cNK Cells Research Articles

Aryl hydrocarbon receptor inhibition promotes hematolymphoid development from human pluripotent stem cells

AbstractThe aryl hydrocarbon receptor (AHR) plays an important physiological role in hematopoiesis. AHR is highly expressed in hematopoietic stem and progenitor cells (HSPCs) and inhibition of AHR results in a marked expansion of human umbilical cord blood–derived HSPCs following cytokine stimulation. It is unknown whether AHR also contributes earlier in human hematopoietic development. To model hematopoiesis, human embryonic stem cells (hESCs) were allowed to differentiate in defined conditions in the presence of the AHR antagonist StemReginin-1 (SR-1) or the AHR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). We demonstrate a significant increase in CD34+CD31+ hematoendothelial cells in SR-1–treated hESCs, as well as a twofold expansion of CD34+CD45+ hematopoietic progenitor cells. Hematopoietic progenitor cells were also significantly increased by SR-1 as quantified by standard hematopoietic colony-forming assays. Using a clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9)-engineered hESC-RUNX1c-tdTomato reporter cell line with AHR deletion, we further demonstrate a marked enhancement of hematopoietic differentiation relative to wild-type hESCs. We also evaluated whether AHR antagonism could promote innate lymphoid cell differentiation from hESCs. SR-1 increased conventional natural killer (cNK) cell differentiation, whereas TCDD treatment blocked cNK development and supported group 3 innate lymphoid cell (ILC3) differentiation. Collectively, these results demonstrate that AHR regulates early human hematolymphoid cell development and may be targeted to enhance production of specific cell populations derived from human pluripotent stem cells.

Conventional NK cells and ILC1 are partially ablated in the livers of Ncr1iCreTbx21fl/fl mice

Mouse liver contains both Eomes-dependent conventional natural killer (cNK) cells and Tbet-dependent liver-resident type I innate lymphoid cells (ILC1). In order to better understand the role of ILC1, we attempted to generate mice that would lack liver ILC1, while retaining cNK, by conditional deletion of Tbet in NKp46+ cells. Here we report that the Ncr1iCreTbx21fl/fl mouse has a roughly equivalent reduction in both the cNK and ILC1 compartments of the liver, limiting its utility for investigating the relative contributions of these two cell types in disease models. We also describe the phenotype of these mice with respect to NK cells, ILC1 and NKp46+ ILC3 in the spleen and small intestine lamina propria.

Tissue-resident liver NK cell responses to MCMV infection

Abstract Natural Killer (NK) cells belong to the ILC1 subgroup, which contains conventional NK (cNK) cells, ILC1 and tissue-resident NK (trNK) cells. The murine liver is home to both cNK cells and trNK cells. In this organ, cNK cells and trNK cells can be distinguished based on the expression of the transcription factors Eomes and T-bet. cNK cells are double positive for Eomes and T-bet while trNK cells do not express Eomes. During viral infection, the fate of the activated cNK cell population is relatively well defined. However, the fate of the trNK cell population remains unexplored. Using the MCMV model of infection, we found that a contraction phase precedes a replenishment of the trNK cell subset, which inversely correlates with cNK cell kinetics. We sought to determine whether the trNK cell response was a direct result of MCMV infection or an indirect response to inflammatory milieu. In order to help distinguish between these two possibilities, mice were injected with the iNKT ligand a-galactosylceramide (a-GalCer). We found that treatment with a-GalCer lead to an initial contraction phase of liver trNK cells, indicating that the phenotype observed is independent of MCMV infection. Altogether, these data suggest that liver cNK and trNK cell subsets, which arise from distinct developmental pathways, perform different functions in this organ.

