Role Of Extracellular Vesicle-Induced Myeloid-Derived Suppressor Cells In Acute Myeloid Leukemia

Background and objectiveAcute myeloid leukemia(AML)is the most common malignant of the hematopoietic system and the leukemia cells have the characteristics of avoiding immune destruction.Myeloid-derived suppressor cells(MDSCs)immunosuppressive cells derived from bone marrow that promote the immune escape of tumor cells in the tumor microenvironment.Tumor cells promote the production of MDSCs by secreting cytokines,chemokines,inflammatory mediators and extracellular vesicles(EVs).EVs as mediator in intercellular communication and play an important role in development,metastasis and immunity of tumors.Studies have shown that extracellular vesicles derived from AML(AML-EVs)play an important role in inhibiting bone marrow hematopoiesis,providing a suitable microenvironment for tumor cells,as a novel marker and judging the prognosis of AML.Leukemia cells and MDSCs originate from bone marrow hematopoietic cells and exist in the bone marrow microenvironment.However,the regulatory mechanism of MDSCs in AML patients and the differences between bone marrow and peripheral blood MDSCs have not been systematically studied.Whether AML cells can regulate the proliferation of MDSCs through EVs remains unclear.This study aimed to investigate the frequency of MDSCs in newly diagnosed AML patients,their relationship between MDSCs and risk stratification,the influence of MDSCs on prognosis of AML,meanwhile observe the induction effect of AML-EVs on MDSCs.Methods1.BM or PB from newly diagnosed AML patients and healthy donors(HD)was collected to extract mononuclear cells(MNCs),and the percentage of MDSCs and its subpopulation was determined by flow cytometry.2.Analyzed the relationship between the percentage of MDSCs in newly diagnosed AML patients and FAB classification,AML risk stratification,chromosome karyotypes,genes were analyzed.The influence of the percentage of MDSCs on prognosis was observed.3.EVs in the serum from HDs and AML patients were extracted and identified by flow cytometry,Western bot and nanoparticle tracking analysis(NTA).4.AML-EVs and HD-EVs were incubated with peripheral blood mononuclear cells(PBMCs)or MNCs from hematopoietic stem cell suspension(HSC MNCs).And the percentage of MDSCs were detected by flow cytometry.Results1.The percentage of MDSCs was significantly higher in newly diagnosed AML patients than that in HDs,and there was no significant difference in the percentage of MDSCs between PB and BM.2.The percentage of MDSCs was positively correlated with AML risk stratification,which the higher risk displayed the elevated MDSCs.3.The percentage of MDSCs was positively correlated with chromosome karyotype,which the worse karyotype displayed the elevated MDSCs.4.The percentage of MDSCs in the WT1 gene positive group was higher than that in the negative group,with statistical significance.5.The percentage of MDSCs varied among AML with different fusion genes,the percentage of MDSCs was higher in AML with NUP98-HOXA9 fusion gene and was lower in AML with AML-ETO,CBFβ-MYH11,and DEK-CAN fusion genes.6.The percentage of MDSCs varied among AML patients with different gene mutations.The percentage of MDSCs was higher in patients with FLT3-ITD,SETBP1,ASXL1,SF3B1 gene mutation,while was lower in patients with CEBPA,FLT3-TKD,IDH,TET2 gene mutation.7.The percentage of MDSCs was decreased with the application of chemotherapy drugs.However,and there was no statistical difference in the percentage MDSCs at the time of diagnosis among CR,PR and NR group,and there was no statistical difference in the percentage of MDSCs at the time of diagnosis between MRD positive group and negative group.8.AML patients were categorized into low-MDSCs and high-MDSCs groups based on the percentage of MDSCs at the time of diagnosis,and the overall survival(OS)of AML was significantly longer in the low-MDSC group than that in the high-MDSC group.9.The percentage of MDSCs was no significant change in PBMCs incubated with AML-EVs.AML-EVs incubated with HSC MNCs resulted in decreased HLA-DR expression,increased CD 11b expression and increased the percentage of MDSCs.Conclusions1.MDSCs may be involved in the occurrence and development of AML,and the percentage of MDSCs may be one of the factors of poor prognosis in AML patients.2.AML-EVs could induce the generation of MDSCs,and AML-EVs play an important role in the recurrence of leukemia.