Granzyme B directly and efficiently cleaves several downstream caspase substrates: implications for CTL-induced apoptosis

Cell type-specific regulation of the pentose phosphate pathway during development and metabolic stress-driven autoimmune diseases: Relevance for inflammatory liver, renal, endocrine, cardiovascular and neurobehavioral comorbidities, carcinogenesis, and aging

The pathogenesis of autoimmunity is incompletely understood which limits the development of effective therapies. New compelling evidence indicates that the pentose phosphate pathway (PPP) profoundly regulate lineage development in the immune system that are influenced by genetic and environmental factors during metabolic stress underlying the development of autoimmunity. The PPP provides two unique metabolites, ribose 5-phosphate for nucleotide biosynthesis in support of cell proliferation and NADPH for protection against oxidative stress. The PPP operates two separate branches, oxidative (OxPPP) and non-oxidative (NOxPPP). While the OxPPP functions in all organisms, the NOxPPP reflects adaptation to niche-specific metabolic requirements. The OxPPP primarily depends on glucose 6-phosphate dehydrogenase (G6PD), whereas transaldolase (TAL) controls the rate and directionality of metabolic flux though the NOxPPP. G6PD is essential for normal development but its partial deficiency protects from malaria. Although men and mice lacking TAL develop normally, they exhibit liver cirrhosis progressing to hepatocellular carcinoma. Mechanistic target of rapamycin-dependent loss of paraoxonase 1 drives autoimmunity and cirrhosis in TAL deficiency, while hepatocarcinogenesis hinges on polyol pathway activation via aldose reductase (AR). Accumulated polyols, such as erythritol, xylitol, and sorbitol, which are commonly used as non-caloric sweeteners, may act as pro-inflammatory oncometabolites under metabolic stress, such as TAL deficiency. The TAL/AR axis is identified as a checkpoint of pathogenesis and target for treatment of metabolic stress-driven systemic autoimmunity with relevance for inflammatory liver, renal and cardiovascular disorders, diabetes, carcinogenesis, and aging.

The ubiquitin ligase NKLAM promotes apoptosis and suppression of cell growth

Natural killer lytic-associated molecule (NKLAM), also known as RNF19b, is a member of the RING-in between-RING-RING (RBR) E3 ubiquitin ligase family and plays a pivotal role in immune regulation. We identified a critical cysteine residue at position 301 essential for NKLAM's ubiquitin ligase function. Site-directed mutagenesis of this residue to serine or alanine abrogated the ligase activity of NKLAM. Utilizing inducible expression systems in two different cell lines, HEK293 embryonic kidney cells and K562 myeloid leukemia cells, we demonstrated that wild-type (WT) NKLAM, but not the catalytically inactive NKLAM alanine mutant (C301A), inhibited cellular proliferation, as evidenced by reduced cell numbers and decreased metabolic activity. Moreover, NKLAM expression led to a significant decrease in the abundance and stability of the proto-oncogene c-Myc, a key regulator of proliferation. NKLAM facilitated the proteasomal degradation of c-Myc, with a reduction in c-Myc half-life from 27 min to 12 min and restoration of c-Myc levels upon proteasome inhibition. Notably, prolonged NKLAM expression induced apoptosis, measured by annexin-V staining and caspase activation. Strikingly, the serine mutant, C301S, while lacking ubiquitin ligase activity, induced apoptosis comparable to WT NKLAM, highlighting an alternative pathway for NKLAM-mediated inhibition of cellular homeostasis. Our findings indicate that NKLAM is a cytolytic protein with multifaceted roles in cellular proliferation and apoptosis.

Executioner caspases degrade essential mediators of pathogen-host interactions to inhibit growth of intracellular Listeria monocytogenes

Cell death mediated by executioner caspases is essential during organ development and for organismal homeostasis. The mechanistic role of activated executioner caspases in antibacterial defense during infections with intracellular bacteria, such as Listeria monocytogenes, remains elusive. Cell death upon intracellular bacterial infections is considered altruistic to deprive the pathogens of their protective niche. To establish infections in a human host, Listeria monocytogenes deploy virulence mediators, including membranolytic listeriolysin O (LLO) and the invasion associated protein p60 (Iap), allowing phagosomal escape, intracellular replication and cell-to-cell spread. Here, by means of chemical and genetical modifications, we show that the executioner caspases-3 and -7 efficiently inhibit growth of intracellular Listeria monocytogenes in host cells. Comprehensive proteomics revealed multiple caspase-3 substrates in the Listeria secretome, including LLO, Iap and various other proteins crucially involved in pathogen-host interactions. Listeria secreting caspase-uncleavable LLO or Iap gained significant growth advantage in epithelial cells. With that, we uncovered an underappreciated defense barrier and a non-canonical role of executioner caspases to degrade virulence mediators, thus impairing intracellular Listeria growth.

Natural Killer cells at the frontline in the fight against cancer

Natural Killer (NK) cells are innate immune cells that play a pivotal role as first line defenders in the anti-tumor response. To prevent tumor development, NK cells are searching for abnormal cells within the body and appear to be key players in immunosurveillance. Upon recognition of abnormal cells, NK cells will become activated to destroy them. In order to fulfill their anti-tumoral function, they rely on the secretion of lytic granules, expression of death receptors and production of cytokines. Additionally, NK cells interact with other cells in the tumor microenvironment. In this review, we will first focus on NK cells' activation and cytotoxicity mechanisms as well as NK cells behavior during serial killing. Lastly, we will review NK cells' crosstalk with the other immune cells present in the tumor microenvironment.

Peripheral Blood CD8+ T-Lymphocyte Immune Response in Benign and Subpopulations of Breast Cancer Patients

Peripheral blood CD8+ T lymphocytes play a crucial role in cell-mediated immunity and tumor-related immune responses in breast cancer. In this study, label-free quantification analysis and gene set enrichment analysis (GSEA) of CD8+ T lymphocytes in the peripheral blood of benign patients and patients with different breast cancer (BC) subtypes, i.e., luminal A, luminal B, and triple-negative breast cancer (TNBC), were performed using nano-UHPLC and Orbitrap mass spectrometry. Differential protein expression in CD8+ T lymphocytes revealed significant downregulation (log2 FC ≥ 0.38 or ≤-0.38, adj. p < 0.05), particularly in proteins involved in cytotoxicity, cytolysis, and proteolysis, such as granzymes (GZMs) and perforin 1 (PRF1). This downregulation was observed in the benign group (GZMH, GZMM, and PRF1) and luminal B (GZMA, GZMH) subtypes, whereas granzyme K (GZMK) was upregulated in TNBC in comparison to healthy controls. The RNA degradation pathway was significantly downregulated (p < 0.05, normalized enrichment score (NES) from -1.47 to -1.80) across all BC subtypes, suggesting a potential mechanism for regulating gene expression during T cell activation. Also, the Sm-like proteins (LSM2, LSM3, and LSM5) were significantly downregulated in the RNA degradation pathway. Proteomic analysis of CD8+ T lymphocytes in peripheral blood across different breast cancer subtypes provides a comprehensive view of the molecular mechanisms of the systemic immune response that can significantly contribute to advancements in the diagnosis, treatment, and prognosis of this disease.

Granzyme F: Exhaustion Marker and Modulator of Chimeric Antigen Receptor T Cell-Mediated Cytotoxicity

Granzymes are a family of proteases used by CD8 T cells to mediate cytotoxicity and other less-defined activities. The substrate and mechanism of action of many granzymes are unknown, although they diverge among the family members. In this study, we show that mouse CD8+ tumor-infiltrating lymphocytes (TILs) express a unique array of granzymes relative to CD8 T cells outside the tumor microenvironment in multiple tumor models. Granzyme F was one of the most highly upregulated genes in TILs and was exclusively detected in PD1/TIM3 double-positive CD8 TILs. To determine the function of granzyme F and to improve the cytotoxic response to leukemia, we constructed chimeric Ag receptor T cells to overexpress a single granzyme, granzyme F or the better-characterized granzyme A or B. Using these doubly recombinant T cells, we demonstrated that granzyme F expression improved T cell-mediated cytotoxicity against target leukemia cells and induced a form of cell death other than chimeric Ag receptor T cells expressing only endogenous granzymes or exogenous granzyme A or B. However, increasing expression of granzyme F also had a detrimental impact on the viability of the host T cells, decreasing their persistence in circulation in vivo. These results suggest a unique role for granzyme F as a marker of terminally differentiated CD8 T cells with increased cytotoxicity, but also increased self-directed cytotoxicity, suggesting a potential mechanism for the end of the terminal exhaustion pathway.

