Inclusion Criteria:

- Patients ≥18 years of age with a hematologic malignancy other than aplastic anemia or
primary myelofibrosis, scheduled to undergo RIC allogeneic SCT with a peripheral
blood stem cell graft from an unrelated donor, using Flu/Bu conditioning and Tac/MTX
GVHD prophylaxis. The following diagnoses are included:

- Acute leukemia - AML, ALL or acute biphenotypic leukemia. Patients will have
documentation of complete remission within 6 weeks prior to their transplant.
Complete remission is defined as <5% blasts on a bone marrow biopsy and absence of
any known extramedullary disease.

- Chronic myelogenous leukemia in any stage, but with documentation of <5% blasts on a
bone marrow biopsy within 6 weeks prior to transplant.

- Myelodysplastic syndrome of any subtype, but with documentation of <5% blasts on a
bone marrow biopsy within 6 weeks prior to transplant.

- Myeloproliferative disorders other than primary myelofibrosis.

- Lymphoma - All types of lymphoma are eligible.

- CLL and PLL.

- Patients who meet institutional eligibility criteria for allogeneic SCT:

- Renal function: Serum creatinine ≤2.

- Hepatic function: Baseline direct bilirubin, ALT or AST lower than three times the
upper limit of normal.

- Pulmonary disease: FVC or FEV1 ≥ 40% predicted.

- Cardiac ejection fraction ≥ 40%.

- Availability of an unrelated donor, identified and screened by the NMDP. The donor
will have at least 7/8 HLA-A, -B, -C and -DRB1 matching by high resolution molecular
typing and will meet NMDP eligibility criteria to serve as a peripheral blood
stem-cell donor.

- Karnofsky score ≥ 70% at the time of screening.

- Capacity to understand and sign the study informed consent form.

- Negative pregnancy test. Women of childbearing potential (not having had a
hysterectomy, a bilateral oophorectomy or bilateral tubal ligation, or be
post-menopausal with a total cessation of menses of > 1 year) must agree to use
documented reliable method(s) of contraception. Men should agree to use condoms
during the study period.

Exclusion Criteria:

- Patients with aplastic anemia or primary myelofibrosis. Patients with marrow fibrosis
secondary to MDS, AML or a myeloproliferative disorder other than primary
myelofibrosis are eligible.

- Patients who are not expected to be available for follow-up in our institution for at
least 180 days after the transplant.

- Prior allogeneic SCT.

- Uncontrolled bacterial, viral or fungal infections.

- Patients who receive maraviroc for the treatment of HIV infection.

- Patients receiving other investigational drugs for GVHD. Co-enrollment in other
clinical trials that do not include experimental GVHD therapies is allowed.

- Patients with prior malignancies are excluded unless treated with curative intent and
known to be free of disease for at least 2 years.