Inclusion Criteria:

          1. Written informed consent

          2. Histologically confirmed adult patients diagnosed with CD20-positive monomorphic PTLD,
             DLBCL irrespective of EBV association

          3. Patients having undergone solid organ transplantation (heart, lung, liver, kidney,
             pancreas, small intestine transplantation, etc or a combination of the organ
             transplantations mentioned).

          4. No prior treatment for PTLD, DLBCL except reduction of immunosuppression

          5. At least one measurable lesion ≥ 1.5 cm in greatest transverse diameter by spiral CT

          6. Performance status: Eastern Cooperative Oncology Group (ECOG) 0-2.

          7. Age ≥ 19

          8. Adequate renal function: serum creatinine level < 2.0 mg/dL

          9. Adequate liver functions: Transaminase (AST/ALT) < 3 X upper normal value (or < 5 x
             ULN in the presence of DLBCL involvement of the liver), bilirubin < 2 X upper normal
             value (or < 5 x ULN in the presence of DLBCL involvement of the liver)

         10. Adequate hematological function: hemoglobin ≥ 9.0 g/dL absolute neutrophil count (ANC)
             ≥ 1,500/μL and platelet count ≥ 75,000/μL, unless abnormalities are due to bone marrow
             involvement by lymphoma. (Platelet transfusions to help patients meet eligibility
             criteria are not allowed within 3 days before study enrollment).

         11. Life expectancy 6 months

         12. A negative serum or urine pregnancy test prior to treatment must be available both for
             pre menopausal women and for women who are < 1 years after the onset of menopause.

         13. Female patients of child bearing potential must use an effective method of birth
             control (i.e. hormonal contraceptive, intrauterine device,diaphragm with spermicide,
             condom with spermicide or abstinence) during treatment period and 12 month thereafter;
             Males must use an effective method of birth control during treatment period and 12
             months thereafter.

        Exclusion Criteria:

          1. Other subtypes PTLD than monomorphic CD20 (+) DLBCL

          2. Previous treatment for PTLD, DLBCL with immunotherapy or chemotherapy except for
             short-term corticosteroids (duration of ≤ 8 days) before inclusion (Low dose steroid
             as immunosuppressant are allowed.)

          3. central nervous system (CNS) involvement by lymphoma or any evidence of spinal cord
             compression.

          4. Prior history of malignancies other than lymphoma (except for basal cell or squamous
             cell carcinoma of the skin, early gastric cancer or carcinoma in situ of the cervix or
             breast or untreated prostatic cancer without any plan for a treatment) unless the
             patient has been free of the disease for ≥ 3 years

          5. Patients with a known history of HIV or HCV seropositivity.

          6. Patients with active hepatitis B i. HBsAg positive or ii. HBsAg negative, anti-HBc-Ab
             positive and HBV-DNA PCR positive patients

          7. Pregnant or lactating women

          8. Men who are not surgically sterile or women of childbearing potential not employing
             adequate contraception

          9. Other serious illness or medical conditions i. Evidence of current uncontrolled
             cardiovascular conditions, including uncontrolled hypertension, uncontrolled cardiac
             arrhythmias, symptomatic congestive heart failure, unstable angina, or myocardial
             infarction within the past 6 months ii. History of significant neurological or
             psychiatric disorders including dementia or seizures iii. Active, uncontrolled
             infections requiring systemic antibiotic therapy or other serious infections within 14
             days before study enrollment iv. Other serious medical illnesses

         10. Known hypersensitivity to any of the study drugs or its ingredients

         11. Concomitant administration of any other experimental drug under investigation, or
             concomitant chemotherapy, hormonal therapy, or immunotherapy.