Eculizumab to Treat Thrombotic Microangiopathy/Atypical Hemolytic Uremic Syndrome -Associated Multiple Organ Dysfunction Syndrome in Hematopoietic Stem Cell Transplant Recipients

Inclusion Criteria: * Patients of any age undergoing allogeneic or autologous HCT * Histologic TMA diagnosis OR clinical TMA diagnosis and presenting with high risk disease features including elevated plasma sC5b-9 above laboratory normal value (≥244ng/ml) and proteinuria measured as ≥30mg/dL of protein on random urinalysis x2 or protein/creatinine ratio ≥1mg/mg or patient receiving renal replacement therapy. * Minimum weight of ≥ 5kg. Exclusion Criteria: * Known hypersensitivity to any constituent of the study medication. * Subjects with unresolved serious Neisseria meningitides infection or progressive severe infection. * Patients with diagnosis of TTP as defined by ADAMST13 activity test \<10%. * Patients previously treated with eculizumab or other complement blocker for TMA within the 60 days prior to first dose of study treatment.