The study is researching an experimental drug called REGN5837 in combination with another experimental drug, odronextamab (called "study drugs"). The aim of the study is to see how safe and tolerable the study drugs are, and to define the recommended dose for phase 2. The study is looking at several other research questions, including: * What side effects may happen from taking the study drugs * How much study drug is in the blood at different times * Whether the body makes antibodies against the study drugs (that could make the drugs less effective or could lead to side effects) * To find out how well the study drugs work against relapsed or refractory aggressive B-cell non-Hodgkin lymphomas (B-NHLs)