Molecular Monitoring With Circulating Tumor DNA and Nivolumab Maintenance

Inclusion Criteria: * Patients must have a tissue diagnosis of diffuse large B cell lymphoma, with a negative PET/CT scan performed within 28 days of study enrollment, with one of the following clinical features: high risk IPI, ABC-subtype DLBCL, Double hit/ triple hit DLBCL, Ki67\>90%, or MYC translocation. * Patients can have any number of prior therapies and any amount of time period from the last therapy as long as they have complete response as seen in PET/CT at the time of enrolment. * Patients with prior salvage chemo-immunotherapy, radiation therapy, autologous transplantation are included * Prior radiation therapy must be completed at least 2 weeks prior to study enrollment * Autologous transplant must have been done 100 days prior to the study enrollment * Age \> 18 years. * ECOG performance status ≤ 2 * Life expectancy of at least 3 months * A formalin fixed tissue block or equivalent of 24 slides of the tumor sample for analyses by Adaptive Sequenta and NeoGenomics must be available for analysis. * Patients must be off cancer-directed therapy for at least 3 weeks (2 weeks for oral agents prior to day 1 of the study * Patients must have suitable organ and marrow function as defined below * Absolute neutrophil count \> 500/mm3 * Platelets \> 20,000/mm3 * Total bilirubin \< 2.5 times the ULN * AST/ALT (SGOT/SGPT) \< 2 times institutional normal limits * Creatinine ≤1.5 times normal institutional limits OR * Creatinine clearance \> 40 ml/min for patients * Ability to understand and willingness to sign a written informed consent and HIPAA consent document * WOCBP and sexually active, non-sterile men must be willing to use acceptable method of contraception. WOCBP must agree to not get pregnant and sexually active, non-sterile men must agree not to impregnate a woman for at least 18 weeks after the last dose of nivolumab Exclusion Criteria: * Patients with second malignancies (except monoclonal B cells of undetermined significance, antecendant indolent non Hodgkin lymphoma, non-melanomatous skin cancers, papillary thyroid carcinomas, ductal carcinoma in-situ, superficial bladder cancer, prostate cancer or in situ cervical cancers) are excluded unless a complete remission was achieved at least 3 years prior to enrollment and no additional therapy is required or anticipated to be required during the treatment. * Subjects with active autoimmune disease or a syndrome that requires systemic corticosteroids * Subjects who received non-oncology vaccine therapies for prevention of infectious disease within 4 weeks of study drug administration. * Prior therapy with an anti-PD-1, anti-PD-L1, anti-PD-L2 agent * Any contraindication to therapy with nivolumab * Prior allogeneic transplantation * Known hepatitis B virus (HBV) or hepatitis C virus (HCV) infection. Patients with documented cure from HCV infection will be included * Known uncontrolled human immunodeficiency virus (HIV) infection or known acquired immunodeficiency syndrome (AIDS). Patients with documented controlled HIV infection (CD4 \> 200 and undetectable viral load) will be included. * Any condition requiring systemic treatment with corticosteroids (\> 10 mg daily prednisone or equivalent) or other immunosuppressive medications within 14 days prior to first dose of study drug. Inhaled or topical steroids and adrenal replacement steroid doses \> 10 mg daily prednisone or equivalent are permitted in the absence of active autoimmune disease. * History of anaphylactic reaction to monoclonal antibody therapy * Poor psychiatric risk * Patients receiving other investigational agents * Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements. * Pregnant or breast feeding. Refer to section 4.4 for further details