Inclusion criteria for study registration:

          1. Age 16 or over

          2. Primary refractory classical Hodgkin lymphoma or classical Hodgkin lymphoma in first
             relapse

          3. About to receive, or within 14 days of receiving first 2 cycles of first or second
             line salvage therapy (4 cycles if receiving treatment with brentuximab vedotin)

          4. Fit for autologous stem cell transplantation

          5. Written informed consent

          6. Willing to comply with the contraceptive requirements of the trial

        Exclusion criteria for study registration:

          1. Nodular lymphocyte predominant Hodgkin lymphoma

          2. Women who are pregnant or breastfeeding

          3. History of colitis, inflammatory bowel disease or pneumonitis

          4. Patients with autoimmune disorders, except patients with vitiligo, diabetes mellitus
             type 1, hypo- and hyperthyroidism not requiring immunosuppressive therapy

          5. Known history of hepatitis B or C infection

          6. Known HIV infection

          7. History of allergy (including severe/life threatening skin reaction) to monoclonal
             antibodies, anaphylaxis or uncontrolled allergy

          8. Major surgery within 4 weeks prior to registration

          9. Myocardial infarction, unstable angina, coronary artery bypass graft, cerebrovascular
             accident or transient ischaemic attack within the past 6 months

         10. Non-haematological malignancy within the past 3 years (with some exceptions - listed
             in protocol)

        Inclusion criteria for trial treatment:

          1. Has received 2 cycles of first or second line salvage chemotherapy, (4 cycles if
             receiving treatment with brentuximab vedotin)

          2. PET positive (Deauville score 4 or 5) after 2 cycles of first or second line salvage
             chemotherapy (4 cycles if receiving treatment with brentuximab vedotin)

          3. Fit for further salvage chemotherapy

          4. ECOG performance status 0-1

          5. Creatinine clearance >30ml/min calculated by Cockcroft-Gault formula

          6. Bilirubin <1.5 x ULN, ALT/AST <2.5 x ULN

          7. Adequate bone marrow function (Hb >80g/l, Platelets >50 x 10^9/l, neutrophils >1.0 x
             10^9/l)

        Exclusion criteria for trial treatment:

          1. Deauville score 1-3 after 2 cycles of first or second line salvage chemotherapy (4
             cycles if receiving treatment with brentuximab vedotin)

          2. Positive serology for hepatitis B or C (unless due to vaccination)

          3. Active infection requiring systemic therapy

          4. Ongoing requirement for immunosuppressive therapy, apart from inhaled, intranasal,
             topical corticosteroids or systemic corticosteroids at low doses (≤10mg prednisolone
             per day, or the equivalent)

          5. Chemo- or radiotherapy or corticosteroids at a dose of more than 10mg per day
             prednisolone or equivalent within 14 days prior to response PET-CT. NOTE:
             corticosteroids can be used AFTER a positive PET-CT scan for symptomatic disease but
             must be weaned to a dose of prednisolone ≤10mg/day or less (or equivalent) at least 7
             days prior to starting nivolumab.

          6. Treatment with any investigational agent within 28 days prior to planned start of
             nivolumab

          7. Ongoing grade 2-4 non-haematological toxicities related to prior Hodgkin lymphoma
             treatments, with the exception of alopecia and grade 2 fatigue

          8. Pregnant or breastfeeding women