Comparative analysis of conventional natural killer cell responses to acute infection with Toxoplasma gondii strains of different virulence

Abstract Toxoplasma gondii is an obligate intracellular parasitic protozoan present in 30% of humans and a significant health concern in immunocompromised people. Conventional Natural Killer Cells (cNK), members of group 1 innate lymphoid cells, are critical for early immunity to T. gondii via IFNγ production. However, little is understood about how cNK cell functionality, subpopulations, maturation and proliferation are affected by parasite infection and parasite virulence. Here we comprehensively performed this analysis with Type I virulent RH, Type II avirulent ME49 and fully attenuated Type I cps1-1 strains. In response to these three parasite strains, murine cNK cells produce IFNγ and become cytotoxic and polyfunctional (IFNγ+CD107a+) at the site of infection. In contrast to virulent RH and avirulent ME49 T. gondii strains, attenuated cps1-1 strain induced only local cNK cell responses. RH and ME49 infection significantly decreased cNK cell frequency and numbers in spleen compared with cps1-1 parasites. Responding cNK cell subsets expressing activating receptors and inhibitory receptors were similar regardless of parasite infection strain. 5 days post infection cNK cells did not proliferate, however, cellular maturation (CD27, CD11b and KLRG1) was impacted by parasite strain. cNK cell maturation was reduced after RH or ME49 infection compared with cps1-1 infection. Interestingly, KLRG1 was highly expressed on immature not mature cNK cells after RH infection. Results suggest increased parasite virulence differentially impacts cNK cell maturation during acute T. gondii infection. Different cNK cell responses could impact early immunity and susceptibility to these strains.

Expression of the inhibitory receptor NKG2A correlates with increased liver and splenic NK cell response to activating receptor engagement.

IntroductionNatural killer (NK) cells play a critical role in the innate immune response to viruses and tumors, and comprise a large proportion of the hepatic lymphocyte population. They must remain tolerant to non‐pathogenic antigens while protecting the host from harmful agents. Herein, we investigate how the NK cell response to activation receptor engagement is altered in the liver.MethodsIn this study, we assess IFN‐γ production and degranulation of splenic NK cells and selected subsets of liver NK cells. Flow cytometry (FCM) was used to asses IFN‐γ production and degranulation following stimulation of the NK cells with plate bound antibodies to activating receptors.ResultsWe show that smaller percentages of hepatic NK cells produce interferon (IFN)–γ and/or degranulate than do splenic NK cells upon stimulation through activating receptors. We also found that smaller percentages of the circulating NK (cNK) cells in the liver produce IFN‐γ and/or degranulate, compared to the liver tissue resident NK (trNK) cells. In addition, IFN‐γ production by liver cNK cells is not increased in IL‐10 deficient mice, suggesting that their hyporesponsiveness is not mediated by the presence of this anti‐inflammatory cytokine in the hepatic microenvironment. On the other hand, liver trNK cells express higher levels of the inhibitory receptor NKG2A than do cNK cells, correlating with their increased IFN‐γ production and degranulation.ConclusionsLiver cNK cells’ hyporesponsiveness to stimulation through activating receptors is independent of IL‐10, but correlates with decreased NKG2A expression compared to trNK cells. In addition, we demonstrate that liver NK cells become further hyporesponsive upon continuous engagement of an activating receptor on their cell surface.

Tissue-resident natural killer cells in the livers.

Nature killer (NK) cells are important lymphocytes of the innate immune system, well known for their pivotal roles in immune surveillance and defense against tumor and virus-infected cells. Current studies have revealed that NK cells are not a homogeneous population, but instead consist of distinct subsets with diverse characteristics. As an organ with predominant innate immunity, the liver is enriched with NK cells, among which two distinct NK cell subsets have recently been identified: conventional NK (cNK) cells and tissue-resident NK (trNK) cells. Liver trNK cells are markedly different from cNK cells in many aspects, representing a new lineage of innate lymphoid cell (ILC) family. Here, we summarize the phenotypic and functional features of liver trNK cells, and review current knowledge regarding developmental pathway of liver trNK cells. We also overview recent advances in human liver trNK cells and discuss the striking shared hallmarks of trNK cells in different tissues.

