EMA Maintains Negative Opinion on Narsoplimab for TA-TMA

Omeros Corporation’s narsoplimab has failed to secure European regulatory approval for hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA), with the European Medicines Agency’s Committee for Medicinal Products for Human Use (CHMP) maintaining its negative opinion following re-examination. The decision leaves the United States as the only market with an approved therapy for the severe transplant complication.

CHMP Maintains Negative Opinion After Re-examination

The CHMP’s decision follows its original negative opinion in June 2026. During re-examination, the committee convened an eight-member ad hoc expert group comprising hematologists, statisticians and transplant physicians, alongside two patient representatives, to address a three-part question prepared by the committee.

According to the final minutes of the closed meeting, the expert group recommended that external experts review individual patient-level data to better understand factors associated with treatment response and survival. Omeros said it had submitted substantial patient-level data to the CHMP in August as part of its re-examination request, but the committee did not provide those data to the expert group.

The company expressed disappointment with the outcome, arguing that the clinical evidence, US regulatory decision and experience with compassionate use support narsoplimab’s benefit-risk profile. However, the announcement does not provide a detailed account of the CHMP’s final scientific objections or explain how the submitted evidence influenced its reassessment.

Narsoplimab Targets Complement-Mediated Endothelial Injury

Narsoplimab, marketed as YARTEMLEA in the United States, is a fully human monoclonal antibody that inhibits mannan-binding lectin-associated serine protease-2 (MASP-2), the effector enzyme of the lectin pathway of the complement system.

In TA-TMA, transplant-related endothelial injury and complement activation contribute to small-vessel damage and thrombus formation. By selectively inhibiting MASP-2, narsoplimab blocks lectin pathway activation while preserving the classical and alternative complement pathways.

TA-TMA can develop after autologous or allogeneic hematopoietic stem cell transplantation, although it is more prevalent following allogeneic procedures. Severe disease can cause multiorgan injury, particularly kidney damage, and carries substantial mortality. Despite this clinical burden, no therapy has received marketing authorization for TA-TMA in Europe.

US Approval Contrasts With European Regulatory Outcome

The US Food and Drug Administration approved narsoplimab under the YARTEMLEA brand in December 2025 for TA-TMA in adults and children aged two years and older. It remains the only FDA-approved treatment for the condition.

Omeros also highlights the drug’s safety profile, noting that it does not carry a boxed warning, a risk evaluation and mitigation strategy (REMS), or a vaccination requirement. These features distinguish its regulatory profile from that of certain other systemic complement inhibitors, although they do not independently establish comparative safety or efficacy.

The divergent US and European outcomes underscore the importance of evaluating how regulators interpret clinical evidence, particularly in severe diseases with limited treatment options and complex transplant-related complications.

Commercial Strategy and Development Plans

Omeros is commercializing YARTEMLEA directly in the United States. The company had planned to license European Union commercialization rights to a third party if marketing authorization was granted, but the negative opinion prevents that strategy from proceeding on the anticipated basis.

The company also intends to terminate its European compassionate-use programme because of increasing demand for commercial supplies in the United States. Patients already receiving treatment through the programme will receive sufficient drug to complete their respective treatment courses.

Omeros said it is working to enable fully reimbursed named-patient access to YARTEMLEA in Europe and other regions where permitted.

Beyond TA-TMA treatment, the company plans to expand its MASP-2 programme through narsoplimab, the long-acting antibody OMS1029 and oral small-molecule inhibitors. Clinical studies in acute respiratory distress syndrome and prevention of high-risk TA-TMA in paediatric patients are planned to begin later in 2026.

The immediate challenge remains European access to narsoplimab. While US approval establishes a regulatory pathway for the drug, the repeated negative CHMP opinion leaves its European development and commercialization prospects uncertain.

Reference

Omeros Corporation Receives CHMP Negative Opinion Following Re-Examination of European Marketing Authorization Application for Narsoplimab in TA-TMA, Omeros, 16 October 2026

Yartemlea, CHMP Opinion, EMA, 16 October 2026