Orphan granzymes find a home

Exploring GZMK as a prognostic marker and predictor of immunotherapy response in breast cancer: unveiling novel insights into treatment outcomes

BACKGROUND

Granzyme K (GZMK) is a crucial mediator released by immune cells to eliminate tumor cells, playing significant roles in inflammation and tumorigenesis. Despite its importance, the specific role of GZMK in breast cancer and its mechanisms are not well understood.

METHODS

We utilized data from the TCGA and GEO databases and employed a range of analytical methods including GO, KEGG, GSEA, ssGSEA, and PPI to investigate the impact of GZMK on breast cancer. In vitro studies, including RT-qPCR, CCK-8 assay, cell cycle experiments, apoptosis assays, Celigo scratch assays, Transwell assays, and immunohistochemical methods, were conducted to validate the effects of GZMK on breast cancer cells. Additionally, Cox regression analysis integrating TCGA and our clinical data was used to develop an overall survival (OS) prediction model.

RESULTS

Analysis of clinical pathological features revealed significant correlations between GZMK expression and lymph node staging, differentiation grade, and molecular breast cancer subtypes. High GZMK expression was associated with improved OS, progression-free survival (PFS), and recurrence-free survival (RFS), as confirmed by multifactorial Cox regression analysis. Functional and pathway enrichment analyses of genes positively correlated with GZMK highlighted involvement in lymphocyte differentiation, T cell differentiation, and T cell receptor signaling pathways. A robust association between GZMK expression and T cell presence was noted in the breast cancer tumor microenvironment (TME), with strong correlations with ESTIMATEScore (Cor = 0.743, P < 0.001), ImmuneScore (Cor = 0.802, P < 0.001), and StromalScore (Cor = 0.516, P < 0.001). GZMK also showed significant correlations with immune checkpoint molecules, including CTLA4 (Cor = 0.856, P < 0.001), PD-1 (Cor = 0.82, P < 0.001), PD-L1 (Cor = 0.56, P < 0.001), CD48 (Cor = 0.75, P < 0.001), and CCR7 (Cor = 0.856, P < 0.001). Studies indicated that high GZMK expression enhances patient responsiveness to immunotherapy, with higher levels observed in responsive patients compared to non-responsive ones. In vitro experiments confirmed that GZMK promotes cell proliferation, cell division, apoptosis, cell migration, and invasiveness (P < 0.05).

CONCLUSION

Our study provides insights into the differential expression of GZMK in breast cancer and its potential mechanisms in breast cancer pathogenesis. Elevated GZMK expression is associated with improved OS and RFS, suggesting its potential as a prognostic marker for breast cancer survival and as a predictor of the efficacy of immunotherapy.

Granzymes in health and diseases: the good, the bad and the ugly

Granzymes are a family of serine proteases, composed of five human members: GA, B, H, M and K. They were first discovered in the 1980s within cytotoxic granules released during NK cell- and T cell-mediated killing. Through their various proteolytic activities, granzymes can trigger different pathways within cells, all of which ultimately lead to the same result, cell death. Over the years, the initial consideration of granzymes as mere cytotoxic mediators has changed due to surprising findings demonstrating their expression in cells other than immune effectors as well as new intracellular and extracellular activities. Additional roles have been identified in the extracellular milieu, following granzyme escape from the immunological synapse or their release by specific cell types. Outside the cell, granzyme activities mediate extracellular matrix alteration via the degradation of matrix proteins or surface receptors. In certain contexts, these processes are essential for tissue homeostasis; in others, excessive matrix degradation and extensive cell death contribute to the onset of chronic diseases, inflammation, and autoimmunity. Here, we provide an overview of both the physiological and pathological roles of granzymes, highlighting their utility while also recognizing how their unregulated presence can trigger the development and/or worsening of diseases.

Perforin and granzyme A release as novel tool to measure NK cell activation in chickens

Natural killer (NK) cells are cytotoxic lymphocytes that are present in the circulation but also in many organs including spleen and gut, where they play an important role in the defense against infections. Interaction of NK cells with target cells leads to degranulation, which results in the release of perforin and granzymes in the direct vicinity of the target cell. Chicken NK cells have many characteristics similar to their mammalian counterparts and based on similarities with studies on human NK cells, surface expression of CD107 was always presumed to correlate with granule release. However, proof of this degranulation or in fact the actual presence of perforin (PFN) and granzyme A (GrA) in chicken NK cells and their release upon activation is lacking. Therefore, the purpose of the present study was to determine the presence of perforin and granzyme A in primary chicken NK cells and to measure their release upon degranulation, as an additional tool to study the function of chicken NK cells. Using human specific antibodies against PFN and GrA in fluorescent and confocal microscopy resulted in staining in chicken NK cells. The presence of PFN and GrA was also confirmed by Western blot analyses and its gene expression by PCR. Stimulation of NK cells with the pectin SPE6 followed by flow cytometry resulted in reduced levels of intracellular PFN and GrA, suggesting release of PFN and GrA. Expression of PFN and GrA reversely correlated with increased surface expression of the lysosomal marker CD107. Finally it was shown that the supernatant of activated NK cells, containing the NK cell granule content including PFN and GrA, was able to kill Escherichia coli. This study correlates PFN and GrA release to activation of chicken NK cells and establishes an additional tool to study activity of cytotoxic lymphocytes in chickens.

Human Granzyme K Is a Feature of Innate T Cells in Blood, Tissues, and Tumors, Responding to Cytokines Rather than TCR Stimulation

NK cells and CD8 T cells use cytotoxic molecules to kill virally infected and tumor cell targets. While perforin and granzyme B (GzmB) are the most commonly studied lytic molecules, less is known about granzyme K (GzmK). However, this granzyme has been recently associated with improved prognosis in solid tumors. In this study, we show that, in humans, GzmK is predominantly expressed by innate-like lymphocytes, as well as a newly identified population of GzmK+CD8+ non- mucosal-associated invariant T cells with innate-like characteristics. We found that GzmK+ T cells are KLRG1+EOMES+IL-7R+CD62L-Tcf7int, suggesting that they are central memory T and effector memory T cells. Furthermore, GzmK+ cells are absent/low in cord blood, suggesting that GzmK is upregulated with immune experience. Surprisingly, GzmK+ cells respond to cytokine stimuli alone, whereas TCR stimulation downregulates GzmK expression, coinciding with GzmB upregulation. GzmK+ cells have reduced IFN-γ production compared with GzmB+ cells in each T cell lineage. Collectively, this suggests that GzmK+ cells are not naive, and they may be an intermediate memory-like or preterminally differentiated population. GzmK+ cells are enriched in nonlymphoid tissues such as the liver and adipose. In colorectal cancer, GzmK+ cells are enriched in the tumor and can produce IFN-γ, but GzmK+ expression is mutually exclusive with IL-17a production. Thus, in humans, GzmK+ cells are innate memory-like cells that respond to cytokine stimulation alone and may be important effector cells in the tumor.

Role of the granzyme family in rheumatoid arthritis: Current Insights and future perspectives

Rheumatoid arthritis (RA) is a complex autoimmune disease characterized by chronic inflammation that affects synovial tissues of multiple joints. Granzymes (Gzms) are serine proteases that are released into the immune synapse between cytotoxic lymphocytes and target cells. They enter target cells with the help of perforin to induce programmed cell death in inflammatory and tumor cells. Gzms may have a connection with RA. First, increased levels of Gzms have been found in the serum (GzmB), plasma (GzmA, GzmB), synovial fluid (GzmB, GzmM), and synovial tissue (GzmK) of patients with RA. Moreover, Gzms may contribute to inflammation by degrading the extracellular matrix and promoting cytokine release. They are thought to be involved in RA pathogenesis and have the potential to be used as biomarkers for RA diagnosis, although their exact role is yet to be fully elucidated. The purpose of this review was to summarize the current knowledge regarding the possible role of the granzyme family in RA, with the aim of providing a reference for future research on the mechanisms of RA and the development of new therapies.

