Emerging themes in uterine natural killer cell heterogeneity and function

Addressing Natural Killer Cell Dysfunction and Plasticity in Cell-Based Cancer Therapeutics

Natural killer (NK) cells are cytotoxic group 1 innate lymphoid cells (ILC), known for their role as killers of stressed, cancerous, and virally infected cells. Beyond this cytotoxic function, NK cell subsets can influence broader immune responses through cytokine production and have been linked to central roles in non-immune processes, such as the regulation of vascular remodeling in pregnancy and cancer. Attempts to exploit the anti-tumor functions of NK cells have driven the development of various NK cell-based therapies, which have shown promise in both pre-clinical disease models and early clinical trials. However, certain elements of the tumor microenvironment, such as elevated transforming growth factor (TGF)-β, hypoxia, and indoalemine-2,3-dioxygenase (IDO), are known to suppress NK cell function, potentially limiting the longevity and activity of these approaches. Recent studies have also identified these factors as contributors to NK cell plasticity, defined by the conversion of classical cytotoxic NK cells into poorly cytotoxic, tissue-resident, or ILC1-like phenotypes. This review summarizes the current approaches for NK cell-based cancer therapies and examines the challenges presented by tumor-linked NK cell suppression and plasticity. Ongoing efforts to overcome these challenges are discussed, along with the potential utility of NK cell therapies to applications outside cancer.

Modeling Trophoblast Cell-Guided Uterine Spiral Artery Transformation in the Rat

The rat possesses hemochorial placentation with deep intrauterine trophoblast cell invasion and trophoblast-guided uterine spiral artery remodeling, which resembles human placentation. Uterine spiral arteries are extensively remodeled to deliver sufficient supply of maternal blood and nutrients to the developing fetus. Inadequacies in these key processes negatively impact fetal growth and development. Recent innovations in genome editing combined with effective phenotyping strategies have provided new insights into placental development. Application of these research approaches has highlighted both conserved and species-specific features of hemochorial placentation. The review provides foundational information on rat hemochorial placental development and function during physiological and pathological states, especially as related to the invasive trophoblast cell-guided transformation of uterine spiral arteries. Our goal is to showcase the utility of the rat as a model for in vivo mechanistic investigations targeting regulatory events within the uterine-placental interface.

Mesenchymal stromal cell-derived extracellular vesicle therapy prevents preeclamptic physiology through intrauterine immunomodulation†

Human umbilical cord-derived mesenchymal stromal cells (MSCs) are a widely recognized treatment modality for a variety of preclinical disease models and have been transitioned to human clinical trials. We have previously shown in neonatal lung disease that the therapeutic capacity of MSCs is conferred by their secreted extracellular vesicles (MEx), which function primarily through immunomodulation. We hypothesize that MEx have significant therapeutic potential pertinent to immune-mediated gestational diseases. Of particular interest is early-onset preeclampsia, which can be caused by alterations of the maternal intrauterine immune environment. Using a heme-oxygenase-1 null mouse model of pregnancy loss with preeclampsia-like features, we examined the preventative effects of maternal MEx treatment early in pregnancy. Heme oxygenase-1 null females (Hmox1-/-) or wild-type control females were bred in homozygous matings followed by evaluation of maternal and fetal parameters. A single dose of MEx was administered intravenously on gestational day (GD)1 to Hmox1-/- females (Hmox1-/- MEx). Compared with untreated Hmox1-/- females, Hmox1-/- MEx-treated pregnancies showed significant improvement in fetal loss, intrauterine growth restriction, placental spiral artery modification, and maternal preeclamptic stigmata. Biodistribution studies demonstrated that MEx localize to a subset of cells in the preimplantation uterus. Further, mass cytometric (CyTOF) evaluation of utero-placental leukocytes in Hmox1-/- MEx versus untreated pregnancies showed alteration in the abundance, surface marker repertoire, and cytokine profiles of multiple immune populations. Our data demonstrate the therapeutic potential of MEx to optimize the intrauterine immune environment and prevent maternal and fetal sequelae of preeclamptic disease.

