Characterisation of peri-implantation endometrial Treg and identification of an altered phenotype in recurrent pregnancy loss

Ingrid Granne,Jennifer H Southcombe,Tim Child,Siobhan Quenby,Helena Rodriguez-Caro,Elizabeth O'Donnell,Jan J Brosens,Mengni Shen,Gurmeher Chadha

doi:10.1038/s41385-021-00451-1

Abstract

Recurrent Pregnancy Loss (RPL) affects 2–4% of couples, and with increasing numbers of pregnancy losses the risk of miscarrying a euploid pregnancy is increased, suggesting RPL is a pathology distinct from sporadic miscarriage that is due largely to lethal embryonic aneuploidy. There are a number of conditions associated with RPL including unspecified “immune” pathologies; one of the strongest candidates for dysregulation remains T regulatory cells as depletion in the very early stages of pregnancy in mice leads to pregnancy loss. Human endometrial Treg and conventional CD4T cells were isolated during the peri-implantation period of the menstrual cycle in normal women. We identified an endometrial Treg transcriptomic signature and validated an enhanced regulatory phenotype compared to peripheral blood Treg. Parous women had an altered endometrial Treg transcriptome compared to nulliparity, indicating acquired immune memory of pregnancy within the Treg population, by comparison endometrial conventional CD4T cells were not altered. We compared primary and secondary RPL to nulliparous or parous controls respectively. Both RPL subgroups displayed differentially expressed Treg gene transcriptomes compared to controls. We found increased cell surface S1PR1 and decreased TIGIT protein expression by Treg in primary RPL, confirming the presence of altered Treg in the peri-implantation RPL endometrium.

Highlights

The female reproductive tract (FRT) is a mucosal barrier tissue and like other mucosa, immune cells infiltrate the stromal layers adjacent to the epithelial surface
Decreased numbers of FOXP3+ cells are found in endometrium of patients with Recurrent Pregnancy Loss (RPL) compared to fertile controls,[11] in humans FOXP3 can be expressed by activated T cells and other cells[12] and the phenotype and functional nature of these cells has not been clearly elucidated
CD4T cells comprise 43.0 ± 9.5% of the total CD3 positive T cell population, which is a lower proportion than the equivalent compartment in the peripheral blood, Fig. 1b

Summary

INTRODUCTION

The female reproductive tract (FRT) is a mucosal barrier tissue and like other mucosa, immune cells infiltrate the stromal layers adjacent to the epithelial surface. Of specific interest are the Treg cells, which in mice have been show to prime tolerance, as depletion during early stages of pregnancy during embryonic implantation leads to pregnancy loss.[8] Murine Treg cells are pivotal to tolerance of paternal alloantigen.[9] The transcription factor FOXP3 confers regulatory lineage commitment to Tregs, multiple mechanisms of action are known such as high CD25 expression which consumes IL-2 preventing effector T cell functions, CTLA4 driven inhibition of antigen presenting cells, and inhibitory cytokine production (IL10, TGF-beta and IL-35).[10] Decreased numbers of FOXP3+ cells are found in endometrium of patients with RPL compared to fertile controls,[11] in humans FOXP3 can be expressed by activated T cells and other cells[12] and the phenotype and functional nature of these cells has not been clearly elucidated. Compared the transcriptional and protein expression profiles of endometrial Tregs in controls versus RPL

RESULTS

Granne et al 5

Recurrent Pregnancy Loss