Three Types of Functional Regulatory T Cells Control T Cell Responses at the Human Maternal-Fetal Interface

During pregnancy, maternal regulatory T cells (Tregs) are important in establishing immune tolerance to invading fetal extravillous trophoblasts (EVTs). CD25(HI)FOXP3+ Tregs are found at high levels in decidual tissues and have been shown to suppress fetus-specific and nonspecific responses. However, limited data are available on additional decidual Treg types and the mechanisms by which they are induced. This study investigated three distinct decidual CD4+ Treg types in healthy pregnancies with a regulatory phenotype and the ability to suppress T cell responses: CD25(HI)FOXP3+, PD1(HI)IL-10+, and TIGIT+FOXP3(dim). Moreover, co-culture of HLA-G+ EVTs or decidual macrophages with blood CD4+ T cells directly increased the proportions of CD25(HI)FOXP3+ Tregs compared to T cells cultured alone. EVTs also increased PD1(HI) Tregs that could be inhibited by HLA-C and CD3 anti-bodies, suggesting an antigen-specific induction. The presence of distinct Treg types may allow for the modulation of a variety of inflammatory responses in the placenta.