Safety and Efficacy of NK520 to Treat Pediatric Relapsed/Refractory Acute Myeloid Leukemia

Inclusion Criteria: 1. Participants must be between 6 and 18 years; 2. Diagnostic Criteria: Meet the 2022 World Health Organization (WHO) diagnostic criteria for AML, unsuitable for current treatments or patients with relapsed/refractory AML after ≥2 lines of therapy. The definition of relapsed/refractory acute myeloid leukemia is based on the 2017 Chinese Guidelines for Diagnosis and Treatment: a. Relapsed AML: Diagnosis is confirmed when leukemia cells reappear in the peripheral blood or bone marrow blast cells exceed 5% after complete remission (CR) (excluding reasons such as bone marrow regeneration post-consolidation chemotherapy) or there is extramedullary infiltration by leukemia cells; b. Refractory AML: Initial cases unresponsive after two cycles of standard regimen treatment; recurrence within 12 months after CR and consolidation therapy; recurrence beyond 12 months with ineffectiveness of conventional chemotherapy; those who have relapsed twice or more; or persistent extramedullary leukemia; 3. For participants under 16 years old, Lansky performance status must be ≥50%; for participants aged 16 or older, Karnofsky performance status must be ≥50%; 4. Expected survival of at least 12 weeks; 5. Normal Organ Function. Exclusion Criteria: 1. Acute promyelocytic leukemia, chronic myeloid leukemia, acute mixed lineage leukemia, or known central nervous system leukemia; 2. AML associated with congenital syndromes, such as Down syndrome, Fanconi anemia, Bloom syndrome, Kostmann syndrome, or congenital aplastic anemia; 3. Severe bleeding tendency or coagulation disorders, or currently receiving thrombolytic therapy; 4. HIV-infected individuals, or individuals with known active syphilis infection; 5. Receipt of live attenuated vaccines within 2 weeks before the first dose or planned during the study period; 6. Participation in another clinical trial and receipt of investigational drug within 4 weeks prior to the first dose; 7. Receipt of immune-modulatory drugs (including thymosin, interferons, except for local use to manage conditions like pleural or ascites fluid) within 2 weeks before the first dose; 8. At screening, positive hepatitis B or C viral markers as follows: * HBsAg positive with serum HBV-DNA level ≥1×10\^3 copies/mL or above normal range; * Positive for HCV antibodies; 9. Any other condition or situation in which the investigator deems the patient unsuitable for participation in this study.