Donor Stem Cell Transplant Followed By Donor White Blood Cell Infusions in Treating Young Patients With Hematologic Cancer

OBJECTIVES: * Determine the feasibility of allogeneic hematopoietic stem cell transplantation using a reduced-intensity conditioning regimen, in terms of whole blood engraftment rate at 100 days post transplant, in pediatric patients with hematopoietic malignancies who are at high risk for complications with conventional transplantation. * Determine the feasibility of donor lymphocyte infusions (DLIs), in terms of number of patients who receive at least one DLI by 12 months post transplant, in patients treated with this regimen. * Determine the toxicities of the conditioning regimen, in terms of 100-day post transplant nonrelapse-related death rate, in these patients. * Determine the toxicity of DLI, in terms of acute and chronic graft-vs-host disease rate and 12-month post transplant nonrelapse-related death rate, in these patients. OUTLINE: This is a pilot study. * Reduced-intensity conditioning regimen: Patients receive fludarabine IV on days -6 to -2; antithymocyte globulin IV on days -5 to -2; and melphalan IV on days -3 and -2. * Transplantation: Patients undergo allogeneic peripheral blood stem cell transplantation on day 0. Patients also receive filgrastim (G-CSF) IV beginning on day 5 and continuing until blood counts recover. * Graft-vs-host disease (GVHD) prophylaxis: Patients receive cyclosporine IV or orally beginning on day -1 and continuing until at least day 28 and methotrexate IV on days 1, 3, and 6. * Donor lymphocyte infusion (DLI): Patients with mixed chimerism, no acute GVHD requiring therapy, and no relapse/progression post transplant at day 90 may receive DLI. At least 30 days after discontinuation of immunosuppression, patients may receive up to 2 DLIs at least 8-12 weeks apart in the absence of GVHD. At the completion of study treatment, patients are followed periodically for 2 years. PROJECTED ACCRUAL: A total of 10 patients will be accrued for this study.