The purpose of this study is to evaluate the ability of sirolimus to prevent graft versus host disease (GVHD) in patients following stem cell transplant from a related donor.

• Therapy to prevent GVHD will consist of an infusion of tacrolimus intravenously and sirolimus orally once per day starting 3 days before stem cell infusion. This will take place in the hospital where the patient will remain for the duration of the transplant.
• Sirolimus will continue for 9 weeks at at stable dose, then will be tapered by 1/3 on week 9 and 1/3 on week 17. It will be stopped on week 26 if there is no significant evidence of GVHD. These dose modifications will occur at home and patients will be seen weekly for the first 2 months after discharge.
• If GVHD is present, the tapering schedule wil be slower and based upon the patient's clinical condition.
• Tacrolimus will be given orally once the patient is discharged from the hospital and will be tapered at the same schedule as sirolimus. Blood levels of both tacrolimus and sirolimus will be monitored and the dose adjusted accordingly.
• During the year following stem cell transplant, blood work will be performed to evaluate the immune system and GVHD.

Inclusion Criteria:

• Patients with hematologic malignancies who will undergo allogeneic HSCT from matched family-members.
• Age greater than 18
• ECOG performance status 0-2
• Total bilirubin < 2.0 mg/dl
• AST < 90 IU
• Serum creatinine < 2.0 mg/dl

Exclusion Criteria:

• Active, uncontrolled infection
• Ejection fraction < 45% by echocardiogram or MUGA scan
• Forced vital capacity < 60%
• Uncontrolled hypertension
• Second transplantation
• Evidence of HIV infection
• Cholesterol > 300 mg/dl
• Relapsed aggressive Burkitt's or Burkitt's-like lymphoma