Osteosarcoma is a highly malignant tumor that originates from mesenchymal tissue and is characterized by the production of bone-like stroma by spindle-shaped malignant tumor cells. It occurs in the distal femur, proximal tibia and proximal hazel bone at the stem marrow end. Osteosarcoma is the 3rd most common malignant tumor in children and adolescents, with rapid growth, early metastasis and poor prognosis. In the past 20 years, the survival rate has reached 60%-70% after comprehensive chemotherapy and surgery; however, the 5-year survival rate of osteosarcoma in children is still low, especially in children with multiple transitions of both lungs at the beginning of the disease. 1.Pre-operative chemotherapy (5 courses) after pathological diagnosis of osteosarcoma is carried out in the pediatric oncology specialty, and the chemotherapy regimen is SMHPO-OT12 based on the T12 regimen. 2.Osteosarcoma seedling preparation: the child is determined to retain the osteosarcoma seedling before the orthopedic surgery in our hospital and contact with the staff of the Biotherapy Technology Center, and the tumor tissue is retained during the surgery and sent to the Biotherapy Center for freezing and storage. 3.Post-operative chemotherapy (16 courses of treatment for tumor necrosis rate >90% and 13 courses of treatment for tumor necrosis rate <90% as determined by post-operative pathology) will be implemented in the pediatric oncology specialty. 4.The timing and indications of DC-CIK cell infusion combined with interleukin 2 immune maintenance therapy for osteosarcoma tumor: PETCT will be performed 1 month after completion of all chemotherapy to determine the absence of local and distant recurrence and metastasis, and normal blood image and organ function examination. 5.Osteosarcoma vaccine DC-CIK cell infusion combined with interleukin 2 immune maintenance treatment method: The single course method is briefly described as follows: (1) Day 0 (the day of blood collection): 30-50ml of peripheral blood is drawn (2) Day 8: DC vaccine is injected subcutaneously (3) Day 14-21: DC-CIK cells are stimulated by intravenous infusion of osteosarcoma vaccine (the specific time depends on the cell status) (4) 1 week before and after the infusion of DC-CIK cells, interleukin 2 (IL-2) 400,000 U/m^2 subcutaneously, once a day for 7 days; that is, 3 days before the infusion of CIK killer cells, the day of infusion and 3 days after the infusion. 6.Course of treatment: 12～18 courses of treatment in the first year after the end of chemotherapy, 1～2 times/month in the first half year and 1 time/month in the second half year, 6 courses of treatment in the second year after the end of chemotherapy, 1 time/2 months. 7.Cost: Osteosarcoma vaccine custodian fee is 6000 RMB in the 1st year, and 200 RMB/year afterwards; each course of treatment: Osteosarcoma vaccine DC-CIK cell infusion treatment is 12,000 RMB, DC vaccine injection is 3,000 RMB.