Granzyme B: pro-apoptotic, antiviral and antitumor functions

The root of many evils: indolent large granular lymphocyte leukaemia and associated disorders

Large granular lymphocytes (LGL) leukaemia can arise from either natural killer (NK) cells or cytotoxic T lymphocytes (CTL). The T-cell form of LGL leukaemia has significant overlap with other haematological disorders and autoimmune diseases. Here we provide an overview of LGL biology. We also focus discussion on the indolent LGL leukaemia related disorders and their causal relationships. We then discuss the potential relationships and distinctions between indolent LGL leukaemia and non-malignant clonal lymphocyte expansion that occur in otherwise healthy individuals, especially elder people.

Proteases in lymphocyte killer function: redundancy, polymorphism and questions remaining

Proteases of the serine and cysteine protease families are involved in many processes crucial to the lytic functions of cytotoxic T lymphocytes and natural killer cells. In this study we describe those functions and attempt to place them in the pathophysiological context of defence to pathogen invasion. In particular, we stress that the co-evolution of pathogens with the immune systems of higher organisms over evolutionary time has ensured that redundancy, flexibility and polymorphism of the proteases can be identified, both within the protease repertoire of a given species, and by comparing orthologous protease functions across species.

Variant of TYR and autoimmunity susceptibility loci in generalized vitiligo

BACKGROUND

Generalized vitiligo is an autoimmune disease characterized by melanocyte loss, which results in patchy depigmentation of skin and hair, and is associated with an elevated risk of other autoimmune diseases.

METHODS

To identify generalized vitiligo susceptibility loci, we conducted a genomewide association study. We genotyped 579,146 single-nucleotide polymorphisms (SNPs) in 1514 patients with generalized vitiligo who were of European-derived white (CEU) ancestry and compared the genotypes with publicly available control genotypes from 2813 CEU persons. We then tested 50 SNPs in two replication sets, one comprising 677 independent CEU patients and 1106 CEU controls and the other comprising 183 CEU simplex trios with generalized vitiligo and 332 CEU multiplex families.

RESULTS

We detected significant associations between generalized vitiligo and SNPs at several loci previously associated with other autoimmune diseases. These included genes encoding major-histocompatibility-complex class I molecules (P=9.05x10(-23)) and class II molecules (P=4.50x10(-34)), PTPN22 (P=1.31x10(-7)), LPP (P=1.01x10(-11)), IL2RA (P=2.78x10(-9)), UBASH3A (P=1.26x10(-9)), and C1QTNF6 (P=2.21x10(-16)). We also detected associations between generalized vitiligo and SNPs in two additional immune-related loci, RERE (P=7.07x10(-15)) and GZMB (P=3.44x10(-8)), and in a locus containing TYR (P=1.60x10(-18)), encoding tyrosinase.

CONCLUSIONS

We observed associations between generalized vitiligo and markers implicating multiple genes, some associated with other autoimmune diseases and one (TYR) that may mediate target-cell specificity and indicate a mutually exclusive relationship between susceptibility to vitiligo and susceptibility to melanoma.

Perforin: more than just a pore-forming protein

Cellular apoptosis induced by T cells is mainly mediated by two pathways. One, granule exocytosis utilizes perforin/granzymes. The other involves signaling through death receptors of the TNF-alpha R super-family, especially FasL. Perforin plays a central role in apoptosis induced by granzymes. However, the mechanisms of perforin-mediated cytotoxicity are still not elucidated completely. Perforin is not only a pore-forming protein, but also performs multiple biological functions or perforin performs one biological function (cytolysis), but has multiple biological implications in the cellular immune responses, including regulation of proliferation of CD8+ CTLs.

