Bone Marrow Transplant Studies for Safe and Effective Treatment of Leukemia

One of the most effective ways of preventing lethal graft-versus-host disease (GVHD) after allogeneic bone marrow transplantation (BMT) for leukemia is to remove T-lymphocytes from the transplanted marrow. The reduced early mortality from T cell depletion is however offset by an increased risk of leukemic relapse and infection. We have shown that bone marrow transplants for leukemia depleted of T cells by elutriation and followed by delayed add-back of donor T cells reduces GVHD while preserving an immune response to the hematologic malignancy (the so-called graft-versus-leukemia (GVL) or graft-versus-myeloma effect). The study highlighted a possible benefit of large doses of marrow progenitor cells on transplant outcome. GVHD was reduced but not prevented by T cell depletion of the marrow. The first objective of our BMT studies is to prevent GVHD from the transplant while conserving GVL reactivity. This is a prerequisite to our second objective of determining the risk of GVHD and the benefit from GVL from add-back of donor lymphocytes. These studies will provide the basis for a planned trial adding back donor lymphocytes selected in vitro to confer immunity against infectious agents and residual leukemia without causing GVHD. In this study we will evaluate the use of T cell depleted peripheral blood progenitor cells (PBPC) (instead of bone marrow) to optimize the stem cell and lymphocyte dose. Donors will be given G-CSF and their mobilized PBPC harvested by leukapheresis. To minimize acute GVHD, the transplant will be T cell depleted, using a new technique developed in normal volunteers which improves T cell depletion and reduces stem cell loss (protocol 96-H-0049). The study has two phases: The first phase evaluates engraftment and GVHD following T cell depleted PBPC transplants. Stopping rules will be used to make modifications to the protocol in the event of graft failure. Cyclosporine will be withdrawn from the protocol if the incidence of acute GVHD is low or absent. In the second phase patients will receive add-back of donor lymphocytes on day 45 and day 100 post transplant to prevent relapse and confer donor-immune function. The risk of acute GVHD following this procedure will be determined. It is planned to treat up to 55 patients aged between 10 and 60 years. The end points of the study are graft take; acute and chronic GVHD, leukemic relapse, transplant-related and all causes of mortality, cytomegalovirus reactivation and leukemia-free survival. Patients will be followed for 5 years.