Decoding the mechanisms of chimeric antigen receptor (CAR) T cell-mediated killing of tumors: insights from granzyme and Fas inhibition

Chimeric antigen receptor (CAR) T cell show promise in cancer treatments, but their mechanism of action is not well understood. Decoding the mechanisms used by individual T cells can help improve the efficacy of T cells while also identifying mechanisms of T cell failure leading to tumor escape. Here, we used a suite of assays including dynamic single-cell imaging of cell-cell interactions, dynamic imaging of fluorescent reporters to directly track cytotoxin activity in tumor cells, and scRNA-seq on patient infusion products to investigate the cytotoxic mechanisms used by individual CAR T cells in killing tumor cells. We show that surprisingly, overexpression of the Granzyme B (GZMB) inhibitor, protease inhibitor-9 (PI9), does not alter the cytotoxicity mediated by CD19-specific CAR T cells against either the leukemic cell line, NALM6; or the ovarian cancer cell line, SkOV3-CD19. We designed and validated reporters to directly assay T cell delivered GZMB activity in tumor cells and confirmed that while PI9 overexpression inhibits GZMB activity at the molecular level, this is not sufficient to impact the kinetics or magnitude of killing mediated by the CAR T cells. Altering cytotoxicity mediated by CAR T cells required combined inhibition of multiple pathways that are tumor cell specific: (a) B-cell lines like NALM6, Raji and Daudi were sensitive to combined GZMB and granzyme A (GZMA) inhibition; whereas (b) solid tumor targets like SkOV3-CD19 and A375-CD19 (melanoma) were sensitive to combined GZMB and Fas ligand inhibition. We realized the translational relevance of these findings by examining the scRNA-seq profiles of Tisa-cel and Axi-cel infusion products and show a significant correlation between GZMB and GZMA expression at the single-cell level in a T cell subset-dependent manner. Our findings highlight the importance of the redundancy in killing mechanisms of CAR T cells and how this redundancy is important for efficacious T cells.

Macro CD5L+ deteriorates CD8+T cells exhaustion and impairs combination of Gemcitabine-Oxaliplatin-Lenvatinib-anti-PD1 therapy in intrahepatic cholangiocarcinoma

Intratumoral immune status influences tumor therapeutic response, but it remains largely unclear how the status determines therapies for patients with intrahepatic cholangiocarcinoma. Here, we examine the single-cell transcriptional and TCR profiles of 18 tumor tissues pre- and post- therapy of gemcitabine plus oxaliplatin, in combination with lenvatinib and anti-PD1 antibody for intrahepatic cholangiocarcinoma. We find that high CD8 GZMB+ and CD8 proliferating proportions and a low Macro CD5L+ proportion predict good response to the therapy. In patients with a poor response, the CD8 GZMB+ and CD8 proliferating proportions are increased, but the CD8 GZMK+ proportion is decreased after the therapy. Transition of CD8 proliferating and CD8 GZMB+ to CD8 GZMK+ facilitates good response to the therapy, while Macro CD5L+-CD8 GZMB+ crosstalk impairs the response by increasing CTLA4 in CD8 GZMB+. Anti-CTLA4 antibody reverses resistance of the therapy in intrahepatic cholangiocarcinoma. Our data provide a resource for predicting response of the combination therapy and highlight the importance of CD8+T-cell status conversion and exhaustion induced by Macro CD5L+ in influencing the response, suggesting future avenues for cancer treatment optimization.

Imaging and monitoring of granzyme B in the immune response

Significant progress has been made in tumor immunotherapy that uses the human immune response to kill and remove tumor cells. However, overreactive immune response could lead to various autoimmune diseases and acute rejection. Accurate and specific monitoring of immune responses in these processes could help select appropriate therapies and regimens for the patient and could reduce the risk of side effects. Granzyme B (GzmB) is an ideal biomarker for immune response, and its peptide substrate could be coupled with fluorescent dyes or contrast agents for the synthesis of imaging probes activated by GzmB. These small molecules and nanoprobes based on PET, bioluminescence imaging, or fluorescence imaging have proved to be highly GzmB specific and accuracy. This review summarizes the design of different GzmB-responsive imaging probes and their applications in monitoring of tumor immunotherapy and overreactive immune response. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

Resisting T cell attack: tumor-cell-intrinsic defense and reparation mechanisms

Cytotoxic T lymphocytes (CTLs) are antigen-specific killer cells equipped to identify and eliminate host cells that have been altered through infection or transformation. Both chimeric antigen-receptor (CAR) T cell therapies and immune checkpoint blockade (ICB) therapies are based on successful elimination of tumor cells by cytotoxic effectors. In this opinion article, we outline cell-intrinsic mechanisms by which tumor cells defend against CTLs, highlighting pathways that confer resistance and proposing opportunities for combination therapies. We discuss how exogenous killing entities [e.g., supramolecular attack particles (SMAPs)] offer a novel strategy to circumvent cellular resistance mechanisms. Our opinion article highlights the importance of identifying, quantifying, and targeting tumor defense mechanisms at the interface between tumor cells and CTLs as a critical consideration in the development of immunotherapy approaches.

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.

Noncytotoxic Roles of Granzymes in Health and Disease

Granzymes are serine proteases previously believed to play exclusive and somewhat redundant roles in lymphocyte-mediated target cell death. However, recent studies have challenged this paradigm. Distinct substrate profiles and functions have since emerged for each granzyme while their dysregulated proteolytic activities have been linked to diverse pathologies.

Recent advances in cutaneous lupus

Cutaneous lupus erythematosus (CLE) is an inflammatory and autoimmune skin condition that affects patients with systemic lupus erythematosus (SLE) and exists as an isolated entity without associated SLE. Flares of CLE, often triggered by exposure to ultraviolet (UV) light result in lost productivity and poor quality of life for patients and can be associated with trigger of systemic inflammation. In the past 10 years, the knowledge of CLE etiopathogenesis has grown, leading to promising targets for better therapies. Development of lesions likely begins in a pro-inflammatory epidermis, conditioned by excess type I interferon (IFN) production to undergo increased cell death and inflammatory cytokine production after UV light exposure. The reasons for this inflammatory predisposition are not well-understood, but may be an early event, as ANA + patients without criteria for autoimmune disease exhibit similar (although less robust) findings. Non-lesional skin of SLE patients also exhibits increased innate immune cell infiltration, conditioned by excess IFNs to release pro-inflammatory cytokines, and potentially increase activation of the adaptive immune system. Plasmacytoid dendritic cells are also found in non-lesional skin and may contribute to type I IFN production, although this finding is now being questioned by new data. Once the inflammatory cycle begins, lesional infiltration by numerous other cell populations ensues, including IFN-educated T cells. The heterogeneity amongst lesional CLE subtypes isn't fully understood, but B cells appear to discriminate discoid lupus erythematosus from other subtypes. Continued discovery will provide novel targets for additional therapeutic pursuits. This review will comprehensively discuss the contributions of tissue-specific and immune cell populations to the initiation and propagation of disease.