Reciprocal granzyme/perforin-mediated death of human regulatory and responder T cells is regulated by interleukin-2 (IL-2)

Human CD4(+)CD25(high)FOXP3(+) T regulatory cells (Treg) can suppress responder T cell (RC) functions by various mechanisms. In co-cultures of Treg and autologous activated RC, both cell subsets up-regulate the expression of granzymes and perforin, which might contribute to Treg-mediated suppression. Here, we investigate the sensitivity and resistance of Treg and RC to granzyme/perforin-mediated death. CD4(+)CD25(neg) RC were single cell-sorted from the peripheral blood of 25 cancer patients and 15 normal controls. These RC were carboxyfluorescein diacetate succinimidyl ester (CFSE) labeled and co-cultured with autologous CD4(+)CD25(high)FOXP3(+) Treg +/- 150 or +/-1,000 IU/mL of interleukin-2 (IL-2) to evaluate suppression of RC proliferation. In addition, survival of the cells co-cultured for 24 h and 5 days was measured using a flow-based cytotoxicity assay. Freshly isolated Treg and RC expressed granzyme A (GrA), granzyme B (GrB), and perforin. Percentages of positive cells were higher in cancer patients than controls (p < 0.01) and increased upon OKT3 and IL-2 stimulation. Treg, co-cultured with RC at 150 IU/mL of IL-2, no longer expressed cytotoxins and became susceptible to RC-mediated, granzyme/perforin-dependent death. However, in co-cultures with 1,000 IU/mL of IL-2, Treg became resistant to apoptosis and induced GrB-dependent, perforin-independent death of RC. When the GrB inhibitor I or GrB-specific and GrA-specific small inhibitory ribonucleic acids were used to block the granzyme pathway in Treg, RC death, and Treg-mediated suppression of RC, proliferation were significantly inhibited. Human CD4(+)CD25(high) Treg and CD4(+)CD25(neg) RC reciprocally regulate death/growth arrest by differentially utilizing the granzyme-perforin pathway depending on IL-2 concentrations.

Granzymes in cancer and immunity

Cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells are indispensable factors in the body's ongoing defence against viral infection and tumor development. CTL/NK cells recognize and kill infected or aberrant target cells by two major pathways: either through introduction of a battery of proteases - called granzymes - to the target cell cytosol, or through TNF superfamily-dependent killing. During granzyme-dependent killing, target cell death is quick and efficient and is mediated by multiple granzymes, acting via redundant cell death pathways. Although granzyme-mediated cell death has been intensively studied, recent work has also hinted at an alternative, proinflammatory role for these enzymes. Thus, in addition to their well-established role as intracellular effectors of target cell death, recent data suggest that granzymes may have an extracellular role in the propagation of immune signals. In this study, we discuss the role of granzymes as central factors in antitumor immunity, as well possible roles for these proteases as instigators of inflammation.

Caspase-dependent inhibition of mousepox replication by gzmB

Background

Ectromelia virus is a natural mouse pathogen, causing mousepox. The cytotoxic T (Tc) cell granule serine-protease, granzyme B, is important for its control, but the underlying mechanism is unknown. Using ex vivo virus immune Tc cells, we have previously shown that granzyme B is able to activate several independent pro-apoptotic pathways, including those mediated by Bid/Bak/Bax and caspases-3/-7, in target cells pulsed with Tc cell determinants.

Methods and Findings

Here we analysed the physiological relevance of those pro-apoptotic pathways in ectromelia infection, by incubating ectromelia-immune ex vivo Tc cells from granzyme A deficient (GzmB⁺ Tc cells) or granzyme A and granzyme B deficient (GzmA×B^−/− Tc cell) mice with ectromelia-infected target cells. We found that gzmB-induced apoptosis was totally blocked in ectromelia infected or peptide pulsed cells lacking caspases-3/-7. However ectromelia inhibited only partially apoptosis in cells deficient for Bid/Bak/Bax and not at all when both pathways were operative suggesting that the virus is able to interfere with apoptosis induced by gzmB in case not all pathways are activated. Importantly, inhibition of viral replication in vitro, as seen with wild type cells, was not affected by the lack of Bid/Bak/Bax but was significantly reduced in caspase-3/-7-deficient cells. Both caspase dependent processes were strictly dependent on gzmB, since Tc cells, lacking both gzms, neither induced apoptosis nor reduced viral titers.

