Inclusion Criteria:  Men and women ≥ 18 years of age. Patients must have histologic confirmation of Cluster of Differentiation (CD)19 and CD20-positive Follicular Lymphoma (FL) (grade 1, 2 and 3A) 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. 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.  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 Progression or relapsed within 24 months after FL diagnosis in patients previously treated with ≥1 line of systemic therapy; or Second FL relapse/progression after ≥1 line of systemic therapy. Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2. Life expectancy of greater than 6 weeks.  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:  FL grade 3B or transformed FL. Patients with standardized uptake value (SUV) ≥ 14 on FDG-PET/CT and inaccessible biopsy site. > 2 lines of systemic immunochemotherapy for treatment of FL. Patients with clinically significant pleural effusions and/or ascites requiring drainage or associated with shortness of breath. Patients receiving any other investigational agents. Patients with known central nervous system involvement of lymphoma. 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). Breastfeeding or pregnant women. 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. Human immunodeficiency virus (HIV) infection. Patients with impaired decision-making capacity.