BCR-ABL enhances differentiation of long-term repopulating hematopoietic stem cells

In a previously developed inducible transgenic mouse model of chronic myeloid leukemia, we now demonstrate that the disease is transplantable using BCRABL⁺ Lin^-Sca-1⁺c-kit⁺ (LSK) cells. Interestingly, the phenotype is more severe when unfractionated bone marrow cells are transplanted, yet neither progenitor cells (Lin ^-Sca-1^-c-kit⁺), nor mature granulocytes (CD11b⁺Gr-1⁺), nor potential stem cell niche cells (CD45^-Ter119^-) are able to transmit the disease or alter the phenotype. The phenotype is largely independent of BCR-ABL priming before transplantation. However, prolonged BCR-ABL expression abrogates the potential of LSK cells to induce full-blown disease in secondary recipients and increases the fraction of multipotent progenitor cells at the expense of long-term hematopoietic stem cells (LT-HSCs) in the bone marrow. BCR-ABL alters the expression of genes involved in proliferation, survival, and hematopoietic development, probably contributing to the reduced LT-HSC frequency within BCR-ABL⁺ LSK cells. Reversion of BCR-ABL, or treatment with imatinib, eradicates mature cells, whereas leukemic stem cells persist, giving rise to relapsed chronic myeloid leukemia on reinduction of BCR-ABL, or imatinib withdrawal. Our results suggest that BCRABL induces differentiation of LT-HSCs and decreases their self-renewal capacity.