Extensive analysis of the T315I substitution and detection of additional ABL mutations in progenitors and primitive stem cell compartment in a patient with tyrosine kinase inhibitor-resistant chronic myeloid leukemia.

Tyrosine kinase inhibitors (TKIs) have revolutionized the treatment of chronic myeloid leukemia (CML). However, resistance is occasionally observed, mainly due to mutations within the BCR-ABL kinase domain. The T315I substitution confers complete resistance to all TKIs commonly used in clinical practice. To date, the hierarchical level of stem cells in which this mutation initially appears has not been studied. The aim of this study was to evaluate the behavior of T315I mutated cells and to study the presence of potential additional mutations in progenitors and stem cells from a patient with CML. A comprehensive analysis of BCR-ABL(315I) mRNA expressing cells in mononuclear cells, in CD34+ cell populations, and in their primitive long-term culture-initiating cell (LTC-IC) derived progenitors was performed. We show that the T315I substitution arises in primitive Ph1 stem cells without altering their myeloid and erythroid terminal differentiation potential. Leukemic cells expressing a T315I mutated BCR-ABL display a progressive decline in LTC-IC assays as described for non-mutated CML cells at diagnosis. Finally, in our experiments, additional non-315 ABL mutations were identified in hematopoietic stem cell colonies. This observation is suggestive of genetic instability affecting CML progenitors.