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

Inclusion Criteria: 1. Participants must be between 18 and 75 years; 2. Diagnostic Criteria: Meet the 2016 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: 1. 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; 2. 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. Eastern Cooperative Oncology Group (ECOG) performance status score of 0 to 2; 4. Expected survival of at least 12 weeks; 5. Normal Organ Function. Exclusion Criteria: 1. Acute promyelocytic leukemia; 2. Severe bleeding tendency or coagulation disorders, or currently receiving thrombolytic therapy; 3. Active tuberculosis (TB), currently undergoing anti-TB treatment, or treated for TB within 1 year prior to the study; 4. HIV-infected individuals, or known active syphilis infection; 5. Use of immunosuppressive drugs within 1 week before the first dose, excluding topical, inhaled, or other locally administered glucocorticoids, or physiologic doses of systemic glucocorticoids (not exceeding 10 mg/day prednisone equivalent) for allergic reactions or for managing respiratory distress from asthma, COPD, etc; 6. Receipt of live attenuated vaccines within 2 weeks before the first dose or planned during the study; 7. Participation in another clinical trial and receipt of investigational drug within 4 weeks prior to the first dose; 8. Receipt of immune-modulating drugs (including thymosin, interferons, except for local use to control pleural or ascitic fluid) within 2 weeks prior to the first dose; 9. At screening, hepatitis B or C viral tests positive according to either: * HBsAg positive with serum HBV-DNA titer ≥1×10\^3 copies/mL or above normal limits; * HCV antibody positive; 10. Any other condition or situation in which the investigator deems the patient unsuitable for participation in this study.