The following criteria is provided for health care professionals.

Inclusion Criteria

1. Age≥18 years with hematological malignancies who have undergone allogeneic transplant for hematological malignancy
2. Relapsed disease post-allogeneic transplant defined as follows i. Acute or Chronic Leukemia or myelodysplastic or myeloproliferative disorders or NK cell neoplasms: Bone marrow (BM) with ≥5% disease involvement or peripheral blood evidence of overt relapse ii. Lymphoma: BM evidence of relapsed/persistent disease or PET/CT or CT evidence of persistent/progressive lymphadenopathy consistent with active lymphoma. Active disease defined as nodal lesions greater than 20 mm in the long axis or extranodal lesions >10 mm in long and short axis or bone marrow involvement that is biopsy proven
3. Karnofsky performance status ≥70 (See Appendix A for details)
4. Creatinine ≤ 2x upper limit of normal (ULN)
5. Adequate hepatic function, defined as AST and ALT ≤3 x ULN. Serum bilirubin and alkaline phosphatase ≤3 x ULN, or considered not clinically significant (e.g. Gilbert's or indirect hyperbilirubinemia) or felt to be due to underlying disease.
6. Without evidence of active acute or chronic GVHD
7. Off all immunosuppression and corticosteroids (other than replacement dose steroids defined as equivalent to a maximum of 10 mg Prednisone daily) for ≥10 days from first treatment.
8. Off all disease targeted treatments for ≥10 days to first treatment day
9. Able to provide written informed consent
10. Women of child-bearing potential and men must agree to use adequate contraception for the duration of study participation and for 120 days after the last treatment with nivolumab.
11. No FDA approved, more appropriate therapies available for disease control as determined by the treating physician

Exclusion Criteria

1. Positive beta-HCG in female of child-bearing potential
2. CD3 donor chimerism <5% within 4 weeks of starting study treatment
3. Evidence of active acute or chronic GVHD and/or on treatment for GVHD.
4. Prior administration of donor lymphocyte infusion post-allogeneic transplant within the last 6 months of study treatment
5. History of or active autoimmune disease, or other syndrome that requires systemic steroids.
6. History of allergic reactions attributed to compounds of similar chemical or biologic composition to nivolumab.
7. Uncontrolled or active infections on treatment
8. Confirmed active human immunodeficiency virus (HIV), Hepatitis B or C infection.
9. Presence of ≥grade 3 non-hematologic toxicities as per CTCAE version 5 from any previous treatment unless it is felt to be due to underlying disease.
10. Concurrent use of investigational therapeutic agents or enrollment on another therapeutic clinical trial at any institution.
    1. Minimum of 4 weeks from last dose of investigational agent
11. Prior exposure to PD-1 or CTLA4 antibodies in the post-allogeneic transplant setting. Patients who received such agents pre-allogeneic transplant will NOT be excluded
12. Prior exposure to daratumumab in the post-allogeneic transplant setting within 2 months of start date of treatment with this investigational protocol. Patients who received this agent pre-allogeneic transplant will NOT be excluded
13. Concurrent therapies targeted at disease relapse. However, previous treatments for relapsed disease are allowed. Concurrent active malignancy (exceptions: treated solid malignancy in >2 years' remission, treated basal or squamous cell carcinomas of the skin)
14. History of Crohn's disease or ulcerative colitis
15. History of demyelinating disorder
16. Prior intolerance or allergy to Tocilizumab