Chronic alcohol consumption inhibits peripheral NK cell development and maturation by decreasing the availability of IL-15.

NK cells are innate immune cells and have important roles in antiviral and antitumor immunity. Based on the transcriptional regulation, organ distribution, and cell function, NK cells have recently been further divided into cytotoxic conventional NK cells (cNK) and noncytotoxic helper-like group 1 innate lymphoid cells (ILC1s). It is well known that chronic alcohol consumption decreases peripheral NK cell number and cytolytic activity; however, the underlying mechanism remains to be elucidated. How chronic alcohol consumption affects ILC1s is, to our knowledge, completely unexplored. Herein, we used a well-established mouse model of chronic alcohol consumption to study the effects of alcohol on transcription factor expression, maturation, and cytokine production of cNK cells and ILC1s in various organs. We found that alcohol consumption significantly decreased Eomes-expressing cNK cells in all the examined organs, except BM, but did not significantly affect ILC1s. Alcohol consumption compromised cNK cell development and maturation. Exogenous IL-15/IL-15Rα treatment caused full recovery of Eomes-expressing cNK cell number and maturation. Taken together, our data indicated that chronic alcohol consumption decreases cNK cell number and cytolytic activity by arresting cNK cell development at the CD27+CD11b+ stage. This developmental arrest of NK cells results from a lack of IL-15 availability in the microenvironment. IL-15/IL-15Rα treatment can recover alcohol consumption-induced developmental defect in NK cells.

Abstract IA27: Novel natural killer cell targets for cancer immunotherapy

Abstract Avoiding immune destruction is a hallmark of cancer. Natural killer (NK) cells contribute to tumor immune surveillance and protection from tumor metastasis. The cell surface Ig superfamily molecule CD96 has recently been shown as a negative regulator of mouse NK cell activity, and we have demonstrated that blocking CD96 with a monoclonal antibody inhibited experimental metastases in multiple tumor models. The anti-metastatic activity of anti-CD96 was dependent on NK cells, CD226 (DNAM-1) and IFN-γ, but independent of activating Fc receptors. Anti-CD96 was more effective in combination with anti-CTLA4, anti-PD1, anti-TIGIT, or doxorubicin chemotherapy. Development of additional anti-mouse and anti-human CD96 mAbs will be discussed. Overall these data demonstrate that blocking CD96 is a new and complementary immunotherapeutic strategy to reduce tumor metastases. The activity of NK cells is also governed by the cytokine IL-15, foreign and self-ligands, and a variety of immunosuppressive factors. We have identified CIS (Cytokine-inducible SH2-containing protein; Cish gene) as the critical negative regulator of IL-15 signalling in NK cells and shown the critical intrinsic role of CIS in suppressing NK cell control of tumor initiation and metastasis. The combination of Cish-deficiency and relevant immunotherapies, such as immune checkpoint blockade antibodies, IL-2, and type I interferon revealed further improved control of metastasis. The data clearly indicates that targeting CIS promotes NK cell antitumor functions and CIS holds great promise as a novel target in NK cell immunotherapy. The relative importance of mechanisms that tumors adopt to evade NK cells remains ill defined. Using mice with NK cells that either constitutively, or are unable to, signal via the TGF-β receptor, revealed that TGF-β signaling induces the transdifferentiation of conventional NK (cNK) cells into ILC1. Functional analysis revealed that host protection from tumor initiation and metastasis is mediated by cNK cells, whereas tumor resident ILC1 and ILC1-like cells appear to offer no host protection. These data indicate the plasticity of cNK cells under pathophysiological conditions and a potential new escape mechanism for tumors from innate immunity. Citation Format: Mark J. Smyth, Eva Putz, Stephen Blake, Aaron Gao, Fernando Guimaraes, John Miles, Bill Dougall, Michele WL Teng, Nicholas D. Huntington. Novel natural killer cell targets for cancer immunotherapy [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr IA27.