Significance

Out findings present the first evidence on the biological importance of the independent gzmB-inducible pro-apoptotic pathways in a physiological relevant virus infection model.

Structural basis for proteolytic specificity of the human apoptosis-inducing granzyme M

Granzyme M (GzmM), a unique serine protease constitutively expressed in NK cells, is important for granule-mediated cytolysis and can induce rapid caspase-dependent apoptosis of tumor cells. However, few substrates of GzmM have been reported to date, and the mechanism by which this enzyme recognizes and hydrolyzes substrates is unknown. To provide structural insights into the proteolytic specificity of human GzmM (hGzmM), crystal structures of wild-type hGzmM, the inactive D86N-GzmM mutant with bound peptide substrate, and the complexes with a catalytic product and with a tetrapeptide chloromethylketone inhibitor were solved to 1.96 A, 2.30 A, 2.17 A and 2.70 A, respectively. Structure-based mutagenesis revealed that the N terminus and catalytic triad of hGzmM are most essential for proteolytic function. In particular, D86N-GzmM was found to be an ideal inactive enzyme for functional studies. Structural comparisons indicated a large conformational change of the L3 loop upon substrate binding, and suggest this loop mediates the substrate specificity of hGzmM. Based on the complex structure of GzmM with its catalytic product, a tetrapeptide chloromethylketone inhibitor was designed and found to specifically block the catalytic activity of hGzmM.

Hypoxia-inducible factors regulate tumorigenic capacity of glioma stem cells

Glioblastomas are lethal cancers characterized by florid angiogenesis promoted in part by glioma stem cells (GSCs). Because hypoxia regulates angiogenesis, we examined hypoxic responses in GSCs. We now demonstrate that hypoxia-inducible factor HIF2alpha and multiple HIF-regulated genes are preferentially expressed in GSCs in comparison to non-stem tumor cells and normal neural progenitors. In tumor specimens, HIF2alpha colocalizes with cancer stem cell markers. Targeting HIFs in GSCs inhibits self-renewal, proliferation, and survival in vitro, and attenuates tumor initiation potential of GSCs in vivo. Analysis of a molecular database reveals that HIF2A expression correlates with poor glioma patient survival. Our results demonstrate that GSCs differentially respond to hypoxia with distinct HIF induction patterns, and HIF2alpha might represent a promising target for antiglioblastoma therapies.

Immunohistochemical analysis of granzyme B in non-perforated appendicitis--short communication

The aim of the present study was to determine the expression ofgranzyme B in non-perforated appendicitis. Appendix biopsies were obtained from the patients with clinically diagnosed as acute appendicitis and subjects admitted for elective abdominal surgery. All biopsies from the patients were non-perforated and histologically divided into acute and non-acute appendicitis. Granzyme B expression was assessed immunohistochemically. The results showed that granzyme B expression in both acute and non-acute appendicitis was significantly lower than that in the control appendix tissues (P < 0.05). The expression of this cytotoxic protein in acute and non-acute appendicitis was comparable (P > 0.05). Therefore, the results of the present study suggest that reduced expression of granzyme B in non-perforated appendicitis may reflect low cytotoxic activities which may prevent tissue damage.

Distinct profiles of cytotoxic granules in memory CD8 T cells correlate with function, differentiation stage, and antigen exposure

