Identification of a cellular immune signature unique to clinically-significant villitis of unknown etiology - Project Summary/Abstract Fetal growth restriction (FGR), defined by a fetus failing to fulfill its growth potential, is a common complication of pregnancy, associated with several adverse neonatal outcomes, including stillbirth. Villitis of unknown etiology (VUE) is a chronic inflammatory lesion of placental villi, associated with late-onset FGR (onset after 34 weeks gestation). VUE, defined by infiltration of chorionic villi with maternal T cells and an expansion of fetal- derived macrophages (so-called Hofbauer cells), is most common at term and considered to be a form of allograft rejection. Unlike infectious villitis, VUE lesions have a risk of recurrence in subsequent pregnancies with the same partner, leading to worsening FGR and even stillbirth. However, based on histopathologic features alone, it is difficult to identify clinically-significant VUE (e.g., those that are causative of FGR and thus highly likely to recur): there is much disagreement about criteria for grading this lesion, with published studies and our own preliminary data from over 3,500 placentas, showing no difference in FGR between low- and high- grade VUE. Over the past ~15 years, several studies have advanced our knowledge of this lesion, including identification of regulatory T cells, activation of the JAK-STAT pathway in syncytiotrophoblast (STB), and upregulation of chemokines CXCL9 and CXCL13, in regions of VUE, pointing to chemoattractant-driven immune cell infiltration in the development of this lesion. Furthermore, comparison of immune checkpoint pathways in infectious villitis vs. VUE have pointed to a loss of immune tolerance only in the latter form of this lesion. Most recently, application of spatial ‘omics technologies to this lesion has led to identification of T cells with an activated memory phenotype, and Hofbauer cells with upregulated PD-L1 checkpoint receptors. However, these latter studies have involved evaluation of a small number of cases, still leaving a rather incomplete understanding of VUE pathophysiology, particularly with respect to distinguishing between clinically-significant, rather than benign, VUE. We therefore propose to apply high-throughput mass cytometry to identify cellular signature(s) specific to VUE associated with FGR, e.g., cases with the highest potential for recurrence. We hypothesize that SGA-associated VUE is characterized by a distinct cellular profile, comprised of chronic immune responses and trophoblast and/or endothelial damage, and propose to test this in a cohort of previously-banked placental tissues (Aim 1) and prospectively-banked placental immune cell isolates (Aim 2), using state-of-the-art mass cytometry. Successful completion of this proposal will begin to unravel the detailed pathophysiology of VUE, identify cellular signatures which distinguish clinically-significant lesions associated with FGR, and lay the foundation for diagnostic biomarker discovery for late-onset FGR, which is often associated with stillbirth.
