Allogeneic hematopoietic stem cell transplantation (aHSCT) can cure patients with a variety of bone marrow failure syndromes (BMFS) including severe aplastic anemia (SAA), paroxysmal nocturnal hemoglobinuria (PNH) or myelodysplastic syndrome (MDS) associated with cytopenias. Patients with BMFS have traditionally been transplanted with bone marrow (BM) as a stem cell source. Although chronic graft versus host disease (cGVHD) occurs less commonly with BM compared to filgrastim (G-CSF) mobilized peripheral blood stem cell (PBSC) transplants, BM allografts have lower CD34+ progenitor cell numbers, which increases the risk of graft rejection in heavily transfused BMFS patients to 15-20 percent. To overcome this risk, our group developed a novel transplant approach for patients at high risk for graft rejection that utilized cyclophosphamide, fludarabine and anti-thymocyte globulin (ATG) conditioning followed by infusion of a CD34+ cell rich, T-cell replete G-CSF mobilized PBSC allograft. Remarkably, in 56 consecutive BMFS patients who had multiple risk factors for graft rejection who underwent this transplant approach graft rejection did not occur, with all patients achieving complete donor lymphohematopoietic chimerism. Unfortunately, recipients of G-CSF mobilized PBSC had a higher incidence of chronic GVHD than has historically been observed with BM transplantation (72 percent vs. 50 percent cumulative incidence of cGVHD at 1 year respectively). G-CSF mobilized PBSC transplants contained approximately a 20 fold higher dose of T-cells that had undergone a TH- 2 type cytokine polarization, a factor which likely contributed to this high incidence of cGVHD. In this protocol, we attempt to prevent graft failure and to reduce the incidence of cGVHD by transplanting high numbers of CD34+ selected PBSC co-infused with a reduced dose of non-mobilized donor T-cells that have not undergone a TH-2 cytokine polarization.