FDA Clears First Therapy for Transplant Associated Thrombotic Microangiopathy

Omeros Corporation said on December 24 that the U.S. Food and Drug Administration approved YARTEMLEA, branded as narsoplimab wuug, for the treatment of hematopoietic stem cell transplant associated thrombotic microangiopathy, commonly called TA TMA. The company described the antibody as the first and only approved inhibitor of the lectin pathway of complement and the first FDA approved therapy for TA TMA, a complication of stem cell transplantation that clinicians say can be rapidly fatal.

Narsoplimab is a fully human monoclonal antibody that targets mannan binding lectin associated serine protease 2, or MASP 2, the effector enzyme of the lectin pathway. Omeros and subsequent reporting describe MASP 2 inhibition as preventing lectin pathway mediated endothelial injury in small vessels and reducing thrombus formation, the hallmarks of TA TMA. The company release framed the approval as offering treatment options for both adults and children facing the condition.

Gregory A. Demopulos, chairman and chief executive officer of Omeros, said the FDA decision “marks a defining milestone for Omeros and, more importantly, for patients and families facing TA TMA,” and that approval enables offering “the first FDA approved therapy for this frequently fatal complication, with robust response data and a benefit risk profile that supports confident use in both adults and children.” Miguel Angel Perales, chief of the Adult Bone Marrow Transplantation Service at Memorial Sloan Kettering Cancer Center, described the data package as “compelling,” saying narsoplimab delivers robust response rates and improved survival with a favorable benefit risk and a safety profile consistent with that seen in patients undergoing hematopoietic stem cell transplantation.

The approval follows a regulatory path that included a Complete Response Letter from the FDA on October 18, 2021 and a resubmission acceptance of the biologics license application on May 6, 2025 with a company cited PDUFA target in late September. Reporting around the resubmission contained differing accounts of later PDUFA timing, and Omeros publicly announced the approval on December 24.

Analysts and investors reacted quickly. Seeking Alpha reported that Omeros shares rose nearly 80 percent on the approval and that the company’s market value exceeded one billion dollars in that analysis, with a peak revenue opportunity for YARTEMLEA estimated at about three hundred million dollars. Those estimates underscore how commercial viability, reimbursement decisions, and manufacturing capacity will shape patient access.

Clinicians welcomed a targeted option for a condition with high mortality, but experts cautioned that clinicians must still see full trial data and the FDA approval letter to evaluate numeric efficacy and safety details. Public health implications extend beyond clinical efficacy. Equitable access for patients who are already marginalized in transplant care, transparent pricing, insurer coverage decisions, and systems for post approval surveillance will determine whether the drug reaches those most in need.

As hospitals and transplant centers consider integration of YARTEMLEA into protocols, regulators and the company will face pressure to ensure supply reliability and to support real world evidence collection. For patients and families who have had precious little recourse against TA TMA, approval is an important step. Translating that step into equitable, sustained benefit will require focused policy attention and clinical stewardship.