Granzyme K+ CD8 T cells form a core population in inflamed human tissue

T cell-derived pro-inflammatory cytokines are a major driver of rheumatoid arthritis (RA) pathogenesis. Although these cytokines have traditionally been attributed to CD4 T cells, we have found that CD8 T cells are notably abundant in synovium and make more interferon (IFN)-γ and nearly as much tumor necrosis factor (TNF) as their CD4 T cell counterparts. Furthermore, using unbiased high-dimensional single-cell RNA-seq and flow cytometric data, we found that the vast majority of synovial tissue and synovial fluid CD8 T cells belong to an effector CD8 T cell population characterized by high expression of granzyme K (GzmK) and low expression of granzyme B (GzmB) and perforin. Functional experiments demonstrate that these GzmK+ GzmB+ CD8 T cells are major cytokine producers with low cytotoxic potential. Using T cell receptor repertoire data, we found that CD8 GzmK+ GzmB+ T cells are clonally expanded in synovial tissues and maintain their granzyme expression and overall cell state in blood, suggesting that they are enriched in tissue but also circulate. Using GzmK and GzmB signatures, we found that GzmK-expressing CD8 T cells were also the major CD8 T cell population in the gut, kidney, and coronavirus disease 2019 (COVID-19) bronchoalveolar lavage fluid, suggesting that they form a core population of tissue-associated T cells across diseases and human tissues. We term this population tissue-enriched expressing GzmK or TteK CD8 cells. Armed to produce cytokines in response to both antigen-dependent and antigen-independent stimuli, CD8 TteK cells have the potential to drive inflammation.

Granzymes-Their Role in Colorectal Cancer

Colorectal cancer (CRC) is among the most common malignancies worldwide. CRC is considered a heterogeneous disease due to various clinical symptoms, biological behaviours, and a variety of mutations. A number of studies demonstrate that as many as 50% of CRC patients have distant metastases at the time of diagnosis. However, despite the fact that social and medical awareness of CRC has increased in recent years and screening programmes have expanded, there is still an urgent need to find new diagnostic tools for early detection of CRC. The effectiveness of the currently used classical tumour markers in CRC diagnostics is very limited. Therefore, new proteins that play an important role in the formation and progression of CRC are being sought. A number of recent studies show the potential significance of granzymes (GZMs) in carcinogenesis. These proteins are released by cytotoxic lymphocytes, which protect the body against viral infection as well specific signalling pathways that ultimately lead to cell death. Some studies suggest a link between GZMs, particularly the expression of Granzyme A, and inflammation. This paper summarises the role of GZMs in CRC pathogenesis through their involvement in the inflammatory process. Therefore, it seems that GZMs could become the focus of research into new CRC biomarkers.

How to Reliably Define Human CD8+ T-Cell Subsets: Markers Playing Tricks

In recent years, our understanding about the functional complexity of CD8+ T-cell populations has increased tremendously. The immunology field is now facing challenges to translate these insights into phenotypic definitions that correlate reliably with distinct functional traits. This is key to adequately monitor and understand compound immune responses including vaccination and immunotherapy regimens. Here we will summarize our understanding of the current state in the human CD8+ T-cell subset characterization field. We will address how reliably the currently used cell surface markers are connected to differentiation status and function of particular subsets. By restricting ourselves to CD8+ αβ T cells, we will focus mostly on major histocompatibility complex (MHC) class I-restricted virus- and tumor-specific T cells. This comes with a major advantage as fluorescently labeled peptide-loaded MHC class I multimers have been widely used to identify and characterize these cells.

Oxidative and Non-Oxidative Antimicrobial Activities of the Granzymes

Cell-mediated cytotoxicity is an essential immune defense mechanism to fight against viral, bacterial or parasitic infections. Upon recognition of an infected target cell, killer lymphocytes form an immunological synapse to release the content of their cytotoxic granules. Cytotoxic granules of humans contain two membrane-disrupting proteins, perforin and granulysin, as well as a homologous family of five death-inducing serine proteases, the granzymes. The granzymes, after delivery into infected host cells by the membrane disrupting proteins, may contribute to the clearance of microbial pathogens through different mechanisms. The granzymes can induce host cell apoptosis, which deprives intracellular pathogens of their protective niche, therefore limiting their replication. However, many obligate intracellular pathogens have evolved mechanisms to inhibit programed cells death. To overcome these limitations, the granzymes can exert non-cytolytic antimicrobial activities by directly degrading microbial substrates or hijacked host proteins crucial for the replication or survival of the pathogens. The granzymes may also attack factors that mediate microbial virulence, therefore directly affecting their pathogenicity. Many mechanisms applied by the granzymes to eliminate infected cells and microbial pathogens rely on the induction of reactive oxygen species. These reactive oxygen species may be directly cytotoxic or enhance death programs triggered by the granzymes. Here, in the light of the latest advances, we review the antimicrobial activities of the granzymes in regards to their cytolytic and non-cytolytic activities to inhibit pathogen replication and invasion. We also discuss how reactive oxygen species contribute to the various antimicrobial mechanisms exerted by the granzymes.

NKG2A expression identifies a subset of human Vδ2 T cells exerting the highest antitumor effector functions

Human Vδ2 cells are innate-like γδ T effectors performing potent immune surveillance against tumors. The constitutive expression of NKG2A identifies a subset of Vδ2 T cells licensed with an intrinsic hyper-responsiveness against cancer. Indeed, the transcriptomic profiles of NKG2A⁺ and NKG2A^- cells characterize two distinct "intralineages" of Vδ2 T lymphocytes that appear early during development, keep their phenotypes, and show self-renewal capabilities in adult life. The hyper-responsiveness of NKG2A⁺ Vδ2 T cells is counterbalanced by the inhibitory signaling delivered by human leukocyte antigen E (HLA-E) expressed on malignant cells as a tumor-escape mechanism. However, either masking or knocking out NKG2A restores the capacity of Vδ2 T cells to exert the highest effector functions even against HLA-E⁺ tumors. This is highly relevant in the clinic, as the different degrees of engagement of the NKG2A-HLA-E checkpoint in hepatocellular carcinoma, glioblastoma, and non-small cell lung cancer directly impact patients' overall survival. These findings open avenues for developing combined cellular and immunologic anticancer therapies.

Noncytotoxic functions of killer cell granzymes in viral infections

Cytotoxic lymphocytes produce granules armed with a set of 5 serine proteases (granzymes (Gzms)), which, together with the pore-forming protein (perforin), serve as a major defense against viral infections in humans. This granule-exocytosis pathway subsumes a well-established mechanism in which target cell death is induced upon perforin-mediated entry of Gzms and subsequent activation of various (apoptosis) pathways. In the past decade, however, a growing body of evidence demonstrated that Gzms also inhibit viral replication and potential reactivation in cell death–independent manners. For example, Gzms can induce proteolysis of viral or host cell proteins necessary for the viral entry, release, or intracellular trafficking, as well as augment pro-inflammatory antiviral cytokine response. In this review, we summarize current evidence for the noncytotoxic mechanisms and roles by which killer cells can use Gzms to combat viral infections, and we discuss the potential thereof for the development of novel therapies.

