Analysis of TCR Repertoire and PD-1 Expression in Decidual and Peripheral CD8+ T Cells Reveals Distinct Immune Mechanisms in Miscarriage and Preeclampsia.

Keiko Morita,Akitoshi Nakashima,Shigeru Saito,Akemi Ushijima,Eiji Kobayashi,Sayaka Tsuda,Hiroshi Hamana,Kei Tsuda,Hiroyuki Kishi,Tomoko Shima

doi:10.3389/fimmu.2020.01082

Abstract

CD8+ T cells, the most abundant T cell subset in the decidua, play a critical role in the maintenance of pregnancy. The majority of decidual CD8+ T cells have an effector memory phenotype, while those in the peripheral blood display a naive phenotype. An increased amount of highly differentiated CD8+ T cells in the decidua indicates local antigen stimulation and expansion, albeit these CD8+ T cells are suppressed. In decidual CD8+ T cells, co-inhibitory molecules such as PD-1, TIM-3, LAG-3, and CTLA-4 are upregulated, reflecting the suppression of cytotoxicity. Previous studies established the importance of the PD-1/PD-L1 interaction for feto-maternal tolerance. CD8+ T cells could directly recognize fetal-specific antigens, such as HLA-C, expressed by trophoblasts. However, although fetal-specific CD8+ T cells have been reported, their TCR repertoires have not been identified. In this study, we analyzed the TCR repertoires of effector memory CD8+ T cells (CD8+ EM cells) and naive CD8+ T cells (CD8+ N cells) in the decidua and peripheral blood of women with normal or complicated pregnancy and examined PD-1 expression at a single-cell level to verify whether antigen-specific CD8+ T cells accumulate in the decidua and to identify immunological differences related to the suppression of antigen-specific CD8+ T cells between normal pregnancy, miscarriage, and preeclampsia. We observed that some TCRβ repertoires, which might recognize fetal or placental antigens, were clonally expanded. The population size of clonally expanded CD8+ EM cells was higher in the decidua than in the peripheral blood. CD8+ EM cells began to express PD-1 during the course of normal pregnancy. We found that the total proportion of decidual CD8+ EM cells not expressing PD-1 was increased both in miscarriage and in preeclampsia cases, although a different mechanism was responsible for this increase. The amount of cytotoxic CD8+ EM cells increased in cases of miscarriage, whereas the expression of PD-1 in clonally expanded CD8+ EM cells was downregulated in preeclampsia cases. These results demonstrated that decidual CD8+ EM cells were able to recognize fetal-specific antigens at the feto-maternal interface and could easily induce fetal rejection.

Highlights

Immune tolerance to the “semi-allogeneic” fetus is important for successful pregnancy
We further examined the expression of programmed cell death-1 (PD-1) in these cells, to clarify whether antigen-specific CD8+ T cells accumulated in the decidua, and to identify the mechanisms underlying their suppression during normal pregnancy, miscarriage, and preeclampsia
To examine functional differences between peripheral CD8+ T cells and decidual CD8+ T cells, we compared the proportion of effector memory CD8+ T cells (CD8+ EM cells) and naive CD8+ T cells (CD8+ N cells) in the peripheral blood mononuclear cells (PBMC) and decidua

Summary

Introduction

Immune tolerance to the “semi-allogeneic” fetus is important for successful pregnancy. Maternal regulatory T cells (Treg cells) play an important role in the maintenance of pregnancy by preventing rejection [3, 4]. CD8+ T cells become predominant among decidual immune cells and play a major role in feto-maternal tolerance. The main population among decidual CD8+ T cells (dCD8+ T cells) is represented by effector memory CD8+ T cells (CD8+ EM cells) that are thought to potentially induce fetal rejection, while the predominant population among peripheral CD8+ T cells (pCD8+ T cells) are naive CD8+ T cells (CD8+ N cells) [5]. Decidual CD8+ EM cells (dCD8+ EM cells) exhibit higher production of interferon-γ (IFN-γ) and interleukin-4 (IL-4), as well as reduced perforin and granzyme B expression, compared to peripheral CD8+ EM cells (pCD8+ EM cells) [5, 6]. The cytotoxicity of CD8+ T cells in the decidua is regulated so as to promote immune tolerance against fetal antigens during pregnancy, albeit these cells maintain a cytotoxic potential against virus-infected cells [17]

Methods

Results

Conclusion