CD9 is a leukemic stem cell-specific marker in human acute myeloid leukemia

Abstract Background: Leukemia stem cells (LSCs) are responsible for the initiation, progressing and relapse of acute myeloid leukemia (AML). Therefore, the therapy strategy of targeting LSCs is hopeful to eradicate AML. In this study, we aimed to identify LSCs-specific surface markers and uncover the underlying mechanism of AML LSCs.Methods: Microarray gene expression data were used to investigate the candidate AML-LSCs specific markers. CD9 expression was evaluated by flow cytometry (FC) in AML cell lines, patients with AML and normal donors. 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. Effects of alpha-2-macroglobulin (A2M) on CD9+ cells were analyzed in the aspects of proliferation, drug resistance and migration.Results：CD9, as a cell surface protein, is specifically expressed on AML LSCs, but barely can be detected on normal hematopoietic stem cells (HSCs). CD9+ cells exhibits more resistance to chemotherapy drugs and higher migration potential than CD9-negative (CD9-) cells. More importantly, CD9+ cells possess the ability to reconstitute human AML in immunocompromised mice and promote leukemia growth, suggesting CD9+ cells define the LSCs population. Furthermore, we identified A2M as an important role in CD9+ LSCs stemness maintenance. Knock down of A2M impairs drug-resistance and migration of CD9+ cells.Conclusion: Our findings suggested that CD9 is a new biomarker of AML LSCs and may serve as a promising therapeutic target.