Differentiation of uterine tissue-resident natural killer cells

For a pregnancy to succeed, the immune environment at the maternal-fetal interface must be precisely regulated to support fetal development. Uterine natural killer (uNK) cells–the most abundant lymphocyte at the maternal- fetal interface–are thought to contribute to various physiological aspects of gestation crucial for fetal development. Their critical role in pregnancy is evidenced by studies linking abnormalities in uNK cells to adverse pregnancy outcomes, particularly in uterine transplant recipients. Our preliminary findings provide the first direct evidence showing that the loss of uNK cells in the pregnant murine uterus significantly reduces litter sizes and increases resorption rates, further underscoring their indispensable role in pregnancy. Despite mounting evidence linking uNK cell dysfunction with adverse pregnancy outcomes, critical knowledge gaps in uNK cell biology persist, particularly regarding the origins and functional specialization of these cells within the uterine microenvironment. Our lab has previously shown that the uNK cell population is heterogeneous, consisting of both tissue-resident NK (trNK) cells and conventional NK (cNK) cells. While the developmental trajectory of cNK cells has been well-established, the developmental origins of uterine trNK cells remain unresolved. Here, we will investigate the origins and differentiation of uterine trNK cells in the virgin and pregnant murine uterus. Our preliminary findings show that both trNK cells and cNK cells in the murine uterus are Eomesodermin-dependent both at steady-state and during pregnancy, suggesting uterine trNK cells derive from the cNK cell lineage. Additionally, our initial studies demonstrate that progenitors in the bone marrow can give rise to uterine trNK cells. Together, our data support the central hypothesis that uterine trNK cells originate from the cNK cell lineage and are derived from either 1) early NK cell precursors in the bone marrow or 2) mature cNK cells in the periphery. Recognizing that these possibilities are not mutually exclusive, we will clarify the origins and developmental kinetics of uterine trNK cells using cutting-edge techniques and novel mouse models, including adoptive transfer studies in a newly engineered reporter mouse as well as advanced whole-mount confocal imaging. We also hypothesize that peripheral cNK cells can differentiate into uterine trNK cells during murine pregnancy and are driven to do so by molecular factors in the pregnant uterus. To explore the potential plasticity of peripheral cNK cells in the pregnant uterus, we will leverage innovative mouse models and state-of-the-art spatial transcriptomics to identify key regulatory signals and cell populations governing this transition. Collectively, this proposal will address key gaps in uNK cell biology by providing critical insights into the origins and differentiation of uNK cells that have the potential to uncover novel therapeutic targets for patients with uNK cell abnormalities, particularly uterine transplant recipients, ultimately improving reproductive health outcomes. Project Number: 1F30HD118750-01A1 | Fiscal Year: 2026 | NIH Institute/Center: Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) | Principal Investigator: Josselyn Barahona | Institution: WASHINGTON UNIVERSITY, SAINT LOUIS, MO | Award Amount: $36,673 | Activity Code: F30 | Study Section: Special Emphasis Panel[ZRG1 F06A-D (20)] View on NIH RePORTER: https://reporter.nih.gov/project-details/1F30HD11875001A1