We are doing this study to find out if an experimental drug called CT01681 (the study drug) is a safe and effective option for people who get CAR T-cell therapy as a treatment for diffuse large B cell lymphoma (DLBCL). We want to know if the study drug has the potential to lower or prevent certain side effects of CAR T-cell therapy. The possible side effects of CAR T-cell therapy that the study drug is being developed to protect against are called cytokine release syndrome and immune effector cell-associated neurotoxicity syndrome. This study is enrolling people who will receive an available form of CAR T-cell therapy called YESCARTA.