Acute Myeloid Leukemia (AML) is a cancer of the blood and bone marrow. This study is testing a new treatment for people whose AML has come back or isn't responding to normal treatments. The treatment uses special cells called **CAR-NK cells**, which are modified natural killer cells that target cancer cells. These cells are developed from healthy donors and are meant to attack leukemia that shows a marker called **CD123**.

Participants in this study will first receive chemotherapy with drugs called Fludarabine and Cyclophosphamide, followed by the new treatment. Doctors will check for any side effects and how well the treatment works. Participants must be 18 or older, have a certain level of health, and cannot have any active brain leukemia or serious infections.

• **Duration**: Participants must be willing to use contraception for 12 months.
• **Visits Required**: Regular visits for monitoring safety and effectiveness.
• **Risks**: Potential side effects from chemotherapy and new treatment.