• Patients must have histologically documented history of large B-cell lymphoma, including diffuse large B-cell lymphoma (DLBCL) not otherwise specified, primary mediastinal large B-cell lymphoma, high grade B-cell lymphoma, and DLBCL arising from follicular lymphoma.

• Adult males or females must be of age ≥18 years or older at time of signing informed consent.

• Patients must be capable of understanding the protocol with willingness to comply with all study procedures including availability for the duration of the study.

• Patients must be able to understand and willing to sign a written informed consent form (ICF) document.

• Measurable PET/CT positive disease (partial response or stable disease per the 2014 Lugano Classification) on PET/CT obtained at least 21 days after, but no more than 60 days after CAR-T with axicabtagene-ciloleucel.

• Eastern Cooperative Oncology Group (ECOG) performance status 0-2.

• Participants must have adequate organ and bone marrow function.

• Patients must have adequate hepatic function.

• Patients must have adequate renal function.

• Baseline Oxygen Saturation \>92% on room air.

• Females of reproductive potential must avoid pregnancy for at least 4 weeks before beginning lenalidomide therapy, during therapy, during dose interruptions and for at least 4 weeks after completing therapy. Females must commit either to abstain continuously from heterosexual sexual intercourse or to use two methods of reliable birth control, beginning 4 weeks prior to initiating treatment with lenalidomide, during therapy, during dose interruptions and continuing for 4 weeks following discontinuation of lenalidomide therapy.