‣ To be eligible for the study, participants must meet all of the following criteria:

• Give informed consent and sign a written informed consent form.

• Age ≤ 18 years, no gender limitation.

• Karnofsky (≥16 years) or Lansky (\<16 years) (Appendix 2) performance status score of at least 50 (Appendix 2).

• Diagnosis of high-risk and relapsed/refractory pediatric soft tissue sarcoma, confirmed by clinical criteria, and who have undergone prior comprehensive treatment (surgery, chemotherapy, radiation, and/or stem cell transplantation).

• Estimated survival time of at least 12 weeks.

• Complete recovery from all acute toxicities of prior anti-cancer chemotherapy, such as bone marrow suppression with recovery to grade I.

• Myelosuppressive chemotherapy: at least 21 days after the last myelosuppressive chemotherapy (42 days if prior use of nitrosourea).

• Experimental drugs or anti-cancer therapies other than chemotherapy: not used within 28 days prior to the planned start of NK cell immunotherapy. Must be fully recovered from the clinical significant toxicity of the therapy.

• Hematopoietic growth factors: at least 14 days after the last administration of long-acting growth factor or 3 days after the last administration of short-acting growth factor.

⁃ X-ray therapy (XRT): at least 14 days after local palliative XRT (small field mouth) or at least 42 days after other substantive bone marrow (BM) irradiation, including prior radioactive iodine-131 meta-iodobenzylguanidine (131I-MIBG) treatment.

⁃ Stem cell transplantation without whole-body irradiation (TBI): no evidence of active graft versus host disease (GvHD), and at least 56 days after transplantation or stem cell transplantation.

⁃ Laboratory tests during the screening period must meet the following conditions:

⁃ Absolute neutrophil count (ANC) ≥ 1.0 × 10\^9/L (ANC ≥ 0.5 × 10\^9/L if bone marrow involvement).

⁃ Platelet count (PLT) ≥ 75 × 10\^9/L (PLT ≥ 20 × 10\^9/L if bone marrow involvement).

⁃ Bilirubin ≤ 1.5 times the upper limit of normal (ULN). Creatinine ≤ 1.5 times the ULN (calculated according to the standard Cockcroft-Gault formula).

⁃ ALT/AST ≤ 3 times the ULN (can be relaxed to 5 times the ULN if liver metastasis is present).

⁃ Ability to comply with outpatient treatment, laboratory monitoring, and necessary clinical visits during the study. For pediatric or adolescent participants, the parent/guardian must be able to understand, consent, and sign the study informed consent form (ICF) and applicable child consent form before initiating any protocol-related procedures. The participant will be able to express their consent (where applicable) under the consent of the parent/guardian.