FDA Approves First Treatment for Stem Cell Transplant–Associated Thrombotic Microangiopathy

The U.S. Food and Drug Administration (FDA) has approved Yartemlea (narsoplimab‑wuug), marking the first authorized therapy for hematopoietic stem cell transplant‑associated thrombotic microangiopathy (TA‑TMA) in adults and children aged 2 years and older. The decision represents a major milestone for patients facing one of the most severe complications of stem cell transplantation.

A Serious Post‑Transplant Complication

TA‑TMA is a potentially life‑threatening condition in which small blood clots form within tiny blood vessels following a hematopoietic stem cell transplant. These clots can cause significant organ injury, most commonly affecting the kidneys, cardiovascular system, and gastrointestinal tract. Prior to this approval, clinicians had no FDA‑approved treatment options specifically targeting the disorder.

Clinical Data Supporting Approval

The FDA’s decision was based on results from a single‑arm, open‑label study enrolling 28 patients, supported by additional data from 19 patients treated through an expanded access program.

Patients in the pivotal TA‑TMA study received Yartemlea intravenously once weekly, either at 4 mg/kg or a fixed 370 mg dose. The primary endpoint was TMA response, which required:

Improvement in key laboratory markers (lactate dehydrogenase and platelet count), and
Either improved organ function or elimination of transfusion needs.

Key findings:

61% of patients in the main study achieved a TMA response.
In the expanded access cohort, response rates were 67% in pediatric patients and 69% in adults, demonstrating consistent benefit across age groups.

Safety Profile

The most commonly reported adverse events included:

Viral infections
Sepsis
Hemorrhage
Gastrointestinal symptoms (diarrhea, vomiting, nausea)
Neutropenia
Fever
Fatigue
Low potassium levels

Clinicians are advised to closely monitor patients for signs of serious infections throughout treatment.

Regulatory Designations Underscore Unmet Need

To accelerate its review, Yartemlea received several FDA designations:

Priority Review
Breakthrough Therapy Designation
Orphan Drug Designation

These distinctions reflect both the severity of TA‑TMA and the lack of existing therapeutic options.