Inclusion Criteria:

- Recipients of allogeneic stem cell transplantation with myeloablative or
non-myeloablative conditioning regimens

- 100 days or more past stem cell transplantation

- Recipients of matched or mismatched, related or unrelated adult donor stem cells

- Must have cGVHD requiring systemic therapy

- No addition or subtraction of other immunosuppressive medications. The dose of
immunosuppressive medicines may be adjusted based on the therapeutic range of that
drug. However, if cGVHD occurs during a taper of immune suppression, the
medication(s) may not be increased back up to therapeutic level, but will continue a
the taper dose for the 15 week study duration

- Adequate bone marrow, hepatic and renal function as outlined in the protocol

- Does not require hemodialysis

- 18 years of age or older

- ECOG Performance Status of 0-2 or Karnofsky performance score of 70% or greater

- Life expectancy of more than 3 months

Exclusion Criteria:

- Systemic steroid therapy in the 4 weeks prior to enrollment

- Active malignant disease after transplantation. Complete resection of basal cell
carcinoma or squamous cell carcinoma of the skin, an in situ malignancy, or low-risk
prostate cancer after curative therapy will not be considered in this category

- Active uncontrolled infection

- Peripheral neuropathy CTC Grade 1 (or greater) with pain in the 4 weeks before
enrollment. Other neurological deficits must be reviewed with the study PI prior to
study entry

- Myocardial infarction within 6 months prior to enrollment or has NYHA Class III or IV
heart failure, uncontrolled angina, severe uncontrolled ventricular arrhythmias, or
electrocardiographic evidence of acute ischemia or active conduction system
abnormalities

- Hypersensitivity to bortezomib, boron, or mannitol

- Female subject is pregnant or breast-feeding

- Serious medical or psychiatric illness likely to interfere with participation in this
clinical study