All About (NK Cell-Mediated) Death in Two Acts and an Unexpected Encore: Initiation, Execution and Activation of Adaptive Immunity

NK cells are key mediators of immune cell-mediated cytotoxicity toward infected and transformed cells, being one of the main executors of cell death in the immune system. NK cells recognize target cells through an array of inhibitory and activating receptors for endogenous or exogenous pathogen-derived ligands, which together with adhesion molecules form a structure known as immunological synapse that regulates NK cell effector functions. The main and best characterized mechanisms involved in NK cell-mediated cytotoxicity are the granule exocytosis pathway (perforin/granzymes) and the expression of death ligands. These pathways are recognized as activators of different cell death programmes on the target cells leading to their destruction. However, most studies analyzing these pathways have used pure recombinant or native proteins instead of intact NK cells and, thus, extrapolation of the results to NK cell-mediated cell death might be difficult. Specially, since the activation of granule exocytosis and/or death ligands during NK cell-mediated elimination of target cells might be influenced by the stimulus received from target cells and other microenvironment components, which might affect the cell death pathways activated on target cells. Here we will review and discuss the available experimental evidence on how NK cells kill target cells, with a special focus on the different cell death modalities that have been found to be activated during NK cell-mediated cytotoxicity; including apoptosis and more inflammatory pathways like necroptosis and pyroptosis. In light of this new evidence, we will develop the new concept of cell death induced by NK cells as a new regulatory mechanism linking innate immune response with the activation of tumour adaptive T cell responses, which might be the initiating stimulus that trigger the cancer-immunity cycle. The use of the different cell death pathways and the modulation of the tumour cell molecular machinery regulating them might affect not only tumour cell elimination by NK cells but, in addition, the generation of T cell responses against the tumour that would contribute to efficient tumour elimination and generate cancer immune memory preventing potential recurrences.

Multiparameter Longitudinal Imaging of Immune Cell Activity in Chimeric Antigen Receptor T Cell and Checkpoint Blockade Therapies

Longitudinal multimodal imaging presents unique opportunities for noninvasive surveillance and prediction of treatment response to cancer immunotherapy. In this work we first designed a novel granzyme B activated self-assembly small molecule, G-SNAT, for the assessment of cytotoxic T lymphocyte mediated cancer cell killing. G-SNAT was found to specifically detect the activity of granzyme B within the cytotoxic granules of activated T cells and engaged cancer cells in vitro. In lymphoma tumor-bearing mice, the retention of cyanine 5 labeled G-SNAT-Cy5 correlated to CAR T cell mediated granzyme B exocytosis and tumor eradication. In colorectal tumor-bearing transgenic mice with hematopoietic cells expressing firefly luciferase, longitudinal bioluminescence and fluorescence imaging revealed that after combination treatment of anti-PD-1 and anti-CTLA-4, the dynamics of immune cell trafficking, tumor infiltration, and cytotoxic activity predicted the therapeutic outcome before tumor shrinkage was evident. These results support further development of G-SNAT for imaging early immune response to checkpoint blockade and CAR T-cell therapy in patients and highlight the utility of multimodality imaging for improved mechanistic insights into cancer immunotherapy.

Greek Fire, Poison Arrows, and Scorpion Bombs: How Tumor Cells Defend Against the Siege Weapons of Cytotoxic T Lymphocytes

CD8⁺ cytotoxic T lymphocytes (CTLs) are the main cellular effectors of the adaptive immune response against cancer cells, which in turn have evolved sophisticated cellular defense mechanisms to withstand CTL attack. Herein we provide a critical review of the pertinent literature on early and late attack/defense events taking place at the CTL/target cell lytic synapse. We examine the earliest steps of CTL-mediated cytotoxicity (“the poison arrows”) elicited within seconds of CTL/target cell encounter, which face commensurately rapid synaptic repair mechanisms on the tumor cell side, providing the first formidable barrier to CTL attack. We examine how breach of this first defensive barrier unleashes the inextinguishable “Greek fire” in the form of granzymes whose broad cytotoxic potential is linked to activation of cell death executioners, injury of vital organelles, and destruction of intracellular homeostasis. Herein tumor cells deploy slower but no less sophisticated defensive mechanisms in the form of enhanced autophagy, increased reparative capacity, and dysregulation of cell death pathways. We discuss how the newly discovered supra-molecular attack particles (SMAPs, the “scorpion bombs”), seek to overcome the robust defensive mechanisms that confer tumor cell resistance. Finally, we discuss the implications of the aforementioned attack/defense mechanisms on the induction of regulated cell death (RCD), and how different contemporary RCD modalities (including apoptosis, pyroptosis, and ferroptosis) may have profound implications for immunotherapy. Thus, we propose that understanding and targeting multiple steps of the attack/defense process will be instrumental to enhance the efficacy of CTL anti-tumor activity and meet the outstanding challenges in clinical immunotherapy.

Intersection Between Large Granular Lymphocyte Leukemia and Rheumatoid Arthritis

Large granular lymphocyte (LGL) leukemia, a rare hematologic malignancy, has long been associated with rheumatoid arthritis (RA), and the diseases share numerous common features. This review aims to outline the parallels and comparisons between the diseases as well as discuss the potential mechanisms for the relationship between LGL leukemia and RA. RA alone and in conjunction with LGL leukemia exhibits cytotoxic T-cell (CTL) expansions, HLA-DR4 enrichment, RA-associated autoantibodies, female bias, and unknown antigen specificity of associated T-cell expansions. Three possible mechanistic links between the pathogenesis of LGL leukemia and RA have been proposed, including LGL leukemia a) as a result of longstanding RA, b) as a consequence of RA treatment, or c) as a driver of RA. Several lines of evidence point towards LGL as a driver of RA. CTL involvement in RA pathogenesis is evidenced by citrullination and granzyme B cleavage that modifies the repertoire of self-protein antigens in target cells, particularly neutrophils, killed by the CTLs. Further investigations of the relationship between LGL leukemia and RA are warranted to better understand causal pathways and target antigens in order to improve the mechanistic understanding and to devise targeted therapeutic approaches for both disorders.

Interplay between Cell Death and Cell Proliferation Reveals New Strategies for Cancer Therapy

Cell division and cell death are fundamental processes governing growth and development across the tree of life. This relationship represents an evolutionary link between cell cycle and cell death programs that is present in all cells. Cancer is characterized by aberrant regulation of both, leading to unchecked proliferation and replicative immortality. Conventional anti-cancer therapeutic strategies take advantage of the proliferative dependency of cancer yet, in doing so, are triggering apoptosis, a death pathway to which cancer is inherently resistant. A thorough understanding of how therapeutics kill cancer cells is needed to develop novel, more durable treatment strategies. While cancer evolves cell-intrinsic resistance to physiological cell death pathways, there are opportunities for cell cycle agnostic forms of cell death, for example, necroptosis or ferroptosis. Furthermore, cell cycle independent death programs are immunogenic, potentially licensing host immunity for additional antitumor activity. Identifying cell cycle independent vulnerabilities of cancer is critical for developing alternative strategies that can overcome therapeutic resistance.

Is Mitochondrial Oxidative Stress a Viable Therapeutic Target in Preeclampsia?

Despite considerable research efforts over the past few decades, the pathology of preeclampsia (PE) remains poorly understood with no new FDA-approved treatments. There is a substantial amount of work being conducted by investigators around the world to identify targets to develop therapies for PE. Oxidative stress has been identified as one of the crucial players in pathogenesis of PE and has garnered a great deal of attention by several research groups including ours. While antioxidants have shown therapeutic benefit in preclinical models of PE, the clinical trials evaluating antioxidants (vitamin E and vitamin C) were found to be disappointing. Although the idea behind contribution of mitochondrial oxidative stress in PE is not new, recent years have seen an enormous interest in exploring mitochondrial oxidative stress as an important pathological mediator in PE. We and others using animals, cell models, and preeclamptic patient samples have shown the evidence for placental, renal, and endothelial cell mitochondrial oxidative stress, and its significance in PE. These studies offer promising results; however, the important and relevant question is can we translate these results into clinical efficacy in treating PE. Hence, the purpose of this review is to review the existing literature and offer our insights on the potential of mitochondrial antioxidants in treating PE.

