FDA Approves Yartemlea for Rare, Life-Threatening Stem Cell Transplant Complication

The FDA has approved Yartemlea (narsoplimab-wuug) injection for the treatment of hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA). This condition is rare and often life-threatening.

The approval is for adults and children aged two and older, and establishes Omeros’ Yartemlea as the first FDA-approved treatment for TA-TMA. It is also a novel drug approved by the FDA.

TA-TMA is a serious issue that can arise after a stem cell transplant. It occurs when small blood vessels are damaged, leading to tiny clots that block blood flow. This can harm organs, especially the kidneys, but it can also impact the heart, lungs and gastrointestinal tract.

This condition is most common after allogeneic stem cell transplants and has historically been associated with high mortality, mainly in patients with high-risk TA-TMA.

Patients with TA-TMA often develop signs of small blood vessel injury, including low platelet counts, anemia, kidney problems such as protein in the urine or high blood pressure, and symptoms affecting the gastrointestinal tract or nervous system.

Until now, care has mainly focused on supportive measures and off-label therapies.

Yartemlea is a fully human monoclonal antibody that blocks mannan-binding lectin-associated serine protease-2 (MASP-2). MASP-2 plays a crucial role in the lectin pathway of the complement system. By inhibiting this enzyme, the therapy prevents activation of the pathway, which is believed to contribute to blood vessel injury and clot formation in TA-TMA. The therapy does not target specific biomarkers and is indicated for use only after a TA-TMA diagnosis.

The FDA’s approval for Yartemlea came from a pivotal study involving 28 adults with high-risk TA-TMA. This study was supported by data from an expanded access program that included both adult and pediatric patients.

In the pivotal study, patients received intravenous narsoplimab once a week, using either a weight-based dose of 4 mg/kg or a fixed dose of 370 mg. The main goal was complete response, defined by improvement in key lab markers of thrombotic microangiopathy, including platelet counts and lactate dehydrogenase levels, alongside either improved organ function or no longer needing blood transfusions.

The study found that 61% of patients achieved a complete response. In the expanded access program, the complete response rate was 68%, with similar results in both adult and pediatric patients. Across both groups, about 73% to 74% of patients were alive 100 days after a TA-TMA diagnosis, based on all-cause mortality.

All patients met criteria for high-risk TA-TMA, a group typically linked to poor outcomes.

Clinical data supporting narsoplimab in high-risk TA-TMA have been published in peer-reviewed journals, including analyses of survival outcomes in adult and pediatric patients.

Omeros plans to launch Yartemlea in the US in January 2026. Billing codes for diagnosis and procedures are already available, and a patient support program should launch in the first quarter of 2026.

According to Reuters, Omeros has set the US list price of Yartemlea at $36,000 per single-dose vial, with pricing disclosed following the FDA approval.

The European Medicines Agency (EMA) is also reviewing a marketing authorization application for Yartemlea in TA-TMA, with a decision expected in mid-2026.

In addition, Omeros has progressed other complement-pathway programs besides Yartemlea. In December 2025, the company completed an asset purchase and licensing agreement with Novo Nordisk for zaltenibart (OMS906), a late-stage investigational monoclonal antibody that targets MASP-3, which is an upstream activator of the alternative complement pathway.

Zaltenibart is still in clinical development for various blood and kidney disorders, including paroxysmal nocturnal hemoglobinuria and certain renal diseases.

Beyond TA-TMA, Omeros is also working on earlier-stage programs in oncology and immunology. This includes preclinical biologics and small-molecule candidates aimed at treating immune-mediated diseases.

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