Patient description: The patient is a 23-year-old man who came to the hospital with high blood pressure (175/95 mmHg) and signs of septicemia. He developed respiratory failure requiring mechanical ventilation and renal failure requiring hemodialysis. His blood smear showed microangiopathic hemolytic anemia and thrombocytopenia. His blood tests revealed elevated lactate dehydrogenase and reduced human complement C3 levels with a normal coagulation profile. He was diagnosed with atypical hemolytic uremic syndrome. He was treated with plasma exchange and corticosteroids. He has been previously vaccinated with meningococcal group ACWY conjugate vaccine and meningococcal group B vaccine. The genetic survey revealed ADAMTS13 >10%.

Clinical trial eligibility criteria: eligible ages (years): 4.0-75.0,  Severe Aplastic Anemia (SAA) Hypo-Plastic Myelodysplastic Syndrome (MDS) Diagnosed with severe aplastic anemia with bone marrow cellularity <30% (excluding lymphocytes) associated with RBC or platelet transfusion dependence and/or neutropenia (absolute neutrophil count less than or equal to 1000 cells/ microL or for patients receiving granulocyte transfusions, absolute neutrophil count less than or equal to 1000 cells/ uL before beginning granulocyte transfusions). OR --History of severe aplastic anemia transformed to MDS. that meet the following a) International Prognostic Scoring System (IPSS) risk category of INT-1 or greater, b) <5% myeloblasts and <30% of cellularity in the bone marrow on screening morphologic analysis. OR --PNH that is either refractory to treatment with eculizumab/ravulizumab or occurs in patients who don t have access to treatment with eculizumab associated with either a) life- threatening thrombosis and/or b) cytopenia associated with transfusion dependence and/or c) recurrent and debilitating hemolytic crisis Subjects with severe aplastic anemia, hypoplastic MDS or PNH with associated bone marrow failure syndromes who have intolerance of or failure to respond to standard immunosuppressive therapy Availability of at least one HLA haploidentical (i.e. > 5/10 and less than or equal to 8/10 HLA match) related donor (HLAA, B, C, DR, and DQ loci) who is available to donate stem cell graft (6-75 years old) The patient does not have any HLA antibodies detectable against any of the mismatched HLA alleles expressed by the haplo-donor Ages 4-55 years inclusive Ability to comprehend the investigational nature of the study and provide informed consent. The procedure will be explained to subjects aged 4-17 years with formal consent being obtained from parents or legal guardian  (ANY OF THE Availability of an HLA identical or 9/10 HLA matched (HLA A, B, C, DR, and DQ loci) -relative to serve as a stem cell donor The patient is deemed to be a candidate for a 10/10 HLA matched unrelated stem cell transplant (availability of a donor and resources required for such a transplant) The patient is eligible for transplantation using an ex vivo expanded cord blood unit on NHLBI protocol 17-H-0091 ECOG performance status of 2 or more Major anticipated illness or organ failure incompatible with survival from transplant Current pregnancy, or unwillingness to take oral contraceptives or use a barrier method of birth control or practice abstinence to refrain from pregnancy, if of childbearing potential for one year HIV positive Diagnosis of Fanconi s anemia (by chromosome breakage study) Diffusion capacity of carbon monoxide (DLCO) <40% using DLCO corrected for Hgb or lung volumes (patients under the age of 10 may be excluded from this criterion if they have difficulty performing the test correctly and thus are unable to have their DLCO assessed)