The role of CD8+ Granzyme B+ T cells in the pathogenesis of Takayasu's arteritis

OBJECTIVE

T cell-mediated immune response plays a key role in Takayasu arteritis (TAK). Although previous studies have showed the roles of CD4⁺T cell and its subsets in TAK, the change of CD8⁺ T cell subsets remains unclear. This study investigated the role of CD8⁺ T cell subsets in TAK.

METHODS

The study consisted of 56 TA patients and 51 healthy controls. The percentages of CD8⁺T cells, CD8⁺GranzymeB⁺ T cells, CD8⁺Perforin⁺ T cells, and CD8⁺IFN-γ⁺ T cells in blood samples were analyzed by flow cytometry.

RESULTS

We found that the percentages of CD8⁺GranzymeB⁺ T cells (P = 0.030), CD8⁺Perforin⁺ T cells (P = 0.000), and CD8⁺IFN-γ⁺ T cells (P = 0.002) in CD8⁺T cells were higher in TAK patients compared to control group. After 6 months of treatment, the proportion of CD8⁺T cells in lymphocytes were significantly lower in TAK patients than the baseline assessment (P = 0.033). A lower ratio of CD8⁺GranzymeB⁺ T cells/CD8⁺ T cells were showed in TAK patents after treatment compared with TAK patients before treatments (P = 0.011). The change of CD8⁺GranzymeB⁺ T cells/CD8⁺ T cells ratio was positively correlated with the change of ITAS (r = 0.721, P = 0.002) and ITAS-A (r = 0.637, P = 0.008). Finally, the immunofluorescence staining showed the infiltration of CD8⁺ Granzyme B ⁺ cells in the aortic tissue of TAK patients.

CONCLUSION

Our results disclose that the CD8⁺ T lymphocytes may play a role in TAK pathogenesis. Targeting CD8⁺GranzymeB⁺ T lymphocytes or Granzyme B inhibitors could be a potential therapeutic approach for the treatment of TAK. Key Points • Our study investigated role the of CD8⁺ T cell subsets in TAK. • We found the percentages of CD8⁺GranzymeB⁺ T cells, CD8⁺Perforin⁺ T cells, and CD8⁺IFN-γ⁺ T cells in CD3⁺CD8⁺T cells were higher in TAK patients. • The proportion of CD8⁺T cells in lymphocytes and the ratio of CD8⁺GranzymeB⁺ T cells/CD8⁺ T cells were significantly lower in TAK patients after treatment.

Taa Cells and Granzyme K: Old Players with New Tricks

Inflammaging is associated with chronic diseases, but tissue-specific changes in the immune system remain unknown. In this issue of Immunity, Mogilenko et al. use single-cell RNA sequencing, flow cytometry, and mass cytometry to describe age-related differences, including the accumulation of age-associated T cells that contribute to inflammaging.

Extracellular Granzyme K Modulates Angiogenesis by Regulating Soluble VEGFR1 Release From Endothelial Cells

Angiogenesis is crucial for normal development and homeostasis, but also plays a role in many diseases including cardiovascular diseases, autoimmune diseases, and cancer. Granzymes are serine proteases stored in the granules of cytotoxic cells, and have predominantly been studied for their pro-apoptotic role upon delivery in target cells. A growing body of evidence is emerging that granzymes also display extracellular functions, which largely remain unknown. In the present study, we show that extracellular granzyme K (GrK) inhibits angiogenesis and triggers endothelial cells to release soluble VEGFR1 (sVEGFR1), a decoy receptor that inhibits angiogenesis by sequestering VEGF-A. GrK does not cleave off membrane-bound VEGFR1 from the cell surface, does not release potential sVEGFR1 storage pools from endothelial cells, and does not trigger sVEGFR1 release via protease activating receptor-1 (PAR-1) activation. GrK induces de novo sVEGFR1 mRNA and protein expression and subsequent release of sVEGFR1 from endothelial cells. GrK protein is detectable in human colorectal tumor tissue and its levels positively correlate with sVEGFR1 protein levels and negatively correlate with T4 intratumoral angiogenesis and tumor size. In conclusion, extracellular GrK can inhibit angiogenesis via secretion of sVEGFR1 from endothelial cells, thereby sequestering VEGF-A and impairing VEGFR signaling. Our observation that GrK positively correlates with sVEGFR1 and negatively correlates with angiogenesis in colorectal cancer, suggest that the GrK-sVEGFR1-angiogenesis axis may be a valid target for development of novel anti-angiogenic therapies in cancer.

Intracellular expression of granzymes A, B, K and M in blood lymphocyte subsets of critically ill patients with or without sepsis

Sepsis is a complex syndrome related to an infection-induced exaggerated inflammatory response, which is associated with a high mortality. Granzymes (Gzm) are proteases mainly found in cytotoxic lymphocytes that not only have a role in target cell death, but also as mediators of infection and inflammation. In this study we sought to analyse the intracellular expression of GzmA, B, M and K by flow cytometry in diverse blood lymphocyte populations from 22 sepsis patients, 12 non-infected intensive care unit (ICU) patients and 32 healthy controls. Additionally, we measured GzmA and B plasma levels. Both groups of patients presented decreased percentage of natural killer (NK) cells expressing GzmA, B and M relative to healthy controls, while sepsis patients showed an increased proportion of CD8⁺ T cells expressing GzmB compared to controls. Expression of GzmK remained relatively unaltered between groups. Extracellular levels of GzmB were increased in non-infected ICU patients relative to sepsis patients and healthy controls. Our results show differential alterations in intracellular expression of Gzm in sepsis patients and non-infected critically ill patients compared to healthy individuals depending on the lymphocyte population and on the Gzm.

Intracellular and Extracellular Roles of Granzyme K

Granzymes are a family of serine proteases stored in granules inside cytotoxic cells of the immune system. Granzyme K (GrK) has been only limitedly characterized and knowledge on its molecular functions is emerging. Traditionally GrK is described as a granule-secreted, pro-apoptotic serine protease. However, accumulating evidence is redefining the functions of GrK by the discovery of novel intracellular (e.g. cytotoxicity, inhibition of viral replication) and extracellular roles (e.g. endothelial activation and modulation of a pro-inflammatory immune cytokine response). Moreover, elevated GrK levels are associated with disease, including viral and bacterial infections, airway inflammation and thermal injury. This review aims to summarize and discuss the current knowledge of i) intracellular and extracellular GrK activity, ii) cytotoxic and non-cytotoxic GrK functioning, iii) the role of GrK in disease, and iv) GrK as a potential therapeutic target.

Extracellular Granzyme A Promotes Colorectal Cancer Development by Enhancing Gut Inflammation

If not properly regulated, the inflammatory immune response can promote carcinogenesis, as evident in colorectal cancer (CRC). Aiming to gain mechanistic insight into the link between inflammation and CRC, we perform transcriptomics analysis of human CRC, identifying a strong correlation between expression of the serine protease granzyme A (GzmA) and inflammation. In a dextran sodium sulfate and azoxymethane (DSS/AOM) mouse model, deficiency and pharmacological inhibition of extracellular GzmA both attenuate gut inflammation and prevent CRC development, including the initial steps of cell transformation and epithelial-to-mesenchymal transition. Mechanistically, extracellular GzmA induces NF-κB-dependent IL-6 production in macrophages, which in turn promotes STAT3 activation in cultured CRC cells. Accordingly, colon tissues from DSS/AOM-treated, GzmA-deficient animals present reduced levels of pSTAT3. By identifying GzmA as a proinflammatory protease that promotes CRC development, these findings provide information on mechanisms that link immune cell infiltration to cancer progression and present GzmA as a therapeutic target for CRC.