Cellular and Molecular Crosstalk of Graft Endothelial Cells During AMR: Effector Functions and Mechanisms

Graft endothelial cell (EC) injury is central to the pathogenesis of antibody-mediated rejection (AMR). The ability of donor-specific antibodies (DSA) to bind C1q and activate the classical complement pathway is an efficient predictor of graft rejection highlighting complement-dependent cytotoxicity as a key process operating during AMR. In the past 5 y, clinical studies further established the cellular and molecular signatures of AMR revealing the key contribution of other, IgG-dependent and -independent, effector mechanisms mediated by infiltrating NK cells and macrophages. Beyond binding to alloantigens, DSA IgG can activate NK cells and mediate antibody-dependent cell cytotoxicity through interacting with Fcγ receptors (FcγRs) such as FcγRIIIa (CD16a). FcRn, a nonconventional FcγR that allows IgG recycling, is highly expressed on ECs and may contribute to the long-term persistence of DSA in blood. Activation of NK cells and macrophages results in the production of proinflammatory cytokines such as TNF and IFNγ that induce transient and reversible changes in the EC phenotype and functions promoting coagulation, inflammation, vascular permeability, leukocyte trafficking. MHC class I mismatch between transplant donor and recipient can create a situation of "missing self" allowing NK cells to kill graft ECs. Depending on the microenvironment, cellular proximity with ECs may participate in macrophage polarization toward an M1 proinflammatory or an M2 phenotype favoring inflammation or vascular repair. Monocytes/macrophages participate in the loss of endothelial specificity in the process of endothelial-to-mesenchymal transition involved in renal and cardiac fibrosis and AMR and may differentiate into ECs enabling vessel and graft (re)-endothelialization.

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.

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.

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.

Granzyme B Induces IRF-3 Phosphorylation through a Perforin-Independent Proteolysis-Dependent Signaling Cascade without Inducing Cell Death

Granzyme B (GrB) is an immune protease implicated in the pathogenesis of several human diseases. In the current model of GrB activity, perforin determines whether the downstream actions of GrB occur intracellularly or extracellularly, producing apoptotic cytotoxicity or nonapoptotic effects, respectively. In the current study, we demonstrate the existence of a broad range of GrB-dependent signaling activities that 1) do not require perforin, 2) occur intracellularly, and 3) for which cell death is not the dominant outcome. In the absence of perforin, we show that GrB enzymatic activity still induces substoichiometric activation of caspases, which through nonlethal DNA damage response signals then leads to activity-associated phosphorylation of IFN regulatory factor-3. These findings illustrate an unexpected potential interface between GrB and innate immunity separate from the traditional role of GrB in perforin-dependent GrB-mediated apoptosis that could have mechanistic implications for human disease.

Heat-killed Salmonella Typhimurium protects mice against carbon ion radiation

OBJECTIVE

Patients receiving carbon-ion radiation therapy and astronauts exploring outer space are inevitably exposed to heavy ion radiation. The aim of this study was to develop radioprotectors to minimize the injuries induced by carbon ion radiation.

METHODS

Heat-killed Salmonella Typhimurium (HKST) was administered to mice by gavage prior to irradiation with a ¹²C⁶⁺ heavy ion accelerator. Hematoxylin and eosin staining and immunofluorescence TdT-mediated dUTP Nick-End Labeling staining were used to assess the radioprotective effect of HKST on organ damage and levels of apoptosis, respectively, in mice. To investigate the mechanism underlying the radioprotective effect of HKST, levels of the pro-apoptotic proteins BAX and caspase 3 as well as interferon-regulatory factor (IRF) 3/7 in the femur, testis and intestine were assessed using immunofluorescence.

RESULTS

Injuries induced by carbon ion radiation were significantly eased by pretreatment with HKST. Both apoptosis and high expression levels of pro-apoptotic proteins induced by heavy ion radiation were inhibited by HKST pretreatment. The radioprotective effect of HKST was associated with stimulation of Toll-like receptor signaling mediated by enhanced IRF3 and IRF7 signaling.

CONCLUSION

HKST was an effective radioprotector alleviating damage to multiple organs caused by heavy ion radiation.

SAM50, a side door to the mitochondria: The case of cytotoxic proteases

SAM50, a 7-8 nm diameter β-barrel channel of the mitochondrial outer membrane, is the central channel of the sorting and assembly machinery (SAM) complex involved in the biogenesis of β-barrel proteins. Interestingly, SAM50 is not known to have channel translocase activity; however, we have recently found that this channel is necessary and sufficient for mitochondrial entry of cytotoxic proteases. Cytotoxic lymphocytes eliminate cells that pose potential hazards, such as virus- and bacteria-infected cells as well as cancer cells. They induce cell death following the delivery of granzyme cytotoxic proteases into the cytosol of the target cell. Although granzyme A and granzyme B (GA and GB), the best characterized of the five human granzymes, trigger very distinct apoptotic cascades, they share the ability to directly target the mitochondria. GA and GB do not have a mitochondrial targeting signal, yet they enter the target cell mitochondria to disrupt respiratory chain complex I and induce mitochondrial reactive oxygen species (ROS)-dependent cell death. We found that granzyme mitochondrial entry requires SAM50 and the translocase of the inner membrane 22 (TIM22). Preventing granzymes' mitochondrial entry compromises their cytotoxicity, indicating that this event is unexpectedly an important step for cell death. Although mitochondria are best known for their roles in cell metabolism and energy conversion, these double-membrane organelles are also involved in Ca²⁺ homeostasis, metabolite transport, cell cycle regulation, cell signaling, differentiation, stress response, redox homeostasis, aging, and cell death. This multiplicity of functions is matched with the complexity and plasticity of the mitochondrial proteome as well as the organelle's morphological and structural versatility. Indeed, mitochondria are extremely dynamic and undergo fusion and fission events in response to diverse cellular cues. In humans, there are 1500 different mitochondrial proteins, the vast majority of which are encoded in the nuclear genome and translated by cytosolic ribosomes, after which they must be imported and properly addressed to the right mitochondrial compartment. To this end, mitochondria are equipped with a very sophisticated and highly specific protein import machinery. The latter is centered on translocase complexes embedded in the outer and inner mitochondrial membranes working along five different import pathways. We will briefly describe these import pathways to put into perspective our finding regarding the ability of granzymes to enter the mitochondria.

Tumor necrosis factor alpha (TNF-α) blockade improves natural killer cell (NK) activation, hypertension, and mitochondrial oxidative stress in a preclinical rat model of preeclampsia

The RUPP rat model of Preeclampsia exhibits hypertension (MAP), cytolytic natural killer (cNK) cells, tumor necrosis factor alpha (TNF-α) and mitochondrial Reactive Oxygen Species (mt ROS).  Objective: Does TNF-α blockade with ETAN (Etanercept) decrease cNK cell and mt ROS in RUPP rats.

METHODS

On gestational day 14, RUPP surgery was performed, ETAN (0.4 mg/kg) was administered on day 18, MAP, blood and tissues collected on 19.

RESULTS

MAP, cytolytic NK cells and mt ROS were elevated in RUPP vs. NP and normalized with ETAN.

CONCLUSION

TNF-α blockade lowered blood pressure and improve inflammation and organ function in response to placental ischemia.

Noninvasive optical detection of granzyme B from natural killer cells with enzyme-activated fluorogenic probes

Natural killer (NK) cells are key innate immunity effectors that combat viral infections and control several cancer types. For their immune function, human NK cells rely largely on five different cytotoxic proteases, called granzymes (A/B/H/K/M). Granzyme B (GrB) initiates at least three distinct cell death pathways, but key aspects of its function remain unexplored because selective probes that detect its activity are currently lacking. In this study, we used a set of unnatural amino acids to fully map the substrate preferences of GrB, demonstrating previously unknown GrB substrate preferences. We then used these preferences to design substrate-based inhibitors and a GrB-activatable activity-based fluorogenic probe. We show that our GrB probes do not significantly react with caspases, making them ideal for in-depth analyses of GrB localization and function in cells. Using our quenched fluorescence substrate, we observed GrB within the cytotoxic granules of human YT cells. When used as cytotoxic effectors, YT cells loaded with GrB attacked MDA-MB-231 target cells, and active GrB influenced its target cell-killing efficiency. In summary, we have developed a set of molecular tools for investigating GrB function in NK cells and demonstrate noninvasive visual detection of GrB with an enzyme-activated fluorescent substrate.

