Inclusion Criteria:

          1. Patients must be ≥ 12 months and ≤ 50 years of age at the time of study enrollment.

          2. Patients with histologically confirmed solid tumors with an estimated poor long term
             survival.

          3. Performance Level: Karnofsky ≥ 50% for patients > 16 years of age and Lansky ≥ 60 for
             patients ≤16 years of age.

          4. Patients must be post RIC haploidentical BMT.

          5. Patients must have fully recovered from the acute toxic effects of prior BMT.

          6. Concomitant radiation therapy can be administered in the setting of this trial.

          7. Subjects must consent to allow for a baseline tumor biopsy. If a biopsy is not
             feasible, then archival tumor material must be made available. Tumor biopsies to be
             taken (if a subject's tumor is thought to be reasonably safe and easy to biopsy) at
             baseline (any time prior to the first dose after eligibility is met) and at Cycle 2
             (4-6 cores per time point) or when lesions are visualized on physical examination or
             imaging studies in the case of no identifiable masses at cycle 2. Additional optional
             biopsies may be obtained later in the course of study treatment. The proposed
             investigation is considered a non-significant risk (NSR). A significant risk procedure
             is generally considered to be one for which the procedure-associated absolute risk of
             mortality or major morbidity, in the patient's clinical setting and at the institution
             completing the procedure, is 2% or higher. Diagnostic Tissue Samples Tissue, fluid, or
             blood may be collected from standard of care procedures used to treat or diagnose
             immune related toxicities/GVHD.

          8. Organ Function Requirements:

             I. Adequate Hematologic Parameters:

               1. For patients with solid tumors without known bone marrow involvement:

                    -  Peripheral absolute neutrophil count (ANC) ≥ 500/mm3

                    -  Platelet count ≥ 50,000/mm3

               2. Patients with known bone marrow metastatic disease will be eligible for study
                  without the above criteria. They may receive transfusions provided they are not
                  known to be refractory to red cell or platelet transfusions. These patients will
                  not be evaluable for hematologic toxicity.

             II. Adequate Renal Function Defined as:

               1. Creatinine clearance or radioisotope Glomerular filtration rate (GFR) ≥
                  70ml/min/1.73 m2 or

               2. A serum creatinine based on age/gender as follows:

                    -  Age 1 to <2 years, Male: 0.6 and Female: 0.6

                    -  Age 2 to <6 years, Male: 0.8 and Female: 0.8

                    -  Age 6 to <10 years, Male: 1 and Female:1

                    -  Age 10 to <13 years, Male: 1.2 and Female 1.2

                    -  Age 13 to <16 years, Male: 1.5 and Female 1.4

                    -  Age ≥ 16 years, Male: 1.7 and Female 1.4

             III. Adequate Liver Function Defined as:

               1. Bilirubin (sum of conjugated + unconjugated) ≤1.5 x upper limit of normal (ULN)
                  for age

               2. Serum glutamic pyruvic transaminase (SGPT) (ALT) ≤110 U/L. For the purpose of
                  this study, the ULN for SGPT is 45 U/L.

          9. Patients must have been registered on protocol J12106 "A Phase II Trial of Reduced
             Intensity Conditioning and HLA-matched or Partially HLA-mismatched
             (HLA-haploidentical) Related Donor Bone Marrow Transplant for High-risk Solid Tumors"
             before enrolling on this study.Patient may be screened prior to Day +120 but first
             dose of study drug must be given on or after Day +120.

        Exclusion Criteria:

          1. GVHD: any history of Stage 4 skin GVHD or Stage 3 gut/liver GVHD (a.k.a. overall Grade
             III/IV GVHD) or any severe chronic GVHD. Any person with ≤ Grade II GVHD must be off
             systemic immunosuppressive therapy for at least 2 weeks prior to receiving Nivolumab
             therapy.

          2. Inhaled or topical steroids and adrenal replacement steroid doses are permitted in the
             absence of active auto- or allo-immune disease

          3. BMT-related toxicities: patients who developed idiopathic pneumonia syndrome (IPS) or
             veno-occlusive hepatic disease (VOD) must be off systemic immunosuppression and/or
             defibrotide for at least 14 days to be eligible.

          4. Infection: Patients who have an uncontrolled infection.

          5. Patients who in the opinion of the investigator may not be able to comply with the
             safety monitoring requirements of the study are not eligible.

          6. Has active, known or suspected autoimmune disease. Subjects with vitiligo, type I
             diabetes mellitus, residual hypothyroidism due to autoimmune thyroiditis only
             requiring hormone replacement, or conditions not expected to recur in the absence of
             an external trigger are permitted to enroll.

          7. Allergies and Adverse Drug Reaction

               1. History of allergy to study drug components.

               2. History of severe hypersensitivity reaction to any monoclonal antibody.

          8. Pregnancy or Breast Feeding: Women of childbearing potential (WOCBP) must agree to
             follow instructions for method(s) of contraception for the duration of study treatment
             with nivolumab and 5 months after the last dose of study treatment {i.e., 30 days
             (duration of ovulatory cycle) plus the time required for the investigational drug to
             undergo approximately five half-lives. Males who are sexually active with WOCBP must
             agree to follow instructions for method(s) of contraception for the duration of study
             treatment with nivolumab and 7 months after the last dose of study treatment {i.e., 90
             days (duration of sperm turnover) plus the time required for the investigational drug
             to undergo approximately five half-lives.