• • Histologically confirmed diagnosis of acute myeloid leukemia (AML) according per 2016 World Health Organization (WHO) criteria.

‣ Cluster of differentiation marker (CD)33 and CD123 / interleukin (IL)3RA expression on the subject's blasts, determined by standard Flow AML MRD assay.

⁃ Age ≥ 12

⁃ Relapsed or refractory after one cycle of prior therapy (cytoreductive agents such as hydroxyurea, cyclophosphamide, or a single dose of gemtuzumab ozogamicin are not considered prior treatment regimens).

⁃ Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0, 1, or 2

⁃ Adequate baseline organ function, including cardiac, renal, and hepatic function as defined by:

• Left ventricular ejection fraction (LVEF) ≥ 50% by multi-gated acquisition scan (MUGA) or 2-dimensional (2-D) echocardiogram (ECHO) within 28 days prior to the start of therapy

∙ No clinically significant abnormalities on a 12-lead electrocardiogram (ECG)

∙ Creatinine Clearance (CrCl) ≥ 60mL/min

∙ Serum albumin ≥ 3.2 g/dL (note that albumin infusions are not permitted in order to enable eligibility)

∙ Total bilirubin ≤ 1.5 mg/dL

∙ Aspartate transaminase (AST) and alanine transaminase (ALT) ≤ 2.5 times the upper limit of normal (ULN)

⁃ white blood cell (WBC) \< 20,000/uL on day of first therapy, cytoreduction may be achieved using hydroxyurea.

⁃ Ability to understand and willingness to sign a written informed consent document.

⁃ Able to adhere to study visit schedule and other protocol requirements including follow up for survival assessment.

⁃ If the patient is a woman of child-bearing potential (WOCBP), they should have a negative serum or urine pregnancy test within 1 week prior to tagraxofusp-erzs treatment. (Note: WOCBP include any female who has experienced menarche and who has not undergone successful sterilization (hysterectomy, bilateral tubal ligation or bilateral oophorectomy) or is not postmenopausal (defined as amenorrhea ≥ 12 consecutive months; or women on hormone replacement therapy with documented serum follicle stimulating hormone level ≥ 35 milli-international units per milliliter (mIU/mL).

⁃ Patients agree to use acceptable contraceptive methods for the duration of time in the study, and to continue to use acceptable contraceptive methods for 1 week after the last tagraxofusp-erzs infusion.

⁃ The patient has signed informed consent prior to initiation of any study-specific procedures or treatment. The patient is able to adhere to the study visit schedule and other protocol requirements.