Decidual leucocytes infiltrating human spiral arterioles are rich source of matrix metalloproteinases and degrade extracellular matrix in vitro and in situ

PROBLEM

During pregnancy, the decidual spiral arterioles (SpAs) that supply maternal blood to the placenta undergo a series of changes to optimise the transfer of nutrients and oxygen to the developing foetus. Recent studies have shown that initiation of SpA transformation coincides with decidual leucocyte infiltration. Leucocytes are known to be a source of matrix metalloproteinases (MMPs); however, the complete profile of MMPs expressed by decidual NK cells (dNK) and macrophages has not been characterised. We hypothesised that leucocyte-derived MMPs contribute to SpA remodelling.

METHODS

Decidual NK cells and macrophages were isolated from first trimester decidua and their MMP repertoire profiled by qRT-PCR (n = 10; 5-11 weeks). Dual immunofluorescence was used to localise MMP expression in situ (n = 3; 5-12 weeks). Gelatin zymography was carried out to assess whether leucocyte-derived MMPs can degrade ECM. In situ zymography and immunofluorescence identified MMP activity in tissue-resident dNK and macrophages.

RESULTS

Decidual NK cells cells and macrophages expressed MMP2, -7, -9, -11, -16, -19 and tissue inhibitors of metalloproteinase-1, -2, and -3. Both cell types degraded gelatin using MMP2 and MMP9 and broke down collagen in an in vitro model of the SpA. Extravillous trophoblasts (EVTs) expressed a similar repertoire of MMPs.

CONCLUSION

We suggest that matrix remodelling in SpA is initiated by infiltrating leucocytes, while EVTs become involved at later stages.

Epithelial and stromal-specific immune pathway activation in the murine endometrium post-coitum

The endometrium is a dynamic tissue, demonstrating cyclical growth/remodelling in preparation for implantation. In mice, seminal constituents trigger mechanisms to prepare the endometrium, a process dubbed 'seminal priming' that modifies immune system components and mediates endometrial remodelling in preparation for pregnancy. An array of cytokines has been reported to mediate this interaction, although much of the literature relates to in vitro studies on isolated endometrial epithelial cells. This study measured changes in immune-related gene expression in endometrial epithelial and stromal cells in vivo following natural mating. CD1 mice were naturally mated and sacrificed over the first 4 days post-coitum (n=3 each day). Endometrial epithelial and stromal compartments were isolated by laser capture microdissection. Labelled cRNA was generated and hybridised to genome-wide expression microarrays. Pathway analysis identified several immune-related pathways active within epithelial and stromal compartments, in particular relating to cytokine networks, matrix metalloproteinases and prostaglandin synthesis. Cluster analysis demonstrated that the expression of factors involved in immunomodulation/endometrial remodelling differed between the epithelial and stromal compartments in a temporal fashion. This study is the first to examine the disparate responses of the endometrial epithelial and stromal compartments to seminal plasma in vivo in mice, and demonstrates the complexity of the interactions between these two compartments needed to create a permissive environment for implantation.

Tissue-resident natural killer cells and their potential diversity

Conventional NK cells are well characterized in the mouse spleen and circulate in the blood. Less well described are NK cells found in organs such as the liver, thymus, and uterus. Recently we identified a tissue-resident NK (trNK) cell population in the liver, suggesting a potential diversity of trNK cells in other organs. In this review we compare and contrast the similarities and differences among the subpopulations of NK and innate lymphoid cells to the trNK cells in the liver.

Tissue-resident natural killer (NK) cells are cell lineages distinct from thymic and conventional splenic NK cells

Natural killer (NK) cells belong to the innate immune system; they can control virus infections and developing tumors by cytotoxicity and producing inflammatory cytokines. Most studies of mouse NK cells, however, have focused on conventional NK (cNK) cells in the spleen. Recently, we described two populations of liver NK cells, tissue-resident NK (trNK) cells and those resembling splenic cNK cells. However, their lineage relationship was unclear; trNK cells could be developing cNK cells, related to thymic NK cells, or a lineage distinct from both cNK and thymic NK cells. Herein we used detailed transcriptomic, flow cytometric, and functional analysis and transcription factor-deficient mice to determine that liver trNK cells form a distinct lineage from cNK and thymic NK cells. Taken together with analysis of trNK cells in other tissues, there are at least four distinct lineages of NK cells: cNK, thymic, liver (and skin) trNK, and uterine trNK cells.

