ALBERT

Description: Background: The introduction of BCR/ABL-specific tyrosine kinase inhibitors (TKIs) more than two decades ago revolutionized chronic myelogenous leukemia (CML) therapy. The majority of CML patients treated with TKIs obtain durable cytogenetic and molecular responses. However, only a subgroup of these patients can successfully discontinue TKI therapy and maintain a treatment-free remission (Laneuville et al. 2011). TKI-resistant leukemia stem cells (LSCs) persist in the majority of patients at low levels over a prolonged period. These quiescent, self-renewing LSCs in the BM are the major cause of relapse after drug discontinuation (Holyoake et al, 2017). The selective elimination of LSCs requires the definition of unique signaling pathways that promote self-renewal of LSCs but not of normal HSCs. Based on the documented expression of CD93 on LSCs (Kinstrie et al, 2015), the aim of the present study was to investigate the role of the cell surface receptor CD93 in the regulation of self-renewal of human and murine CML LSCs and its contribution to disease development and progression. Methods and Results: We found CD93 expression on LSCs and leukemia progenitor cells but not on more differentiated leukemia granulocytes in a murine retroviral lineage-negative Sca-1+ c-kit+ (LSK) transduction/transplantation CML model. Next-generation sequencing analysis revealed that Cd93-/- LSCs have a silenced gene expression signature particularly in genes involved in the regulation of gene expression, stem cell maintenance and proliferation. Out of the 1120 genes differentially expressed between BL/6 and Cd93-/- LSCs, 1108 genes were down-regulated. In contrast, naïve BL/6 and Cd93-/- hematopoietic stem cells (HSCs) did not display a dysregulation in these pathways. Functionally, CD93-deficiency in LSCs resulted in impaired self-renewal, reduced LSC frequencies in vitro (at least by a factor of 100, P