Fig. 1

Role of the complement system, including the lectin pathway, in pathophysiology of HSCT-TMA [7, 15]. In Phase 1 (Initiation), factors associated with hematopoietic stem cell transplantation such as calcineurin and mTOR inhibitors, acute graft-versus-host disease, infection, or total body irradiation lead to endothelial injury. In Phase 2 (Progression), the lectin pathway of complement is activated and complement proteins cause further endothelial injury, leading to platelet aggregation and microthrombi formation. In Phase 3 (Thrombosis), further microthrombi formation and mechanical damage lead to HSCT-TMA, organ damage, and organ failure. HSCT-TMA hematopoietic stem cell transplantation-associated thrombotic microangiopathy, mTOR mammalian target of rapamycin