PROJECT SUMMARY This proposal focuses on elucidation of the processes regulating human natural killer (NK) cell development in the healthy state and in the setting of uterine endometrial carcinoma (EC). NK cells are cytotoxic “group 1” innate lymphoid cells (ILCs) that play myriad roles in immunity and are vital to controlling malignant transformation. NK cells undergo terminal differentiation and maturation in various tissues throughout the body, leading to a broad spectrum of NK cell phenotypes and functions. So-called conventional NK cells (cNK) that arise in secondary lymphoid tissues and predominate in the blood have established roles in complementing T cell-mediated immune surveillance. In contrast, specialized tissue-resident NK cells (trNK) and their close cousins, ILC1s, develop in various tissues and are retained there to carry out distinct functions. In the uterus, trNK cells and ILC1s are physiologically designed to support and promote pregnancy by promoting placental tissue invasion, immune suppression, and angiogenesis. We hypothesize that in the setting of EC the normal processes of uterine trNK cell and ILC1 development and function are co-opted by the tumor cells to promote their growth and invasion. Our goals in this proposal are to gain a comprehensive understanding of the cellular and molecular components that regulate human NK cell development in healthy tissues and to determine how these processes are impacted in the setting of EC. Our two specific aims are: 1) To define NK cell and ILC1 developmental pathways in human tissues; and 2) To determine how NK cell development and function are shaped by human EC. In particular, in Aim 1 we will test the hypothesis that all NK cells and ILC1s stem from a common group 1 ILC precursor cell, which we have recently identified in human lymphoid tissues. We propose a series of experiments to test our hypothesis and to determine the molecular regulation of the NK cell versus ILC1 developmental axis stemming from the novel precursor cell. Further, we will elucidate the developmental pathways of NK cells and ILC1s in the healthy human uterus, testing the hypothesis that uterine NK cells and ILC1s also stem from a similar group 1 ILC precursor cell but ultimately terminally differentiate through pathways distinct from those in lymphoid tissues. In Aim 2 we will test the hypothesis that NK cell development from the common group 1 ILC precursor is skewed towards the production of ILC1s and poorly cytotoxic uterine trNK cells that are permissive if not promoting of tumor growth. Through our proposed studies we will determine how NK cell development, functional diversity, and plasticity are shaped by EC. The clinical importance of these studies lies in the fact that EC is the most common gynecologic malignancy in the United States and is the sixth leading cause of cancer death in women. Further, we predict that the knowledge gained from our studies will improve our fundamental understand of huma...