UC San Diego

Chronic myeloid leukemia (CML) is a cancer where a hematopoietic stem cell (HSC) has been identified and suggested to give rise to this cancer by acquisition of BCR-ABL, a fusion gene that produces a constitutively active protein tyrosine kinase product p210BCR-ABL. Although the initiating event of BCR-ABL expression occurs at the HSC level, inappropriate self-renewal pathway activation in granulocyte-macrophage progenitors represents a critical event in progression to blast crisis. However, the sequence of events required for the evolution of leukemic stem cell responsible for progression to blast crisis has not been firmly elucidated. Blast crisis is the most challenging phase of CML to treat and thus, demands further understanding. Efforts to model mechanisms of disease persistence and progression as well as therapeutic resistance in human cells have been limited by the relative dearth of CML patient blood and bone marrow samples. Previous research suggests that human embryonic stem cells (hESCs) may provide a limitless and consistent source of primitive hematopoietic cells. We have used a mouse aorta gonad mesonephros stromal cell line to differentiate hESCs to hematopoietic precursor cells. In these hESC differentiating cultures we observed that the addition of vascular endothelial growth factor and basic fibroblast growth factor enhance hemogenic endothelial cell generation from the hESC line less prone to hematopoietic differentiation. Furthermore, a transcription factor necessary for hematopoietic specification, c-Myb, is not sufficiently expressed in hESC derived CD34+ cells. With c -Myb over-expression, gene expression in CD34-, CD34+CD31-, and CD34+CD31+ hESC derived populations is altered. Expressing BCR-ABL in hESC derived CD34+ cells was able to confer primary engraftment in highly immunocompromised mice, but secondary engraftment was only achieved with the addition of constitutively active [Beta]-catenin, which is involved in self-renewal. BCR-ABL reduced the self-renewal capacity of cord blood stem and progenitor cells in vitro, which suggest the addition of constitutively active [Beta] -catenin is required to support the self-renewal of BCR- ABL+ cells. These findings implicate [Beta]-catenin plays a role in CML and suggest hESC can be used for the modeling of both CML and hematopoietic development