Comparative Analysis of Conventional Natural Killer Cell Responses to Acute Infection with Toxoplasma gondii Strains of Different Virulence.

Conventional natural killer (cNK) cells, members of group 1 innate lymphoid cells, are a diverse cell subpopulation based on surface receptor expression, maturation, and functional potential. cNK cells are critical for early immunity to Toxoplasma gondii via IFNγ production. Acute cNK cell responses to infection with different strains of T. gondii have not yet been characterized in detail. Here, we comprehensively performed this analysis with Type I virulent RH, Type II avirulent ME49, and fully attenuated Type I cps1-1 strains. In response to these three parasite strains, murine cNK cells produce IFNγ and become cytotoxic and polyfunctional (IFNγ+CD107a+) at the site of infection. In contrast to virulent RH and avirulent ME49 T. gondii strains, attenuated cps1-1 induced only local cNK cell responses. Infections with RH and ME49 parasites significantly decreased cNK cell frequency and numbers in spleen 5 days post infection compared with cps1-1 parasites. cNK cell subsets expressing activating receptors Ly49H, Ly49D, and NKG2D and inhibitory receptors Ly49I and CD94/NKG2A were similar when compared between the strains and at 5 days post infection. cNK cells were not proliferating (Ki67−) 5 days post infection with any of the strains. cNK cell maturation as measured by CD27, CD11b, and KLRG1 was affected after infection with different parasite strains. RH and ME49 infection significantly reduced mature cNK cell frequency and increased immature cNK cell populations compared with cps1-1 infection. Interestingly, KLRG1 was highly expressed on immature cNK cells after RH infection. After RH and ME49 infections, CD69+ cNK cells in spleen were present at higher frequency than after cps1-1 infection, which may correlate with loss of the mature cNK cell population. Cytokine multiplex analysis indicated cNK cell responses correlated with peritoneal exudate cell, spleen, and serum proinflammatory cytokine levels, including IL-12. qPCR analysis of parasite-specific B1 gene revealed that parasite burdens may affect cNK cell responses. This study demonstrates infection with RH and ME49 parasites impacts cNK cell maturation during acute T. gondii infection. Different cNK cell responses could impact early immunity and susceptibility to these strains.

NK cells activated by Interleukin-4 in cooperation with Interleukin-15 exhibit distinctive characteristics

Natural killer (NK) cells are known to be activated by Th1-type cytokines, such as IL-2, -12, or -18, and they secrete a large amount of IFN-γ that accelerates Th1-type responses. However, the roles of NK cells in Th2-type responses have remained unclear. Because IL-4 acts as an initiator of Th2-type responses, we examined the characteristics of NK cells in mice overexpressing IL-4. In this study, we report that IL-4 overexpression induces distinctive characteristics of NK cells (B220(high)/CD11b(low)/IL-18Rα(low)), which are different from mature conventional NK (cNK) cells (B220(low)/CD11b(high)/IL-18Rα(high)). IL-4 overexpression induces proliferation of tissue-resident macrophages, which contributes to NK cell proliferation via production of IL-15. These IL-4-induced NK cells (IL4-NK cells) produce higher levels of IFN-γ, IL-10, and GM-CSF, and exhibit high cytotoxicity compared with cNK cells. Furthermore, incubation of cNK cells with IL-15 and IL-4 alters their phenotype to that similar to IL4-NK cells. Finally, parasitic infection, which typically causes strong Th2-type responses, induces the development of NK cells with characteristics similar to IL4-NK cells. These IL4-NK-like cells do not develop in IL-4Rα KO mice by parasitic infection. Collectively, these results suggest a novel role of IL-4 in immune responses through the induction of the unique NK cells.