Cytotoxic Lymphocytes Target HIV-1 Gag Through Granzyme M-Mediated Cleavage

Untreated HIV-1 infection leads to a slow decrease in CD4⁺ T cell lymphocytes over time resulting in increased susceptibility to opportunistic infections (acquired immunodeficiency syndrome, AIDS) and ultimately death of the infected individual. Initially, the host's immune response controls the infection, but cannot eliminate the HIV-1 from the host. Cytotoxic lymphocytes are the key effector cells in this response and can mediate crucial antiviral responses through the release of a set of proteases called granzymes towards HIV-1-infected cells. However, little is known about the immunological molecular mechanisms by which granzymes could control HIV-1. Since we noted that HIV-1 subtype C (HIV-1C) Gag with the tetrapeptide insertion PYKE contains a putative granzyme M (GrM) cleavage site (KEPL) that overlaps with the PYKE insertion, we analyzed the proteolytic activity of GrM towards Gag. Immunoblot analysis showed that GrM could cleave Gag proteins from HIV-1B and variants from HIV-1C of which the Gag-PYKE variant was cleaved with extremely high efficiency. The main cleavage site was directly after the insertion after leucine residue 483. GrM-mediated cleavage of Gag was also observed in co-cultures using cytotoxic lymphocytes as effector cells and this cleavage could be inhibited by a GrM inhibitor peptide. Altogether, our data indicate towards a noncytotoxic immunological mechanism by which GrM-positive cytotoxic lymphocytes target the HIV-1 Gag protein within infected cells to potentially control HIV-1 infection. This mechanism could be exploited in new therapeutic strategies to treat HIV-1-infected patients to improve immunological control of the infection.

Perforin and granzymes in neurological infections: From humans to cattle

Perforin and granzymes are essential components of the cytotoxic granules present in cytotoxic T lymphocytes and natural killer cells. These proteins play a crucial role in a variety of conditions, including viral infections, tumor immune surveillance, and tissue rejection. Besides their beneficial effect in most of these situations, perforin and granzymes have also been associated with tissue damage and immune diseases. Moreover, it has been reported that perforin and granzymes released during viral infections could contribute to the pathogenesis of diseases. In this review, we summarize the information available on human perforin and granzymes and their relationship with neurological infections and immune disorders. Furthermore, we compare this information with that available for bovine and present data on perforin and granzymes expression in cattle infected with bovine alphaherpesvirus types1 and -5. To our knowledge, this is the first review analyzing the impact of perforin and granzymes on neurological infections caused by bovine herpesviruses.

Physics-driven identification of clinically approved and investigation drugs against human neutrophil serine protease 4 (NSP4): A virtual drug repurposing study

Neutrophils synthesize four immune associated serine proteases: Cathepsin G (CTSG), Elastase (ELANE), Proteinase 3 (PRTN3) and Neutrophil Serine Protease 4 (NSP4). While previously considered to be immune modulators, overexpression of neutrophil serine proteases correlates with various disease conditions. Therefore, identifying novel small molecules that can potentially control or inhibit the proteolytic activity of these proteases is crucial to revert or temper the aggravated disease phenotype. To the best of our knowledge, although there is limited data for inhibitors of other neutrophil protease members, there is no previous clinical study of a synthetic small molecule inhibitor targeting NSP4. In this study, an integrated molecular modeling algorithm was performed within a virtual drug repurposing study to identify novel inhibitors for NSP4, using clinically approved and investigation drugs library (∼8000 compounds). Based on our rigorous filtration, we found that following molecules Becatecarin, Iogulamide, Delprostenate and Iralukast are predicted to block the activity of NSP4 by interacting with core catalytic residues. The selected ligands were energetically more favorable compared to the reference molecule. The result of this study identifies promising molecules as potential lead candidates.

Loss of BAP1 expression is associated with an immunosuppressive microenvironment in uveal melanoma, with implications for immunotherapy development

Immunotherapy using immune checkpoint inhibitors (ICIs) induces durable responses in many metastatic cancers. Metastatic uveal melanoma (mUM), typically occurring in the liver, is one of the most refractory tumours to ICIs and has dismal outcomes. Monosomy 3 (M3), polysomy 8q, and BAP1 loss in primary uveal melanoma (pUM) are associated with poor prognoses. The presence of tumour‐infiltrating lymphocytes (TILs) within pUM and surrounding mUM – and some evidence of clinical responses to adoptive TIL transfer – strongly suggests that UMs are indeed immunogenic despite their low mutational burden. The mechanisms that suppress TILs in pUM and mUM are unknown. We show that BAP1 loss is correlated with upregulation of several genes associated with suppressive immune responses, some of which build an immune suppressive axis, including HLA‐DR, CD38, and CD74. Further, single‐cell analysis of pUM by mass cytometry confirmed the expression of these and other markers revealing important functions of infiltrating immune cells in UM, most being regulatory CD8⁺ T lymphocytes and tumour‐associated macrophages (TAMs). Transcriptomic analysis of hepatic mUM revealed similar immune profiles to pUM with BAP1 loss, including the expression of IDO1. At the protein level, we observed TAMs and TILs entrapped within peritumoural fibrotic areas surrounding mUM, with increased expression of IDO1, PD‐L1, and β‐catenin (CTNNB1), suggesting tumour‐driven immune exclusion and hence the immunotherapy resistance. These findings aid the understanding of how the immune response is organised in BAP1⁻ mUM, which will further enable functional validation of detected biomarkers and the development of focused immunotherapeutic approaches. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Mechanisms of Apoptosis Resistance to NK Cell-Mediated Cytotoxicity in Cancer

Natural killer (NK) cells are major contributors to immunosurveillance and control of tumor development by inducing apoptosis of malignant cells. Among the main mechanisms involved in NK cell-mediated cytotoxicity, the death receptor pathway and the release of granules containing perforin/granzymes stand out due to their efficacy in eliminating tumor cells. However, accumulated evidence suggest a profound immune suppression in the context of tumor progression affecting effector cells, such as NK cells, leading to decreased cytotoxicity. This diminished capability, together with the development of resistance to apoptosis by cancer cells, favor the loss of immunogenicity and promote immunosuppression, thus partially inducing NK cell-mediated killing resistance. Altered expression patterns of pro- and anti-apoptotic proteins along with genetic background comprise the main mechanisms of resistance to NK cell-related apoptosis. Herein, we summarize the main effector cytotoxic mechanisms against tumor cells, as well as the major resistance strategies acquired by tumor cells that hamper the extrinsic and intrinsic apoptotic pathways related to NK cell-mediated killing.

Killer cell proteases can target viral immediate-early proteins to control human cytomegalovirus infection in a noncytotoxic manner

Human cytomegalovirus (HCMV) is the most frequent viral cause of congenital defects and can trigger devastating disease in immune-suppressed patients. Cytotoxic lymphocytes (CD8⁺ T cells and NK cells) control HCMV infection by releasing interferon-γ and five granzymes (GrA, GrB, GrH, GrK, GrM), which are believed to kill infected host cells through cleavage of intracellular death substrates. However, it has recently been demonstrated that the in vivo killing capacity of cytotoxic T cells is limited and multiple T cell hits are required to kill a single virus-infected cell. This raises the question whether cytotoxic lymphocytes can use granzymes to control HCMV infection in a noncytotoxic manner. Here, we demonstrate that (primary) cytotoxic lymphocytes can block HCMV dissemination independent of host cell death, and interferon-α/β/γ. Prior to killing, cytotoxic lymphocytes induce the degradation of viral immediate-early (IE) proteins IE1 and IE2 in HCMV-infected cells. Intriguingly, both IE1 and/or IE2 are directly proteolyzed by all human granzymes, with GrB and GrM being most efficient. GrB and GrM cleave IE1 after Asp³⁹⁸ and Leu⁴¹⁴, respectively, likely resulting in IE1 aberrant cellular localization, IE1 instability, and functional impairment of IE1 to interfere with the JAK-STAT signaling pathway. Furthermore, GrB and GrM cleave IE2 after Asp¹⁸⁴ and Leu¹⁷³, respectively, resulting in IE2 aberrant cellular localization and functional abolishment of IE2 to transactivate the HCMV UL112 early promoter. Taken together, our data indicate that cytotoxic lymphocytes can also employ noncytotoxic ways to control HCMV infection, which may be explained by granzyme-mediated targeting of indispensable viral proteins during lytic infection.

