Characteristics of plasma exosomes from acute myeloid leukemia patients and their regulatory effects on leukemia stemness-related genes and natural killer cells

Objective To investigate the characteristics of plasma exosomes from patients with acute myeloid leukemia (AML) and explore their effects on the expression of leukemia stemness-related genes and natural killer (NK) cell function in vitro experiments. Methods The newly diagnosed AML patients (the AML group) and healthy individuals undergoing routine physical examinations (the control group) in the First Affiliated Hospital of Soochow University between October 1, 2022, and May 31, 2024 were retrospectively included. Peripheral blood plasma exosomes of the both groups were isolated. Transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA), and Western blotting (WB) were used to compare the morphology, size distribution, protein concentration, and surface marker protein expression. Enrich differentially expressed proteins in exosomes of two groups and analyze pathway enrichment. Leukemia cells treated with different methods were divided into the negative group [treated with phosphate-buffered saline (PBS)], the low-concentration group (treated with 5 mg/L plasma exosomes from AML patients) and the high-concentration group (treated with 10 mg/L plasma exosomes from AML patients). The mRNA expression levels of stemness-related genes (BMI1, OCT4, KLF4, NANOG) in leukemia cells of each group were compared. NK cells treated with different methods were divided into the blank group (treated with PBS), the control group 1 (treate with plasma exosomes from the 10 mg/L control group), and the AML group 1 (treated with plasma exosomes from the 10 mg/L AML group). The killing activity of NK cells against K562 target cells and the expression changes of CD158 series receptors in each group were compared. Results The AML group included 60 patients [37 males, 23 females; age (51±12) years], and the control group included 20 individuals [8 males, 12 females; age (58±17) years]. TEM and NTA analyses revealed that plasma exosomes from the AML group and the control group exhibited similar morphology and size distribution. The exosome protein concentration in the AML group was higher than that in the control group [(281±34) vs (244±24) mg/L, P=0.011]. A total of 62 differentially expressed proteins were identified, mainly enriched in the phosphatidylinositol 3-kinase-protein kinase B (PI3K-Akt) signaling pathway. In the low-concentration group, the mRNA expression levels of leukemia stemness-related genes BMI1 (6.96±1.19 vs 1.00±0.19), OCT4 (1.51±0.32 vs 1.03±0.06), KLF4 (2.18±0.81 vs 1.03±0.03), and NANOG (5.00±2.47 vs 0.93±0.06) were higher than those in the negative group; In the high-concentration group, the mRNA expression levels of leukemia stemness-related genes BMI1 (9.06±3.31 vs 1.00±0.19), OCT4 (1.62±0.33 vs 1.03±0.06), KLF4 (2.32±0.34 vs 1.03±0.03) were higher than those in the negative group (all P<0.05). The killing rate of NK cells against K562 target cells in the AML group 1 (76.95%±3.52% vs 85.75%±1.67% and 87.60%±0.85%, respectively), and the expression level of CD158i on NK cells (33.14%±1.82% vs 41.40%±2.84% and 43.95%±0.08%, respectively) were lower than those in both the control group 1 and the blank group (all P<0.05). Conclusions Plasma exosomes from AML patients show similar morphology and size distribution compared with healthy controls, but the protein expression level is higher than that in the control group. Exosomes can enhance the transcription of leukemia stemness-related genes and suppress NK cell cytotoxicity and surface expression of CD158i receptors.