Human liver contains two populations of NK cells based on CD49e expression

Abstract Natural killer cells are a subset of innate immune lymphocytes that can kill transformed and infected cells, and produce cytokines that modulate the host immune response. Previous studies on human NK cells have primarily characterized NK cells isolated from peripheral blood. However, studies in mice from our lab and others indicate an additional tissue-resident NK (trNK) population that does not re-circulate in contrast to conventional NK (cNK). When the mouse liver was excised and flushed with saline, trNK cells were detected, indicating that the trNK cells reside in the liver sinusoidal space. Recent studies to identify trNK cells in the human liver have concentrated on the differential expression of CD56-dim/bright populations of NK cells and also CD49a, a marker we previously defined for mouse trNK cells in the liver. Herein we obtained samples from liver transplantation cadaveric donors. Matching donor venous blood and serial liver saline flushes were studied. Our preliminary data identifies a subset of putative liver-trNK cells based on lack of CD49e expression which appeared in the terminal liver flush aliquot and was not present in earlier liver flushes nor peripheral blood whereas CD49a expression was not discriminatory. Mass cytometry experiments with cytometry by time-of-flight instrument and a panel of 42 antibodies corroborated these findings. Interestingly, the liver-resident CD49e− cells have elevated EOMES but lower Tbet expression which contrasts the CD49a+ trNK cell populations in human and mouse liver. Finally, the putative trNK cells express different killer immunoglobulin-like receptor (KIR) repertoire than cNK cells thus, a unique population of trNK cells that reside in the sinusoidal space of the human liver.

ILC1s in Tissue Inflammation and Infection.

Innate lymphoid cells (ILCs) are innate immune cells that provide an early source of cytokines to initiate and tailor the immune response to the type of the encountered pathogen or insult. The group 1 ILCs are comprised of conventional natural killer (cNK) cells and subsets of “unconventional NK cells,” termed ILC1s. Although cNK cells and ILC1s share many features, such as certain phenotypic markers and the ability to produce IFN-γ upon activation, it is now becoming apparent that these two subsets develop from different progenitors and show unique tissue distribution and functional characteristics. Recent studies have aimed at elucidating the individual contributions of cNK cells and ILC1s during protective host responses as well as during chronic inflammation. This review provides an overview of the current knowledge of the developmental origins as well as of the phenotypic and functional characteristics of ILC1s.

NCR1+ cells appear early in GALT development of the ovine foetus and acquire a c-kit+ phenotype towards the end of gestation

The amount, distribution and phenotype of ovine NCR1+ cells were investigated during developing GALT from day 70 of gestation. Antibodies against CD3 and CD79 were used to identify the compartments of GALT, and the localization of NCR1+ cells were correlated within these structures. Markers CD34 and c-kit, in addition to Ki67, were used to investigate possible origin and the stage of development of the NCR1+ cells. NCR1+ cells were present as single cells in the subepithelial tissue as early as 70 days of gestation, and were predominantly present in the T cell rich IFAs and domes as these intestinal wall compartments developed. While NCR1+ cells proliferated more intensively at mid-gestation (70–104 days), the number of NCR1+ cells also expressing c-kit, increased at the end of gestation. In conclusion, NCR1+ cells appeared early in T cell areas of the gut and displayed a phenotype consistent with intermediate stages of cNK cells and/or a subpopulation of ILC22.

Liver natural killer cells: subsets and roles in liver immunity.

The liver represents a frontline immune organ that is constantly exposed to a variety of gut-derived antigens as a result of its unique location and blood supply. With a predominant role in innate immunity, the liver is enriched with various innate immune cells, among which natural killer (NK) cells play important roles in host defense and in maintaining immune balance. Hepatic NK cells were first described as ‘pit cells' in the rat liver in the 1970s. Recent studies of NK cells in mouse and human livers have shown that two distinct NK cell subsets, liver-resident NK cells and conventional NK (cNK) cells, are present in this organ. Here, we review liver NK cell subsets in different species, revisiting rat hepatic pit cells and highlighting recent progress related to resident NK cells in mouse and human livers, and also discuss the dual roles of NK cells in liver immunity.