Cytotoxic CD8 T cells exert their antiviral and antitumor activity primarily through the secretion of cytotoxic granules. Degranulation activity and cytotoxic granules (perforin plus granzymes) generally define CD8 T cells with cytotoxic function. In this study, we have investigated the expression of granzyme K (GrmK) in comparison to that of GrmA, GrmB, and perforin. The expression of the cytotoxic granules was assessed in virus-specific CD8 T cells specific to influenza virus, Epstein-Barr virus (EBV), cytomegalovirus (CMV), or human immunodeficiency virus type 1 (HIV-1). We observed a dichotomy between GrmK and perforin expression in virus-specific CD8 T cells. The profile in influenza virus-specific CD8 T cells was perforin(-) GrmB(-) GrmA(+/-) GrmK(+); in CMV-specific cells, it was perforin(+) GrmB(+) GrmA(+) GrmK(-/+); and in EBV- and HIV-1-specific cells, it was perforin(-/+) GrmB(+) GrmA(+) GrmK(+). On the basis of the delineation of memory and effector CD8 T cells with CD45RA and CD127, the GrmK(+) profile was associated with early-stage memory CD8 T-cell differentiation, the perforin(+) GrmB(+) GrmA(+) profile with advanced-stage differentiation, and the GrmB(+) GrmA(+) Grmk(+) profile with intermediate-stage differentiation. Furthermore, perforin and GrmB but not GrmA and GrmK correlated with cytotoxic activity. Finally, changes in antigen exposure in vitro and in vivo during primary HIV-1 infection and vaccination modulated cytotoxic granule profiles. These results advance our understanding of the relationship between distinct profiles of cytotoxic granules in memory CD8 T cells and function, differentiation stage, and antigen exposure.

Regulation of perforin lysis: implications for protein disulfide isomerase proteins

Perforin, a membrane-permeabilizing protein, is important to T cell cytotoxic action. Perforin has potential to damage the T cell in the endoplasmic reticulum (ER), is sequestered in granules, and later is exocytosed to kill cells. In the ER and after exocytosis, calcium and pH favor perforin activity. We found a novel perforin inhibitor associated with cytotoxic T cell granules and termed it Cytotoxic Regulatory Protein 2 (CxRP2). CxRP2 blocked lysis by granule extracts, recombinant perforin and T cells. Its effects lasted for hours. CxRP2 was calcium stable and refractory to inhibitors of granzyme and cathepsin proteases. Through mass spectrometric analysis of active 50-100 kDa proteins, we identified CxRP2 candidates. Protein disulfide isomerase A3 was the strongest candidate but was unavailable for testing; however, protein disulfide isomerase A1 had CxRP2 activity. Our results indicate that protein disulfide isomerases, in the ER or elsewhere, may protect T cells from their own perforin.

Intracellular versus extracellular granzyme B in immunity and disease: challenging the dogma

The cytotoxic granzyme B (GrB)/perforin pathway has been traditionally viewed as a primary mechanism that is used by cytotoxic lymphocytes to eliminate allogeneic, virally infected and/or transformed cells. Although originally proposed to have intracellular and extracellular functions, upon the discovery that perforin, in combination with GrB, could induce apoptosis, other potential functions for this protease were, for the most part, disregarded. As there are 5 granzymes in humans and 11 granzymes in mice, many studies used perforin knockout mice as an initial screen to evaluate the role of granzymes in disease. However, in recent years, emerging clinical and biochemical evidence has shown that the latter approach may have overlooked a critical perforin-independent, pathogenic role for these proteases in disease. This review focuses on GrB, the most characterized of the granzyme family, in disease. Long known to be a pro-apoptotic protease expressed by cytotoxic lymphocytes and natural killer cells, it is now accepted that GrB can be expressed in other cell types of immune and nonimmune origin. To the latter, an emerging immune-independent role for GrB has been forwarded due to recent discoveries that GrB may be expressed in nonimmune cells such as smooth muscle cells, keratinocytes, and chondrocytes in certain disease states. Given that GrB retains its activity in the blood, can cleave extracellular matrix, and its levels are often elevated in chronic inflammatory diseases, this protease may be an important contributor to certain pathologies. The implications of sustained elevations of intracellular and extracellular GrB in chronic vascular, dermatological, and neurological diseases, among others, are developing. This review examines, for the first time, the multiple roles of GrB in disease pathogenesis.

Attenuation of acute lung inflammation induced by cigarette smoke in CXCR3 knockout mice

BACKGROUND

CD8+ T cells may participate in cigarette smoke (CS) induced-lung inflammation in mice. CXCL10/IP-10 (IFNgamma-inducible protein 10) and CXCL9/Mig (monokine induced by IFN-gamma) are up-regulated in CS-induced lung injury and may attract T-cell recruitment to the lung. These chemokines together with CXCL11/ITAC (IFN-inducible T-cell alpha chemoattractant) are ligands for the chemokine receptor CXCR3 which is preferentially expressed chiefly in activated CD8+ T cells. The purpose of this investigation was to study the contribution of CXCR3 to acute lung inflammation induced by CS using CXCR3 knockout (KO) mice.

