Study on Sintilimab in Stage IV High Risk Neuroblastoma

Inclusion Criteria: 1. 12 Months to 12 years 2. Histologic verification of stage IV high risk neuroblastoma at relapse following lack of complete response to at least two lines of therapy 3. Fully recovered from the acute toxic effects of all prior anti-cancer treatment 4. At least 21 days after the last dose of myelosuppressive chemotherapy (42 days if prior nitrosourea) 5. At least 42 days after the completion of any type of immunotherapy, e.g. tumor vaccines 6. At least 56 days must have elapsed after transplant or stem cell infusion; patients with prior allogeneic transplants are not eligible 7. Blood counts recovery including White cell count \>= 750/mm\^3 and Platelet count \>= 50,000/mm\^3 8. Creatinine clearance ≥ 50ml/min 9. Liver function: Total bilirubin ≤ 2 mg/dl, Alanine aminotransferase or Aspartate aminotransferase ≤ 2.5 U/dl (or \< 5 in case of liver impairment) 10. Life expectancy of at least 4 months 11. Negative pregnancy test in women of childbearing potential 12. Use of an effective contraceptive method during the whole treatment and 13. up to 3 months after the completion of treatment in males and females 14. Prior informed consent signed Exclusion Criteria: 1. Patients requiring daily systemic corticosteroids are not eligible; patients must not have received systemic corticosteroids within 7 days of enrollment on study 2. Patients who are currently receiving another investigational drug are not eligible 3. Patients who are currently receiving other anti-cancer agents are not eligible 4. Patients with a history of any grade autoimmune disorder are not eligible; asymptomatic laboratory abnormalities (e.g. antinuclear antibody (ANA), rheumatoid factor, altered thyroid function studies) will not render a patient ineligible in the absence of a diagnosis of an autoimmune disorder 5. Patients with \>= grade 2 hypothyroidism due to history of autoimmunity are not eligible; note: hypothyroidism due to previous irradiation on thyroidectomy will not impact eligibility 6. Patients who have an uncontrolled infection are not eligible. 7. Patients with active autoimmune disease. (any autoimmune state requiring medical treatment-including chronic medications)all immune modifying drugs should be stopped at least 7 days prior to enrollment