IL-7 and the thymus dictate the NK cell 'labor market'

Tissue-Resident NK Cells: Development, Maturation, and Clinical Relevance

Natural killer (NK) cells belong to type 1 innate lymphoid cells (ILC1) and are essential in killing infected or transformed cells. NK cells mediate their effector functions using non-clonotypic germ-line-encoded activation receptors. The utilization of non-polymorphic and conserved activating receptors promoted the conceptual dogma that NK cells are homogeneous with limited but focused immune functions. However, emerging studies reveal that NK cells are highly heterogeneous with divergent immune functions. A distinct combination of several activation and inhibitory receptors form a diverse array of NK cell subsets in both humans and mice. Importantly, one of the central factors that determine NK cell heterogeneity and their divergent functions is their tissue residency. Decades of studies provided strong support that NK cells develop in the bone marrow. However, evolving evidence supports the notion that NK cells also develop and differentiate in tissues. Here, we summarize the molecular basis, phenotypic signatures, and functions of tissue-resident NK cells and compare them with conventional NK cells.

Novel, Non-Gene-Destructive Knock-In Reporter Mice Refute the Concept of Monoallelic Gata3 Expression

Accurately tuned expression levels of the transcription factor GATA-3 are crucial at several stages of T cell and innate lymphoid cell development and differentiation. Moreover, several lines of evidence suggest that Gata3 expression might provide a reliable molecular marker for the identification of elusive progenitor cell subsets at the earliest stages of T lineage commitment. To be able to faithfully monitor Gata3 expression noninvasively at the single-cell level, we have generated a novel strain of knock-in reporter mice, termed GATIR, by inserting an expression cassette encoding a bright fluorescent marker into the 3'-untranslated region of the endogenous Gata3 locus. Importantly, in contrast to three previously published strains of Gata3 reporter mice, GATIR mice preserve physiological Gata3 expression on the targeted allele. In this study, we show that GATIR mice faithfully reflect endogenous Gata3 expression without disturbing the development of GATA-3-dependent lymphoid cell populations. We further show that GATIR mice provide an ideal tool for noninvasive monitoring of Th2 polarization and straightforward identification of innate lymphoid cell 2 progenitor populations. Finally, as our reporter is non-gene-destructive, GATIR mice can be bred to homozygosity, not feasible with previously published strains of Gata3 reporter mice harboring disrupted alleles. The availability of hetero- and homozygous Gata3 reporter mice with an exceptionally bright fluorescent marker, allowed us to visualize allelic Gata3 expression in individual cells simply by flow cytometry. The unambiguous results obtained provide compelling evidence against previously postulated monoallelic Gata3 expression in early T lineage and hematopoietic stem cell subsets.

Timing of Antiretroviral Therapy Initiation Determines Rectal Natural Killer Cell Populations

Despite antiretroviral therapy (ART), innate and adaptive immunologic damage persists in the periphery and gut. T memory stem cells (Tscm) and natural killer (NK) cells are pivotal for host defense. Tscm are memory cells capable of antigen response and self-renewal, and circulating and gut NK cell populations may facilitate HIV control. The impact of early ART on circulating and gut Tscm and NK cells is unknown. We enrolled participants who initiated ART during acute versus chronic HIV-1 infection versus no ART in chronic infection. We performed flow cytometry to identify NK and Tscm cells in the blood and rectum and polymerase chain reaction to quantify the HIV-1 reservoir in both sites. We used the Mann-Whitney U-test and Spearman correlation coefficients for analysis. Participants who started ART in acute infection had lower rectal CD56^brightCD16^dim cell frequencies than participants who started ART in chronic HIV-1 infection and lower CD56^bright and CD56^brightCD16^- cell frequencies than participants with chronic infection without ART. Higher circulating NK cell, CD56^-CD16^bright, CD56^dim, and CD56^dimCD16^bright frequencies correlated with higher HIV-1 DNA levels in rectal CD4⁺ T cells, whereas higher circulating CD4⁺ T cell counts correlated with higher rectal NK, CD56^brightCD16^dim, and CD56^dimCD16^bright frequencies. Peripheral CD56^brightCD16^- cells were inversely associated with rectal CD56^-CD16^bright cells. Rectal CD8⁺ Tscm frequencies were higher in participants without ART than participants with chronic infection on ART. Timing of ART initiation determines rectal NK cell populations, and ART may influence rectal Tscm populations. Whether the gut reservoir contributes to NK cell activation requires further study.

Proteome analysis of human CD56neg NK cells reveals a homogeneous phenotype surprisingly similar to CD56dim NK cells

NK cells lacking CD56 (CD56^neg ) were first identified in chronic HIV-1 infection. However, CD56^neg NK cells also exist in healthy individuals, albeit in significantly lower numbers. Here, we provide an extensive proteomic characterisation of human CD56^neg peripheral blood NK cells of healthy donors and compare them to their CD56^dim and CD56^bright counterparts. Unbiased large-scale surface receptor profiling clustered CD56^neg cells as part of the main NK cell compartment and indicated an overall CD56^dim -like phenotype. Total proteome analyses of CD56^neg NK cells further confirmed their similarity with CD56^dim NK cells, and revealed a complete cytolytic inventory with high levels of perforin and granzyme H and M. In the present study, twelve proteins discriminated CD56^neg NK cells from CD56^dim NK cells with nine up-regulated and three down-regulated proteins in the CD56^neg NK cell population. Those proteins were functionally related to lytic granule composition and transport, interaction with the extracellular matrix, DNA transcription or repair, and proliferation. Corroborating these results, CD56^neg NK cells showed modest cytotoxicity, degranulation, and IFN-ɣ secretion as compared to CD56^dim NK cells. In conclusion, CD56^neg NK cells constitute functionally competent cells sharing many features of bona fide CD56^dim NK cells in healthy individuals, but with some distinct characteristics.

