Inclusion Criteria:  1. AML or acute leukemia of ambiguous lineage (acute undifferentiated leukemia or mixed phenotype acute leukemia) and have (a) refractory leukemia, defined as persistent leukemia after at least two courses of induction chemotherapy, OR (b)relapsed leukemia, defined as ≥ 1% blasts in the bone marrow OR rising MRD by flow cytometry on two or more serial samples.  If an adequate bone marrow sample cannot be obtained, subjects may be enrolled if there is unequivocal evidence of leukemia with ≥ 5% blasts in the peripheral blood.  Exclusion Criteria:  1. Uncontrolled infection. Infections controlled on concurrent anti microbial agents are acceptable, and anti microbial prophylaxis per institutional guidelines are acceptable.