Omeros Corporation's narsoplimab demonstrated a significant survival benefit in patients with hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA), a life-threatening complication of stem cell transplantation. The primary statistical analysis of a pivotal trial showed that narsoplimab-treated patients had an over 3-fold reduction in the risk of mortality compared to a control group (hazard ratio = 0.32, 95% confidence interval: 0.23-0.44, p < 0.00001).
These findings have paved the way for Omeros to resubmit its Biologics License Application (BLA) to the U.S. Food and Drug Administration (FDA) for narsoplimab, aiming to secure its approval as the first therapeutic specifically designed for TA-TMA. The company also plans to submit a marketing authorization application to European regulators by mid-2025.
Robust Survival Analysis
The analysis, conducted by an independent statistical group, compared overall survival in 28 TA-TMA patients treated with narsoplimab in the OMS721-TMA-001 pivotal trial to that of more than 100 similarly high-risk TA-TMA patients in an external control registry who did not receive narsoplimab. The two cohorts had similar demographics, diagnostic criteria, baseline characteristics, underlying diseases, conditioning regimens, and transplant procedures. All patients in both cohorts met the criteria for high risk of death as defined by an international expert panel.
Sensitivity analyses further supported the primary endpoint analysis, demonstrating hazard ratios ranging from 0.24 (95% confidence interval: 0.13, 0.47) to 0.42 (95% confidence interval: 0.21, 0.83) and p-values ranging from less than 0.00001 to 0.0124.
Clinical Perspective
"The results of this comparative survival analysis for narsoplimab in TA-TMA are truly outstanding," stated Alessandro Rambaldi, M.D., Professor of Hematology at the University of Milan. He further noted the impressive benefits observed in high-risk TA-TMA patients treated with narsoplimab through the expanded access program, including those who had failed or stopped C5 inhibitors.
Rafael Duarte, M.D., Ph.D., Associate Professor and Head of Department of Hematology at the University Hospital Puerta de Hierro Majadahonda, Madrid, Spain, explained that TA-TMA is driven by microvascular endothelial dysfunction and complement activation, specifically via the lectin pathway of complement. Narsoplimab targets MASP-2, the key enzyme in the lectin pathway, inhibiting its activation and interrupting the cycle of further endothelial damage.
Narsoplimab's Mechanism of Action
Narsoplimab, also known as OMS721, is a fully human monoclonal antibody that inhibits mannan-binding lectin-associated serine protease-2 (MASP-2), a pro-inflammatory protein target and the effector enzyme of the lectin pathway of complement. Inhibition of MASP-2 leaves intact the antibody-dependent classical complement activation pathway, which is critical for the acquired immune response to infection.
Addressing an Unmet Need
TA-TMA is a significant and often lethal complication of stem cell transplantation, characterized by endothelial cell damage and affecting approximately 40% of allogeneic stem cell transplant recipients. Severe cases can lead to mortality exceeding 90%, and even survivors often experience long-term renal sequelae. Currently, there is no approved therapy or standard of care for TA-TMA.
Expanded Access Program Data
Results from the expanded access program (EAP) for narsoplimab further support its clinical benefit. Analyses of the combined EAP and pivotal trial patients yielded hazard ratios ranging from 0.34 to 0.46 and p-values ranging from less than 0.00001 to 0.00002. In the EAP allogeneic transplant population, 16 adult and 20 pediatric high-risk TA-TMA patients had failed one or more treatment regimens – most commonly eculizumab – prior to receiving narsoplimab, with 1-year survival of 41 and 47 percent, respectively – over 2-fold higher than the less-than-20-percent historical 1-year survival for patients who fail targeted TA-TMA therapy.
Path to Regulatory Approval
Omeros is moving forward with narsoplimab as quickly as possible, targeting BLA resubmission for later this quarter and European MAA submission before mid-year. Two manuscripts, one comparing survival between the pivotal trial and TA-TMA registry patients and the other comparing survival in the EAP to that of TA-TMA registry patients, will be submitted for publication to peer-reviewed journals.
