Bortezomib Plus Tacrolimus and Methotrexate to Prevent Graft Versus Host Disease (GVHD) After Mismatched Allogeneic Non-Myeloablative Blood Stem Cell Transplantation

Inclusion Criteria:

* Patients with hematologic malignancies including myelodysplastic syndrome (MDS), who are at a high risk of complications after myeloablative transplantation
* Patients have a donor (both related and unrelated) who are mismatched according to protocol criteria
* 18 years of age or older
* Performance status 0-2
* Life expectancy of \> 100 days
* Female subject is either post-menopausal or sterilized or willing to use an acceptable form of birth control
* Male subject agrees to use an acceptable form of birth control

Exclusion Criteria:

* Evidence of HIV infection
* Total bilirubin \> 2.0mg/dl that is due to hepatocellular dysfunction
* Aspartate aminotransferase (AST) \> 90
* Known active hepatitis B or C
* Serum creatinine \> 2.0
* Greater than or equal to Grade 2 peripheral neuropathy within 21 days of enrollment
* Prior allogeneic stem cell transplant
* Patients with myeloproliferative disease (e.g. myelofibrosis, essential thrombocythemia, polycythemia vera, chronic myeloid leukemia)
* Myocardial infarction within 6 months prior to enrollment or has NYHA Class III or IV hear failure, uncontrolled angina, severe uncontrolled ventricular arrhythmias, or electrocardiographic evidence of acute ischemia or active conduction system abnormalities
* Hypersensitivity to Velcade, boron or mannitol
* Pregnant or breast feeding
* Patient has received other investigational drugs 14 days before enrollment
* Serious medical or psychiatric illness
* Another active solid tumor malignancy at the time of study entry