Human cytomegalovirus (HCMV) is the leading viral cause of congenital defects, can trigger disease in immune-compromised patients, and plays roles in cancer development. Cytotoxic lymphocytes kill HCMV-infected cells via releasing a set of five cytotoxic serine proteases called granzymes. However, the killing capacity of cytotoxic cells is limited and multiple T cell hits are required to kill a single virus-infected cell. This raises the question whether cytotoxic lymphocytes can use granzymes to control HCMV infection in a noncytotoxic manner. Here, we show that cytotoxic lymphocytes can also use granzymes to inhibit HCMV replication in absence of cell death. All five granzymes cleave and inactivate both viral immediate-early (IE1/2) proteins, which are essential players for initiating HCMV infection. Our data support the model that cytotoxic cells employ granzymes to dampen HCMV replication prior to accumulation of sufficient hits to kill the infected cell.

Immunological microenvironment gene expression in patients with diffuse large B cell non Hodgkin lymphoma

Background

Non Hodgkin lymphoma (NHL) is one of the immune system cancers. The occurrence and progression of malignant lymphomas depends on cellular pathways deregulation. Understanding the relationship between the immune system at the genetic level and malignant transformation is critical to reach its etiology.

Objective

The aim of this work is to evaluate the expression of five immune related genes (PD-1, FOXP3, GrA, GrB and CD11c) in patients with diffuse large B cell non Hodgkin lymphoma (DLBCL).

Materials and methods

This study was conducted on fifty patients with DLBCL and fifty sex and age matched apparently healthy subjects. The participants were subjected to these laboratory investigations: complete blood count, serum lactate dehydrogenase and β2microglobulin (β₂M) levels and determination of PD-1, FOXP3, GrA, GrB and CD11c gene expressions.

Results

The results of this study revealed that PD-1, FOXP3, GrA, GrB and CD11c gene expressions were significantly increased in DLBCL patients.

Conclusion

Patients with DLBCL have variablePD-1, FOXP3,GrA, GrB and CD11cgene expressions levels, which are correlated with the overall survival (OS) indicating that they can be good predictors of outcome in these patients.

Tumor Microenvironment Targeted Nanotherapy

Recent developments in nanotechnology have brought new approaches to cancer diagnosis and therapy. While enhanced permeability and retention effect promotes nano-chemotherapeutics extravasation, the abnormal tumor vasculature, high interstitial pressure and dense stroma structure limit homogeneous intratumoral distribution of nano-chemotherapeutics and compromise their imaging and therapeutic effect. Moreover, heterogeneous distribution of nano-chemotherapeutics in non-tumor-stroma cells damages the non-tumor cells, and interferes with tumor-stroma crosstalk. This can lead not only to inhibition of tumor progression, but can also paradoxically induce acquired resistance and facilitate tumor cell proliferation and metastasis. Overall, the tumor microenvironment plays a vital role in regulating nano-chemotherapeutics distribution and their biological effects. In this review, the barriers in tumor microenvironment, its consequential effects on nano-chemotherapeutics, considerations to improve nano-chemotherapeutics delivery and combinatory strategies to overcome acquired resistance induced by tumor microenvironment have been summarized. The various strategies viz., nanotechnology based approach as well as ligand-mediated, redox-responsive, and enzyme-mediated based combinatorial nanoapproaches have been discussed in this review.

T Cells and Regulated Cell Death: Kill or Be Killed

Cell death plays two major complementary roles in T cell biology: mediating the removal of cells that are targeted by T cells and the removal of T cells themselves. T cells serve as major actors in the adaptive immune response and function by selectively killing cells which are infected or dysfunctional. This feature is highly involved during homeostatic maintenance, and is relied upon and modulated in the context of cancer immunotherapy. The vital recognition and elimination of both autoreactive T cells and cells which are unable to recognize threats is a highly selective and regulated process. Moreover, detection of potential threats will result in the activation and expansion of T cells, which on resolution of the immune response will need to be eliminated. The culling of these T cells can be executed via a multitude of cell death pathways which are used in context-specific manners. Failure of these processes may result in an accumulation of misdirected or dysfunctional T cells, leading to complications such as autoimmunity or cancer. This review will focus on the role of cell death regulation in the maintenance of T cell homeostasis, as well as T cell-mediated elimination of infected or dysfunctional cells, and will summarize and discuss the current knowledge of the cellular mechanisms which are implicated in these processes.

CD45+CD33lowCD11bdim myeloid-derived suppressor cells suppress CD8+ T cell activity via the IL-6/IL-8-arginase I axis in human gastric cancer

Myeloid-derived suppressor cells (MDSCs) are a prominent component of the pro-tumoral response. The phenotype of and mechanisms used by MDSCs is heterogeneous and requires more precise characterization in gastric cancer (GC) patients. Here, we have identified a novel subset of CD45⁺CD33^lowCD11b^dim MDSCs in the peripheral blood of GC patients compared to healthy individuals. CD45⁺CD33^lowCD11b^dim MDSCs morphologically resembled neutrophils and expressed high levels of the neutrophil marker CD66b. Circulating CD45⁺CD33^lowCD11b^dim MDSCs effectively suppressed CD8⁺ T cells activity through the inhibition of CD8⁺ T cell proliferation and interferon-γ (IFN-γ) and granzyme B (GrB) production. The proportion of CD45⁺CD33^lowCD11b^dim MDSCs also negatively correlated with the proportion of IFN-γ⁺CD8⁺ T cell in the peripheral blood of GC patients. GC patient serum-derived IL-6 and IL-8 activated and induced CD45⁺CD33^lowCD11b^dim MDSCs to express arginase I via the PI3K-AKT signaling pathway. This pathway contributed to CD8⁺ T cell suppression as it was partially rescued by the blockade of the IL-6/IL-8-arginase I axis. Peripheral blood CD45⁺CD33^lowCD11b^dim MDSCs, as well as IL-6, IL-8, and arginase I serum levels, positively correlated with GC progression and negatively correlated with overall patient survival. Altogether, our results highlight that a subset of neutrophilic CD45⁺CD33^lowCD11b^dim MDSCs is functionally immunosuppressive and activated via the IL-6/IL-8-arginase I axis in GC patients.