DOI:http://dx.doi.org/10.7554/eLife.01659.001

Our immune system has white blood cells that migrate throughout the body in search of invading microbes or diseased and damaged cells. When these events are encountered, the white blood cells move into the affected tissue and launch an immune response to eliminate the threat.

Natural killer cells are white blood cells that kill cells that are infected with viruses or are cancerous. Most of what is known about conventional natural killer cells is derived from studying the spleen, which filters the blood and contains many immune cells. Natural killer cells also circulate around the body or are found within other tissues, and it was thought that both types of cells were either the same, or that one type could develop into the other. However, the thymus—an organ that is another source of white blood cells—contains a sub-population of natural killer cells that are distinct from the conventional splenic natural killer cells. Furthermore, recent work revealed the existence of two types of natural killer cells within the liver: some of these cells were similar to the conventional splenic natural killer cells that circulate throughout the body, while others appeared to be ‘tissue-resident’ natural killer cells that were poised to deliver an immune response.

Now Sojka et al. show that the tissue-resident natural killer cells found in the liver are a distinct lineage of cells. These cells mature independently from the conventional natural killer cells found in the spleen, and the natural killer cells found in the thymus. Moreover, the skin contains tissue-resident natural killer cells similar to those in the liver; whilst natural killer cells that had previously been discovered in the uterus were shown to contain a fourth distinct tissue-resident lineage.

The work of Sojka et al. will encourage a full re-evaluation of the roles played by natural killer cells to determine which populations of these cells are responsible for implementing immune responses. Furthermore, a more thorough understanding of how tissue-resident natural killer cells function to eliminate diseased or damaged cells, such as cancerous cells, could also contribute to future efforts to develop new anti-cancer treatments.

DOI:http://dx.doi.org/10.7554/eLife.01659.002

Receptors for non-MHC ligands contribute to uterine natural killer cell activation during pregnancy in mice

INTRODUCTION

Activated uterine natural killer (uNK) cells are abundant in early human and mouse decidual basalis. In mice, distinct uNK cell subsets support early endothelial tip cell induction, the pruning of new vessels and initiation of spiral arterial modification. While genetic studies indicate that NK/uNK cell activation via receptors recognizing Class I MHC-derived peptides promotes human pregnancy, roles for other activation receptors expressed by NK cells, such as the aryl hydrocarbon receptor (AHR) and natural cytotoxicity receptors (NCR) are undefined in human or mouse pregnancies.

METHODS

Expression of AHR and NCR1 (ortholog of human NKp46) by gestation day (gd)10.5 mouse uNK cell subsets was measured by quantitative real-time RT-PCR. Early implantation sites from mice lacking expression of either receptor were examined histologically.

RESULTS

Gd10.5 uNK cell subsets, separated by reactivity to Dolichos biflorus agglutinin lectin, differed in relative transcript abundance for Ahr and Ncr1. Quantitative histology revealed that, in comparison to C57BL/6 controls, implant sites from gd10.5 Ahr(-/-) and gd6.5-12.5 UkCa:B6.Ncr1(Gfp/Gfp) mice had normal uNK cell abundance but the uNK cells were smaller than normal and unable to trigger spiral arterial remodeling. Whole mount immunohistochemistry comparisons of viable, gd6.5-8.5 Ncr1(Gfp/Gfp) and C57BL/6 implant sites revealed deficits in implant site angiogenesis and conceptus growth in Ncr1(Gfp/Gfp).

DISCUSSION

In mice, activation of AHR and of NCR1 by endogenous, as yet undefined ligands, contributes to uNK cell activation/maturation and angiogenic functions during early to mid-gestation pregnancy. MHC-independent activation of uNK cells also likely makes critical contributions to human pregnancy success.