CD56bright NK IL-7Rα expression negatively associates with HCV level, and IL-7-induced NK function is impaired during HCV and HIV infections

Several lines of evidence support the concept that NK cells play an important role in control of hepatitis C virus (HCV) infection via cytokine secretion and cytotoxicity. IL-7 is a homeostatic cytokine with a role in T cell development, activation, proliferation, and cytokine secretion. The IL-7Rα chain [cluster of differentiation (CD)127] is expressed on NK cells, with greatest abundance on the CD56^brightCD16^dim/- (CD56^bright) subset. Here, we measured CD127 expression on CD56^bright, CD56^dimCD16⁺ (CD56^dim), or CD56^negCD16⁺ (CD56^neg) NK cell subsets of 25 uninfected donors (UD); 34 chronic HCV-infected, treatment-naïve; 25 HIV-infected, virally suppressed on antiretroviral therapy (ART); and 42 HCV-HIV-coinfected subjects on ART. Interestingly, CD127 expression on CD56^bright NK cells negatively correlated with HCV plasma levels in HCV monoinfection and HCV-HIV coinfection. IL-7 induced CD69 expression, as well as IFN-γ production, in CD56^bright NK cells and also enhanced the IFN-α-induced CD69 expression on these cells. The latter was impaired in HIV infection. Furthermore, IL-7 induced B cell lymphoma 2 (BCL-2) expression and cell cycling of CD56^bright NK cells, and this effect was impaired in HCV- and HIV-infected subjects. Whereas IL-7-stimulated CD56^bright NK cell degranulation appeared intact in all cohorts, we observed impaired IL-7-activated NK cell cytolytic function in HCV- and HIV-infected subjects. Finally, IL-7-induced phosphorylation of STAT-5 (pSTAT-5) signaling was impaired in NK cells of subjects with chronic viral infection, and this was reversible upon 6 mo of viral suppression with IFN-free HCV therapy. These results implicate that IL-7-dependent NK cell activation and effector function may be other host immune surveillance mechanisms that are impaired in viral infections.

A prostate cancer vaccine comprising whole cells secreting IL-7, effective against subcutaneous challenge, requires local GM-CSF for intra-prostatic efficacy

A panel of cytokine-secreting RM-9 prostate cancer cells were tested as whole cell vaccines to determine their capacity to evoke an anti-prostate cancer immune response. In our model, vaccines secreting mGM-CSF or mIL-7 resulted in the highest increase in circulating T lymphocytes after vaccination, prolonged survival and, in a proportion of animals, tumor-free survival. Anti-tumor effects were more evident after a subcutaneous RM-9 challenge than after an intraprostatic challenge. However, when the RM-9/mGM-CSF cell line was used as intraprostatic tumor challenge, protection after RM-9/mIL-7 vaccination was restored.

Killer cells in chronic obstructive pulmonary disease

COPD (chronic obstructive pulmonary disease) is a treatable and preventable disease state, characterized by progressive airflow limitation that is not fully reversible. It is a current and growing cause of mortality and morbidity worldwide, with the WHO (World Health Organization) projecting that total deaths attributed to COPD will increase by more than 30% in the next 10 years. The pathological hallmarks of COPD are destruction of the lung parenchyma (pulmonary emphysema), inflammation of the central airways (chronic bronchitis) and inflammation of the peripheral airways (respiratory bronchiolitis). The destructive changes and tissue remodelling observed in COPD are a result of complex interactions between cells of the innate and adaptive immune systems. The focus of the present review is directed towards the role of CD8(+) T-lymphocytes, NK (natural killer) cells and NKT cells (NK T-cells). These three classes of killer cell could all play an important part in the pathogenesis of COPD. The observed damage to the pulmonary tissue could be caused in three ways: (i) direct cytotoxic effect against the lung epithelium mediated by the activities of perforin and granzymes, (ii) FasL (Fas ligand)-induced apoptosis and/or (iii) cytokine and chemokine release. The present review considers the role of these killer cells in COPD.

Stromal-cell regulation of natural killer cell differentiation

Natural killer (NK) cells are bone-marrow-derived lymphocytes that play a crucial role in host defense against some viral and bacterial infections, as well as against tumors. Their phenotypic and functional maturation requires intimate interactions between the bone marrow stroma and committed precursors. In parallel to the identification of several phenotypic and functional stages of NK cell development, recent studies have shed new light on the role of stromal cells in driving functional maturation of NK cells. In this review, we provide an overview of the role of bone marrow microenvironment in NK cell differentiation.