Allogeneic peripheral blood stem cell transplantation as an alternative to allogeneic bone marrow transplantation.

BMT, including 1) rapid hematopoietic engraftment, 2) less requirement for blood transfusion, antibiotic therapy and hospitalization days, and 3) avoidance of.risks and discomfort associated with general anesthesia for collecting hematopoietic stem cells (2). Taking these advantages into consideration, the use of PBSCwas applied for syngeneic and allogeneic transplantation in the early 1990' s. Subsequently, allogeneic PBSC transplantation (allo-PBSCT) has been increasingly used for the treatment of hematologic malignancy (3). Recent clinical evidences clearly indicate that allo-PBSCT can be used as an alternative to allogeneic BMT(allo-BMT) (4, 5). Similarly to auto-PBSCT, rapid engraftment of neutrophils and/or platelets has been assessed after allo-PBSCT in manyclinical trials. Since PBSCallografts contain 10-fold more T lymphocytes than BMallografts, there is a major concern about the increased risk of graft-vs-host disease (GVHD). However, a significant increase in the incidence or severity of acute GVHDhas not been demonstrated.In contrast, there are somereports which claim a relatively high incidence of chronic GVHD(6). Recently we reported a Japanese multicenter pilot study of allo-PBSCT for the treatment of standard-risk leukemia (7). Twenty-two patients with standard-risk leukemia were transplanted with granulocyte-colony stimulating factor (G-CSF)mobilized PBSC from an HLA-identical sibling donor, and received cyclosporine and methotrexate for GVHDprevention. Median days to reach an absolute neutrophil count of >500/|ul and platelets >50,000/jal were 12 (9-20) and 16 (1132), respectively. Grade II-IV acute GVHDdeveloped in 6/21 (29%) and extensive chronic GVHDin 12/20 (60%). Thus, our observations also indicate that allo-PBSCT is characterized by rapid hematologic engraftment, no increase of acute GVHD and an increased risk of chronic GVHD,and can be used as an alternative to allo-BMT. At least more than 50%of patients with acute myelogenous leukemia, acute lymphoblastic leukemia and chronic myelogenous leukemia can be cured by treatment with allo-BMT when they are transplanted during the first remission or chronic phase. In the setting of allo-BMT, the cure of leukemia is due to the eradication of residual leukemic cells provided by the pretransplant marrow-lethal chemoradiotherapy or chemotherapy and the antileukemic effects associated with acute and/ or chronic GVHD.These antileukemic effects of allo-BMT are referred to as graft-versus-leukemia (GVL) effects and are