Abstract: ObjectiveTo study the changes of programmed death factor-1／programmed death factor-1 ligand （PD-1／PD-L1） in patients with myelodysplastic syndrome （MDS） before and after using decitabine （DAC）. MethodsFrom Jan 2016 to Jan 2017， 18 cases newly diagnosed as MDS with WHO 2008 type WPSS prognostic stratification in middlerisk group and highrisk group were enrolled. Patients were applied with DAC （20 mg／m2 d1~d5， 21~28 days as a cycle） for 2 cycles. Five patients with nonmalignant hematologic diseases were treated as control. Peripheral blood and bone marrow cells were collected before and after DAC application for 2 cycles. FCM was used to determine PD1 of CD3+CD4+T and CD3+CD8+T cells in peripheral blood lymphocytes and PDL1 in bone marrow progenitor cells before and after treatment with DAC. The relative expression of PD1mRNA and PDL1mRNA in peripheral blood and bone marrow mononuclear cells before and after DAC treatment was detected by QPCR. PD1／PDL1 level was compared between remission group （n=5）and nonremission group（n=13）. ResultsFCM analysis showed that the proportion of PD1of CD3+CD4+T and CD3+CD8+T lymphocytes， and PDL1 of bone marrow monounclear cells in middlerisk group after DAC treatment was （11.43±1.88）％， （11.46±1.60）％ and （16.59±0.72）％， and the data in highrisk group after treatment were （16.36±3.71） ％， （16.59±3.81）％ and （18.69±1.60）％， all higher than those before treatment and those of control group （P＜0.05）. The proportion of PD1 of CD3+CD4+T and CD3+CD8+T lymphocytes， and PDL1 of bone marrow mononuclear cells in nonremission group was （18.51±2.62）％， （1903±2.18）％ and （19.22±1.40）％， higher than those in remission group （P＜0.05）. QPCR analysis showed that after DAC treatment the relative expression of PD1 mRNA in peripheral blood and PDL1 mRNA in bone marrow mononuclear cells of middlerisk group was 6.32±3.37 and 2.88±1.72， and they were 1255±627 and 7.47±4.90 in high risk group， higher than those before treatment （P＜0.05）. The relative expression of PD1 mRNA of peripheral blood mononuclear cells and PDL1 mRNA of bone marrow mononuclear cells in nonremission group was 1628±464 and 9.16±5.40， significantly higher than those in remission group （P＜0.05）. 
ConclusionAfter treatment with DAC， the expression of PD1／PDL1 in peripheral blood and bone marrow of MDS middlerisk， highrisk patients increased significantly， especially in nonremission group. High expression of PD1／PDL1 may be one of the reasons leading to drug resistance of DAC.

Key words: Myelodysplastic syndrome （MDS）, PD1／PDL1, Decitabine