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

Highlights

• 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.

Abstract

Background

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).

Methods

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.

Results

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.

Conclusions

This study indicated that the dysregulation of MDSCs might impair maternal-fetal immune balance thus resulting in RIF.

Introduction

Recurrent implantation failure (RIF) is diagnosed when women experienced 3 or more frozen or fresh cycles with being transferred high-quality embryos and failed to obtain a clinical pregnancy (Macklon, 2017; Sato et al., 2019). Numerous studies have found that the identifiable causes include parental chromosomal abnormalities, defective embryonic development, uterine anatomic anomalies, and poor endometrium (Yuan et al., 2016; Corroenne et al., 2018; Park et al., 2019; Quintero-Ronderos et al., 2019). Nevertheless, more and more researches have focused on the immunological aspects, especially a failure to establish maternal-fetal immunotolerance for successful implantation.

Lédée et al. reports that, at the time of embryo implantation, the maternal immune system is featured by distinct immunological alterations with enrichment of various immune cells in both peripheral circulation and uterus microenvironment (Lédée et al., 2016). These changes create an immunological tolerance environment which protects embryo expressing paternal antigen from maternal antigen-specific T cells and contributes to successful implantation (Lédée et al., 2016). Breakdown of maternal-fetal tolerance was found to be associated with a poor clinical outcome in pregnant women (Ehrentraut et al., 2019; Verma et al., 2019). Furthermore, dysregulation of implicated immune cells such as uterine natural killer cells (NK), peripheral NK, regulatory T cells (Tregs), T-helper cells have been discovered in RIF (Seshadri and Sunkara, 2014; Jiang et al., 2017; Royster et al., 2019; Sheikhansari et al., 2019).

Myeloid-derived suppressor cells (MDSCs) represent a heterogeneous cell group with attributes in myeloid origin, immature state, and immunosuppressive function (Vetsika et al., 2019). Under pathogenic condition, MDSCs are accumulated by an inflammatory condition which contains mediators such as transforming growth factor (TGF)-β, tumor necrosis factor (TNF)-α, interleukin (IL)1β, IL-6, IL-10 and chemokines such as chemokine (C-C motif) ligand (CCL) 2, CCL3, CCL4, CCL5) (Hawila et al., 2017; Li et al., 2019). They exert immunosuppressive function by different mechanisms: the activation of arginase-1 (Arg-1) and inducible nitric oxide synthase (iNOS) which generates nitric oxide (NO) (Vetsika et al., 2019). These pathways caused a dysregulation of T cell functions by downregulating the ζ chain expression on T cell receptor (TCR), which has a key role in the TCR-mediated antigen recognition and signal transduction (Vetsika et al., 2019; Hassel et al., 2017). In mice, MDSCs can be divided into CD11b⁺Ly6G⁻Ly6C^high monocytic MDSCs (M-MDSCs) and CD11b⁺Ly6G⁺Ly6C^low polymorphonuclear MDSCs (PMN-MDSCs). In human, they are identified as CD33⁺HLA-DR^-/lowCD11b⁺CD14⁺CD15⁻ M-MDSCs and CD33⁺HLA-DR^-/lowCD11b⁺CD14⁻CD15⁺ PMN-MDSCs (Bronte et al., 2016). MDSCs have been reported to expand in different pathological conditions such as cancer, traumas and infectious diseases (Wu and Chiang, 2019; Kustermann et al., 2019; Hollen et al., 2019). Because of the immunosuppressive effect of MDSCs, studies focused on their roles in pregnancy and associated complications in recent years (Pan et al., 2016; Zhao et al., 2015; Ostrand-Rosenberg et al., 2017; Köstlin-Gille et al., 2019; Hu et al., 2019). Studies demonstrated that MDSCs expanded not only in uterus but also in peripheral blood during gestation period (Pan et al., 2016; Ostrand-Rosenberg et al., 2017). In human, PMN-MDSCs are accumulated in peripheral circulation of healthy pregnant women as compared to nonpregnant controls (Köstlin et al., 2014; Bartmann et al., 2016). Reduction of MDSCs was explored both in decidua and in peripheral blood from miscarriage patients (Nair et al., 2015). In addition, depletion of MDSCs was found to result in a significant decrease of Tregs and severe embryo resorption in mice model (Kang et al., 2016).

These growing evidences strengthen that MDSCs have a strong ability to promote maternal immune tolerance. However, whether peripheral MDSCs are associated with RIF is still unknown. In this study, we have assessed the level and function of MDSCs along with its subtypes in RIF patients and pregnant women with first IVF. Our study is the initial research that discovers the reduction of PMN-MDSCs in RIF patients. These findings provide a strategy with which inducing MDSCs could be utilized as a therapeutic option in RIF women.