Inclusion Criteria:

          1. Age ≥18 years at the time of signing the informed consent document.

          2. Histologically confirmed mantle cell lymphoma (confirmation of cyclin D1 positivity on
             diagnostic biopsy).

          3. Subjects must have at least one bi-dimensionally measurable lesion; one of the
             measurements must be ≥1.5 cm in one direction

          4. No prior cytotoxic chemotherapy; prior therapy with single-agent rituximab is
             permitted. Prior involved-field radiotherapy to symptomatic nodal sites of involvement
             is also permitted.

          5. Prior therapy with rituximab is permitted, even in the setting of rituximab-refractory
             disease.

          6. Must meet one of the following criteria:

               1. Not eligible for more intensive cytotoxic chemotherapy or consolidative
                  autologous stem cell transplant based on one or more of the following:

                    -  Clinically significant heart or lung comorbidities, as reflected by at least
                       1 of the following:

                         -  LVEF ≤ 50%

                         -  Chronic stable angina or congestive heart failure controlled with
                            medication

                         -  NYHA class III or IV heart failure

                         -  Symptomatic chronic pulmonary disease or requirement for intermittent
                            or continuous oxygen therapy

                    -  Presence of other medical comorbidity or limitation in functional status
                       which the investigator judges to be incompatible with an acceptable risk to
                       the subject with the use of intensive chemotherapy. The associated
                       comorbidity or functional limitation must be clearly documented in the
                       medical record at the time of enrollment.

                  OR

               2. Subject has been informed of the risks and benefits of intensive chemotherapy and
                  autologous stem cell transplant for treatment of mantle cell lymphoma and has
                  refused this option. This discussion must be clearly documented in the medical
                  record at the time of enrollment.

          7. ECOG performance status of ≤2 at study entry.

          8. Laboratory test results within these ranges:

               1. Absolute neutrophil count ≥1500/µL.

               2. Platelet count ≥100,000/µL.

               3. Subjects with neutrophils <1500/µL or platelets <100,000/µL with splenomegaly or
                  extensive bone marrow involvement as the etiology for their cytopenias are
                  eligible.

               4. Subjects must have adequate renal function with a creatinine clearance of ≥40
                  mL/min as determined by the Cockcroft-Gault calculation.

               5. Total bilirubin ≤2X upper limit laboratory normal (ULN); subjects with
                  nonclinically significant elevations of bilirubin due to Gilbert's disease are
                  not required to meet these criteria.

               6. Serum transaminases AST (SGOT) and ALT (SGPT) ≤5X ULN.

               7. Serum alkaline phosphatase ≤5X ULN.

          9. Disease-free of prior malignancies for ≥2 years with the exception of basal or
             squamous cell skin carcinoma, carcinoma "in situ" of the breast or cervix, or
             localized prostate cancer (treated definitively with hormone therapy, radiotherapy, or
             surgery).

         10. Life expectancy of at least 3 months.

         11. Understand and voluntarily sign an informed consent document.

        Exclusion Criteria:

          1. Subjects are not eligible if there is a prior history or current evidence of central
             nervous system or leptomeningeal involvement.

          2. Concurrent use of other anti-cancer agents or treatments.

          3. Any serious medical condition, laboratory abnormality, or psychiatric illness that
             would prevent the subject from signing the informed consent document or complying with
             the protocol treatment.

          4. Prior malignancy, except for adequately treated basal cell or squamous cell skin
             cancer, in situ cervical or breast cancer, or other cancer from which the subject has
             been disease free for at least 2 years.

          5. Severe or life-threatening anaphylaxis or hypersensitivity reaction when previously
             exposed to rituximab or other mAb therapy.

          6. Known to be positive for HIV or infectious hepatitis (type B or C).

          7. Pregnant or breast-feeding females.

          8. Any condition, including the presence of laboratory abnormalities, which places the
             subject at unacceptable risk if he/she were to participate in the study or confounds
             the ability to interpret data from the study