Ultomiris Fails Phase 3 in HSCT-TMA: Second Alexion Setback This Month

AstraZeneca (AZN) announced on July 27, 2026, that Ultomiris (ravulizumab-cwvz) failed to achieve statistical significance on the primary endpoint of event-free survival through 26 weeks in the Phase 3 ALXN1210-TMA-313 trial. The trial tested the long-acting C5 complement inhibitor against placebo in adults and adolescents aged 12 and older with thrombotic microangiopathy after haematopoietic stem cell transplant (HSCT-TMA), a rare and potentially fatal complication affecting fewer than 6,000 people in the US.

The global, randomized, double-blind, placebo-controlled trial enrolled 146 patients across 18 countries. The primary endpoint measured time from randomization until TMA-related clinical worsening or death. While Ultomiris showed a trend toward treatment benefit at 26 weeks compared to placebo, it did not reach statistical significance. The safety profile was consistent with the known profile of Ultomiris and with complications seen in patients undergoing HSCT.

This is the second Phase 3 failure for AstraZeneca’s Alexion rare disease division in July 2026. On July 9, the company disclosed that eplontersen (Wainua), partnered with Ionis Pharmaceuticals (IONS), missed its primary endpoint in the CARDIO-TTRansform trial for transthyretin-mediated amyloid cardiomyopathy (ATTR-CM), the largest ATTR-CM trial ever conducted. The back-to-back misses put pressure on the Alexion pipeline, which AstraZeneca acquired for $39 billion in 2021.

The HSCT-TMA failure does not kill the entire program. A separate open-label Phase 3 trial in pediatric patients (ALXN1210-TMA-314) demonstrated clinically meaningful overall survival of 87.2% at 26 weeks and 73.4% at 52 weeks. Alexion is advancing regulatory filings for the pediatric population based on those results plus data from ALX-TMA-502, an external control study. The FDA granted Breakthrough Therapy designation for Ultomiris in pediatric HSCT-TMA, and the drug holds Orphan Drug designation in the US and Japan.

The broader Ultomiris franchise remains intact. The drug is already approved for paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic ureaemic syndrome (aHUS), generalized myasthenia gravis (gMG), and neuromyelitis optica spectrum disorder (NMOSD). A separate IgA nephropathy (IgAN) filing based on the I CAN Phase 3 trial, which showed a 43.4% reduction in proteinuria versus placebo at 34 weeks, was granted FDA Priority Review in June 2026 with a PDUFA date anticipated in the fourth quarter. That filing uses a different endpoint (proteinuria reduction) and a different disease mechanism than the HSCT-TMA event-free survival endpoint, so the failure does not directly implicate the IgAN program.

Alexion CEO Marc Dunoyer said the company is “moving forward with regulatory filings” for the pediatric HSCT-TMA indication while continuing discussions with health authorities regarding potential next steps for the adult indication, including additional analyses in the context of real-world data.

AZN closed at $172.48 on July 28, up from $169.64 on July 25. The stock has shown limited reaction to the HSCT-TMA failure, consistent with the indication’s small patient population and the fact that Ultomiris’s commercial trajectory depends on its approved indications and the pending IgAN filing, not on HSCT-TMA.

What to watch next: The Ultomiris IgAN PDUFA in Q4 2026 is the next major Alexion catalyst. If approved, it would be the first C5 complement inhibitor for IgAN. Investors will also be watching for full ALXN1210-TMA-313 results at a forthcoming medical meeting, where secondary endpoint data (overall survival, non-relapse mortality) may clarify whether the adult indication has any regulatory path forward.

What It Means for the Trade

The stock going up on the week of a Phase 3 failure is the market telling you this indication was never in the model — HSCT-TMA affects fewer than 6,000 U.S. patients and the trial missed, so nothing about the Ultomiris revenue trajectory changed. The structural story is the pattern, not the event: two Alexion Phase 3 misses in one month (eplontersen in ATTR-CM on July 9, ravulizumab in adult HSCT-TMA on July 27) invites the question of whether the $39 billion acquisition’s pipeline engine is producing. The honest answer is that these are different failure modes — eplontersen was a partnered, first-in-class program that missed on outcomes in the largest-ever ATTR-CM trial, while the HSCT-TMA miss is a rare-disease expansion where the endpoint (26-week event-free survival in a fragile post-transplant population) was always going to be hard to move. Neither indicts the complement-inhibition platform; both reduce the probability-weighted pipeline value the market assigns to Alexion’s expansion ambitions.

The live catalyst is the one that matters for the next two quarters: the IgAN Priority Review with a Q4 PDUFA. The I CAN Phase 3 showed a 43.4% proteinuria reduction versus placebo at 34 weeks, and IgAN is a far larger and more commercially consequential indication than HSCT-TMA — the market’s next re-rating data point for the Alexion division is a potential approval, not a failure cleanup. A complementary-approach IgAN approval would give Ultomiris a nephrology beachhead in the most active competitive space in rare renal disease.

Mechanism and Program Context

Why the adult trial missed while the pediatric program advances is a familiar rare-disease story about endpoints and heterogeneity. HSCT-TMA is not one disease process — it’s microangiopathy driven by endothelial injury from conditioning regimens, infections, calcineurin inhibitors, and graft complications, with complement amplification as one contributor among several. A C5 inhibitor that halts terminal complement activity may be too far downstream of the multi-hit pathology in adults, where the insult is diverse; the pediatric population is younger, the pathophysiology more homogeneous, and the external-control-supported data (87.2% overall survival at 26 weeks) apparently compelling enough for a Breakthrough-tagged filing. The open-label pediatric data with an external control (ALX-TMA-502) is a weaker evidentiary standard than the failed randomized adult trial — regulators accepted that standard for pediatric rare disease, but the label that results will be narrow, orphan-sized, and unlikely to carry the indication alone.

The franchise context is what protects the stock: Ultomiris is approved in PNH, aHUS, gMG, and NMOSD, and the eight-week dosing convenience keeps it defended against the biosimilar pressure building on the broader complement landscape. The pipeline question is whether complement can extend beyond classical rare diseases into nephrology — IgAN is the test case.

Risks and What Could Go Wrong

1. The IgAN PDUFA disappoints: a CRL or a narrow label in the most-watched rare renal indication would convert a “two bad months” narrative into a pipeline-quality question.
2. The pediatric HSCT-TMA filing relies on open-label plus external-control evidence — a harder regulatory sell than a randomized trial, and the FDA has grown stricter about external controls.
3. Full adult TMA-313 results at the medical meeting show a survival trend that clearly missed, closing the adult door and capping the indication’s value permanently.
4. Eplontersen read-through: the CARDIO-TTRansform miss already impaired one partnered program’s value; a second high-profile Alexion-adjacent failure would compound the credibility discount on the division’s pipeline claims.

Position read: AZN is a diversified mega-cap and Alexion is one division — size positions on the IgAN PDUFA, which is a real binary, not on HSCT-TMA headlines the market has already correctly priced as noise.

Sources: AstraZeneca press release, ClinicalTrials.gov NCT04543591