Impact of brief exercise on peripheral blood NK cell gene and microRNA expression in young adults

Natural killers (NK) cells are unique innate immune cells that increase up to fivefold in the circulating blood with brief exercise and are known to play a key role in first-response defense against pathogens and cancer immunosurveillance. Whether exercise alters NK cell gene and microRNA (miRNA) expression is not known. Thirteen healthy men (20-29 yr old) performed ten 2-min bouts of cycle ergometer exercise at a constant work equivalent to an average of 77% of maximum O2 consumption interspersed with 1-min rest. Blood was drawn before and immediately after the exercise challenge. NK cells were isolated from peripheral blood mononuclear cells using a negative magnetic cell separation method. We used Affymetrix U133+2.0 arrays for gene expression and Agilent Human miRNA V2 Microarray for miRNAs. A stringent statistical approach (false discovery rate < 0.05) was used to determine that exercise significantly altered the expression of 986 genes and 23 miRNAs. Using in silico analysis, we found exercise-related gene pathways where there was a high likelihood of gene-miRNA interactions. These pathways were predominantly associated with cancer and cell communication, including p53 signaling pathway, melanoma, glioma, prostate cancer, adherens junction, and focal adhesion. These data support the hypothesis that exercise affects the gene and miRNA expression pattern in the population of NK cells in the circulation and suggest mechanisms through which physical activity could alter health through the innate immune system.

Imaging of vascular development in early mouse decidua and its association with leukocytes and trophoblasts

In species with endometrial decidualization and hemochorial placentation (humans, mice, and others), leukocytes localize to early implant sites and contribute to decidual angiogenesis, spiral arterial remodeling, and trophoblast invasion. Relationships between leukocytes, trophoblasts, and the decidual vasculature are not fully defined. Early C57BL/6J implant sites were analyzed by flow cytometry to define leukocyte subsets and by whole-mount immunohistochemistry to visualize relationships between leukocytes, decidual vessels, and trophoblasts. Ptprc(+) (CD45(+)) cells increased in decidua between Gestational Day (GD) 5.5 and GD 9.5. Uterine natural killer (uNK) cells that showed dynamic expression of Cd (CD) 69, an activating receptor, and Klrg1 (KLRG1), an inhibitory receptor, localized mesometrially and were the dominant CD45(+) cells between GD 5.5 and GD 7.5. At GD 8.5, immature monocytes that occurred throughout decidua exceeded uNK cells numerically and many leukocytes acquired irregular shapes, and leukocyte-leukocyte conjugates became frequent. Vessels were morphologically heterogeneous and regionally unique. Migrating trophoblasts were first observed at GD 6.5 and, at GD 9.5, breached endothelium, entered vascular lumens, and appeared to occlude some vessels, as described for human spiral arteries. No leukocyte-trophoblast conjugates were detected. Whole-mount staining gave unparalleled decidual vascular detail and cell-specific positional information. Its application across murine models of pregnancy disturbances should significantly advance our understanding of the maternal-fetal interface.

Peripheral blood stem cell transplants do not result in endometrial stromal engraftment

OBJECTIVE

To determine whether peripheral blood stem cell transplant (PBSCT) result in engraftment of donor stem cells in the recipient uterus.

DESIGN

Prospective clinical and laboratory research.

SETTING

Translational medicine research hospital. PATIENT(S)/ANIMAL(S): Macaque and human bone marrow transplant recipients.

INTERVENTION(S)

Rhesus macaques received autologous transduced immunoselected cytokine-mobilized CD34+ cells after total body irradiation. Vector constructs expressed green fluorescent protein. In the human subjects, prior PBSCT subjects underwent endometrial biopsy and bone marrow aspiration. Macaque and human endometrial and bone marrow cells were isolated and cultured. Fluorescent microscopy, flow cytometry, and polymerase chain reaction (PCR) were used to evaluate for the presence of donor-derived cells.

MAIN OUTCOME MEASURE(S)

Presence of donor cells in recipient endometrium and bone marrow stroma.

RESULT(S)

The macaque endometrial cells did not exhibit evidence of green fluorescent protein labeling. Human endometrial cells were cultured and the absence of donor blood contamination was verified. The PCR evaluation of the human endometrial cells did not demonstrate evidence of donor short tandem repeats.

CONCLUSION(S)

The PBSCT did not result in engraftment of donor-derived cells in the endometrium.