Biological effects of T315I-mutated BCR-ABL in an embryonic stem cell-derived hematopoiesis model

The occurrence of T315I mutation during the course of targeted therapies of chronic myeloid leukemia is a major concern because it confers resistance to all currently approved tyrosine kinase inhibitors. The exact phenotype of the hematopoietic stem cell and the hierarchical level of the occurrence of this mutation in leukemic hematopoiesis has not been determined. To study the effects of T315I-mutated breakpoint cluster region-abelson (BCR-ABL) in a primitive hematopoietic stem cell, we have used the murine embryonic stem cell (mESC)-derived hematopoiesis model. Native and T315I-mutated BCR-ABL were introduced retrovirally in mESC-derived embryonic bodies followed by induction of hematopoiesis. In several experiments, T315I-mutated and nonmutated BCR-ABL-transduced embryonic bodies rapidly generated hematopoietic cells on OP-9 feeders, with evidence of hematopoietic stem cell markers. After injection into NOD/SCID mice, these cells induced myeloid and lymphoid leukemias, whereas transplantation of control (nontransduced) hematopoietic cells failed to produce any hematopoietic reconstitution in vivo. Moreover, the expression of native and T315I-mutated BCR-ABL conferred to mESC-derived hematopoietic cells a self-renewal capacity demonstrated by the generation of leukemias after secondary transplantations. Secondary leukemias were more aggressive with evidence of extramedullary tumors. The expression of stem cell regulator Musashi-2 was found to be increased in bone marrow of leukemic mice. These data show that T315I-mutated BCR-ABL is functional at the stem cell level, conferring to mESC-derived leukemic cells a long-term hematopoietic repopulation ability. This model could be of interest to test the efficiency of drugs at the stem cell level in leukemias with T315I mutation.