This study is researching a combination of 2 experimental drugs, referred to as "study drugs", called odronextamab (also known as REGN1979) and cemiplimab (also known as REGN2810). The study is focused on patients who have relapse/refractory aggressive B-cell lymphoma. The aim of the study is to see how safe and tolerable the study drugs are, and to define the recommended dose regimen for the combination with odronextamab. This study is also looking at several other research questions, including: * What side effects may happen from taking the study drugs * How effective the study drugs are against the disease * How much study drug is in the blood at different times * Whether the body makes substances or protein called antibodies against the study drugs (that could make the drugs less effective or could lead to side effects)