Ipilimumab With or Without Nivolumab in Relapsed/Refractory cHL

Inclusion Criteria: * Patients must have histologically determined classic Hodgkin lymphoma with pathologic review at the participating institution. * Participants must have measurable disease, defined as a lymph node or tumor mass ≥1.5 cm in at least one dimension by CT, PET/CT, or MR. Imaging must have been completed no greater than 6 weeks prior to study enrollment. Measurable disease that has previously been irradiated is permissible only if there has been evidence of progression since the radiation. * Patients must have progressed after two or more lines of systemic treatment, including autologous stem cell transplantation, if eligible. * Progression of disease or relapse following treatment with nivolumab or pembrolizumab. Intervening treatments with between PD-1 mAb therapy and the trial are permitted. * Patients may have had a prior autologous stem cell transplant and may have been treated with chimeric antigen receptor T-cells (CAR T-cells). * Age ≥18 years. * Eastern Cooperative Oncology Group (ECOG) performance status 0-2 (see Appendix A) * Adequate hematologic and organ function as defined below: * Absolute neutrophil count \> 1.0x109/L unless due to marrow involvement by lymphoma in which case ANC must be \>0.75x109/L. Growth factor support is allowed provided it is received at least 5 days prior to enrollment labs. * Platelets \> 75 x109/L, unless due to marrow involvement by lymphoma, in which case platelets must be \>50 x109/L * Estimated GFR (by Cockr…