METHODS

Mice (n = 8 per group) were placed in a closed plastic box connected to a smoke generator and were exposed whole body to the tobacco smoke of five cigarettes four times a day for three days. Lung pathological changes, expression of inflammatory mediators in bronchoalveolar lavage (BAL) fluid and lungs at mRNA and protein levels, and lung infiltration of CD8+ T cells were compared between CXCR3-/- mice and wild type (WT) mice.

RESULTS

Compared with the WT littermates, CXCR3 KO mice showed less CS-induced lung inflammation as evidenced by less infiltration of inflammatory cells in airways and lung tissue, particularly fewer CD8+ T cells, lower levels of IFNgamma and CXCR3 ligands (particularly CXCL10).

CONCLUSION

Our findings show that CXCR3 is important in promoting CD8+ T cell recruitment and in initiating IFNgamma and CXCL10 release following CS exposure. CXCR3 may represent a promising therapeutic target for acute lung inflammation induced by CS.

Analysis of protein processing by N-terminal proteomics reveals novel species-specific substrate determinants of granzyme B orthologs

Using a targeted peptide-centric proteomics approach, we performed in vitro protease substrate profiling of the apoptotic serine protease granzyme B resulting in the delineation of more than 800 cleavage sites in 322 human and 282 mouse substrates, encompassing the known substrates Bid, caspase-7, lupus La protein, and fibrillarin. Triple SILAC (stable isotope labeling by amino acids in cell culture) further permitted intra-experimental evaluation of species-specific variations in substrate selection by the mouse or human granzyme B ortholog. For the first time granzyme B substrate specificities were directly mapped on a proteomic scale and revealed unknown cleavage specificities, uncharacterized extended specificity profiles, and macromolecular determinants in substrate selection that were confirmed by molecular modeling. We further tackled a substrate hunt in an in vivo setup of natural killer cell-mediated cell death confirming in vitro characterized granzyme B cleavages next to several other unique and hitherto unreported proteolytic events in target cells.

Differential proteome expression associated with urokinase plasminogen activator receptor (uPAR) suppression in malignant epithelial cancer

Dysregulation of the plasminogen activation cascade is a prototypic feature in many malignant epithelial cancers. Principally, this is thought to occur through activation of overexpressed urokinase plasminogen activator (uPA) concomitant with binding to its high specificity cell surface receptor urokinase plasminogen activator receptor (uPAR). Up-regulation of uPA and uPAR in cancer appears to potentiate the malignant phenotype, either (i) directly by triggering plasmin-mediated degradation or activation of uPA's or plasmin's proteolytic targets (e.g., extracellular matrix zymogen proteases or nascent growth factors) or indirectly by simultaneously altering a range of downstream functions including signal transduction pathways ( Romer, J. ; Nielsen, B. S. ; Ploug, M. The urokinase receptor as a potential target in cancer therapy Curr. Pharm. Des. 2004, 10 ( 19), 235976 ). Because many malignant epithelial cancers express high levels of uPAR, uPA or other components of the plasminogen activation cascade and because these are often associated with poor prognosis, characterizing how uPAR changes the downstream cellular "proteome" is fundamental to understanding any role in cancer. This study describes a carefully designed proteomic study of the effects of antisense uPAR suppression in a previously studied colon cancer cell line (HCT116). The study utilized replicate 2DE gels and two independent gel image analysis software packages to confidently identify 64 proteins whose expression levels changed (by > or =2 fold) coincident with a moderate ( approximately 40%) suppression of cell-surface uPAR. Not surprisingly, many of the altered proteins have previously been implicated in the regulation of tumor progression (e.g., p53 tumor suppressor protein and c-myc oncogene protein among many others). In addition, through a combination of proteomics and immunological methods, this study demonstrates that stathmin 1alpha, a cytoskeletal protein implicated in tumor progression, undergoes a basic isoelectric point shift (p I) following uPAR suppression, suggesting that post-translational modification of stathmin occur secondary to uPAR suppression. Overall, these results shed new light on the molecular mechanisms involved in uPAR signaling and how it may promulgate the malignant phenotype.

