Nivolumab With Gemcitabine, Oxaliplatin + Rituximab in r/r Elderly Lymphoma Patients

Inclusion Criteria: * patients with first relapse or progression of an aggressive Non-Hodgkin's lymphoma * all patient \>65 years of age or \> 18 years if not eligible for neither autologous nor allogeneic stem cell transplantation * all patient \>65 years of age or older than 18 years if HCT-CI score \> 2 or patients who underwent prior autologous stem cell transplantation and are not eligible for allogeneic stem cell Transplantation * All risk groups (IPI 0 to 5) * Diagnosis of aggressive Non-Hodgkin's lymphoma, based on an excisional biopsy of a lymph node or on an appropriate sample of a lymph node or of an extranodal involvement at initial diagnosis or relapse or Progression. The entities treated in the study will be based on the WHO 2017 classification. * ECOG 0 - 2 * only one prior chemotherapy regimen including an anthracycline. The last cytotoxic drug must be given at least four weeks before entering the study. Rituximab must be part of the first-line regimen in case of B-cell lymphoma (except for primary CD20- negative lymphoma). Patients may have received prior radiation therapy as part of their first-line therapy * Men who are sexually active with women of childbearing potential (WOCBP) must not father a child during and up to 6 months after GemOx and up to 12 months after Rituximab and/or Nivolumab. They are advised to do cryoconservation of sperm prior to treatment. * Written informed consent of the patient * Patient must be covered by social security system Exclusion Criteria: * Already initiated lymphoma therapy after first relapse or progression * Serious accompanying disorder or impaired organ function * WBC \< 2.5 G/l, Neutrophils \< 2 G/l, Platelets \< 100 G/l * Prolongation of QTc interval \> 450 ms, demonstrated in one electrocardiogram (done as triplicate). This does not apply for patients with a block of the right and/or left bundle branch. * Family history for Long QT-Syndrome * active, known or suspected autoimmune disease * no requirement for immunosuppressive doses of systemic corticosteroids * Chronic active hepatitis B or C * HIV-infection * Patients with a severe immunodeficiency * Previous therapy with Nivolumab,Gemcitabine or Oxaliplatin * Patients with a "currently active" second malignancy other than non-melanoma skin cancer * CNS involvement of lymphoma * Persistent neuropathy grade \>2 * Pregnancy or breast-feeding women * Women of childbearing potential * Active serious infections not controlled by oral and/or intravenous antibiotics or anti-fungal medication * Any medical condition which in the opinion of the investigator places the subject at an unacceptably high risk for toxicities * Lymphomas other than those listed in the inclusion criteria notably indolent lymphoma, Mantle cell lymphoma, Burkitt lymphoma, adult T-cell leukemia/lymphoma. * Persons not able to understand the impact, nature, risks and consequences of the trial (including language barrier) * Persons not agreeing to the transmission of their pseudonymous data * Persons depending on sponsor or investigator * Persons from highly protected Groups * Allergies and Adverse Drug Reaction History to study drug components * Participation in another clinical trial with drug intervention within 4 weeks prior to start of the first cycle and during the study. However, participation in a clinical trial of firstline therapy of lymphoma is allowed.