Serial changes in two immune checkpoint receptors and ligands, Tim-3/Gal-9 and PD-1/PD-L1 in peripheral blood prior to miscarriage: Comparison with pregnancies resulting in a live birth

Abstract

Problem: Immune checkpoints Tim-3/Gal-9 and PD-1/PL-1 are involved in the maintenance of maternal-fetal immune tolerance systematically and locally. This study aimed to compare the serial changes of Tim-3/Gal-9, and PD-1/PL-1 in peripheral blood over a 4-week period after blastocyst transfer, between women who had a live birth and those who miscarried.

Methods of study: Serial blood samples were obtained on the day of ET, and 9, 16, 23, and 30 days after ET for the measurement of Tim-3 and PD-1 expressions on various lymphocytes by flow cytometry. Concentrations of serum Gal-9 and PD-L1 were measured by ELISA.

Results: In pregnancies that resulted in a live birth, a significant and sustained increase in the proportion of Tim-3⁺ pNK cells was observed from the 9^th to 30^th days after ET, whilst the concentration of serum PD-L1 was significantly increased on the 23^rd and 30^th days after ET when compared to the day of ET. In pregnancies that later miscarried, none of the parameters were significantly changed across all the time points examined. When comparing the results between the two groups, the proportion of Tim-3⁺ CD56^dim NK cells in the women who had a live birth was significantly higher than that in women who miscarried from the 9^th to 30^th day after ET.

Conclusion: A significant and sustained increase in the proportion of Tim-3⁺ pNK cells was observed in pregnancies resulting in a live birth but not in pregnancies resulting in a miscarriage, suggesting the changes may be associated with successful pregnancy outcomes.

Keywords: PD-1; Tim-3; live birth; miscarriage; natural killer (NK) cells.