CD34 and acute lymphoblastic leukemia: At least three different clusters, within B-ALL, depending on the differentiation stage of the leukemic blasts have been clearly identified in Mexican children: ProB (CD34+CD10+CD19+), PreB (CD34-CD10+CD19+) or the combination of both ProB and PreB precursors (10).Moreover, hematopoietic stem cells (HSCs) reside and are maintained in specialized microenvironments within the BM known as niches, which are comprised of various cell types, including stromal cells, particularly mesenchymal stromal cells (MSCs) (11).