Conditioning Regimen for Allogeneic Hematopoietic Stem Cell Transplantation of Patients With Hematological Diseases

CAMPATH-1H will be given as a daily IV infusion for three days. Fludarabine will be given as a daily IV infusion for four days. Anti-CD45 will be given as a daily IV infusion for 4 days. Patients will then receive radiotherapy (also known as Total Body Irradiation or TBI) for one day. A summary of the treatment follows: * Day - 8: CAMPATH-1H and Fludarabine * Day - 7: CAMPATH-1H and Fludarabine * Day - 6: CAMPATH-1H and Fludarabine * Day - 5: Anti-CD45 and Fludarabine * Day - 4: Anti-CD45 * Day - 3: Anti-CD45 * Day - 2: Anti-CD45 * Day - 1: TBI * Day 0: Stem Cell Infusion (transplant) To help prevent the body from developing GVHD, patients will also receive the drug FK506, starting two days before the transplant and continuing for at least one month. Both the CAMPATH-1H and the Anti-CD45 can cause allergic reactions so patients will be given drugs to help prevent those reactions before receiving daily doses. To see how CAMPATH-1H works in patients with hematologic malignancies, some patients will be asked to participate in pharmacokinetic studies. For this, approximately 13 blood samples will be taken from the central line scheduled before each infusion on Day -8 to Day -6, daily thereafter until Day 0, and then approximately once per week on days 7, 14, 21 and 28 post transplant. No more than 5 teaspoonfuls total will be drawn. To see how Anti-CD45 works in patients with hematologic malignancies some patients will be asked to participate in pharmacokinetic studies. Approximately 22 blood samples will be taken from the central line scheduled before, during and after each infusion and after the end of the last infusion of Anti-CD45. No more than 10 teaspoonfuls total will be drawn over the course of the four anti-CD45 infusions.