CD33 and acute myeloid leukemia: AML with an immunophenotypic signature similar to monocyte progenitors (MPs) and granulocyte progenitors (GPs) is phenotypically negative for CD34, positive for myeloid markers CD13, CD33, and variable for CD117, with varying levels of HLA-DR expression (≥20% for MP-like and <20% for GP-like).