Successful engraftment of allogeneic peripheral blood stem cell transplantafter nonmyeloablative preparative regimen with cytarabine and cyclophosphamide: Report of 2 cases

We report our experience with allogeneic peripheral blood stem cell transpl antation (allo-PBSCT) following a nonmyeloablative conditioning regimen con sisting of cytarabine (8 g/m(2)) and cyclophosphamide (120 mg/kg) in the tr eatment of 2 patients aged 50 and 55 years with refractory chronic myelomon ocytic leukemia and chronic myeloid leukemia in accelerated phase, respecti vely. Our nonmyeloablative regimen was well tolerated by older patients at high risk of regimen-related toxicity by the conventional conditioning regi men but was immunosuppressive enough to achieve mixed chimerism. After allo -PBSCT, we monitored chimerism in these patients by fluorescence in situ hy bridization using X- and Y-specific probes and polymerase chain reaction-ba sed analysis of a variable number of tandem repeats. We found that full chi merism and graft-versus-leukemia (GVL) effects could be induced in these pa tients by donor lymphocyte infusions and withdrawal of post transplantation immunosuppressive therapy. Our observations suggest that a nonmyeloablativ e conditioning regimen can establish mixed chimerism and that donor lymphoc yte infusion may induce GVL effects in older patients at high risk of regim en-related toxicity. Int J Hematol. 2000;72:499-503. (C)2000 The Japanese S ociety of Hematology.