Tissue-Resident NK Cells Mediate Ischemic Kidney Injury and Are Not Depleted by Anti–Asialo-GM1 Antibody

NK cells are innate lymphoid cells important for immune surveillance, identifying and responding to stress, infection, and/or transformation. Whereas conventional NK (cNK) cells circulate systemically, many NK cells reside in tissues where they appear to be poised to locally regulate tissue function. In the present study, we tested the contribution of tissue-resident NK (trNK) cells to tissue homeostasis by studying ischemic injury in the mouse kidney. Parabiosis experiments demonstrate that the kidney contains a significant fraction of trNK cells under homeostatic conditions. Kidney trNK cells developed independent of NFIL3 and T-bet, and they expressed a distinct cell surface phenotype as compared with cNK cells. Among these, trNK cells had reduced asialo-GM1 (AsGM1) expression relative to cNK cells, a phenotype observed in trNK cells across multiple organs and mouse strains. Strikingly, anti-AsGM1 Ab treatment, commonly used as an NK cell-depleting regimen, resulted in a robust and selective depletion of cNKs, leaving trNKs largely intact. Using this differential depletion, we tested the relative contribution of cNK and trNK cells in ischemic kidney injury. Whereas anti-NK1.1 Ab effectively depleted both trNK and cNK cells and protected against ischemic/reperfusion injury, anti-AsGM1 Ab preferentially depleted cNK cells and failed to protect against injury. These data demonstrate unanticipated specificity of anti-AsGM1 Ab depletion on NK cell subsets and reveal a new approach to study the contributions of cNK and trNK cells in vivo. In total, these data demonstrate that trNK cells play a key role in modulating local responses to ischemic tissue injury in the kidney and potentially other organs.

Differential phenotypic and functional properties of liver-resident NK cells and mucosal ILC1s

Group 1 innate lymphoid cells (ILCs) consist of conventional natural killer (cNK) cells, tissue-resident NK cells and mucosal ILC1s. Recently identified liver-resident NK cells, which can mount contact hypersensitivity responses, and mucosal ILC1s that are involved in pathogenesis of colitis are distinct from cNK cells in several aspects, but the issue of how they are related to each other has not been clearly clarified. Here, we show that liver-resident NK cells and mucosal ILC1s have different phenotypes, as evidenced by distinct expression patterns of homing-associated molecules. Moreover, mucosal ILC1s exhibit tissue residency akin to liver-resident NK cells. Importantly, liver-resident NK cells express relative high levels of cytotoxic effector molecules, which are poorly expressed by mucosal ILC1s, and exhibit stronger cytotoxic activity compared with mucosal ILC1s. These results demonstrate differential phenotypic and functional characteristics of liver-resident NK cells and mucosal ILC1s, shedding new light on the diversity of ILC family.

Intrahepatic development of liver-resident natural killer cells (LYM2P.739)

Abstract Natural killer (NK) cells are an important component of the innate immune system and play critical roles in host defense against infections and tumors. Accumulating studies have shown that the NK cell pool is highly heterogeneous, consisting of different cell subsets with distinct phenotypic and functional features. Recently, in collaboration with Professor Wayne Yokoyama, we showed that a novel NK cell subset expressing CD49a and lacking DX5 rarely recirculates and selectively resides in the liver, that is, liver-resident NK cells. While bone marrow (BM) cells are efficient in generating conventional (cNK) cells, the frequency of liver-resident NK cells is significantly reduced after BM transplantation. Conversely, lethally irradiated mice adoptively transferred with fetal liver cells exhibit normal frequency of liver-resident NK cells. Further analyses reveal that the adult liver retains hematopoietic potential and contains a few hematopoietic progenitor cells (HPCs), which are phenotypically distinct from BM lineage (Lin)-negative progenitor cells but resemble fetal liver counterparts. Moreover, adoptive transfer of these adult liver HPCs have the capacity to generate liver-resident NK cells, but not cNK cells. Finally, Liver HPCs express higher levels of the transcription factors that are essential for liver-resident NK cell development than their BM counterparts. Thus, our studies suggest an alternative development pathway for liver-resident NK cells.

