Allogeneic Hematopoietic Stem Cell Transplantation for Severe Aplastic Anemia and Other Bone Marrow Failure Syndromes Using G-CSF Mobilized CD34+ Selected Hematopoietic Precursor Cells Co-Infused With a Reduced Dose of Non-Mobilized Donor T-cells

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%. 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 cGVHD than has historically been observed with BM transplantation (72% vs. 50% 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.

Subjects with BMFS at high risk for graft rejection will undergo allogeneic stem cell transplantation from an HLA identical sibling or match unrelated donor using the identical conditioning regimen utilized in protocol 99- H-0050. Using the Miltenyi CliniMACs system, recipients will receive an allograft on day 0 containing donor CD34+ cells that have been positively selected and T-cell depleted following G-CSF mobilization (goal CD34+ cell dose of 5 x 106 CD34+ cells /kg recipient) combined with 2 x 107 cells/kg of non-mobilized CD3+ T-cells previously collected and cryopreserved from the same donor by apheresis prior to G-CSF mobilization.

Primary objective: To evaluate whether administering a CD34+ selected, T-cell depleted peripheral blood stem cell graft with a concomitant infusion of non-mobilized donor T-cells at a dose that matches the T-cell dose that is infused in historical bone marrow transplant cohorts will reduce the incidence of cGVHD at 1 year to that observed with a conventional bone marrow transplant (50%) without increasing the risk of graft failure. This trial design will allow the trial to stop early if it is unlikely that we have reduced the proportion of one year cGVHD to 50% or if the combined event rate for failed donor engraftment or treatment related mortality (TRM) at day 100 exceeds 20%.

The primary endpoint of this study will be cGVHD at day 365.

Secondary end points include transplant related mortality, engraftment, degree of donor-host chimerism, incidence of acute and chronic graft versus host disease (cGVHD), transplant related morbidity and overall survival. Health related quality of life will also be assessed as a secondary outcome measure pre-transplant, 30 and 100 days post transplant, and every 6 months until 5 years post transplant.