Mechanisms of aberrant tissue residency programming of uterine natural killer cells in uterus transplantation

Abstract Uterine natural killer cells (uNK) are the most common human decidual lymphocytes, but the origin and ontogeny of uNKs remain unclear. Studies of human uterus transplant recipients (UTx) suggest that uNKs originate in the blood, but how these cells become tissue resident and differentiate into decidual NK cells is unknown. We studied the molecular mechanisms governing uNK tissue residency in human endometrium using single-cell RNA-seq and flow cytometry analyses. trNK cells with a CD49a+ CD16− phenotype were the most abundant CD56+ cells in the endometrium of 5 healthy control volunteers (HCs) [27±17% trNK vs. 4±2.7% CD49a− CD16+ conventional NK cells (cNK); p<0.02]. trNK cells differentially expressed genes associated with T cell tissue residency, such as ITGAE and ZNF683, compared to cNK. Although peripheral blood NK cells can express CD103 when incubated with TGF-β, trNKs upregulated CD103 expression in response to IL-15 alone in vitro. Given the dependency of CD103 expression on NFAT signals, we studied CD103 expression on trNKs by incubating human endometrium (n=7) with the calcineurin inhibitor FK506, which decreased IL-15-induced upregulation of CD103 (81% CD103+ [IL-15 alone] vs. 70% CD103− [IL-15 + FK506]; p=0.02). We next tested the in vivo relevance of these findings by comparing the frequency of trNKs in endometrial biopsies of five HCs with two biopsies of one UTx on FK506 immunosuppression. The UTx recipient had significantly fewer trNKs among CD45+ cells in two biopsies (HC: 27±17% vs. UTx: 4.3±2%; p=0.04). Altogether these findings suggest that IL-15-induced calcium signals influence uNK tissue residency, with significant implications for transplant recipients. This work was supported from UAB AMC21 and support of the uterus transplant program from the University of Alabama at Birmingham. P. Porrett is additionally supported by NIH R01 AI145905.