Single-cell profiling of the peripheral blood immune landscape during mid- and late-stage pregnancy.

We aimed to determine the peripheral blood mononuclear cell (PBMC) immune profiles of mid- and late-stage pregnant women to establish a foundation for studying pregnancy-related diseases. Peripheral blood samples were collected from three women each during mid- and late-stage pregnancy, and PBMCs were extracted for single-cell RNA sequencing (scRNA-seq). Peripheral blood samples were also collected for flow cytometry analysis to validate the analytical results. HOPX+ CD4+ T cells, ZNF683+CD8+ T cells, and KLRB1+CD8+ T cells significantly differed in quantitative ratio and gene transcript level between women at mid- and late-stage pregnancy. In late pregnancy, cell-to-cell communication was enhanced and effector CD8+ T cells highly expressed infection-related pathways. A rare T cell subtype, "XIST+ T cells," exhibited high XIST expression, a gene that may be involved in the regulation of immune-related gene transcription and translation, and insulin signaling pathway, during pregnancy. Monocytes exhibited significant proinflammatory and metabolic properties in mid- and late-stage pregnancy, respectively. Natural killer (NK) cells were mainly involved in T- and B-cell-mediated signaling pathways, and in T cell differentiation, in mid-pregnancy. Enhanced innate immunity of NK cells was observed. Moreover, NK cells expressed genes associated with diabetes-related pathways in late-stage pregnancy. To conclude, we present detailed changes in the immune response occurring in pregnant women from mid- to late-stage gestation, revealing significant differences in PBMC subtypes and molecular properties. These findings provide insights into the physiopathological mechanisms of chronic hepatitis B infection, systemic lupus erythematosus, and gestational diabetes mellitus underlying systemic immune responses during mid- and late-stage pregnancy.NEW & NOTEWORTHY There are significant differences in three subtypes of memory/effector T cells (HOPX+ CD4+ T cells, ZNF683+CD8+ T cells, and KLRB1+CD8+ T cells) between mid- and late pregnancy. In late pregnancy, intercellular interaction was enhanced and effector CD8+ T cells highly expressed infection-related pathways. A rare T cell subtype, "XIST+ T cells," may be involved in the regulation of immune-related gene transcription and translation with a strong female bias.