a rare blood disorder that can be fatal, and the FDA remains committed to expanding treatment options for patients with this disease.”

The FDA’s decision was based on results from an ongoing open-label study of patients (age six and over) with SAA who lacked a matched donor. Among 14 evaluated patients, 12 achieved early and sustained neutrophil engraftment, with a median time to neutrophil recovery of 11 days.

At 100 days post-transplant, 86% had maintained neutrophil recovery, and many achieved red blood cell transfusion independence. Both disease-free survival (DFS) and overall survival (OS) were 92%.

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More recent data, presented at the 2025 American Society of Hematology (ASH) Annual Meeting, showed even stronger results: 95% of patients (in a cohort of 19) had rapid neutrophil recovery with a median time of eight days, and OS and DFS bumped up to 94%. There were no cases of severe or chronic graft-versus-host disease (GVHD), and only 16% experienced mild acute GVHD.

These outcomes suggest that Omisirge offers not only speedy and reliable hematopoietic recovery, but also a favorable safety profile compared to traditional donor-based transplants or unmodified cord blood transplants.

As with any stem cell transplant or cell therapy, there are risks. In the clinical study, side effects included febrile neutropenia (low neutrophils with fever), viral and bacterial infections, hyperglycemia, immune thrombocytopenia and pneumonia. Autoimmune cytopenias were seen in about 25% of patients. Therefore, patients will require close monitoring and expert supportive care during the post-transplant period.

A major potential upcoming competitor in SAA is Pfizer, which is working on PF-06462700 (also known as anti-human thymocyte immunoglobulin, equine or eATG), an immunosuppressive agent that is currently in Phase III development for aplastic anemia.