Inclusion Criteria:

          1. Men and women ≥ 18 years of age.

          2. Patients must have histologic confirmation of Cluster of Differentiation (CD)19 and
             CD20-positive Follicular Lymphoma (FL) (grade 1, 2 and 3A)

          3. Patients with relapsed or refractory FL previously treated with ≥1 line of systemic
             therapy having ≥ 1 Groupe d'Etude des Lymphomes (GELF) criteria for therapy,
             Progression of Diseases within 24 months (POD24), or second relapse.

          4. Baseline FDG-PET/CT scans must demonstrate positive lesions compatible with CT defined
             anatomical tumor sites. Patients should have at least one measurable site of disease
             per Lugano classification.

          5. Patient should have ≥ 1 Groupe d'Etude des Lymphomes (GELF) criteria for treatment
             initiation).

               -  Involvement of ≥3 nodal sites, each with diameter of ≥3 cm

               -  Any nodal or extranodal tumor mass with a diameter of ≥7 cm

               -  B symptoms (fever ≥ 38 degrees Celsius of unclear etiology, night sweats, weight
                  loss > 10% within the prior 6 months).

               -  Risk of local compressive symptoms that may result in organ compromise

               -  Splenomegaly or splenic lesion without splenomegaly

               -  Leukopenia (leukocytes < 1000/mm3)

               -  Leukemia (> 5.000 lymphoma cells/mm3)

               -  Bone lesions detected on FDG-PET/CT; or

          6. Progression or relapsed within 24 months after FL diagnosis in patients previously
             treated with ≥1 line of systemic therapy; or

          7. Second FL relapse/progression after ≥1 line of systemic therapy.

          8. Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2.

          9. Life expectancy of greater than 6 weeks.

         10. Patients must have normal organ and marrow function as defined below,

               -  Absolute neutrophil count ≥1000/mm3 (unless due to lymphoma involvement of the
                  bone marrow or spleen).

               -  Platelets ≥100,000/mm3.

               -  Hemoglobin ≥ 10 g/dL or ≥8 g/dL in case of bone marrow involvement by lymphoma.

               -  Total bilirubin < 1.5 x within normal institutional limits (unless due to
                  lymphoma involvement of liver or a known history of Gilbert's disease).

               -  Gamma-Glutamyl Transpeptidase (GGT)/Aspartate Aminotransferase
                  (AST)/(SGOT)/Alanine Aminotransferase (ALT)(SGPT) ≤ 2.5 × institutional upper
                  limit of normal.

               -  Creatinine within normal institutional limits, or creatinine clearance ≥40
                  mL/min/1.73 m2 for patients with creatinine levels above institutional normal
                  (unless due to lymphoma).

        Exclusion Criteria:

          1. FL grade 3B or transformed FL.

          2. Patients with standardized uptake value (SUV) ≥ 14 on FDG-PET/CT and inaccessible
             biopsy site.

          3. > 2 lines of systemic immunochemotherapy for treatment of FL.

          4. Patients with clinically significant pleural effusions and/or ascites requiring
             drainage or associated with shortness of breath.

          5. Patients receiving any other investigational agents.

          6. Patients with known central nervous system involvement of lymphoma.

          7. Uncontrolled intercurrent illness such as: history of Myocardial Infarction (MI) in
             the last 6 months, congestive heart failure New York Heart Association (NYHA) Class
             III-IV, uncontrolled or symptomatic arrhythmia, stroke in last 6 months, liver
             cirrhosis, and autoimmune disorder requiring immunosuppression or long-term
             corticosteroids (>10 mg daily prednisone equivalent).

          8. Breastfeeding or pregnant women.

          9. Serologic status reflecting active hepatitis B or C infection. Patients that are
             positive for hepatitis B core antibody, hepatitis B surface antigen (HBsAg), or
             hepatitis C antibody will need a negative polymerase chain reaction (PCR) prior to
             enrollment. (PCR positive patients will be excluded.) Hepatitis C antibody positive
             patients are eligible if PCR is negative. Hepatitis B core antibody (+) patients
             without evidence of HBsAg or Hep B PCR (+) are eligible with appropriate Hepatitis B
             reactivation prophylaxis.

         10. Human immunodeficiency virus (HIV) infection.

         11. Patients with impaired decision-making capacity.