FDA Approves First-Ever TA-TMA Therapy: Narsoplimab Shows 61% Response Rate in High-Risk Patients
Key Insights
The FDA approved narsoplimab (Yartemlea (search)) as the first and only therapy for transplant-associated thrombotic microangiopathy (search) (TA-TMA (search)), marking a breakthrough for patients with this devastating complication.
Clinical trials demonstrated a 61% complete response rate in the primary study and 73-74% 100-day survival rates, representing a 3-4 fold reduction in mortality risk compared to external controls.
The approval covers both adult and pediatric patients aged 2 years and older, with the drug showing consistent efficacy across age groups in real-world expanded access programs.
The US Food and Drug Administration has approved narsoplimab-wuug (search) (Yartemlea (search)) for the treatment of hematopoietic stem cell transplant-associated thrombotic microangiopathy (search) (TA-TMA (search)), making it the first and only approved therapy for this life-threatening complication. The approval, announced December 24, 2025, by Omeros Corporation, represents a significant breakthrough for patients who previously had no effective treatment options.
Addressing Critical Unmet Medical Need
"This approval is a long-awaited breakthrough in hematopoietic cell transplantation and TA-TMA (search) care," said Miguel-Angel Perales, MD, chief of the Adult Bone Marrow Transplantation Service at Memorial Sloan Kettering Cancer Center. "Until now, we've lacked an effective TA-TMA therapy and relied largely on supportive measures such as modifying calcineurin inhibitors (search), which can significantly increase the risk of life-threatening graft-versus-host disease (search)."
The approval covers both adults and children aged 2 years and older, addressing a critical gap in pediatric care. "Just as in adults, narsoplimab's indication to treat TA-TMA (search) in children two years of age and older is tremendously important," said Michelle Schoettler, MD, assistant professor of Pediatric Oncology and Hematopoietic Cellular Therapy at Emory University.
Novel Mechanism of Action
Narsoplimab is a fully human monoclonal antibody targeting mannan-binding lectin-associated serine protease-2 (search) (MASP-2 (search)), the effector enzyme of the lectin pathway of complement. Crucially, inhibition of MASP-2 leaves intact the antibody-dependent classical complement activation pathway, preserving a critical component of the acquired immune response to infection.
Strong Clinical Efficacy Data
The approval was based on results from a single-arm, open-label study in 28 adults with TA-TMA (search), supported by additional data from an expanded access program involving 221 adult and pediatric patients. Efficacy was measured by TMA complete response (CR), defined as improvement in key laboratory markers including platelet counts and LDH levels, together with either improved organ function or transfusion independence.
The primary study achieved a 61% complete response rate (17 out of 28 patients), while the expanded access program demonstrated a 68% response rate (13 out of 19 evaluable patients). Across both studies, 100-day survival from the time of TMA diagnosis was 73% (95% confidence interval, 52-86) and 74% (95% CI, 48-88), respectively.
All patients met international harmonization criteria for high-risk TA-TMA (search), classifying each as having a poor prognosis and high risk of death. In peer-reviewed publications, treatment with narsoplimab was associated with a 3- to 4-fold reduced risk of mortality compared with an external control cohort.
Real-World Evidence Supports Efficacy
Research findings published in Bone Marrow Transplant in 2024 demonstrated narsoplimab's effectiveness in real-world settings. Among 20 patients enrolled between January 2018 and August 2023, approximately 65% responded to treatment and achieved transfusion independence with significant clinical improvement. The 100-day overall survival following TA-TMA (search) diagnosis was approximately 70% overall and 100% for responders.
A 2025 study published in the American Journal of Hematology showed that 1-year overall survival in pediatric patients with high-risk TA-TMA (search) who received narsoplimab as first-line therapy was approximately 75.0%, compared to 56.2% in those receiving it as second- or later-line therapy. For adults, 1-year survival rates were approximately 58.0% for first-line therapy and 40.5% for second- or later-line therapy.
Safety Profile and Treatment Benefits
In previously refractory high-risk patients who had failed or discontinued prior regimens including off-label complement inhibitors and/or defibrotide, narsoplimab was associated with 50% 1-year survival, compared with historical 1-year survival rates reported as less than 20%.
The most common adverse reactions (≥20%) were viral infections, sepsis, hemorrhage, diarrhea, vomiting, nausea, neutropenia, pyrexia, fatigue, and hypokalemia. Serious adverse reactions occurred in 61% of patients, with fatal adverse reactions reported in 7% of patients. Notably, narsoplimab has no Boxed Warning and no Risk Evaluation and Mitigation Strategy (REMS), and vaccinations are not required prior to treatment.
Regulatory Journey and Future Impact
Omeros initially received a Complete Response Letter from the FDA, which expressed difficulty in estimating the treatment effect of narsoplimab in HSCT-TMA. The company subsequently filed a Class 2 resubmission with data comparing overall survival for narsoplimab-treated patients to an external control group, demonstrating clinically meaningful and statistically significant improvements in survival.
"Based on a compelling data package, narsoplimab delivers robust response rates and improved survival in TA-TMA (search), with a favorable benefit-risk profile and a safety profile consistent with that seen in patients undergoing hematopoietic stem cell transplantation," Perales noted. "As the first and only drug approved for TA-TMA, narsoplimab is a practice-changing advance for patients facing this devastating complication."