EGFR-targeted CAR-T cells are potent and specific in suppressing triple-negative breast cancer both in vitro and in vivo

Objectives

Triple-negative breast cancer (TNBC) is well known for its strong invasiveness, rapid recurrence and poor prognosis. Immunotherapy, including chimeric antigen receptor-modified T (CAR-T) cells, has emerged as a promising tool to treat TNBC. The identification of a specific target tumor antigen and the design of an effective CAR are among the many challenges of CAR-T therapy.

Methods

We reported that epidermal growth factor receptor (EGFR) is highly expressed in TNBC and consequently designed an optimal third generation of CAR targeting EGFR. The efficacy of primary T lymphocytes infected with EGFR CAR lentivirus (EGFR CAR-T) against TNBC was evaluated both in vitro and in vivo. The signalling pathways activated in tumor and EGFR CAR-T cells were revealed by RNA sequencing analysis.

Results

Third-generation EGFR CAR-T cells exerted potent and specific suppression of TNBC cell growth in vitro, whereas limited cytotoxicity was observed towards normal breast epithelial cells or oestrogen receptor-positive breast cancer cells. This capability was further demonstrated in vivo in a xenograft mouse model, with minimal off-tumor cytotoxicity. Mechanistically, in vitro stimulation with TNBC cells induced the expansion of naïve-associated EGFR CAR-T cells and enhanced their persistence. Furthermore, EGFR CAR-T cells activated the interferon γ, granzyme-perforin-PARP and Fas-FADD-caspase signalling pathways in TNBC cells.

Conclusion

We demonstrate that EGFR is a relevant immunotherapeutic target in TNBC, and EGFR CAR-T exhibits potent and specific antitumor activity against TNBC, suggesting the potential of this third-generation EGFR CAR-T as an immunotherapy tool to treat TNBC in the clinic.

Generation of Distinct Patterns of Rheumatoid Arthritis Autoantigens by Peptidylarginine Deiminase Types 2 and 4 During Perforin-Induced Cell Damage

OBJECTIVE

To address the independent roles of peptidylarginine deiminase type 2 (PAD2) and PAD4 in generating rheumatoid arthritis (RA) autoantigens by using a system that mimics intracellular citrullination in the RA joint.

METHODS

PAD2- or PAD4-expressing 293T cells and mock-transfected cells were used as targets in cytotoxic assays using lymphokine-activated killer cells, cytotoxic YT cell granule contents, or purified human perforin. Protein citrullination and autoantigen production were determined by immunoblotting using the anti-modified citrulline-Senshu method and RA sera (n = 30), respectively.

RESULTS

RA sera recognized at least 3 categories of autoantigens in PAD-expressing target cells killed by the cytotoxic lymphocyte granule-induced death pathway. These included: 1) autoantigens targeted in their native form, 2) citrullinated antigens, and 3) antigens cleaved by cytotoxic proteases (e.g., granzymes). Interestingly, although target cells expressing PAD2 or PAD4 showed prominent hypercitrullination of a broad range of proteins during cytotoxic granule-induced cell damage, autoantibodies in RA sera targeted only a very limited number of antigens in hypercitrullinated cells. Furthermore, RA sera showed distinct reactivities to autoantigens generated by PAD2 or PAD4.

CONCLUSION

The cytotoxic granule-induced death pathway has the capacity to modify antigens by inducing hypercitrullination and antigen cleavage in target cells. Interestingly, among a large number of citrullinated proteins generated by PAD2 and PAD4 in cells, only a few are likely involved in the production of autoantibodies in RA.

Development of a human immuno-oncology therapeutic agent targeting HER2: targeted delivery of granzyme B

Background

Immunotherapeutic approaches designed to augment T and B cell mediated killing of tumor cells has met with clinical success in recent years suggesting tremendous potential for treatment in a broad spectrum of tumor types. After complex recognition of target cells by T and B cells, delivery of the serine protease granzyme B (GrB) to tumor cells comprises the cytotoxic insult resulting in a well-characterized, multimodal apoptotic cascade.

Methods

We designed a recombinant fusion construct, GrB-Fc-4D5, composed of a humanized anti-HER2 scFv fused to active GrB for recognition of tumor cells and internal delivery of GrB, simulating T and B cell therapy. We assessed the construct’s antigen-binding specificity and GrB enzymatic activity, as well as in vitro cytotoxicity and internalization into target and control cells. We also assessed pharmacokinetic and toxicology parameters in vivo.

Results

GrB-Fc-4D5 was highly cytotoxic to Her2 positive cells such as SKBR3, MCF7 and MDA-MB-231 with IC₅₀ values of 56, 99 and 27 nM, respectively, and against a panel of HER2+ cell lines regardless of endogenous expression levels of the PI-9 inhibitor. Contemporaneous studies with Kadcyla demonstrated similar levels of in vitro activity against virtually all cells tested. GrB-Fc-4D5 internalized rapidly into target SKOV3 cells within 1 h of exposure rapidly delivering GrB to the cytoplasmic compartment. In keeping with its relatively high molecular weight (160 kDa), the construct demonstrated a terminal-phase serum half-life in mice of 39.2 h. Toxicity studies conducted on BALB/c mice demonstrated no statistically significant changes in SGPT, SGOT or serum LDH. Histopathologic analysis of tissues from treated mice demonstrated no drug-related changes in any tissues examined.

Conclusion

GrB-Fc-4D5 shows excellent, specific cytotoxicity and demonstrates no significant toxicity in normal, antigen-negative murine models. This construct constitutes a novel approach against HER2-expressing tumors and is an excellent candidate for further development.

IL-27 enhances IL-15/IL-18-mediated activation of human natural killer cells

BACKGROUND

Natural killer (NK) cells are an emerging new tool for cancer immunotherapy. To develop NK cell therapeutics from peripheral blood mononuclear cells (PBMCs) of healthy donors, substantial expansion of primary NK cells is necessary because of the very low number of these cells in peripheral blood. In this study, we aimed to investigate the effect of various cytokine alone or combinations, in expanded NK cells and to analyze the synergetic effect of cytokine combinations.

METHODS

Human NK cells were isolated from healthy donor PBMC. Purified NK cells were stimulated with single cytokines or combinations of IL-2, IL-15, IL-18, and IL-27. The expanded NK cells were characterized by flow cytometry, cytotoxicity assay, calcein AM assay and Western blot.

RESULTS

We investigated the synergistic effects of each cytokine, namely, IL-2, IL-15, IL-18, and IL-27, on human NK cells isolated from PBMCs of healthy donors and cultured for 21 days. We identified that IL-15/IL-18/IL-27-mediated activation of NK cells most potently increased NK cell proliferation, cytotoxicity, and IFN-ɣ secretion compared with the activation observed with other treatments, including IL-2, IL-15, and IL-15/IL-18. Additionally, the expression of DNAM-1, NKG2D, CD69, and natural cytotoxicity receptors (NCRs; NKp30 and NKp44) increased on day 21 compared to that on day 0, demonstrating the activation of NK cells. In vitro, expanded NK cells were highly cytotoxic against cancer cells, displaying increased perforin and granzyme B accumulation.

CONCLUSIONS

Taken together, these results indicated that IL-27 can synergize on NK cell expansion and activation with IL-15 and IL-18. In addition, we described an improved culture method for ex vivo expansion of human NK cells with IL-15/IL-18/IL-27 stimulation and characterized the response of NK cells to this stimulation.

NK cells switch from granzyme B to death receptor-mediated cytotoxicity during serial killing

Natural killer cells can kill infected and transformed cells via two different cell death mechanisms. Prager et al. show that NK cells quickly kill their first targets by releasing cytotoxic granules and only use the slower death receptor–mediated cytotoxicity for their final kill.

