Deficiency of PD-L1+ Non-Immune Cells in Preterm Labor

The objective of this study was to characterize the cells at the maternal-fetal interface (MFI) in term and preterm pregnancies, each in the laboring and non-laboring state. Using mass cytometry to obtain single-cell resolution, we identified 31 cell populations at the MFI, including 25 immune cell types and six non-immune cell types. Among the immune cells, maternal PD1+ CD8 T cells subsets were less abundant in term laboring compared to term non-laboring. Among the non-immune cells, PD-L1+ maternal (stromal) and fetal (extravillous trophoblast) cells were more abundant in term laboring compared to preterm laboring pregnancies. Consistent with these observations, the expression of CD274, the gene encoding PD-L1, was significantly depressed and less responsive to fetal signaling molecules in cultured mesenchymal stromal cells from the decidua of preterm compared to term pregnancies. Overall, these results suggest that the PD1/PD-L1 pathway at the MFI may perturb the delicate balance between immune tolerance and rejection and contribute to the onset of spontaneous preterm labor.