NK in pregnancy · Impact of Natural Killer Cells on Fetal and Placental Development

Impact of Natural Killer Cells on Fetal and Placental Development

Our research addresses key roles of immune cells at the fetal-maternal interface. In addition to their protective role of the baby from pathogens, these cells have a unique capacity to tune the function of the placenta, a vital organ that supplies the baby with oxygen, nutrients and other growth factors. Natural killer (NK) cells are known as critical sentinels of the innate immune system for their ability to kill infected or malignant cells without prior sensitisation. Recently, NK cells have been recognised as the founders of the new family of innate lymphoid cells (ILCs). Numerous tissue specific ILCs subsets with adaptive immunity and tissue remodelling features are increasingly identified. No organ is richer in NK cells than the uterus. Uterine NK cells (uNK) are from peripheral and resident origin. During pregnancy, their number expand but their precise function together with other uterine ILCs is poorly understood. Pregnancy is the only situation in vertebrates where two genetically distinct organisms co-exist, in which the semi-allogeneic placenta comes into direct contact with the self-guarded womb. In both human and rodents, placental cells behave similarly to tumour cells and invade maternal tissues and vasculature. Conversely, it is known that uNK cells are not good killers. So, what is their function if they don’t kill? In this project, we aimed to study the role of uNK cells at the maternal-fetal interface and how they may impact placental development and fetal growth. Using the mouse model, first, we identified new NK and ILC subsets within uterine sub-compartments and their dynamic distribution prior and during pregnancy. We found that tissue resident NK cells (trNK) predominate within the uterine wall while the frequency of peripheral-like conventional NK cells (cNK) increased in the transformed and highly vascularised uterine mucosa (decidua). In addition, we found that the decidua was devoid of ILC2 and ILC3. Second, we found that uNK cells and ILCs differentially required Nfil3 (Nuclear Factor Interleukin-3), known as a key transcription factor for the development and differentiation of all murine ILCs. Tissue resident uNK, ILC1 and ILC3 developed independently of Nfil3, whereas peripheral NK cells and ILC2 were Nfil3-dependent. Unlike their counter parts in other tissues (i.e. liver), we found that uterine trNK cells expressed Eomes (Eomesodermine), another important transcription factor for conventional NK cells maturation and activation. Conversely, ILC1 did not express Eomes and were identified apart from trNK cells on this basis. Human and murine uterine NK cells (uNK) produce factors active on both blood vessels and the invading fetal placental cells, and contribute to maternal adaptations to pregnancy, as well as to fetal and placental growth. IFN-gamma produced by uNK cells in mice plays essential and non-redundant functions for uterine spiral artery remodeling, which is a critical process that ensures optimal supply of oxygen and nutrients to the fetus. In women, deficient remodelling is associated with complications of pregnancy, including pre-eclampsia, fetal growth restriction and recurrent miscarriage. We have analysed the cytokine profiles of ILCs and uNK cells subsets and found that ILC1, trNK cells and cNK cells produced interferon gamma (IFNg) and that ILC2 and ILC3 recapitulated phenotype and cytokine expression profiles that described in other tissues but their precise roles remain to be defined. However, we found that trNK cells and other NFIL3-independent ILCs at the maternal-fetal interface are not sufficient to mediate normal maternal uterine adaptations to pregnancy. Placentation and fetal growth is compromised in the absence of NFIL3, which emerges as an essential mediator of non-redundant functions for reproduction in mice. Hence, in this study we characterised for the first time conventional, tissue-resident uterine NK cells and other ILCs in wild-type mice during pregnancy. These findings open a new line of research in a fast evolving field and bring insights for translational applications to humans in treating pregnancy disorders. In addition, given the unique placental properties, our multidisciplinary research could have a beneficial impact in understanding other pathologies such as cancer metastasis and rejection of transplantation. Indeed, our findings on the molecular interactions at the fetal-maternal interface are of great interest both for the economy in identifying and developing new diagnostic markers, treatment or preventive therapies, and for the society in improving the quality of individual’s life at its earliest stage (i.e. in the womb). The placenta determines the future health of every one of us. Increasing evidence reveals that abnormalities in antenatal life correlate with metabolic, cardiovascular and cognitive disorders in adult life, all major health burdens in industrialised societies and are the centre of our research interest.

Data: CORDIS, © European Union