CD93 is expressed on chronic myeloid leukemia stem cells and identifies a quiescent population which persists after tyrosine kinase inhibitor therapy

The introduction of BCR-ABL tyrosine kinase inhibitors has revolutionized the treatment of chronic myeloid leukemia (CML). A major clinical aim remains the identification and elimination of low-level disease persistence, termed “minimal residual disease”. The phenomenon of disease persistence suggests that despite targeted therapeutic approaches, BCR-ABL-independent mechanisms exist which sustain the survival of leukemic stem cells (LSCs). Although other markers of a primitive CML LSC population have been identified in the preclinical setting, only CD26 appears to offer clinical utility. Here we demonstrate consistent and selective expression of CD93 on a lin(−)CD34(+)CD38(−)CD90(+) CML LSC population and show in vitro and in vivo data to suggest increased stem cell characteristics, as well as robust engraftment in patient-derived xenograft models in comparison with a CD93(−) CML stem/progenitor cell population, which fails to engraft. Through bulk and single-cell analyses of selected stem cell and cell survival-specific genes, we confirmed the quiescent character and demonstrate their persistence in a population of CML patient samples who demonstrate molecular relapse on TKI withdrawal. Taken together, our results identify that CD93 is consistently and selectively expressed on a lin(−)CD34(+)CD38(−)CD90(+) CML LSC population with stem cell characteristics and may be an important indicator in determining poor TKI responders.