The EMA’s CHMP issued a negative opinion on Omeros’ MAA for YARTEMLEA® (narsoplimab) in TA‑TMA, citing concerns despite prior FDA approval; the company plans re‑examination.
Written By: Farha Farheen, PharmD
Reviewed By: Pharmacally Editorial Team
Omeros Corporation has received a negative opinion from the European Medicines Agency’s (EMA) Committee for Medicinal Products for Human Use (CHMP) on its marketing authorization application (MAA) for YARTEMLEA® (narsoplimab) to treat hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA).
The decision follows an oral explanation meeting in which Omeros presented its case alongside four international experts in hematopoietic cell transplantation. The company did not disclose the specific basis for the committee’s decision.
The company plans to request a formal re-examination of the CHMP opinion and will seek review by an Ad Hoc Expert Group (AHEG), an independent scientific panel convened by the EMA to evaluate complex clinical and scientific issues.
First Approved Therapy in the U.S. Faces European Regulatory Setback
Narsoplimab received U.S. Food and Drug Administration (FDA) approval in December 2025 under the brand name YARTEMLEA®, becoming the first and only approved treatment for TA-TMA in adults and children aged two years and older. However, no therapy has yet been approved for the condition in Europe, leaving patients with limited treatment options.
YARTEMLEA is a fully human monoclonal antibody that selectively inhibits mannan-binding lectin-associated serine protease-2 (MASP-2), the key effector enzyme of the lectin complement pathway. By blocking lectin pathway activation while preserving the classical and alternative complement pathways, the therapy reduces endothelial injury and thrombus formation without broadly suppressing immune function. Unlike other systemic complement inhibitors, YARTEMLEA does not carry a boxed warning, Risk Evaluation and Mitigation Strategy (REMS), or mandatory vaccination requirement in the United States.
Clinical Evidence Supporting the Application
The European application is supported by data from Omeros’ pivotal clinical trial in patients with TA-TMA, supplemented by survival analyses comparing treated patients with external registry controls who did not receive narsoplimab. Additional evidence comes from the company’s global compassionate use program. These datasets also formed the basis of the FDA’s approval decision.
TA-TMA is a severe complication of hematopoietic stem cell transplantation characterized by widespread endothelial injury and complement activation. The condition can develop after both autologous and allogeneic transplantation, although the risk is substantially higher following allogeneic procedures. Recent studies suggest TA-TMA may affect up to 56% of allogeneic transplant recipients, while mortality in severe disease can exceed 90%. Survivors frequently experience long-term kidney damage, including dialysis dependence.
Company Plans to Challenge the CHMP Decision
Omeros Chief Executive Officer Gregory A. Demopulos, MD, expressed disappointment with the CHMP opinion, noting the high mortality associated with TA-TMA and the absence of approved therapies across Europe. He emphasized that the company believes the totality of clinical trial data and real-world evidence supports the efficacy and safety of YARTEMLEA and remains confident that the therapy merits European approval.
While the regulatory review continues, Omeros will maintain its global compassionate use program, prioritizing pediatric patients. The company acknowledged, however, that limited drug supply and access restrictions allow only a small proportion of European patients to receive treatment outside formal regulatory approval.
Path Forward
The upcoming re-examination process and review by the EMA’s Ad Hoc Expert Group will represent the next major regulatory milestone for YARTEMLEA in Europe. A favorable reassessment could provide the first approved treatment option for European patients with TA-TMA, a rare but frequently fatal transplant complication with substantial unmet medical need.
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About the Writer
Farha Farheen, PharmD (LinkedIn) is a pharmacy professional with a strong interest in pharmacovigilance and clinical research. She has completed her Doctor of Pharmacy (Pharm.D) along with her internship as a Clinical Pharmacist. She has hands-on experience in adverse drug reaction (ADR) reporting, safety data documentation, and pharmacovigilance workflows, and is proficient in using VigiFlow. She is also a patent holder for an antibacterial formulation enriched with bioactive substances, granted by the German Patent and Trademark Office.