Omeros seeks EMA approval for narsoplimab to treat stem cell transplant-related TA-TMA

Omeros Corporation (Nasdaq: OMER), a Seattle-based biopharmaceutical company specializing in complement-mediated diseases, has officially submitted a Marketing Authorization Application (MAA) to the European Medicines Agency (EMA) for its lead therapeutic candidate, narsoplimab. The investigational monoclonal antibody targets hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA), a rare but life-threatening complication of stem cell procedures. This application marks a critical regulatory milestone as the developer pursues approval in both the United States and European Union for the same indication, with the EMA review slated to commence in mid-July 2025.

Why is narsoplimab’s application to the EMA a critical move for treating severe transplant-associated TA-TMA in Europe?

The application submitted to the EMA is a significant step in expanding access to narsoplimab, particularly in Europe where treatment options for TA-TMA remain extremely limited. TA-TMA is a multifactorial vascular complication that occurs in up to 40 percent of patients undergoing allogeneic stem cell transplantation. The MAA includes a portfolio of response-based analyses showing a 61 percent response rate in narsoplimab-treated patients, supported by comparative data indicating a threefold increase in survival over a well-matched external control group. Additionally, Omeros has incorporated data from over 130 patients treated under its expanded access program, providing a broad, real-world clinical foundation for regulatory evaluation.

Narsoplimab’s orphan drug designation by the EMA streamlines the centralized procedure, allowing for simultaneous consideration across all EU member states and EEA countries. If approved, the therapeutic could become the first authorized intervention for TA-TMA in Europe, addressing a major unmet clinical need and potentially transforming post-transplant outcomes for thousands of patients annually.

How does the EU submission for narsoplimab align with ongoing FDA review and global regulatory strategy?

Omeros’ push into the European regulatory landscape follows the U.S. Food and Drug Administration’s acceptance of the resubmitted Biologics License Application (BLA) for narsoplimab in the same TA-TMA indication. The FDA has assigned a Prescription Drug User Fee Act (PDUFA) target action date of September 25, 2025. Both applications underscore Omeros’ dual-continent strategy to bring narsoplimab to market through synchronized review processes. The EMA’s Committee for Medicinal Products for Human Use (CHMP) will handle the scientific assessment and is expected to issue its opinion by mid-2026.

This parallel submission strategy reflects growing industry trends where biotech companies pursue transatlantic approvals concurrently to capitalize on data packages, regulatory harmonization, and global revenue potential. Analysts believe that synchronized approvals could offer significant commercial synergies and accelerate patient access in both the U.S. and Europe.

What scientific rationale supports narsoplimab’s development as a targeted treatment for TA-TMA patients?

Narsoplimab, also referred to as OMS721, is a fully human monoclonal antibody designed to inhibit mannan-binding lectin-associated serine protease-2 (MASP-2), the key effector enzyme in the lectin pathway of complement activation. Unlike other complement inhibitors that broadly affect immune pathways, narsoplimab targets MASP-2 without disrupting the classical pathway, thereby preserving host immune defense against infection.

The pathophysiology of TA-TMA involves endothelial injury that activates the lectin pathway, leading to systemic microvascular thrombosis and multi-organ damage. Omeros’ approach aims to block this specific cascade without introducing broader immunosuppression risks. Preclinical and early-phase clinical data have consistently demonstrated the biological plausibility of this mechanism, supported by the survival and response metrics cited in the MAA submission.

The therapy’s unique molecular selectivity and high clinical burden of the target disease have earned it breakthrough therapy and orphan drug designations from the FDA, and orphan status from the EMA, enhancing its regulatory and commercial prospects.

What are institutional investors and analysts signaling about the potential for narsoplimab approval and uptake?

Market sentiment around narsoplimab has shifted cautiously optimistic following the FDA’s acceptance of the revised BLA and now the EMA’s MAA submission. Institutional investors see the dual regulatory progress as a sign of maturing confidence in the therapy’s clinical and statistical underpinnings, particularly given the historical setbacks with earlier BLA filings that triggered FDA scrutiny in 2021 and 2022.

While specific valuation forecasts remain contingent on regulatory success, analysts have noted that approval in either jurisdiction could significantly bolster Omeros’ balance sheet via potential partnerships, licensing deals, or direct commercialization. With TA-TMA lacking an approved therapy, the drug may benefit from first-mover advantage and expedited payer negotiations under orphan drug frameworks.

However, there is also caution, with stakeholders emphasizing that the success of the application hinges on whether regulators accept Omeros’ use of external control datasets and real-world evidence as valid statistical comparators. The EMA and FDA’s tolerance for such methodologies, especially in rare disease contexts, will be closely scrutinized.

What comes next in the regulatory review timeline for narsoplimab across the United States and European Union?

The EMA’s review process is expected to begin in mid-July 2025 and will follow a standard centralized procedure timeline, which typically takes approximately 12 months. The CHMP’s opinion is anticipated by mid-2026, followed by final adoption by the European Commission. If approved, Omeros would gain the right to market narsoplimab across the EU and EEA member countries simultaneously.

In the U.S., the FDA’s September 2025 PDUFA date remains the next pivotal milestone. Omeros is expected to continue engaging with regulatory bodies to address any remaining clinical or statistical inquiries as the agencies complete their reviews. Should either agency request an advisory committee meeting, timelines could shift.

Future updates from the EMA or FDA regarding data adequacy, site inspections, or additional information requests will provide critical insight into the probability of approval. Industry observers also anticipate that Omeros may ramp up manufacturing and distribution planning during this period in anticipation of commercial launch.

What is the broader development pipeline for Omeros beyond narsoplimab and TA-TMA?

While narsoplimab remains the company’s lead program, Omeros has a broader portfolio of complement-related therapies and investigational assets targeting unmet needs in immunology, addiction, and oncology. OMS1029, a long-acting MASP-2 inhibitor, has completed Phase 1 trials and could serve as a follow-on asset in other complement-mediated diseases. OMS906, targeting MASP-3 in the alternative complement pathway, is in clinical trials for paroxysmal nocturnal hemoglobinuria and complement 3 glomerulopathy.

In addition, the American biotech company is advancing OMS527, a phosphodiesterase 7 inhibitor for cocaine use disorder, through trials funded by the National Institute on Drug Abuse. The company’s pipeline includes a robust portfolio of novel immuno-oncology programs, further positioning it as a diversified player in first-in-class therapeutic innovation.

Analysts expect that a regulatory win with narsoplimab could unlock further clinical investment in these adjacent programs, boosting the company’s long-term R&D pipeline value and cross-indication leverage of its MASP-targeting platform.