NK cells eliminate virus-infected and tumor cells by releasing cytotoxic granules containing granzyme B (GrzB) or by engaging death receptors that initiate caspase cascades. The orchestrated interplay between both cell death pathways remains poorly defined. Here we simultaneously measure the activities of GrzB and caspase-8 in tumor cells upon contact with human NK cells. We observed that NK cells switch from inducing a fast GrzB-mediated cell death in their first killing events to a slow death receptor–mediated killing during subsequent tumor cell encounters. Target cell contact reduced intracellular GrzB and perforin and increased surface-CD95L in NK cells over time, showing how the switch in cytotoxicity pathways is controlled. Without perforin, NK cells were unable to perform GrzB-mediated serial killing and only killed once via death receptors. In contrast, the absence of CD95 on tumor targets did not impair GrzB-mediated serial killing. This demonstrates that GrzB and death receptor–mediated cytotoxicity are differentially regulated during NK cell serial killing.

Mitochondrial Entry of Cytotoxic Proteases: A New Insight into the Granzyme B Cell Death Pathway

The mitochondria represent an integration and amplification hub for various death pathways including that mediated by granzyme B (GB), a granule enzyme expressed by cytotoxic lymphocytes. GB activates the proapoptotic B cell CLL/lymphoma 2 (Bcl-2) family member BH3-interacting domain death agonist (BID) to switch on the intrinsic mitochondrial death pathway, leading to Bcl-2-associated X protein (Bax)/Bcl-2 homologous antagonist/killer- (Bak-) dependent mitochondrial outer membrane permeabilization (MOMP), the dissipation of mitochondrial transmembrane potential (ΔΨm), and the production of reactive oxygen species (ROS). GB can also induce mitochondrial damage in the absence of BID, Bax, and Bak, critical for MOMP, indicating that GB targets the mitochondria in other ways. Interestingly, granzyme A (GA), GB, and caspase 3 can all directly target the mitochondrial respiratory chain complex I for ROS-dependent cell death. Studies of ROS biogenesis have revealed that GB must enter the mitochondria for ROS production, making the mitochondrial entry of cytotoxic proteases (MECP) an unexpected critical step in the granzyme death pathway. MECP requires an intact ΔΨm and is mediated though Sam50 and Tim22 channels in a mtHSP70-dependent manner. Preventing MECP severely compromises GB cytotoxicity. In this review, we provide a brief overview of the canonical mitochondrial death pathway in order to put into perspective this new insight into the GB action on the mitochondria to trigger ROS-dependent cell death.

NOD2 agonist murabutide alleviates radiation-induced injury through DNA damage response pathway mediated by ATR

Injury-induced by ionizing radiation (IR) severely reduces the quality of life of victims. The development of radiation protectors is regarded as one of the most resultful strategies to alleviate damages caused by IR exposure. In the present study, we investigated the radioprotective effects of the agonist of nucleotide-binding-oligomerization-domain-containing proteins 2 called murabutide (MBD) and clarified the potential mechanisms. Our results showed that the pretreatment with MBD effectively protected cultured cells and mice against IR-induced toxicity and the pretreatment with MBD in vitro and in vitro also inhibited apoptosis caused by IR exposure. The downregulation of γ-H2AX and the upregulation of ATR signaling pathways by MBD treatment indicated that the radioprotective effects of MBD were due to the stimulation of DNA damage response (DDR) pathway to repair DNA double-strand breaks caused by IR exposure. As the radioprotective effects of MBD were diminished by the ATR selective inhibitor rather than the ATM inhibitor, ATR pathway was confirmed to be a more crucial checkpoint pathway in mediating the stimulation of DDR pathway by MBD. Taken together, our data provide a novel and effective protector to relieve the injury induced by IR exposure.

Microbial killing by NK cells

It is now evident that NK cells kill bacteria, fungi, and parasites in addition to tumor and virus-infected cells. In addition to a number of recent publications that have identified the receptors and ligands, and mechanisms of cytotoxicity, new insights are reflected in the reports from researchers all over the world at the 17th Meeting of the Society for Natural Immunity held in San Antonio, TX, USA from May 28 through June 1, 2018. We will provide an overview of the field and discuss how the presentations at the meeting might shape our knowledge and future directions in the field.

Targeted human cytolytic fusion proteins at the cutting edge: harnessing the apoptosis-inducing properties of human enzymes for the selective elimination of tumor cells

Patient-specific targeted therapy represents the holy grail of anti-cancer therapeutics, allowing potent tumor depletion without detrimental off-target toxicities. Disease-specific monoclonal antibodies have been employed to bind to oncogenic cell-surface receptors, representing the earliest form of immunotherapy. Targeted drug delivery was first achieved by means of antibody-drug conjugates, which exploit the differential expression of tumor-associated antigens as a guiding mechanism for the specific delivery of chemically-conjugated chemotherapeutic agents to diseased target cells. Biotechnological advances have expanded the repertoire of immunology-based tumor-targeting strategies, also paving the way for the next intuitive step in targeted drug delivery: the construction of recombinant protein drugs consisting of an antibody-based targeting domain genetically fused with a cytotoxic peptide, known as an immunotoxin. However, the most potent protein toxins have typically been derived from bacterial or plant virulence factors and commonly feature both off-target toxicity and immunogenicity in human patients. Further refinement of immunotoxin technology thus led to the replacement of monoclonal antibodies with humanized antibody derivatives, including the substitution of non-human toxic peptides with human cytolytic proteins. Preclinically tested human cytolytic fusion proteins (hCFPs) have proven promising as non-immunogenic combinatory anti-cancer agents, however they still require further enhancement to achieve convincing candidacy as a single-mode therapeutic. To date, a portfolio of highly potent human toxins has been established; ranging from microtubule-associated protein tau (MAP tau), RNases, granzyme B (GrB) and death-associated protein kinase (DAPk). In this review, we discuss the most recent findings on the use of these apoptosis-inducing hCFPs for the treatment of various cancers.

Single-Fluorescent Protein Reporters Allow Parallel Quantification of Natural Killer Cell-Mediated Granzyme and Caspase Activities in Single Target Cells

Natural killer (NK) cells eliminate infected and tumorigenic cells through delivery of granzymes via perforin pores or by activation of caspases via death receptors. In order to understand how NK cells combine different cell death mechanisms, it is important to quantify target cell responses on a single cell level. However, currently existing reporters do not allow the measurement of several protease activities inside the same cell. Here, we present a strategy for the comparison of two different proteases at a time inside individual target cells upon engagement by NK cells. We developed single-fluorescent protein reporters containing the RIEAD or the VGPD cleavage site for the measurement of granzyme B activity. We show that these two granzyme B reporters can be applied in combination with caspase-8 or caspase-3 reporters. While we did not find that caspase-8 was activated by granzyme B, our method revealed that caspase-3 activity follows granzyme B activity with a delay of about 6 min. Finally, we illustrate the comparison of several different reporters for granzyme A, M, K, and H. The approach presented here is a valuable means for the investigation of the temporal evolution of cell death mediated by cytotoxic lymphocytes.