Imaging effector functions of human cytotoxic CD4+ T cells specific for Plasmodium falciparum circumsporozoite protein

Malaria vaccines, comprised of irradiated Plasmodium falciparum sporozoites or a synthetic peptide containing T and B cell epitopes of the circumsporozoite protein (CSP), elicit multifunctional cytotoxic and non-cytotoxic CD4(+) T cells in immunised volunteers. Both lytic and non-lytic CD4(+)T cell clones recognised a series of overlapping epitopes within a 'universal' T cell epitope EYLNKIQNSLSTEWSPCSVT of CSP (NF54 isolate) that was presented in the context of multiple DR molecules. Lytic activity directly correlated with T cell receptor (TCR) functional avidity as measured by stimulation indices and recognition of naturally occurring variant peptides. CD4(+) T cell-mediated cytotoxicity was contact-dependent and did not require de novo synthesis of cytotoxic mediators, suggesting a granule-mediated mechanism. Live cell imaging of the interaction of effector and target cells demonstrated that CD4(+) cytotoxic T cells recognise target cells with their leading edge, reorient their cytotoxic granules towards the zone of contact, and form a stable immunological synapse. CTL attacks induced chromatin condensation, nuclear fragmentation and formation of apoptotic bodies in target cells. Together, these findings suggest that CD4(+) CTLs trigger target cell apoptosis via classical perforin/granzyme-mediated cytotoxicity, similar to CD8(+) CTLs, and these multifunctional sporozoite- and peptide-induced CD4(+) T cells have the potential to play a direct role as effector cells in targeting the exoerythrocytic forms within the liver.

Death by a thousand cuts: granzyme pathways of programmed cell death

The granzymes are cell death-inducing enzymes, stored in the cytotoxic granules of cytotoxic T lymphocytes and natural killer cells, that are released during granule exocytosis when a specific virus-infected or transformed target cell is marked for elimination. Recent work suggests that this homologous family of serine esterases can activate at least three distinct pathways of cell death. This redundancy likely evolved to provide protection against pathogens and tumors with diverse strategies for evading cell death. This review discusses what is known about granzyme-mediated pathways of cell death as well as recent studies that implicate granzymes in immune regulation and extracellular proteolytic functions in inflammation.

Construction and preclinical characterization of Fc-mGITRL for the immunotherapy of cancer

PURPOSE

To provide proper costimulation required for effective cancer T-cell immunity, Fc-GITRL fusion proteins were generated for use in immunotherapy protocols.

EXPERIMENTAL DESIGN

Soluble fusion proteins consisting of the Fc fragment of immunoglobulin and the murine glucocorticoid-induced tumor necrosis factor-related receptor ligand (mGITRL) connected with different linkers were genetically engineered and tested for their potency in two BALB/c solid tumor models.

RESULTS

In vivo, construct #178-14 (-5aa, -linker) showed the best activity (>90% tumor reduction) at doses ranging from 5 to 25 microg and was found to be intact by gel electrophoresis. Similar doses used with construct #175-2 (-linker) produced good but not as high tumor regression. Construct #5-1 (+linker), which was found to be relatively unstable by SDS gel electrophoresis, produced <60% tumor regression and required a higher dose (100 microg) to produce optimal results. Survival curves showed that Fc-mGITRL treatment extended the life of 80% of tumor-bearing mice to >3 months compared with controls that died by day 40. T-cell depletion studies showed that CD8(+) T cells play a major role in Fc-mGITRL immunotherapy, and tumors removed from Fc-mGITRL- and DTA-1-treated mice showed a significant influx of granzyme B(+) lymphocytes compared with controls. Finally, T regulatory (Treg) cell assays showed that, unlike other Fc fusion proteins, all three Fc-mGITRL constructs profoundly suppressed Treg activity.

