Inclusion Criteria:

- Patients must have had a prior solid organ or allogeneic stem cell transplant.

- Patients may be newly-diagnosed or relapsed after prior therapy

- Patients must have histologically confirmed CD20+ B-cell PTLD diagnosed according to
WHO criteria. PTLD may be characterized as early lesions, PTLD/polymorphic,
PTLD/monomorphic, or PTLD/other, all of which are eligible for this trial. B-cell
PTLD must be associated with EBV as demonstrated either by detection of EBV antigens
in tumor samples, or by increased EBV quantitative viral load in serum.

- Patients must have measurable disease

- 18 years of age or older

- Estimated life expectancy of > 3 months

- ECOG Performance status of 0, 1, or 2

- Adequate organ and marrow function

- Women of childbearing potential and men must agree to use adequate contraception
prior to study entry and for the duration of study participation.

Exclusion Criteria:

- Patients receiving any other study agents. Patients already on prophylactic doses of
ganciclovir or valganciclovir because of a prior history of CMV infection or because
of risk factors for CMV infection are eligible for the study and may continue CMV
prophylaxis.

- Patients with known brain metastases or central nervous system (CNS) involvement of
their lymphoma.

- Patients with a history of allergic reactions attributed to compounds of similar
chemical or biologic composition to bortezomib, rituximab, ganciclovir or
valgancyclovir.

- Patients with Grade 2 or greater neuropathy within 14 days before enrollment.

- 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.

- Psychiatric illness/social situations that would limit compliance with study
requirements.

- Pregnant or breastfeeding women

- Individuals with a history of malignancy are ineligible except for those outlined in
the protocol

- Known HIV positive individuals

- Active HBV infection may be included only if they are on appropriate anti-hepatitis B
therapy and have an undetectable HBV viral load

- Patient has received other investigational drugs within 14 days before enrollment

- Prior bortezomib