CD30-Redirected Chimeric Antigen Receptor T Cells Target CD30+ and CD30- Embryonal Carcinoma via Antigen-Dependent and Fas/FasL Interactions

Tumor antigen heterogeneity limits success of chimeric antigen receptor (CAR) T-cell therapies. Embryonal carcinomas (EC) and mixed testicular germ cell tumors (TGCT) containing EC, which are the most aggressive TGCT subtypes, are useful for dissecting this issue as ECs express the CD30 antigen but also contain CD30^-/dim cells. We found that CD30-redirected CAR T cells (CD30.CAR T cells) exhibit antitumor activity in vitro against the human EC cell lines Tera-1, Tera-2, and NCCIT and putative EC stem cells identified by Hoechst dye staining. Cytolytic activity of CD30.CAR T cells was complemented by their sustained proliferation and proinflammatory cytokine production. CD30.CAR T cells also demonstrated antitumor activity in an in vivo xenograft NOD/SCID/γcnull (NSG) mouse model of metastatic EC. We observed that CD30.CAR T cells, while targeting CD30⁺ EC tumor cells through the CAR (i.e., antigen-dependent targeting), also eliminated surrounding CD30^- EC cells in an antigen-independent manner, via a cell-cell contact-dependent Fas/FasL interaction. In addition, ectopic Fas (CD95) expression in CD30⁺ Fas^- EC was sufficient to improve CD30.CAR T-cell antitumor activity. Overall, these data suggest that CD30.CAR T cells might be useful as an immunotherapy for ECs. Additionally, Fas/FasL interaction between tumor cells and CAR T cells can be exploited to reduce tumor escape due to heterogeneous antigen expression or to improve CAR T-cell antitumor activity. Cancer Immunol Res; 6(10); 1274-87. ©2018 AACR.

The synthesis of amphiphilic polyethyleneimine/calcium phosphate composites for bispecific T-cell engager based immunogene therapy

Bispecific T-cell engagers (BiTEs) are single chain variable fragments, which could connect the surface antigen on cancer cells and CD₃ ligands on T cells, and then engage the T cells for cancer immunotherapy.

Modularly Constructed Synthetic Granzyme B Molecule Enables Interrogation of Intracellular Proteases for Targeted Cytotoxicity

Targeted therapies promise to increase the safety and efficacy of treatments against diseases ranging from cancer to viral infections. However, the vast majority of targeted therapeutics relies on the recognition of extracellular biomarkers, which are rarely restricted to diseased cells and are thus prone to severe and sometimes-fatal off-target toxicities. In contrast, intracellular antigens present a diverse yet underutilized repertoire of disease markers. Here, we report a protein-based therapeutic platform-termed Cytoplasmic Oncoprotein VErifier and Response Trigger (COVERT)-which enables the interrogation of intracellular proteases to trigger targeted cytotoxicity. COVERT molecules consist of the cytotoxic protein granzyme B (GrB) fused to an inhibitory N-terminal peptide, which can be removed by researcher-specified proteases to activate GrB function. We demonstrate that fusion of a small ubiquitin-like modifier 1 (SUMO1) protein to GrB yields a SUMO-GrB molecule that is specifically activated by the cancer-associated sentrin-specific protease 1 (SENP1). SUMO-GrB selectively triggers apoptotic phenotypes in HEK293T cells that overexpress SENP1, and it is highly sensitive to different SENP1 levels across cell lines. We further demonstrate the rational design of additional COVERT molecules responsive to enterokinase (EK) and tobacco etch virus protease (TEVp), highlighting the COVERT platform's modularity and adaptability to diverse protease targets. As an initial step toward engineering COVERT-T cells for adoptive T-cell therapy, we verified that primary human T cells can express, package, traffic, and deliver engineered GrB molecules in response to antigen stimulation. Our findings set the foundation for future intracellular-antigen-responsive therapeutics that can complement surface-targeted therapies.

Granzyme B enters the mitochondria in a Sam50-, Tim22- and mtHsp70-dependent manner to induce apoptosis

We have found that granzyme B (GB)-induced apoptosis also requires reactive oxygen species resulting from the alteration of mitochondrial complex I. How GB, which does not possess a mitochondrial targeting sequence, enter this organelle is unknown. We show that GB enters the mitochondria independently of the translocase of the outer mitochondrial membrane complex, but requires instead Sam50, the central subunit of the sorting and assembly machinery that integrates outer membrane β-barrel proteins. Moreover, GB breaches the inner membrane through Tim22, the metabolite carrier translocase pore, in a mitochondrial heat-shock protein 70 (mtHsp70)-dependent manner. Granzyme A (GA) and caspase-3 use a similar route to the mitochondria. Finally, preventing GB from entering the mitochondria either by mutating lysine 243 and arginine 244 or depleting Sam50 renders cells more resistant to GB-mediated reactive oxygen species and cell death. Similarly, Sam50 depletion protects cells from GA-, GM- and caspase-3-mediated cell death. Therefore, cytotoxic molecules enter the mitochondria to induce efficiently cell death through a noncanonical Sam50-, Tim22- and mtHsp70-dependent import pathway.

Significant role for IRF3 in both T cell and APC effector functions during T cell responses

Interferon Regulatory Factor (IRF)3 is a crucial transcription factor during innate immune responses. Here we show IRF3 also has a role in adaptive T cell immune responses. Expression of IFN-γ, IL-17, and Granzyme B (GrB) during in vitro T cell responses was impaired when either dendritic cells (DCs) or T cells were derived from IRF3KO mice. Unexpectedly, IRF3-dependent NK-activating molecule (INAM), which is an NK cell activating factor of the DC innate immune response, was induced during the T cell response. Additionally, supernatants from responding T cells induced ISG54 in the RAW264.7 macrophage cell line in an IRF3 dependent manner. Moreover, addition of anti-IFN-γ prevented supernatant induction of ISG54 and recombinant IFN-γ stimulated ISG54 expression. Thus, IRF3 in APCs and T cells is required for optimal T-cell effector function and the ability of T cells to influence innate immune function of APCs.

Granzyme B-truncated VEGF fusion protein represses angiogenesis and tumor growth of OSCC

OBJECTIVE

To evaluate the antitumor effects of fusion protein hGrB-TV of human granzyme B (hGrB) and truncated vascular endothelial growth factor (tVEGF) on human oral squamous cell carcinoma (OSCC) in vitro and in vivo.

METHODS

The fusion protein hGrB-TV was expressed and purified from E. coli bacteria by affinity chromatography. The cytotoxcity of hGrB-TV on VEGFR-2 (Flk-1)(+) OSCC cells was analyzed in vitro. The antitumor therapeutic study was conducted on OSCC xenografts in vivo.

RESULTS

The purified hGrB-TV fusion protein was selectively internalized into VEGFR-2 (Flk-1)(+) OSCC cells and endothelial cells. It can cleave inactive caspase 3 into its active p20 form. The hGrB-TV showed dose-dependent cytotoxicity on VEGFR-2(+) SCC-9 cells. The morphological changes and cytolysis were appeared within dozen minutes. However, no cytotoxicity was observed on VEGFR-2(-) cells. The hGrB alone or tVEGF alone did not have any toxicity on SCC-9 cells. In addition, hGrB-TV treatment completely destroyed the vasculature of the chick chorioallantoic membrane (CAM) in vivo and consequently led to chick embryo development arrest. Most importantly, the fusion protein hGrB-TV inhibited tumor angiogenesis and growth of human OSCC xenografts in nude mice without any apparent toxicity.

CONCLUSIONS

The fusion protein hGrB-TV specifically inhibits angiogenesis and tumor growth of OSCC; hGrB-TV is a powerful and safe therapeutic molecule for tumor therapy.

Purification and characterization of a fish granzymeA involved in cell-mediated immunity

Granzymes are serine proteases involved in the induction of cell death against non-self cells. The enzymes differ in their primary substrate specificity and have one of four hydrolysis activities: tryptase, Asp-ase, Met-ase and chymase. Although granzyme genes have been isolated from several fishes, evidence for their involvement in cytotoxicity has not yet been reported. In the present study, we attempted to purify and characterize a fish granzyme involved in cytotoxicity using ginbuna crucian carp. The cytotoxicity of leukocytes was significantly inhibited by the serine protease inhibitor ''3, 4-dichloroisocoumarin''. In addition, we found that granzymeA-like activity (hydrolysis of Z-GPR-MCA) was inhibited by the same inhibitor and significantly enhanced by allo-antigen stimulation in vivo. Proteins from leukocyte extracts were subjected to two steps of chromatographic purification using benzamidine-Sepharose and SP-Sepharose. The molecular weight of the purified enzyme was estimated to be 26,900 Da by SDS-PAGE analysis. The purified enzyme displayed a Km of 220 μM, a Kcat of 21.7 sec(-1) and a Kcat/Km of 98,796 sec(-1) M(-1) with an optimal pH of 9.5 for the Z-GPR-MCA substrate. The protease was totally inhibited by serine protease inhibitors and showed granzymeA-like substrate specificity. Therefore, we conclude that the purified enzyme belongs to the mammalian granzymeA (EC 3.4.21.78) and appears to be involved in cytotoxicity in fish.

