Study to Assess if ABP798 is Safe & Effective in Treating Non Hodgkin Lymphoma Compared to Rituximab

Inclusion Criteria:

* Males and females 18 years of age and older
* Histological confirmed (by lymph node or extranodal region biopsy), Grade 1, 2, or 3a follicular B-cell NHL expressing CD20 within 12 months before randomization
* Stage 2, 3, or 4 (per Cotswold's Modification of Ann Arbor Staging System) with measurable disease (per International Working Group)

  * subjects must have a baseline scan (computed tomography \[CT\]) of the neck (if palpable lymph node \> 1.0 cm), chest, abdomen, and pelvis to assess disease burden within 6 weeks before randomization
  * subjects must have had a baseline bone marrow biopsy within 12 months before randomization. Previously confirmed positive bone marrow involvement does not need to be repeated for purposes of screening.
* Low tumor burden based on the Groupe d'Etudes des Lymphomes Folliculaires (GELF) criteria

  * largest nodal or extranodal mass ≤ 7 cm
  * no more than 3 nodal sites with diameter \> 3 cm
  * no splenomegaly \> 16cm by CT scan and no symptomatic splenomegaly
  * no significant pleural or peritoneal serous effusions by CT
  * lactate dehydrogenase ≤ upper limit of normal (ULN)
  * no B symptoms (night sweats, fever \[temperature \> 38°C\], weight loss \> 10% in the previous 6 months)

Exclusion Criteria:

* Diffuse large cell component and/or Grade 3b follicular NHL
* History or known presence of central nervous system metastases
* Malignancy other than NHL within 5 years (except treated in-situ cervical cancer, or squamous or basal cell carcinoma of the skin)
* Recent infection requiring a course of systemic anti-infective agents that was completed ≤ 7 days before randomization (with the exception of uncomplicated urinary tract infection)
* Other investigational procedures that can impact the study data, results, or patient safety while participating in this study are excluded; participation in observational studies is allowed.
* Subject is currently enrolled in or has not yet completed at least 30 days or 5 half-lives (whichever is longer) since ending other investigational device or drug study(s), including vaccines, or subject is receiving other investigational agent(s)
* Previous use of either commercially available or investigational chemotherapy, biological, or immunological therapy for NHL (including rituximab or biosimilar rituximab, or other anti-CD20 treatments)
* Systemic corticosteroid use within 3 months before randomization (inhaled are allowable)