Haploidentical HCT for Severe Aplastic Anemia

Immunosuppressant therapy (IST) is the main treatment for SAA for patients who do not have an HLA-matched sibling donor available for transplant. But some patients with SAA do not respond to IST and some others relapse after IST. HCT using an unrelated but HLA-matched donor is the only curative option for these patients but many patients lack a suitable HLA-matched donor. St Jude is trying to increase donor options for these patients by using novel therapeutic strategies by combining two widely used of GVHD prophylaxis methods: i) selective T cell depletion and ii) use of post-transplant cyclophosphamide. This will allow expansion of the donor pool to include haploidentical donors as well as reduce the risk of GVHD. The goal of this protocol is to test whether combining these GVHD prophylaxis approaches will allow use of haploidentical donors, reduce risk of GVHD, reduce transfusion dependence and improve immune reconstitution. For this study chemotherapy, antibodies and radiation will be given to prepare the body to receive donor cells. Participants will then be given the donor cell infusion. Patients will receive two types of donor blood cell products - a progenitor blood cell infusion and then a donor lymphocyte infusion. Both the progenitor blood cell and the donor lymphocyte infusion will be processed in a laboratory at St. Jude using a machine called the CliniMACS™. In this clinical trial, participants will receive a special type of progenitor blood cells (called TCRαβ- depleted blood cells) from the donor. After the donor progenitor cells have started to grow within the body (engraftment), participants will receive a second product that contains mature immune cells. These immune cells called CD45RA-depleted lymphocytes or donor lymphocyte infusion (DLI) will help fight infections in the body after the transplant and strengthen the developing immune system.