FDA approves narsoplimab-wuug for transplant-associated thrombotic microangiopathy

On December 24, 2025, the FDA approved narsoplimab-wuug (Yartemlea; Omeros) for the treatment of hematopoietic stem cell transplant–associated thrombotic microangiopathy (TA-TMA), a severe and often fatal complication following stem cell transplantation. The therapy is approved for adults and pediatric patients aged 2 years and older and becomes the first and only approved inhibitor of the lectin pathway of complement for this indication, according to the approval announcement from the Omeros Corporation.

TA-TMA is a life-threatening condition characterized by endothelial injury, thrombosis, and organ dysfunction following hematopoietic stem cell transplantation. Until now, Omeros stated, management options have been limited, relying largely on supportive care measures and off-label approaches with inconsistent outcomes. The approval of narsoplimab-wuug introduces the first targeted therapy designed to address a key disease driver by selectively inhibiting MASP-2, the effector enzyme of the lectin pathway, while preserving classical and alternative complement activity important for host defense.

“Just as in adults, YARTEMLEA’s indication to treat TA-TMA in children two years of age and older is tremendously important,” said Michelle Schoettler, MD, assistant professor, Pediatric Oncology and Hematopoietic Cellular Therapy, Emory.

"Peer-reviewed clinical publications in TA-TMA have steadily advanced our understanding of the disease in children – its biology, diagnostic criteria, and increasing recognition – and have revealed the limitations and risks of relying on off-label options in this setting. Across the published pediatric experience, YARTEMLEA has produced strong and consistent benefit, including in very high-risk children with organ dysfunction and in those who have failed prior complement-inhibition therapy," added Schoettler. "When used first-line, YARTEMLEA has been associated with approximately 75 percent one-year survival; and even in children refractory to one or more off-label complement inhibitors, one-year survival is approximately triple historical rates that have remained below 20 percent."

Addressing a major unmet need in TA-TMA

The FDA’s decision was supported by results from a single-arm, open-label clinical study in adults with TA-TMA (N=28), along with data from a large expanded access program (EAP) that included both adult and pediatric patients. In the pivotal TA-TMA study, efficacy was evaluated using a composite definition of complete response, which required improvement in platelet counts and lactate dehydrogenase levels together with either improved organ function or transfusion independence. Using this definition, a complete response was achieved in 17 of 28 patients (61%).

Additional support came from the expanded access program, in which 19 patients had evaluable patient-level response data. Among these individuals, 13 patients (68%) achieved a complete response. Across both the clinical study and the EAP, 100-day survival from the time of TA-TMA diagnosis was 73% and 74%, respectively, despite all patients meeting international criteria for high-risk disease and poor prognosis.

Peer-reviewed publications further contextualized these findings, showing that treatment with narsoplimab-wuug was associated with a three- to fourfold lower risk of mortality compared with external control cohorts. In high-risk patients who had failed or discontinued prior off-label therapies, including other complement inhibitors or defibrotide, one-year survival reached 50%, compared with historical rates reported as less than 20%.

Clinical outcomes and safety profile of narsoplimab-wuug

Pediatric experience, including use in very young and high-risk children, demonstrated consistent responses and survival outcomes, supporting its indication beginning at 2 years of age. When used as first-line therapy in children, published data cited approximately 75% one-year survival, with substantially improved outcomes even among those refractory to prior treatments.

Safety findings reflected the complexity of the post-transplant population. In the pivotal study, adverse reactions were reported regardless of causality, with the most common (≥20%) including viral infections, sepsis, hemorrhage, gastrointestinal symptoms, neutropenia, pyrexia, fatigue, and hypokalemia. Serious adverse reactions occurred in 61% of treated patients, and fatal adverse reactions were reported in 7%, including neutropenic sepsis and septic shock. Importantly, no new clinically significant safety signals were identified in the expanded access program.

With FDA approval secured, Omeros is preparing for a US launch planned for January 2026. The availability of narsoplimab-wuug establishes a new standard of care for TA-TMA, offering a targeted option for a complication that has long lacked an approved therapy.

"This approval is a long-awaited breakthrough in hematopoietic cell transplantation and TA-TMA care,” stated Miguel-Angel Perales, MD, chief, Adult Bone Marrow Transplantation Service, Memorial Sloan Kettering Cancer Center. "Until now, we’ve lacked an effective TA-TMA therapy and relied largely on supportive measures such as modifying calcineurin inhibitors, which can significantly increase the risk of life-threatening graft-versus-host disease. Based on a compelling data package, narsoplimab delivers robust response rates and improved survival in TA-TMA, with a favorable benefit-risk profile and a safety profile consistent with that seen in patients undergoing hematopoietic stem cell transplantation. As the first and only drug approved for TA-TMA, narsoplimab is a practice-changing advance for patients facing this devastating complication.”

Reference:

FDA approves Omeros' Yartemlea - first and only therapy indicated for TA-TMA. Omeros Corporation. Press release. December 24, 2025. Accessed January 2, 2026. https://investor.omeros.com/news-releases/news-release-details/fda-approves-omeros-yartemlear-first-and-only-therapy-indicated