In this study, invesigators propose to analyze 150 DLBCL patients, 50 MCL patients, and 100 FL patients to determine the clinical utility of ctDNA- as well as circulating tumor cell (CTC)-based MRD assessment in CAR therapy patients. The project detailed in this protocol will utilize the clonoSEQ platform as specific quantification of residual DLBCL/FL/MCL and correlate its results with radiologic assessment of disease and clinical outcomes. Invesitgators predict there will be a strong correlation between ctDNA and PET/CT and dynamic changes in ctDNA will precede radiologic evidence of disease recurrence in patients following CAR therapy.

Inclusion Criteria:

• Immunophenotypically confirmed diagnosis of follicular lymphoma (FL), Immunophenotypically confirmed diagnosis of Large B Cell Lymphoma (LBCL) (including transformed FL and Primary Mediastinal B-cell Lymphoma) OR Immunophenotypically confirmed diagnosis of mantle cell lymphoma (MCL) undergoing commercially approved CAR-T therapy in accordance with FDA indication with enrollment in this trial prior to CAR infusion
• CAR-T product must meet manufacturer specifications
• PET measurable disease at the time a decision is made to prescribe CAR treatment
• Has sample from diagnosis or relapse available for genomic DNA extraction to identify patient's clonotype via clonoSEQ (see lab manual for details)

Exclusion Criteria:

• Lack of archival diagnostic or fresh/archival relapse tissue for purposes of determining patient's lymphoma clonotype. Given that 5-10% of patients cannot have a clonotype identified by clonoSEQ, those patients will be removed from the study and excluded from analysis, but their samples will continued to be stored for future analysis as improvements to the analysis platform are made.
• No patients are to be excluded on the basis of gender, race, ethnic background, sexual orientation, or other demographic characteristics.

Subjects ≥ 18 years of age, with DLBCL, FL, or MCL who are undergoing standard-of-care CAR therapy.