The role of HLA-C in chronic chorioamnionitis

Chronic inflammation of the placental membranes (chronic chorioamnionitis (CCA)) occurs frequently and involves excessive chorionic trophoblast death and infiltration of maternal CD8 T cells to the chorio-amnion membrane. While the etiology of CCA remains unclear, CCA has been found in the presence and absence of an infective etiology. Increased clarity on the inflammatory factors and fetal or microbial antigens that drive CD8 T cell cytotoxicity and trophoblast death will have profound implications for how CCA is treated. The proposed research investigates how Human Leukocyte Antigen-C (HLA-C) expressed by chorionic trophoblasts promotes cytotoxic CD8 T cell responses during CCA. HLA-C is the only classical Major Histocompatibility Complex (MHC) molecule expressed on chorionic trophoblasts that can present microbial and fetal antigens and directly activate cytotoxic CD8 T cells through the T cell receptor (TCR). HLA-C is unique to humans, and HLA-C orthologues do not exist in rodents or macaques. The proposal builds on our discovery that CD8 T cells in healthy membranes are differentiated memory T cells, which compared to blood memory T cells have vastly reduced expression of the cytotoxic molecule perforin. Moreover, CD8 T cells from healthy membranes respond to TCR stimulation, but do not release cytotoxic granules nor kill sample matched chorionic trophoblasts during co-culture. This suggests that control of CD8 T cell cytotoxicity is critical to avoid trophoblast killing in healthy pregnancy. Preliminary analysis of CD8 T cells in membranes with CCA shows they infiltrate the chorion, upregulate perforin and form direct contacts with chorionic trophoblasts. In many of the trophoblast-T cell contacts perforin is present indicating that these are immune synapses promoting CD8 T cell degranulation and trophoblast killing. Thus, CD8 T cells in CCA acquire higher cytotoxic capabilities that they likely use to kill chorionic trophoblasts. We hypothesize that tight control of CD8 T cell cytotoxicity is required to avoid trophoblast killing in healthy pregnancy. Increased immunogenicity of chorionic trophoblasts, including high expression of HLA-C and lack of inhibitory signaling, elicits CD8 T cell cytotoxicity and trophoblast killing during CCA. To test this, we will i) determine how cytotoxic CD8 T cells contribute to trophoblast death during CCA using state-of-the-art high dimensional flow cytometry (HDFC)-based cytotoxicity assays of primary CD8 T cells and trophoblasts; and ii) Define the cell-cell communication networks that control CD8 T cell killing of chorionic trophoblasts. Cutting-edge machine learning approaches of integrated single cell RNA-seq, HDFC, cytotoxicity and clinical data will be used to identify pathological CD8 T cell and chorionic trophoblast types as well as the disrupted communication networks between them, that contribute to cytotoxicity and trophoblast death. Loss and gain of function interventions using in vitro expanded primary chorionic trophoblast lines will be used to test strategies to protect trophoblasts and reduce CD8 T cell cytotoxicity. Discovering pathological cellular networks and trophoblast antigens that drive CD8 T cell killing of trophoblasts offers transformative insights in the etiology of CCA.