Time-lapse imaging of contact dynamics between natural killer cells and cancer cells (TUM10P.1035)

Abstract Natural killer (NK) cell -mediated killing of cancer cells is essentially dependent on the direct cell-cell interaction. Using time-lapse imaging, we examine how NK cells contact melanoma cells at the single cell level. First, we analyzed contact dynamics of NK cells. Among 1,134 NK cells appeared in 36 movies in time-lapse imaging for 6 h, 121 NK cells (named competent NK, cNK) showed lytic contact with melanoma cells and 158 NK cells (named incompetent NK, iNK) showed non-lytic contact. Although contact numbers of both cell types was similar each other, the duration of contact appeared to be different. cNK cells contacted melanoma cells for 25 min without movement, but iNK cells contacted target cells for 13~14 min with moving around cancer cells. Both cell types moved at average speed of 5~6 um/min before contact and 1.6~2.1 um/min during contact. Next, we analyzed lytic process of melanoma cells, which could be described by two phases: rounding and membrane damage. Immediately after contacting cNK cells, all melanoma cells rounded up and it took 35 min (6-120) having small deviation. Then, melanoma cells lost membrane integrity and it took 103 (6-298) showing big deviation. Together, our data demonstrate that a small fraction of NK cells are cytotoxic to melanoma cells.

PLZF expression maps the early stages of ILC1 lineage development (LYM2P.720)

Abstract Among the variety of tissue-resident NK-like populations recently distinguished from classical recirculating cNK cells, liver innate lymphoid cells type I (ILC1) have been shown to represent a distinct lineage that originates from a novel PLZF-expressing ILC precursor (ILCP) strictly committed to the ILC1, ILC2 and ILC3 lineages. Here, using PLZF-reporter mice and cell transfer assays, we studied the developmental progression of ILC1s and demonstrated substantial overlap with stages previously ascribed to the cNK lineage, including pre-pro-NK, pre-NK precursor (pre-NKP), refined NKP (rNKP) and immature NK (iNK). Although they originated from different precursors, the ILC1 and cNK lineages followed a parallel progression at early stages and diverged later at the iNK stage, with a striking predominance of ILC1s over cNKs early in ontogeny. While a limited set of ILC1 genes were dependent on PLZF for expression, characteristically including Il7r, most of these genes were also differentially expressed between ILC1s and cNKs, indicating that PLZF together with other, yet to be defined, factors contribute to the divergence between these lineages.

PLZF expression maps the early stages of ILC1 lineage development

Among the variety of tissue-resident NK-like populations recently distinguished from recirculating classical NK (cNK) cells, liver innate lymphoid cells (ILC) type 1 (ILC1s) have been shown to represent a distinct lineage that originates from a novel promyelocytic leukaemia zinc finger (PLZF)-expressing ILC precursor (ILCP) strictly committed to the ILC1, ILC2, and ILC3 lineages. Here, using PLZF-reporter mice and cell transfer assays, we studied the developmental progression of ILC1s and demonstrated substantial overlap with stages previously ascribed to the cNK lineage, including pre-pro-NK, pre-NK precursor (pre-NKP), refined NKP (rNKP), and immature NK (iNK). Although they originated from different precursors, the ILC1 and cNK lineages followed a parallel progression at early stages and diverged later at the iNK stage, with a striking predominance of ILC1s over cNKs early in ontogeny. Although a limited set of ILC1 genes depended on PLZF for expression, characteristically including Il7r, most of these genes were also differentially expressed between ILC1s and cNKs, indicating that PLZF together with other, yet to be defined, factors contribute to the divergence between these lineages.