Identification and annotation of bovine granzyme genes reveals a novel granzyme encoded within the trypsin-like locus

Granzymes are a family of serine proteases found in the lytic granules of cytotoxic T lymphocytes and natural killer (NK) cells, which are involved in killing of susceptible target cells. Most information on granzymes and their enzymatic specificities derive from studies in humans and mice. Although granzymes shared by both species show a high level of conservation, the complement of granzyme genes differs between the species. The aim of this study was to identify granzyme genes expressed in cattle, determine their genomic locations and analyse their sequences to predict likely functional specificities. Orthologues of the five granzyme genes found in humans (A, B, H, K and M) were identified, as well a novel gene designated granzyme O, most closely related to granzyme A. An orthologue of granzyme O was found in pigs and a non-function version was detected in the human genome. Use of specific PCRs demonstrated that all of these genes, including granzyme O, are expressed in activated subsets of bovine lymphocytes, with particularly high levels in CD8 T cells. Consistent with findings in humans and mice, the granzyme-encoding genes were located on three distinct genomic loci, which correspond to different proteolytic enzymatic activities, namely trypsin-like, chymotrypsin-like and metase-like. Analysis of amino acid sequences indicated that the granzyme proteins have broadly similar enzymatic specificities to their human and murine counterparts but indicated that granzyme B has a different secondary specificity. These findings provide the basis for further work to examine their role in the cytotoxic activity of bovine CD8 T cells.

Rapid activation of tumor-associated macrophages boosts preexisting tumor immunity

Combined CSF-1R+CD40 antibody therapy induces profound and rapid TAM reprogramming before TAMs are eliminated. This combination of cancer immunotherapies tailored to activate the innate immune system creates an inflamed tumor microenvironment ultimately leading to tumor eradication by the adaptive immunity.

Depletion of immunosuppressive tumor-associated macrophages (TAMs) or reprogramming toward a proinflammatory activation state represent different strategies to therapeutically target this abundant myeloid population. In this study, we report that inhibition of colony-stimulating factor-1 receptor (CSF-1R) signaling sensitizes TAMs to profound and rapid reprogramming in the presence of a CD40 agonist before their depletion. Despite the short-lived nature of macrophage hyperactivation, combined CSF-1R+CD40 stimulation of macrophages is sufficient to create a proinflammatory tumor milieu that reinvigorates an effective T cell response in transplanted tumors that are either responsive or insensitive to immune checkpoint blockade. The central role of macrophages in regulating preexisting immunity is substantiated by depletion experiments, transcriptome analysis of ex vivo sorted TAMs, and gene expression profiling of whole tumor lysates at an early treatment time point. This approach enabled the identification of specific combination-induced changes among the pleiotropic activation spectrum of the CD40 agonist. In patients, CD40 expression on human TAMs was detected in mesothelioma and colorectal adenocarcinoma.

Prognostic relevance of tumor-infiltrating lymphocytes and immune checkpoints in pediatric medulloblastoma

Pediatric medulloblastomas are the most frequently diagnosed embryonal tumors of the central nervous system. Current therapies cause severe neurological and cognitive side effects including secondary malignancies. Cellular immunotherapy might be key to improve survival and to avoid morbidity. Efficient killing of tumor cells using immunotherapy requires to overcome cancer-associated strategies to evade cytotoxic immune responses. Here, we examined the immune response and immune evasion strategies in pediatric medulloblastomas. Cytotoxic T-cells, infiltrating medulloblastomas with variable activation status, showed no correlation with overall survival of the patients. We found limited numbers of PD1⁺ T-cells and complete absence of PD-L1 on medulloblastomas. Medulloblastomas downregulated immune recognition molecules MHC-I and CD1 d. Intriguingly, expression of granzyme inhibitors SERPINB1 and SERPINB4 was acquired in 23% and 50% of the tumors, respectively. Concluding, pediatric medulloblastomas exploit multiple immune evasion strategies to overcome immune surveillance. Absence of PD-L1 expression in medulloblastoma suggest limited or no added value for immunotherapy with PD1/PD-L1 blockers.

Expression of intra- and extracellular granzymes in patients with typhoid fever

BACKGROUND

Typhoid fever, caused by the intracellular pathogen Salmonella (S.) enterica serovar Typhi, remains a major cause of morbidity and mortality worldwide. Granzymes are serine proteases promoting cytotoxic lymphocytes mediated eradication of intracellular pathogens via the induction of cell death and which can also play a role in inflammation. We aimed to characterize the expression of extracellular and intracellular granzymes in patients with typhoid fever and whether the extracellular levels of granzyme correlated with IFN-γ release.

METHODS AND PRINCIPAL FINDINGS

We analyzed soluble protein levels of extracellular granzyme A and B in healthy volunteers and patients with confirmed S. Typhi infection on admission and day of discharge, and investigated whether this correlated with interferon (IFN)-γ release, a cytokine significantly expressed in typhoid fever. The intracellular expression of granzyme A, B and K in subsets of lymphocytic cells was determined using flow cytometry. Patients demonstrated a marked increase of extracellular granzyme A and B in acute phase plasma and a correlation of both granzymes with IFN-γ release. In patients, lower plasma levels of granzyme B, but not granzyme A, were found at day of discharge compared to admission, indicating an association of granzyme B with stage of disease. Peripheral blood mononuclear cells of typhoid fever patients had a higher percentage of lymphocytic cells expressing intracellular granzyme A and granzyme B, but not granzyme K, compared to controls.

CONCLUSION

The marked increase observed in extra- and intracellular levels of granzyme expression in patients with typhoid fever, and the correlation with stage of disease, suggests a role for granzymes in the host response to this disease.

The Untold Story of Granzymes in Oncoimmunology: Novel Opportunities with Old Acquaintances

For more than 20 years perforin and granzymes (GZMs) have been recognized as key cell death executors of cytotoxic T (Tc) and natural killer (NK) cells during cancer immunosurveillance. In immune surveillance, perforin and GZMB, the most potent cytotoxic molecules, act mainly as antitumoral and anti-infectious factors. However, when expressed by immune regulatory cells they may contribute to immune evasion of specific cancer types. By contrast, the other major granzyme, GZMA, seems not to play a major role in Tc/NK cell-mediated cytotoxicity, but acts as a proinflammatory cytokine that might contribute to cancer development. Members of the GZM family also regulate other biological processes unrelated to cell death, such as angiogenesis, vascular integrity, extracellular matrix remodeling, and barrier function, all of which contribute to cancer initiation and progression. Thus, a new paradigm is emerging in the field of oncoimmunology. Can GZMs act as protumoral factors under some circumstances? We review the diverse roles of GZMs in cancer progression, and new therapeutic opportunities emerging from targeting these protumoral roles.

Cytotoxic CD4 T Cells-Friend or Foe during Viral Infection?

CD4 T cells with cytotoxic function were once thought to be an artifact due to long-term in vitro cultures but have in more recent years become accepted and reported in the literature in response to a number of viral infections. In this review, we focus on cytotoxic CD4 T cells in the context of human viral infections and in some infections that affect mice and non-human primates. We examine the effector mechanisms used by cytotoxic CD4 cells, the phenotypes that describe this population, and the transcription factors and pathways that lead to their induction following infection. We further consider the cells that are the predominant targets of this effector subset and describe the viral infections in which CD4 cytotoxic T lymphocytes have been shown to play a protective or pathologic role. Cytotoxic CD4 T cells are detected in the circulation at much higher levels than previously realized and are now recognized to have an important role in the immune response to viral infections.

Granzymes A and K differentially potentiate LPS-induced cytokine response

Granzymes are serine proteases that, upon release from cytotoxic cells, induce apoptosis in tumor cells and virally infected cells. In addition, a role of granzymes in inflammation is emerging. Recently, we have demonstrated that extracellular granzyme K (GrK) potentiates lipopolysaccharide (LPS)-induced cytokine response from monocytes. GrK interacts with LPS, disaggregates LPS micelles, and stimulates LPS-CD14 binding and Toll-like receptor signaling. Here we show that human GrA also potentiates cytokine responses in human monocytes initiated by LPS or Gram-negative bacteria. Similar to GrK, this effect is independent of GrA catalytic activity. Unlike GrK, however, GrA does not bind to LPS, has little influence on LPS micelle disaggregation, and does not augment LPS-CD14 complex formation. We conclude that GrA and GrK differentially modulate LPS-Toll-like receptor signaling in monocytes, suggesting functional redundancy among cytotoxic lymphocyte proteases in the anti-bacterial innate immune response.

