# Sex Hormones-Mediated Modulation of Immune Checkpoints in Pregnancy and Recurrent Pregnancy Loss

## TL;DR

This study explores how sex hormones affect immune checkpoint proteins in pregnant women and those with unexplained recurrent pregnancy loss, revealing differences in immune cell responses.

## Contribution

The study reveals cell-specific modulation of immune checkpoints by sex hormones in pregnancy and unexplained recurrent pregnancy loss.

## Key findings

- Sex hormones modulate immune checkpoint proteins like PD-1, TIM-3, LAG-3, TIGIT, and VISTA in a cell-specific manner.
- Unexplained RPL patients show stronger immune checkpoint responses to sex hormones compared to pregnant women.
- DHT increases VISTA and LAG-3 expression in uRPL patients, while progesterone and estradiol upregulate LAG-3 and TIM-3 in cytotoxic cells.

## Abstract

Recurrent pregnancy loss (RPL) is defined as the loss of two or more pregnancies before the 22nd gestational week and affects 10–15% of clinical pregnancies. Despite extensive diagnostics, over 50% of RPL cases remain unexplained, suggesting an important role for immunological mechanisms. Sex hormones (SH) are key regulators of immune responses during pregnancy; however, their influence on immune checkpoint proteins (ICPs) is poorly understood. This study evaluated the effects of progesterone, β-estradiol, and dihydrotestosterone (DHT) on ICP expression on immune cells, including Treg, NK, NKT, TC, Th, and T cells, collected from pregnant women and patients with unexplained RPL (uRPL). Peripheral blood mononuclear cells from 20 pregnant women and 20 uRPL patients were cultured for 48 h with SH. The expression of the first generation of ICPs—PD-1 and TIM-3—and the second—LAG-3, TIGIT, and VISTA—on T, NK, and NKT cells was analyzed by the flow cytometry method. In pregnant women, SH exerted modest effects, with DHT increasing VISTA and LAG-3 expression, while progesterone and estradiol mainly upregulated LAG-3 and TIM-3 on cytotoxic cells. In contrast, uRPL immune cells showed pronounced SH sensitivity, characterized by increased TIM-3 and VISTA expression and reduced TIGIT expression, particularly after DHT stimulation. In conclusion, SH modulates ICP expression in a cell-specific manner, with stronger effects observed in uRPL patients’ lymphocytes. These findings highlight a potential role for hormonal and ICP-targeted strategies in RPL management.