Study On Immunosuppression Of Myeloid-Derived Suppressor Cells (MDSC) In Myelodysplastic Syndrome

ObjectiveThis study was to detect the level of circulating myeloid-derived suppressor cells (MDSC) of patients with myelodysplastic syndromes (MDS), and the association between MDSC and malignancy in MDS. Investigated the expression of arginase1(ARG1) and inducible nitric oxide synthase (iNOS) of myeloid-derived suppressor cells (MDSC) in patients with myelodysplastic syndromes (MDS) and MDSC-mediated CD8+T cell inhibition. To prove MDSC play an important role in mediating immunosuppression in MDS.MethodsPart Ⅰ The proportion of MDSC (Lin-HLA-DR-CD33+) in peripheral blood of35MDS patients and20normal controls were measured by flow cytometry assay (FCM). After three-month-therapy,14MDS patients were investigated again for their MDSC changes. Part Ⅱ The proportion of MDSC in bone marrow of30MDS patients and19normal controls were measured by FCM. MDSC were isolated from bone marrow of14MDS patients and14normal controls by FCM. The expressions of ARG1and iNOS were analyzed by quantitative RT-PCR (qRT-PCR) and western bolting. Part Ⅲ MDSC and CD8+T cell were isolated from bone marrow of14MDS patients by FCM and microbeads. MDSC-mediated inhibition on CD8+T cells was proved by cocultures with MDSC and CD8+T cells.ResultsPart Ⅰ MDS patient’s median MDSC were1.61%which was higher than that of controls (0.83%, P=0.033). The median MDSC of high-risk MDS patients regarding based on IPSS score was4.45%, which was higher than that of low-risk MDS patients (0.63%, P=0.003). Further more, the median MDSC of high-risk MDS patients regarding based on WPSS score was4.39%, which was higher than that of low-risk MDS patients (0.47%, P=0.002).A negative correlation between MDSC and hemoglobin of MDS patients was observed. There was a significant positive correlation between MDSC and CD34+cells or LDH in MDS.Part Ⅱ MDS patient’s median MDSC were7.29%which was higher than that of controls (2.91%, P=0.012). The expression of ARG1and iNOS mRNA in MDSC of high-risk MDS patients based on IPSS score(IPSS>1) was higher than that of low-risk MDS patients(IPSS≤1)(P<0.05). Only the protein of ARG1was overexpressed, rather than that of iNOS.Part III After coculture with MDSC, the apoptosis ratio of CD8+T cells of MDS patients((64.17±4.86)%) was higher than that of pure CD8+T cells ((54.58+9.95)%, P=0.01). Further more, the production of IFN-γ by CD8+T cells after coculture with MDSC ((551.94±47.39) pg/ml) was lower than that of pure CD8+T cells ((586.04±46.65)pg/ml, P=0.022). About the production of TNF-β, there was no significant difference between CD8+T cells after coculture with MDSC ((216.54±19.46)ng/L) and pure CD8+T cells((225.61±26.68)ng/L, P=0.100).Conclusions(1) The proportion of circulating MDSC was increased significantly in MDS, correlated with the IPSS, WPSS scores. And there was a negative correlation between MDSC and hemoglobin in MDS. MDSC also showed a positive correlation to the level of CD34+cells and lactate dehydrogenase in MDS, which hint the tumor load in patients. These data indicate that the increased level of circulating MDSC might involve in MDS pathogenesis.(2) The proportion of MDSC in bone marrow was increased significantly in MDS. MDSC overexpressed ARG1in MDS patients and correlated to the malignancy of this disease.(3) In vitro, MDSC could increase the apoptosis of CD8+T cells, and inhibite the production of IFN-γ by CD8+T cells. These findings suggest MDSC mediated the response of immunosuppression in MDS.