FDA Approves YARTEMLEA: A Breakthrough in Complement Pathway Inhibition

The final days of 2025 witnessed a significant milestone in transplantation medicine, as the Food and Drug Administration granted approval to YARTEMLEA (narsoplimab-wuug) on December 24th—the first and only therapy indicated for hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA). This approval represents more than a mere regulatory achievement; it marks the culmination of decades of research into the lectin pathway of complement, a sophisticated component of the innate immune system whose dysregulation underlies numerous pathological conditions.

YARTEMLEA, a fully human monoclonal antibody, operates through a mechanism of exquisite specificity: it selectively inhibits mannan-binding lectin-associated serine protease-2 (MASP-2), the effector enzyme of the lectin complement pathway. This precision enables the therapeutic to prevent lectin pathway-mediated cellular injury—including the endothelial damage in small blood vessels characteristic of TA-TMA—whilst preserving the classical and alternative complement pathways essential to host defense mechanisms.

The regulatory decision was substantiated by compelling clinical evidence, including a pivotal single-arm study demonstrating complete response rates of 61% in adults with TA-TMA, alongside data from an expanded access program wherein patients exhibited three- to fourfold reductions in mortality risk compared with external control cohorts. In pediatric and adult patients refractory to prior therapies, one-year survival approached 75% when narsoplimab was employed as first-line treatment—a remarkable improvement over historical survival rates that languished below 20%.

With its scheduled United States launch in January 2026, YARTEMLEA enters clinical practice as Omeros Corporation’s first FDA approval after more than three decades of endeavor, whilst simultaneously establishing a new therapeutic paradigm for patients confronting this devastating complication of stem cell transplantation. The European Medicines Agency is currently reviewing a marketing authorization application, with a decision anticipated in mid-2026.