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Objective: To study the expression of CD70 and the methylation level of CD70 promoter in immuno-related pancytopenia（IRP）patients, and explore the role of CD70 in the pathogenesis of IRP., Methods: Thirty- five IRP patients and fifteen healthy donors were enrolled in this study. Peripheral blood mononuclear cells were isolated from venous blood by density gradient centrifugation, and CD4(+) T cells were isolated by immunomagnetic beads. The mRNA level and the percentage of CD70 of CD4(+) T cells were measured by real- time quantitative polymerase chain reaction（RT- PCR）and flow cytometry respectively. Methylation- Specific PCR（MSP）was performed to determine the methylation level of CD70 promoter., Results: The percentage of CD70 expression on CD4(+) T cells of untreated IRP patients［（7.46±1.51）%］was significantly higher than that of recovered ones［（5.95±1.34）%］and normal controls［（1.83 ± 0.60）%］, and that of recovered IRP patients was significantly higher than of normal controls（P<0.05）. The relative expressions of CD70 mRNA in CD4(+) T cells were 2.314（0.200-6.084）, 1.021（0.135-3.434）, 0.353（0.008-2.258）in three groups respectively. The differences among untreated IRP patients, recovered IRP patients and normal controls were significant（P<0.05）. The CD70 promoter methylation level in CD4(+) T cells of all IRP patients was significantly lower than that of normal controls （P<0.05）. The expression of CD70 positively correlated to the ratio of CD5(+) B cells（r=0.533, P<0.01）., Conclusion: The overexpression of CD70 may lead to immunologic disarrangement of patients, which may play important role in the pathogenesis of IRP.