Omeros's Narsoplimab (Yartemlea) Faces Negative CHMP Opinion, Highlighting US-EU Regulatory Divide
On June 26, 2026, Omeros Corporation announced that the European Medicines Agency's (EMA) Committee for Medicinal Products for Human Use (CHMP) adopted a negative opinion on its Marketing Authorization Application (MAA) for narsoplimab (Yartemlea) for the treatment of hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA).
This regulatory setback represents a stark regulatory divide between European and U.S. regulators, who evaluated the exact same clinical dataset but reached opposite conclusions.1234
The Regulatory Divide: FDA vs. EMA
- U.S. FDA Approval (December 2025): The FDA approved narsoplimab under the brand name YARTEMLEA® for the treatment of TA-TMA in adults and children aged two years and older. It is the first and only FDA-approved therapy for this severe, often-fatal transplant complication.
- EMA CHMP Rejection (June 2026): The CHMP remained unconvinced by Omeros’ pivotal trial and real-world historical control data, concluding that the drug's benefit-risk balance could not be established. The committee cited insufficient clinical efficacy data to support a positive recommendation.
Omeros to Seek Re-Examination and AHEG Review
Omeros has announced that it does not accept the CHMP's negative opinion and intends to formally request a re-examination. As part of the re-examination procedure, Omeros will seek a review by an Ad Hoc Expert Group (AHEG). The AHEG is an independent panel of external clinical and scientific experts convened by the EMA specifically to evaluate clinical considerations in rare and complex indications where there are no approved therapies.
The Clinical Burden of TA-TMA
TA-TMA is a severe, endothelial-injury-driven complication of stem cell transplantation, with activation of the lectin pathway of complement playing a central pathogenesis role. Mortality in severe TA-TMA can exceed 90 percent, and survivors frequently suffer from permanent kidney damage and dialysis dependence.
Yartemlea is a fully human monoclonal antibody that selectively inhibits MASP-2, the effector enzyme of the lectin pathway, preventing complement-mediated endothelial damage while preserving classical and alternative pathway immune functions.
Compassionate Use Continues in Europe
While Omeros pursues the re-examination and AHEG review, the company plans to continue providing narsoplimab to patients in Europe under its global compassionate use program, with a priority on pediatric patients. However, Omeros noted that due to drug supply and access constraints, compassionate use can only reach a small fraction of the patients who could benefit from a full European commercial launch.
"We are disappointed by the CHMP’s opinion, particularly given the lethal nature of TA-TMA, the absence of an approved treatment for this condition in Europe, and the totality of the clinical trial and real-world data supporting narsoplimab’s efficacy and safety. We look forward to meeting with the AHEG and believe strongly that YARTEMLEA warrants approval in Europe, just as it received approval in the U.S." — Gregory A. Demopulos, M.D., Chairman and CEO of Omeros Corporation
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An instance of A stark transatlantic regulatory split leaves patients in one hemisphere stranded without critical therapies. — European and American agencies reviewed the identical clinical package for narsoplimab but split entirely, leaving EU transplant patients without a marketed therapeutic option. ↩︎
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An instance of Identical clinical trial packages no longer secure synchronized transatlantic drug approvals. — The FDA approved narsoplimab while the EMA's CHMP rejected the exact same core trial data, highlighting divergent regulatory standards. ↩︎
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An instance of A stark transatlantic regulatory divide isolates patients in one hemisphere from life-changing orphan therapies. — European regulators rejected a rare and life-saving transplant drug on clinical data that was deemed fully sufficient to secure an active commercial approval from the FDA. ↩︎
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An instance of Identical clinical trial packages no longer secure synchronized transatlantic drug approvals. — The EMA rejected a rare disease therapy that had already been successfully approved by the U.S. FDA, splitting the global market in half. ↩︎