The primary immune response to Vaccinia virus vaccination includes cells with a distinct cytotoxic effector CD4 T-cell phenotype

BACKGROUND

Smallpox was eradicated by a global program of inoculation with Vaccinia virus (VV). Robust VV-specific CD4 T-cell responses during primary infection are likely essential to controlling VV replication. Although there is increasing interest in cytolytic CD4 T-cells across many viral infections, the importance of these cells during acute VV infection is unclear.

METHODS

We undertook a detailed functional and genetic characterization of CD4 T-cells during acute VV-infection of humans. VV-specific T-cells were identified by up-regulation of activation markers directly ex vivo and through cytokine and co-stimulatory molecule expression. At day-13-post primary inoculation with VV, CD38highCD45RO+ CD4 T-cells were purified by cell sorting, RNA isolated and analysed by microarray. Differential expression of up-regulated genes in activated CD4 T-cells was confirmed at the mRNA and protein levels. We compared analyses of VV-specific CD4 T-cells to studies on 12 subjects with primary HIV infection (PHI). VV-specific T-cells lines were established from PBMCs collected post vaccination and checked for cytotoxicity potential.

RESULTS

A median 11.9% CD4 T-cells were CD38highCD45RO+ at day-13 post-VV inoculation, compared to 3.0% prior and 10.4% during PHI. Activated CD4 T-cells had an up-regulation of genes related to cytolytic function, including granzymes K and A, perforin, granulysin, TIA-1, and Rab27a. No difference was seen between CD4 T-cell expression of perforin or TIA-1 to VV and PHI, however granzyme k was more dominant in the VV response. At 25:1 effector to target ratio, two VV-specific T-cell lines exhibited 62% and 30% cytotoxicity respectively and CD107a degranulation.

CONCLUSIONS

We show for the first time that CD4 CTL are prominent in the early response to VV. Understanding the role of CD4 CTL in the generation of an effective anti-viral memory may help develop more effective vaccines for diseases such as HIV.

Oropharyngeal squamous cell carcinomas differentially express granzyme inhibitors

Objectives

Patients with human papillomavirus (HPV)-positive oropharyngeal squamous cell carcinomas (OPSCCs) have an improved prognosis compared to HPV-negative OPSCCs. Several theories have been proposed to explain this relatively good prognosis. One hypothesis is a difference in immune response. In this study, we compared tumor-infiltrating CD3+, CD4+, CD8+ T-cells, and granzyme inhibitors (SERPINB1, SERPINB4, and SERPINB9) between HPV-positive and HPV-negative tumors and the relation with survival.

Methods

Protein expression of tumor-infiltrating lymphocytes (TILs) (CD3, CD4, and CD8) and granzyme inhibitors was analyzed in 262 OPSCCs by immunohistochemistry (IHC). Most patients (67 %) received primary radiotherapy with or without chemotherapy. Cox regression analysis was carried out to compare overall survival (OS) of patients with low and high TIL infiltration and expression of granzyme inhibitors.

Results

HPV-positive OPSCCs were significantly more heavily infiltrated by TILs (p < 0.001) compared to HPV-negative OPSCCs. A high level of CD3+ TILs was correlated with a favorable outcome in the total cohort and in HPV-positive OPSCCs, while it reached no significance in HPV-negative OPSCCs. There was expression of all three granzyme inhibitors in OPSCCs. No differences in expression were found between HPV-positive and HPV-negative OPSCCs. Within the group of HPV-positive tumors, a high expression of SERPINB1 was associated with a significantly worse overall survival.

Conclusion

HPV-positive OPSCCs with a low count of CD3+ TILs or high expression of SERPINB1 have a worse OS, comparable with HPV-negative OPSCCs. This suggests that the immune system plays an important role in the carcinogenesis of the virally induced oropharynx tumors.

Pediatric Primitive Neuroectodermal Tumors of the Central Nervous System Differentially Express Granzyme Inhibitors

BACKGROUND

Central nervous system (CNS) primitive neuroectodermal tumors (PNETs) are malignant primary brain tumors that occur in young infants. Using current standard therapy, up to 80% of the children still dies from recurrent disease. Cellular immunotherapy might be key to improve overall survival. To achieve efficient killing of tumor cells, however, immunotherapy has to overcome cancer-associated strategies to evade the cytotoxic immune response. Whether CNS-PNETs can evade the immune response remains unknown.

METHODS

We examined by immunohistochemistry the immune response and immune evasion strategies in pediatric CNS-PNETs.

RESULTS

Here, we show that CD4+, CD8+, γδ-T-cells, and Tregs can infiltrate pediatric CNS-PNETs, although the activation status of cytotoxic cells is variable. Pediatric CNS-PNETs evade immune recognition by downregulating cell surface MHC-I and CD1d expression. Intriguingly, expression of SERPINB9, SERPINB1, and SERPINB4 is acquired during tumorigenesis in 29%, 29%, and 57% of the tumors, respectively.

CONCLUSION

We show for the first time that brain tumors express direct granzyme inhibitors (serpins) as a potential mechanism to overcome cellular cytotoxicity, which may have consequences for cellular immunotherapy.

Granzyme M and K release in human experimental endotoxemia

Granzymes are serine proteases involved in killing of tumor cells and virally infected cells. However, granzymes are also upregulated in blood under inflammatory conditions and contribute to cytokine release and processing. Here, we show that granzyme M (GrM) and to a lesser extent GrK are transiently elevated in the circulation following LPS administration in humans. GrM is released upon stimulation of whole blood with LPS or the gram-negative bacteria Escherichia coli BL21, Pseudomonas aeruginosa, and Neisseria meningitidis. GrK is only released upon stimulation with P. aeruginosa. Thus, GrM and GrK are differentially released in response to LPS and gram-negative bacteria.

Granule Associated Serine Proteases of Hematopoietic Cells - An Analysis of Their Appearance and Diversification during Vertebrate Evolution

Serine proteases are among the most abundant granule constituents of several hematopoietic cell lineages including mast cells, neutrophils, cytotoxic T cells and NK cells. These proteases are stored in their active form in the cytoplasmic granules and in mammals are encoded from four different chromosomal loci: the chymase locus, the met-ase locus, the T cell tryptase and the mast cell tryptase locus. In order to study their appearance during vertebrate evolution we have performed a bioinformatic analysis of related genes and gene loci from a large panel of metazoan animals from sea urchins to placental mammals for three of these loci: the chymase, met-ase and granzyme A/K loci. Genes related to mammalian granzymes A and K were the most well conserved and could be traced as far back to cartilaginous fish. Here, the granzyme A and K genes were found in essentially the same chromosomal location from sharks to humans. However in sharks, no genes clearly identifiable as members of the chymase or met-ase loci were found. A selection of these genes seemed to appear with bony fish, but sometimes in other loci. Genes related to mammalian met-ase locus genes were found in bony fish. Here, the most well conserved member was complement factor D. However, genes distantly related to the neutrophil proteases were also identified in this locus in several bony fish species, indicating that this locus is also old and appeared at the base of bony fish. In fish, a few of the chymase locus-related genes were found in a locus with bordering genes other than the mammalian chymase locus and some were found in the fish met-ase locus. This indicates that a convergent evolution rather than divergent evolution has resulted in chymase locus-related genes in bony fish.

