Although the in vitro resistance of quiescent primitive stem cells to TKI was shown more than a decade ago [5], the in vivo study of quiescent primitive LSCs in CML patients is difficult as these cells are overgrown by normal stem cells [16], and the expression of BCR-ABL1 mRNA is weak in the most primitive fraction [17, 18]. This evidence concerns the gene ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive.