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Phagocytosis checkpoints on hematopoietic stem cells in patients with myelodysplastic syndromes. BACKGROUND: The myelodysplastic syndrome (MDS) is a high-risk hemocytopenia easily converted to acute myeloid leukemia. CD47 plays an important role in regulating phagocytosis, and its role in the pathogenesis of MDS is unclear. METHODS: CD47 and PI3K/AKT/mTOR on CD34+ CD38- cells were detected by flow cytometry. NF-κB, PI3K, AKT, PTEN, and mTOR mRNA overexpressed in CD34+ CD38- CD47+ cells were performed by real-time quantitative transcriptase-polymerase chain reaction. Phagocytic capacity of macrophages was measured with carboxyfluorescein succinimidyl ester and fluorescent microspheres. Sorted CD34+ CD38- CD47+ cells were injected into NOD-Prkdcscid Il2rgnull mice. RESULTS: The expression of CD47 on CD34+ CD38- cells of the patients in high-risk MDS based on IPSS-R/WPSS score was higher than that in low-risk MDS and controls. The signaling pathway of PI3K/AKT/mTOR is active in CD34+ CD38- CD47+ cells of MDS patients. CD47 overexpressing CD34+ CD38- cells has antiphagocytosis. CD47 overexpressing leukemia stem cell (LSC) -transplanted mice has a short survival time. The macrophages originated from MDS might elicit a pro-tumor response in MDS by inhibiting phagocytosis. CONCLUSIONS: Phagocytosis checkpoints are impaired in MDS. High expression of CD47 on CD34+CD38- cells indicates poor clinical prognosis in MDS.