A High Yield and Cost-efficient Expression System of Human Granzymes in Mammalian Cells

When cytotoxic T lymphocytes (CTL) or natural killer (NK) cells recognize tumor cells or cells infected with intracellular pathogens, they release their cytotoxic granule content to eliminate the target cells and the intracellular pathogen. Death of the host cells and intracellular pathogens is triggered by the granule serine proteases, granzymes (Gzms), delivered into the host cell cytosol by the pore forming protein perforin (PFN) and into bacterial pathogens by the prokaryotic membrane disrupting protein granulysin (GNLY). To investigate the molecular mechanisms of target cell death mediated by the Gzms in experimental in-vitro settings, protein expression and purification systems that produce high amounts of active enzymes are necessary. Mammalian secreted protein expression systems imply the potential to produce correctly folded, fully functional protein that bears posttranslational modification, such as glycosylation. Therefore, we used a cost-efficient calcium precipitation method for transient transfection of HEK293T cells with human Gzms cloned into the expression plasmid pHLsec. Gzm purification from the culture supernatant was achieved by immobilized nickel affinity chromatography using the C-terminal polyhistidine tag provided by the vector. The insertion of an enterokinase site at the N-terminus of the protein allowed the generation of active protease that was finally purified by cation exchange chromatography. The system was tested by producing high levels of cytotoxic human Gzm A, B and M and should be capable to produce virtually every enzyme in the human body in high yields.

Granzymes regulate proinflammatory cytokine responses

Granzymes (Grs) are serine proteases mainly produced by cytotoxic lymphocytes and are traditionally considered to cause apoptosis in tumor cells and virally infected cells. However, the cytotoxicity of several Grs is currently being debated, and additional, predominantly extracellular, functions of Grs in inflammation are emerging. Extracellular soluble Grs are elevated in the circulation of patients with autoimmune diseases and infections. Additionally, Grs are expressed by several types of immune cells other than cytotoxic lymphocytes. Recent research has revealed novel immunomodulatory functions of Grs. In this review, we provide a comprehensive overview on the role of Grs in inflammation, highlighting their role in cytokine induction and processing.

Infection history determines the differentiation state of human CD8+ T cells

After the resolution of the acute phase of infection, otherwise quiescent antigen-experienced CD8(+) T cells confer rapid protection upon reinfection with viral pathogens or, in the case of persistent viruses, help to maintain control of the infection. Depending on the type of virus, antigen-specific CD8(+) T cells have distinct traits, ranging from typical memory cell properties in the case of rapidly cleared viruses to immediate effector functions for persistent viruses. We here show that both the differentiation stage, defined by the expression of cell surface markers, such as CD45RA, CCR7, CD28, and CD27, and distinct expression levels of T-bet and eomesodermin (Eomes) predict the functional profile of antigen-experienced CD8(+) T cells. Furthermore, virus-specific CD8(+) T cells targeting different respiratory syncytial virus-, influenza A virus-, Epstein-Barr virus (EBV)-, human cytomegalovirus (hCMV)-, and HIV-1-specific epitopes adopt distinct T-bet and Eomes expression patterns that appear to be installed early during the primary response. Importantly, the associations between surface phenotype, T-bet/Eomes expression levels, and the expression of markers that predict CD8(+) T-cell function change according to viral infection history, particularly against the background of HIV-1 and, to lesser extent, of human cytomegalovirus and/or Epstein-Barr virus infection. Thus, the functionality of human antigen-experienced CD8(+) T cells follows at least two dimensions, one outlined by the surface phenotype and another by the T-bet/Eomes expression levels, which are determined by previous or persistent viral challenges.

IMPORTANCE

Functional human CD8(+) T-cell subsets have been defined using surface markers like CD45RA, CCR7, CD28, and CD27. However, the induction of function-defining traits, like granzyme B expression, is controlled by transcription factors like T-bet and Eomes. Here, we describe how T-bet and Eomes levels distinctly relate to the expression of molecules predictive for CD8(+) T-cell function in a surface phenotype-independent manner. Importantly, we found that central memory and effector memory CD8(+) T-cell subsets differentially express T-bet, Eomes, and molecules predictive for function according to viral infection history, particularly so in the context of HIV-1 infection and, to lesser extent, of latent EBV- and/or hCMV-infected, otherwise healthy adults. Finally, we show that the distinct phenotypes and T-bet/Eomes levels of different virus-specific CD8(+) T-cell populations are imprinted early during the acute phase of primary infection in vivo. These findings broaden our understanding of CD8(+) T-cell differentiation.

Substrate specificity of human granzyme 3: analyses of the P3-P2-P1 triplet using fluorescence resonance energy transfer substrate libraries

Granzyme 3 (Gr3) is known as a tryptase-type member of the granzyme family and exists in the granules of immunocompetent cells. Granule proteases including granzymes, are transported into the cytoplasm of tumor cells or virus-infected cells by perforin function, degrade cytoplasmic or nuclear proteins and subsequently cause the death of the target cells. Recently, although several substrates of Gr3 in vivo have been reported, these hydrolyzed sites were unclear or lacked consistency. Our previous study investigated the optimal amino acid triplet (P3-P2-P1) as a substrate for Gr3 using a limited combination of amino acids at the P2 and P3 positions. In the present study, new fluorescence resonance energy transfer (FRET) substrate libraries to screen P2 and P3 positions were synthesized, respectively. Using these substrate libraries, the optimal amino acid triplet was shown to be Tyr-Phe-Arg as a substrate for human Gr3. Moreover, kinetic analyses also showed that the synthetic substrate FRETS-YFR had the lowest Km value for human Gr3. A substantial number of membrane proteins possessed the triplet Tyr-Phe-Arg and some of them might be in vivo substrates for Gr3. The results might also be a great help for preparing specific inhibitors to manipulate Gr3 activity both in vitro and in vivo.

Granzyme K synergistically potentiates LPS-induced cytokine responses in human monocytes

Granzymes are serine proteases released by cytotoxic lymphocytes to induce apoptosis in virus-infected cells and tumor cells. Evidence is emerging that granzymes also play a role in controlling inflammation. Granzyme serum levels are elevated in patients with autoimmune diseases and infections, including sepsis. However, the function of extracellular granzymes in inflammation largely remains unknown. Here, we show that granzyme K (GrK) binds to Gram-negative bacteria and their cell-wall component lipopolysaccharide (LPS). GrK synergistically enhances LPS-induced cytokine release in vitro from primary human monocytes and in vivo in a mouse model of LPS challenge. Intriguingly, these extracellular effects are independent of GrK catalytic activity. GrK disaggregates LPS from micelles and augments LPS-CD14 complex formation, thereby likely boosting monocyte activation by LPS. We conclude that extracellular GrK is an unexpected direct modulator of LPS-TLR4 signaling during the antimicrobial innate immune response.

Blood and beyond: properties of circulating and tissue-resident human virus-specific αβ CD8(+) T cells

CD8(+) αβ T-cell responses form an essential line of defence against viral infections. An important part of the mechanisms that control the generation and maintenance of these responses have been elucidated in experimental mouse models. In recent years it has become clear that CD8(+) T-cell responses in humans not only show similarities, but also display differences to those occurring in mice. Furthermore, while several viral infections occur primarily in specialised organ systems, for obvious reasons, most human CD8(+) T-cell investigations were performed on cells deriving from the circulation. Indeed, several lines of evidence now point to essential functional differences between virus-specific CD8(+) memory T cells found in the circulation and those providing protection in organ systems, such as the lungs. In this review, we will focus on summarising recent insights into human CD8(+) T-cell differentiation in response to several viruses and emphasise that for a complete understanding of anti-viral immunity, it is pivotal to scrutinize such responses in both blood and tissue.