Complement blockade for TA-TMA: lessons learned from a large pediatric cohort treated with eculizumab

Area of Science:

• Hematology
• Immunology
• Nephrology

Background:

• Overactivated complement is a high-risk feature in hematopoietic stem cell transplant (HSCT) recipients with transplant-associated thrombotic microangiopathy (TA-TMA).
• Untreated TA-TMA in HSCT recipients is associated with dismal outcomes.
• Pediatric HSCT recipients with high-risk TA-TMA (hrTA-TMA) and multiorgan injury present a critical clinical challenge.

Purpose of the Study:

• To evaluate the efficacy of the complement blocker eculizumab in pediatric HSCT recipients with hrTA-TMA and multiorgan injury.
• To assess the impact of eculizumab treatment on 1-year post-HSCT survival.
• To identify factors influencing treatment response and outcomes.

Main Methods:

• Retrospective analysis of 64 pediatric HSCT recipients with hrTA-TMA treated with eculizumab.
• Pharmacokinetic/pharmacodynamic-guided dosing of eculizumab.
• Comparison of survival rates with a previously reported untreated cohort.
• Analysis of complement activation markers (sC5b-9) and clinical factors (intestinal bleeding, proteinuria, GFR recovery).

Main Results:

• 1-year post-HSCT survival improved to 66% in eculizumab-treated patients, compared to 16.7% in untreated patients.
• Responding patients received a median of 11 eculizumab doses, with treatment discontinuation at a median of 66 days.
• Higher baseline sC5b-9 levels correlated with reduced response and increased eculizumab doses.
• Patients with intestinal bleeding had faster eculizumab clearance, required more doses, and had lower 1-year survival (44%).
• Over 70% of survivors had proteinuria; GFR recovery was a median 20% lower than pre-HSCT GFR.

Conclusions:

• Complement blockade with eculizumab is an effective therapeutic strategy for hrTA-TMA in pediatric HSCT recipients.
• Some patients with severe disease may not achieve a complete response, highlighting the need for early intervention.
• Further research is warranted to identify and target additional endothelial injury pathways in severe TA-TMA.