To study the effects of the different i-niche cells in supporting lymphoid and myeloid cell types we co-culture leukemia cells from a patient with infant ALL/t(4; 11) who initially presented with a CD34+CD19+CD33+CD15− immunophenotype, but relapsed at 5 months with a myeloid CD34+CD19−CD33+CD15+ leukemia. This evidence concerns the gene CD33 and acute lymphoblastic leukemia.