DNA binding activity of Ku during chemotherapeutic agent-induced early apoptosis

Ku protein is a heterodimer composed of two subunits, and is capable of both sequence-independent and sequence-specific DNA binding. The former mode of DNA binding plays a crucial role in DNA repair. The biological role of Ku protein during apoptosis remains unclear. Here, we show characterization of Ku protein during apoptosis. In order to study the DNA binding properties of Ku, we used two methods for the electrophoresis mobility shift assay (EMSA). One method, RI-EMSA, which is commonly used, employed radiolabeled DNA probes. The other method, WB-EMSA, employed unlabeled DNA followed by western blot and detection with anti-Ku antiserum. In this study, Ku-DNA probe binding activity was found to dramatically decrease upon etoposide treatment, when examined by the RI-EMSA method. In addition, pre-treatment with apoptotic cell extracts inhibited Ku-DNA probe binding activity in the non-treated cell extract. The inhibitory effect of the apoptotic cell extract was reduced by DNase I treatment. WB-EMSA showed that the Ku in the apoptotic cell extract bound to fragmented endogenous DNA. Interestingly, Ku in the apoptotic cell extract purified by the Resource Q column bound 15-bp DNA in both RI-EMSA and WB-EMSA, whereas Ku in unpurified apoptotic cell extracts did not bind additional DNA. These results suggest that Ku binds cleaved chromosomal DNA and/or nucleosomes in apoptotic cells. In conclusion, Ku is intact and retains DNA binding activity in early apoptotic cells.

Development of autoantibodies against muscle-specific FHL1 in severe inflammatory myopathies

Mutations of the gene encoding four-and-a-half LIM domain 1 (FHL1) are the causative factor of several X-linked hereditary myopathies that are collectively termed FHL1-related myopathies. These disorders are characterized by severe muscle dysfunction and damage. Here, we have shown that patients with idiopathic inflammatory myopathies (IIMs) develop autoimmunity to FHL1, which is a muscle-specific protein. Anti-FHL1 autoantibodies were detected in 25% of IIM patients, while patients with other autoimmune diseases or muscular dystrophies were largely anti-FHL1 negative. Anti-FHL1 reactivity was predictive for muscle atrophy, dysphagia, pronounced muscle fiber damage, and vasculitis. FHL1 showed an altered expression pattern, with focal accumulation in the muscle fibers of autoantibody-positive patients compared with a homogeneous expression in anti-FHL1-negative patients and healthy controls. We determined that FHL1 is a target of the cytotoxic protease granzyme B, indicating that the generation of FHL1 fragments may initiate FHL1 autoimmunity. Moreover, immunization of myositis-prone mice with FHL1 aggravated muscle weakness and increased mortality, suggesting a direct link between anti-FHL1 responses and muscle damage. Together, our findings provide evidence that FHL1 may be involved in the pathogenesis not only of genetic FHL1-related myopathies but also of autoimmune IIM. Importantly, these results indicate that anti-FHL1 autoantibodies in peripheral blood have promising potential as a biomarker to identify a subset of severe IIM.

Live cell evaluation of granzyme delivery and death receptor signaling in tumor cells targeted by human natural killer cells

Growing interest in natural killer (NK) cell-based therapy for treating human cancer has made it imperative to develop new tools to measure early events in cell death. We recently demonstrated that protease-cleavable luciferase biosensors detect granzyme B and pro-apoptotic caspase activation within minutes of target cell recognition by murine cytotoxic lymphocytes. Here we report successful adaptation of the biosensor technology to assess perforin-dependent and -independent induction of death pathways in tumor cells recognized by human NK cell lines and primary cells. Cell-cell signaling via both Fc receptors and NK-activating receptors led to measurable luciferase signal within 15 minutes. In addition to the previously described aspartase-cleavable biosensors, we report development of granzyme A and granzyme K biosensors, for which no other functional reporters are available. The strength of signaling for granzyme biosensors was dependent on perforin expression in IL-2-activated NK effectors. Perforin-independent induction of apoptotic caspases was mediated by death receptor ligation and was detectable after 45 minutes of conjugation. Evidence of both FasL and TRAIL-mediated signaling was seen after engagement of Jurkat cells by perforin-deficient human cytotoxic lymphocytes. Although K562 cells have been reported to be insensitive to TRAIL, robust activation of pro-apoptotic caspases by NK cell-derived TRAIL was detectable in K562 cells. These studies highlight the sensitivity of protease-cleaved luciferase biosensors to measure previously undetectable events in live cells in real time. Further development of caspase and granzyme biosensors will allow interrogation of additional features of granzyme activity in live cells including localization, timing, and specificity.

Functional expression cloning identifies COX-2 as a suppressor of antigen-specific cancer immunity

The efficacy of immune surveillance and antigen-specific cancer immunotherapy equally depends on the activation of a sustained immune response targeting cancer antigens and the susceptibility of cancer cells to immune effector mechanisms. Using functional expression cloning and T-cell receptor (TCR) transgenic mice, we have identified cyclooxygenase 2/prostaglandin-endoperoxide synthase 2 (COX-2) as resistance factor against the cytotoxicity induced by activated, antigen-specific T cells. Expressing COX-2, but not a catalytically inactive COX-2 mutant, increased the clonogenic survival of E1A-transformed murine cancer cells when cocultured with lymphocytes from St42Rag2^−/− mice harboring a transgenic TCR directed against an E1A epitope. COX-2 expressing tumors established in immune-deficient mice were less susceptible to adoptive immunotherapy with TCR transgenic lymphocytes in vivo. Also, immune surveillance of COX-2-positive tumor cells in TCR transgenic mice was less efficient. The growth of murine MC-GP tumors, which show high endogenous COX-2 expression, in immunocompetent mice was effectively suppressed by treatment with a selective COX-2 inhibitor, celecoxib. Mechanistically, COX-2 expression blunted the interferon-gamma release of antigen-specific T cells exposed to their respective cellular targets, and increased the expression of interleukin-4 and indoleamine 2,3-dioxygenase by tumor cells. Addition of interferon-gamma sensitized COX-2 expressing cancer cells to tumor suppression by antigen-specific T cells. In conclusion, COX-2, which is frequently induced in colorectal cancer, contributes to immune evasion and resistance to antigen-specific cancer immunotherapy by local suppression of T-cell effector functions.

Granzyme B-activated p53 interacts with Bcl-2 to promote cytotoxic lymphocyte-mediated apoptosis

Granzyme B (GzmB) plays a major role in CTLs and NK cell-mediated elimination of virus-infected cells and tumors. Human GzmB preferentially induces target cell apoptosis by cleaving the proapoptotic Bcl-2 family member Bid, which, together with Bax, induces mitochondrial outer membrane permeabilization. We previously showed that GzmB also induces a rapid accumulation of the tumor-suppressor protein p53 within target cells, which seems to be involved in GzmB-induced apoptosis. In this article, we show that GzmB-activated p53 accumulates on target cell mitochondria and interacts with Bcl-2. This interaction prevents Bcl-2 inhibitory effect on both Bax and GzmB-truncated Bid, and promotes GzmB-induced mitochondrial outer membrane permeabilization. Consequently, blocking p53-Bcl-2 interaction decreases GzmB-induced Bax activation, cytochrome c release from mitochondria, and subsequent effector caspases activation leading to a decreased sensitivity of target cells to both GzmB and CTL/NK-mediated cell death. Together, our results define p53 as a new important player in the GzmB apoptotic signaling pathway and in CTL/NK-induced apoptosis.