It has been a long road for Omeros. Four years after failing to secure FDA approval for its stem cell transplant therapy narsoplimab, the Seattle-based company has finally achieved the regulatory breakthrough it had been pursuing.
With an FDA approval granted on Christmas Eve, narsoplimab becomes Omeros’ first U.S. authorization in the company’s 31-year history. Marketed under the name Yartemlea, the drug is now the first approved therapy for hematopoietic stem cell transplant-related thrombotic microangiopathy (TA-TMA) and is cleared for use in patients aged 2 years and above.
As a first-in-class inhibitor of the lectin pathway, Yartemlea works by selectively targeting MASP-2, the pathway’s key effector enzyme, suppressing harmful activation while maintaining complement activity needed for immune defense.
Miguel-Angel Perales, who heads the Adult Bone Marrow Transplantation Service at Memorial Sloan Kettering Cancer Center, stated in a release that the approval represents a delayed advance in hematopoietic cell transplantation and TA-TMA treatment, noting that clinicians had no proper TA-TMA option and depended on supportive steps like adjusting calcineurin inhibitors, a strategy that can raise the risk of life-threatening graft-against-host disease.
Following the announcement, Omeros’ stock surged nearly 80%, reaching $16.04 on Christmas Eve, before pulling back to close at $14.55 on Boxing Day.
TA-TMA is a severe and frequently deadly complication associated with stem cell transplantation, marked by widespread damage to the vascular endothelium and injury to multiple organs. The condition can arise after either autologous or allogeneic hematopoietic stem cell transplants, though it is seen more often in patients receiving allogeneic procedures.
Approximately 30,000 allogeneic stem cell transplants are carried out each year across the U.S. and Europe. According to Omeros, published research suggests that TA-TMA may develop in as many as 56% of patients undergoing allogeneic transplantation.
The nod arrived more than four years after the FDA issued Omeros a complete response letter, turning down narsoplimab on the grounds that the company’s single-arm phase 2 study did not adequately demonstrate the drug’s treatment effect, as per the regulators.
As Omeros challenged that decision, the FDA outlined a potential route forward. The agency advised the company to evaluate overall survival starting from the first dose among the 28 treated patients and compare those outcomes against an external registry comprising more than 100 TA-TMA patients who had not been treated with narsoplimab.
Omeros submitted this comparative survival analysis to the FDA as part of its most recent application, which was filed in March this year.
Omeros reported complete response (CR) rates of just over 60% in the clinical trial and 68% in the Expanded Access Program (EAP). CR was defined as improved platelet counts and LDH levels, along with either enhanced organ function or independence from transfusions, the company said.
Yartemlea does not carry a boxed warning, though 61% of patients experienced adverse events. These included kidney injury, acute respiratory failure as well as septic shock, among others. Fatal adverse events occurred in 7% of patients, including cases of neutropenic sepsis.
The FDA approval of Yartemlea represents a meaningful shift in how TA-TMA may be managed in clinical practice. Until now, treatment options were limited to off-label interventions and supportive care, leaving physicians with few tools to directly address the underlying disease process.
For transplant centers, the availability of an FDA-approved therapy offers a standardized treatment pathway and may improve early intervention strategies for high-risk patients. Experts note that earlier diagnosis combined with targeted therapy could help reduce organ damage and improve survival outcomes.
From a commercial perspective, the FDA decision also provides Omeros with its first marketed product in the U.S., potentially stabilizing a company that has faced years of regulatory and financial uncertainty. Analysts expect the approval to renew interest in the company’s broader pipeline and reshape its long-term outlook.
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