• Men and women ≥ 18 years of age.

• Patients must have histologic confirmation of Follicular Lymphoma (FL) (grade 1, 2 and 3A). Note: Participants who have received previous CD19-directed therapy must have a biopsy which shows CD19 expression after completion of the CD19-directed therapy.

• 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, or 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 relapse within 24 months of frontline treatment in patients previously treated with ≥1 line of systemic therapy; or

• Second FL relapse/progression after ≥1 line of systemic therapy. These patients will be eligible independently of GELF criteria and POD24.

• 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 or ≥ 60,000/mm3 in case of bone marrow involvement by lymphoma.

‣ 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 ≥30 ml/min/1.7m\^2 for patients with creatinine levels above institutional normal (unless due to lymphoma).