BOSTON, Mass., July 27, 2026
Alexion, AstraZeneca Rare Disease announced high-level results from its global Phase 3 clinical program evaluating Ultomiris (ravulizumab) for hematopoietic stem cell transplant-associated thrombotic microangiopathy (HSCT-TMA), revealing different outcomes between adult/adolescent and pediatric patient populations. The ALXN1210-TMA-313 study in adults and adolescents did not achieve statistical significance for its primary endpoint of event-free survival through 26 weeks compared with placebo, while the ALXN1210-TMA-314 pediatric trial demonstrated clinically meaningful overall survival rates of 87.2% at 26 weeks and 73.4% at 52 weeks. The findings support ongoing regulatory submissions for pediatric patients while additional analyses continue for the adult indication.
Adult Phase 3 Study Misses Primary Endpoint
The randomized, double-blind, placebo-controlled ALXN1210-TMA-313 trial enrolled 146 adult and adolescent patients across 18 countries to evaluate Ultomiris in patients with HSCT-TMA, a rare and life-threatening complication that can occur following hematopoietic stem cell transplantation. Although the study failed to meet its primary endpoint of event-free survival, investigators reported a trend toward clinical benefit with Ultomiris compared to placebo. Alexion stated that discussions with global health authorities are continuing regarding the interpretation of the results, including the integration of real-world evidence from the ALX-TMA-502 observational study. Researchers noted that conducting placebo-controlled studies in HSCT-TMA remains particularly challenging because of the disease’s rarity, severity, and complex clinical presentation.
Pediatric Results Support Regulatory Filings
The Phase 3 ALXN1210-TMA-314 pediatric study, involving 41 patients from seven countries, produced encouraging survival outcomes that reinforce the therapeutic potential of Ultomiris in children with HSCT-TMA. Based on these findings, together with supportive evidence from the ALX-TMA-502 real-world study, Alexion is advancing regulatory filings for pediatric use of Ultomiris. The therapy already holds U.S. FDA Breakthrough Therapy Designation for pediatric HSCT-TMA and Orphan Drug Designation in both the United States and Japan for this indication. Company leadership emphasized that improving survival in children with this devastating transplant complication remains a major clinical priority and that the pediatric data could provide the foundation for the first targeted treatment option for these patients.
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Safety Profile Remains Consistent as Development Continues
Across both Phase 3 studies, Ultomiris demonstrated a safety profile consistent with its established clinical experience and with expectations for patients undergoing hematopoietic stem cell transplantation. Ultomiris, a long-acting C5 complement inhibitor, is already approved globally for multiple rare diseases including paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic uremic syndrome (aHUS), generalized myasthenia gravis (gMG), and neuromyelitis optica spectrum disorder (NMOSD). Alexion plans to present the complete clinical findings at an upcoming medical conference while continuing regulatory discussions for pediatric HSCT-TMA and evaluating potential next steps for expanding the therapy into the adult transplant-associated TMA setting.
Source: Alexion, AstraZeneca Rare Disease press release
