CD9, a potential leukemia stem cell marker, regulates drug resistance and leukemia development in acute myeloid leukemia

Background Leukemia stem cells (LSCs) are responsible for the initiation, progression, and relapse of acute myeloid leukemia (AML). Therefore, a therapeutic strategy targeting LSCs is a potential approach to eradicate AML. In this study, we aimed to identify LSC-specific surface markers and uncover the underlying mechanism of AML LSCs. Methods Microarray gene expression data were used to investigate candidate AML-LSC-specific markers. CD9 expression in AML cell lines, patients with AML, and normal donors was evaluated by flow cytometry (FC). The biological characteristics of CD9-positive (CD9 + ) cells were analyzed by in vitro proliferation, chemotherapeutic drug resistance, migration, and in vivo xenotransplantation assays. The molecular mechanism involved in CD9 + cell function was investigated by gene expression profiling. The effects of alpha-2-macroglobulin (A2M) on CD9 + cells were analyzed with regard to proliferation, drug resistance, and migration. Results CD9, a cell surface protein, was specifically expressed on AML LSCs but barely detected on normal hematopoietic stem cells (HSCs). CD9 + cells exhibit more resistance to chemotherapy drugs and higher migration potential than do CD9-negative (CD9 − ) cells. More importantly, CD9 + cells possess the ability to reconstitute human AML in immunocompromised mice and promote leukemia growth, suggesting that CD9 + cells define the LSC population. Furthermore, we identified that A2M plays a crucial role in maintaining CD9 + LSC stemness. Knockdown of A2M impairs drug resistance and migration of CD9 + cells. Conclusion Our findings suggest that CD9 is a new biomarker of AML LSCs and is a promising therapeutic target.