Please refer to section 10 4. Bone marrow aspirate and biopsy only required on day 1 of cycle 4. Follow Up Study Assessments Toxicity Assessment Visit (+/- 7 days)0 Months 1-6 (+/- 7 days) Progression Free Survival1 (+/- 14 days) Survival Follow-Up (every 6 months for 5 years) History, physical exam, weight and height X X Vital Signs2 X X Ambulatory O2 sat3 X X ECOG performance score X X CBC, differential, platelet count, and blood chemistries X X TSH, Free T4, Free T3 X X Evaluation of Creatinine Clearance X X Quantitative serum immunoglobulins X X SPEP and immunofixation X X 24 Hour Urine for UPEP, protein excretion and immunofixation X X4 Bone Marrow Biopsy and Aspirate X X5 X5 Serum free light chain ratio X X B2M, CRP X Toxicity Assessment X X Skeletal Survey or alternative imaging X6 Con Meds X X Survival status X X Study tubes X7 0. Only required for patients who are removed from treatment due to progressive disease or to start alternative anti-myeloma therapy per MD discretion 1. Every 3 months after 6 month follow up visit for 5 years 2. Vitals (BP, HR, Temp, RR, O2 sat) to be taken within 15 minutes prior to start of nivolumab infusion and within 15 minutes following completion. 3. A O2 saturation reading at rest and on exertion should be obtained during each study visit. DF/HCC Protocol #: 18-280 Protocol Version Date: 10.17.2020 34 4. Only required for participants with +UPEP at baseline, otherwise random UPEP is permitted. If the random UPEP is positive, a 24-hour urine collection is required. 5. At Months 1, 3 and 6 follow up and at time of progression. 6. Months 1 and 6 only 7. Please refer to section 10 At Time of Disease Progression Study Assessments At Time of Disease Progression Quantitative serum immunoglobulins X SPEP and immunofixation X 24 Hour Urine for UPEP, protein excretion and immunofixation1 X Bone Marrow Biopsy and Aspirate X Serum free light chain ratio X Study tubes2 X 1. Only required for participants with +UPEP at baseline, otherwise random UPEP is permitted. If the random UPEP is positive, a 24-hour urine collection is required. 2.