Hematopoietic stem cell transplant-associated thrombotic microangiopathy: current paradigm and novel therapies

Hematopoietic stem cell transplantation-associated thrombotic microangiopathy (TA-TMA) remains a difficult complication to address due to its high mortality rate, lack of standard diagnostic criteria and limited therapeutic options. Underscoring this challenge is the complex pathophysiology involved and multiple contributing factors that converge on a final pathway involving widespread endothelial injury and complement activation. In addressing our current understanding of TA-TMA, we highlight the risk factors leading to endothelial damage and a pathophysiological cascade that ensues. We have also compared the different definition criteria and biomarkers that can enable early intervention in TA-TMA patients. Current first-line management includes discontinuation or alteration of the immunosuppressive regimen, treatment of co-existing infectious and GVHD, aggressive hypertension control and supportive therapy. We discuss current pharmacological therapies, including newer agents that target the complement cascade and nitric oxide pathways.