HOXA10-Overexpression causes severe perturbations in human hematopoiesis

Normal hematopoiesis is linked to the differential expression of multiple members of the Hox transcription factor family. Moreover, studies in murine transplantation models have shown that overexpression of A cluster HOX genes (i.e. HOXA10, HOXA9) is leukemogenic. We have now tested directly the impact of dysregulated HOXA10 expression on human hematopoietic cells in vitro and in vivo using highly purified CD34+/GFP+ cells transduced with a MSCV vector carrying a HOXA10-IRES-GFP cassette or a GFP cassette only (control). HOXA10 altered lineage differentiation with a 85% reduction in BFU-E colony formation (P = 0.017) and increased the self-renewal of clonogenic progenitor cells with an over 120 fold increase in secondary colony formation which were predominantly of blast morphology compared to control. The in vitro data were extended by in vivo analysis of NOD/SCID mice fulfilling the criteria of lymphomyeloid engraftment with transduced human cells. 12 wks post transplantation there was a 2 fold increase in the total number of clonogenic progenitors per 10 6 engrafted CD34+ human cells in the HOXA10- transduced compartment (P = 0.04). Furthermore, ex vivo HOXA10 overexpressing progenitors formed a 19 fold increased number of blast colonies. HOXA10 also markedly impaired in vivo differentiation into B cells (70% drop in absolute number). Imbalanced HOXA10 expression thus initiates profound perturbations in human hematopoiesis pointing to a potential role of abnormally increased self-renewal and altered lineage differentiation in HOX gene-associated leukemogenesis.