CD33 and leukemia: As summarized in Fig. 4A, viable single cells were stained for CD45 and sub-gated into the CD56-/CD19+ fraction (6.5%) to demonstrate the absence of CD20 expression, but the co-expression of CD33 on these CD19+ cells, similar to the mixed-lineage-leukemia pro-B phenotype well-known from t(4;11) patients.