Successful engraftment of allogeneic peripheral blood stem cell transplant after nonmyeloablative preparative regimen with cytarabine and cyclophosphamide: report of 2 cases

We report our experience with allogeneic peripheral blood stem cell transplantation (allo-PBSCT) following a nonmyeloablative conditioning regimen consisting of cytarabine (8 g/m2) and cyclophosphamide (120 mg/kg) in the treatment of 2 patients aged 50 and 55 years with refractory chronic myelomonocytic leukemia and chronic myeloid leukemia in accelerated phase, respectively. Our nonmyeloablative regimen was well tolerated by older patients at high risk of regimen-related toxicity by the conventional conditioning regimen but was immunosuppressive enough to achieve mixed chimerism. After allo-PBSCT, we monitored chimerism in these patients by fluorescence in situ hybridization using X- and Y-specific probes and polymerase chain reaction-based analysis of a variable number of tandem repeats. We found that full chimerism and graft-versus-leukemia (GVL) effects could be induced in these patients by donor lymphocyte infusions and withdrawal of posttransplantation immunosuppressive therapy. Our observations suggest that a nonmyeloablative conditioning regimen can establish mixed chimerism and that donor lymphocyte infusion may induce GVL effects in older patients at high risk of regimen-related toxicity.