REGN1979 vs Investigator's Choice in Previously Untreated Participants w/ Follicular Lymphoma

Study Purpose

This study is researching an experimental drug called odronextamab, referred to as study drug. The study is focused on participants with previously untreated follicular lymphoma (a type of non-Hodgkin lymphoma or NHL). This study will be made up of two parts: Part 1 (non-randomized) and Part 2 (randomized - controlled). The aim of Part 1 of the study is to see how safe and tolerable the study drug is when given alone. The aim of Part 2 of the study is to see how the study drug works compared to rituximab (called the "comparator drug") and chemotherapy (the current standard of care for NHL). Standard of care means the usual medication expected and used when receiving treatment for a condition. The study is looking at several other research questions, including: - What side effects may happen from taking the study drug - How much study drug is in the blood at different times - Whether the body makes antibodies against the study drug (which could make the study drug less effective or could lead to side effects) - How the study drug affects quality of life and ability to complete routine daily activities.