Impaired myeloid-derived suppressor cells are associated with recurrent implantation failure: A case-control study

•RIF patients showed significant reductions of blood PMN-MDSCs, M-MDSCs, Tregs and NO production by PMN-MDSCs.•The expression of ζ chain on CD4+ TCR and CD8+TCR displayed a remarkable upregulation in RIF patients.•RIF patients presented a lower concentration of CCL5 and TGF-β.•TCR ζ chain on CD4+ and CD8+ Teffs was negatively correlated with the percentage of PMN-MDSCs and the amount of NO production by PMN-MDSCs.•The frequency of PMN-MDSCs had positive correlations with the concentration of CCL5 and TGF-β. Studies have reported that myeloid-derived suppressor cells (MDSCs) contribute to maintain pregnancy. The aim of this case-control study was to test whether there is a dysregulation of peripheral MDSCs in recurrent implantation failure (RIF). 26 RIF patients and 30 controls were recruited. Flow cytometry was applied to characterize polymorphonuclear (PMN)-MDSCs, monocytic-MDSCs (M-MDSCs), effector T cells (Teffs) and regulatory T cells (Tregs) in blood. ELISA was used to define MDSCs correlative cytokines and chemokines in serum from all patients. Compared with controls, RIF patients showed significant reductions of blood PMN-MDSCs, M-MDSCs, Tregs and NO production by PMN-MDSCs, whereas the expression of ζ chain on CD4+T cell receptor (TCR) and CD8+TCR displayed a remarkable upregulation in RIF patients. Moreover, RIF patients presented a lower concentration of serum chemokine (C-C motif) ligand (CCL) 5 and transforming growth factor (TGF)-β than those from controls. Furthermore, the level of TCR ζ chain on CD4+ and CD8+ Teffs was negatively correlated not only with the percentage of PMN-MDSCs, but also with the amount of NO produced by PMN-MDSCs. The frequency of PMN-MDSCs had positive correlations with the concentration of CCL5 and TGF-β. This study indicated that the dysregulation of MDSCs might impair maternal-fetal immune balance thus resulting in RIF.