It's been a long time coming: Four years after Omeros came up short in its bid to gain an FDA approval for stem cell transplant drug narsoplimab, the Seattle biotech has finally scored its long-awaited nod.
With a Christmas Eve thumbs-up for narsoplimab, the FDA has delivered Omeros its first U.S. approval in its 31 years. Taking on the commercial name Yartemlea, it also becomes the first treatment for hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA). The first-in-class lectin pathway inhibitor is for patients age 2 and older.
By selectively inhibiting MASP-2, which is the effector enzyme of the lectin pathway, Yartemlea blocks activation while preserving complement functions important for host defense.
“This approval is a long-awaited breakthrough in hematopoietic cell transplantation and TA-TMA care,” Miguel-Angel Perales, M.D., chief of the Adult Bone Marrow Transplantation Service at Memorial Sloan Kettering Cancer Center, said in a release. “Until now, we’ve lacked an effective TA-TMA therapy and relied largely on supportive measures such as modifying calcineurin inhibitors, which can significantly increase the risk of life-threatening graft-versus-host disease.”
With the news, Omeros’ share price spiked by 78% to $16.04 on Christmas Eve before settling in at $14.55 on Dec 26.
TA-TMA is an often-fatal complication of stem cell transplantation, which can lead to generalized endothelial dysfunction and multiorgan injury. It can occur after autologous or allogeneic hematopoietic stem cell transplants, with a higher prevalence following allogeneic transplant. Roughly 30,000 allogeneic transplants are performed each year in the U.S. and Europe. Studies estimate that TA-TMA develops in up to 56% of allogeneic transplant recipients, Omeros said.
The approval came more than four years after the FDA sent Omeros a complete response letter, rejecting narsoplimab because the company’s single-arm phase 2 trial failed to reveal the treatment effect of the drug, according to the regulator.
In the process of Omeros appealing the decision, the FDA opened the door to a path forward, recommending the company compare overall survival from time of the first dosing of the 28 patients from the trial to data from an external control registry of more than 100 TA-TMA patients, none of whom had received narsoplimab. Omeros took these data to the agency as part of the latest application in March of this year.
They revealed complete response (CR) rates of 61% in the trial and 68% in an expanded access program (EAP), with CR defined as improvement in platelet counts and LDH levels plus either improved organ function or transfusion independence, Omeros said. As for 100-day survival from TA-TMA diagnosis, there was a 73% rate in the trial and 74% in the EAP for all-cause mortality.
There is no boxed warning with Yartemlea, but adverse reactions occurred in 61% of those who received it, including acute kidney injury, acute respiratory failure, neutropenic sepsis, septic shock and pulmonary edema. Fatal adverse reactions were reported in 7% of patients, including neutropenic sepsis and septic shock.
There is no need for a vaccination before taking Yartemlea, and there is no Risk Evaluation and Mitigation Strategy program tied to its use.
Omeros expected to gain approval for Yartemlea in September, but, a month earlier, the FDA informed the company that it was moving its decision date three months later to December. The delay was not a complete surprise as it came after the regulator had asked Omeros for additional information on its submission earlier in the year.
“FDA’s approval of Yartemlea marks a defining milestone for Omeros and, more importantly, for patients and families facing TA-TMA,” Gregory Demopulos, M.D., CEO of Omeros, said in a release. “With our U.S. launch planned for January 2026, our focus is on ensuring rapid, reliable access so that Yartemlea can be used when TA-TMA is recognized and time is critical.”
Omeros has submitted an application for the approval of Yartemlea in Europe with a decision expected in the middle of 2026, Omeros added.
The company did not reveal what it will charge for Yartemlea. Omeros will provide more information during a webcast Wednesday, Jan. 7.
To help facilitate its launch, Omeros has sold its most advanced pipeline candidate, zaltenibart, which is in under investigation in the rare blood disorder paroxysmal nocturnal hemoglobinuria. Novo Nordisk bought the MASP-3 inhibitor for a headline value of $2.1 billion, which includes a $340 million payment upfront. The Danish company now will initiate a phase 3 trial of the treatment.