Written By: Pharmacally Medical News Desk
The U.S. Food and Drug Administration has approved Omeros YARTEMLEA (Narsoplimab-wuug) for hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA), an often-fatal complication that occurs after stem cell transplantation. With this decision, YARTEMLEA becomes the first and only approved therapy for TA-TMA in adults and children two years of age and older. In the clinical development program, YARTEMLEA demonstrated meaningful outcomes.
Complete response rates reached 61% in the pivotal study and 68% among evaluable patients in the expanded access program. Survival at 100 days from TA-TMA diagnosis was 73% in the pivotal trial and 74% in the expanded access dataset. All patients were classified as high-risk using international harmonization criteria, indicating severe disease at baseline.
Building on these outcomes, Omeros chairman and chief executive officer Gregory A. Demopulos, M.D., stated that the approval represents a defining milestone not only for the company but for patients, families, and transplant teams. He emphasized that the focus now shifts to reliable and rapid access so physicians can begin treatment quickly when TA-TMA is identified. He also acknowledged the long-standing collaboration among investigators, caregivers, and patients who helped bring the therapy forward.
The FDA’s decision was supported by data from a single-arm, open-label adult study (NCT02222545) and an expanded access program (NCT04247906) involving both adults and children. Complete response was defined as improvement in platelet counts and LDH levels along with either improved organ function or freedom from transfusions. In addition to strong response rates, survival findings were encouraging and published analyses suggested a three- to fourfold reduction in mortality when compared with external control cohorts.
Among patients who had failed prior therapies, including off-label complement inhibitors or defibrotide, one-year survival reached roughly 50 percent, compared with historical expectations below 20 percent.
YARTEMLEA’s safety profile was consistent with the transplant population. The most frequently reported adverse reactions included Viral infections, Sepsis, Bleeding, Gastrointestinal symptoms, Neutropenia, Fever, Fatigue and Electrolyte disturbances.
Serious adverse events were reported in 61% of patients and fatal events in 7%, although no new safety concerns emerged in broader real-world experience.
Safety data remained consistent with transplant risks. Transplant experts provided additional context for the approval. Miguel-Angel Perales, M.D., described YARTEMLEA as a practice-changing option that replaces the historic reliance on supportive interventions that sometimes-increased other complications, such as graft-versus-host disease.
Pediatric specialist Michelle Schoettler, M.D., noted that the ability to treat children two years and older is particularly meaningful, with published reports showing strong benefit even among children who previously failed complement-inhibitor therapy. First-line use in this population has been associated with roughly 75% one-year survival.
From an implementation standpoint, Omeros plans a U.S. launch in January 2026. Beyond the United States, a marketing authorization application is under review with the European Medicines Agency, with a decision expected mid-2026.
YARTEMLEA is a lectin pathway inhibitor that works by selectively blocking MASP-2, preventing lectin-pathway activation while preserving other complement functions needed for immune defense. It is approved for the treatment of TA-TMA in adults and children two years and older.
TA-TMA develops after hematopoietic stem cell transplantation and is more common following allogeneic procedures. The condition involves endothelial damage, complement activation, and microvascular clot formation that can progress to organ failure. With approximately 30,000 allogeneic transplants performed annually across the United States and Europe, and estimates suggesting TA-TMA may occur in up to 56% of recipients, the availability of an approved targeted treatment represents a significant advance in care with U.S. launch imminent.
References
FDA Approves Omeros’ YARTEMLEA® – First and Only Therapy Indicated for TA-TMA, 24 December 2025, https://investor.omeros.com/news-releases/news-release-details/fda-approves-omeros-yartemlear-first-and-only-therapy-indicated
Safety and Efficacy Study of OMS721 in Patients with Thrombotic Microangiopathies, ClinicalTrials.gov ID NCT02222545, https://clinicaltrials.gov/study/NCT02222545
Khaled SK et al, Narsoplimab, a Mannan-Binding Lectin-Associated Serine Protease-2 Inhibitor, for the Treatment of Adult Hematopoietic Stem-Cell Transplantation-Associated Thrombotic Microangiopathy. J Clin Oncol. 2022 Aug 1;40(22):2447-2457. doi: 10.1200/JCO.21.02389. Epub 2022 Apr 19. PMID: 35439028; PMCID: PMC9467678.
Single Patient Expanded Access Treatment Plan for the Investigational Product Narsoplimab, ClinicalTrials.gov ID NCT04247906, https://clinicaltrials.gov/study/NCT04247906
Schoettler ML et al, Compassionate Use Narsoplimab for Severe Refractory Transplantation-Associated Thrombotic Microangiopathy in Children. Transplant Cell Ther. 2024 Mar;30(3):336.e1-336.e8. Doi: 10.1016/j.jtct.2023.12.017. Epub 2023 Dec 23. PMID: 38145741; PMCID: PMC11163410.