Omeros Corporation's new therapy has set a new standard of care for a condition long marked by high mortality and limited treatment options. 

The pharma major has secured US Food and Drug Administration approval for Yartemlea (narsoplimab-wuug), marking the first-ever authorized treatment for transplant-associated thrombotic microangiopathy (TA-TMA), a rare and frequently fatal complication of hematopoietic stem cell transplantation.  

The decision positions Yartemlea as the first and only approved inhibitor of the lectin pathway of complement, a key driver of the disease. 

The drug is approved for use in adults and children aged two years and older. Yartemlea works by selectively inhibiting MASP-2, the effector enzyme of the lectin pathway, halting disease-causing complement activation while preserving immune functions critical for host defense. 

“This approval is a long-awaited breakthrough in hematopoietic cell transplantation and TA-TMA care,” stated Miguel-Angel Perales, Chief of the Adult Bone Marrow Transplantation Service at 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.” 

The FDA approval is based on results from a single-arm, open-label clinical study involving 28 adults with TA-TMA, supported by data from an expanded access program that included 221 adult and pediatric patients.  

Among patients with evaluable response data, complete responses—defined by improvement in key laboratory markers alongside improved organ function or transfusion independence—were achieved in 61% of patients in the clinical study and 68% in the expanded access program. 

Survival outcomes were similarly strong in a population universally classified as high-risk. Across both data sets, approximately three-quarters of patients were alive 100 days after TA-TMA diagnosis, a notable improvement over historical expectations for the condition. 

“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, M.D., Assistant Professor of Pediatric Oncology and Hematopoietic Cellular Therapy at Emory University.  

“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.  

"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.  

"My clinical experience with Yartemlea through the expanded access program, including in very young patients, has reinforced that it needs to be readily available for children when TA-TMA emerges. With this approval, effective TA-TMA therapy can become the pediatric standard instead of the exception."