CONCLUSIONS

These studies suggest that a stable, intact Fc-mGITRL fusion protein can provide missing costimulation for the immunotherapy of solid tumors. In addition, Fc-mGITRL may alter Treg activity to enhance its effectiveness for tumor immunotherapy.

Interleukin-12 is necessary for the priming of CD4+ T cells required during the elicitation of HIV-1 gp120-specific cytotoxic T-lymphocyte function

The mechanism of the T-cell response and cytokine induction to restrict human immunodeficiency virus 1 (HIV-1) infection is not clear. During early infection, HIV-infected individuals have a high frequency of virus-specific cytotoxic T lymphocytes (CTLs) that effectively reduces the viral load. However, the CTLs are unable to clear the virus at later stages of infection, leading to disease progression. Dysregulation of cytokines like interleukin-12 (IL-12) and interferon-gamma (IFN-gamma) as a result of the interaction of HIV-1-specific T cells with antigen-presenting cells is one of the possible causes of CTL dysfunction. Secretion of IL-12 is reduced with the progression of HIV infection, correlating with impaired CTL function; however, the role of IL-12 in CTL regulation awaits elucidation. Here, we have studied the role of IL-12 in CTL dysfunction by using DNA immunization of wild-type (WT) and IL-12-deficient mice with HIV-1 gp120 complementary DNA. It was observed that the CTL response in IL-12-deficient mice was significantly less than that in WT mice. Our results further demonstrated that coimmunization with IL-12 vector restored the impaired CTL response in IL-12-deficient mice. However, immunization with IL-12 vector failed to rescue the CTL response in IFN-gamma deficient mice, suggesting that the CTL-promoting function of IL-12 is IFN-gamma-mediated. Our data suggest a phase-specific role of IL-12 in the CTL response, specifically in the priming of CD4+ T cells that provide help to CD8+ T cells. Our results also suggest that IL-12 is vital for the priming of antigen-specific T cells and plays an essential role in IFN-gamma induction in T cells.

Taming cancer by inducing immunity via dendritic cells

Immunotherapy seeks to mobilize a patient's immune system for therapeutic benefit. It can be passive, i.e. transfer of immune effector cells (T cells) or proteins (antibodies), or active, i.e. vaccination. In cancer, passive immunotherapy can lead to some objective clinical responses, thus demonstrating that the immune system can reject tumors. However, passive immunotherapy is not expected to yield long-lived memory T cells that might control tumor outgrowth. Active immunotherapy with dendritic cell (DC)-based vaccines has the potential to induce both tumor-specific effector and memory T cells. Early clinical trials testing vaccination with ex vivo-generated DCs pulsed with tumor antigens provide a proof-of-principle that therapeutic immunity can be elicited. Yet, there is a need to improve their efficacy. The next generation of DC vaccines is expected to generate large numbers of high-avidity effector CD8(+) T cells and to overcome regulatory T cells. Therapeutic vaccination protocols will combine improved ex vivo DC vaccines with therapies that offset the suppressive environment established by tumors.

Immunological aspects of axon injury in multiple sclerosis

The role of immune-mediated axonal injury in the induction of nonremitting functional deficits associated with multiple sclerosis is an area of active research that promises to substantially alter our understanding of the pathogenesis of this disease and modify or change our therapeutic focus. This review summarizes the current state of research regarding changes in axonal function during demyelination, provides evidence of axonal dysmorphia and degeneration associated with demyelination, and identifies the cellular and molecular effectors of immune-mediated axonal injury. Finally, a unifying hypothesis that links neuronal stress associated with demyelination-induced axonal dysfunction to immune recognition and immunopathology is provided in an effort to shape future experimentation.

Granzyme B production distinguishes recently activated CD8(+) memory cells from resting memory cells

For immune diagnostic purposes it would be critical to be able to distinguish between ongoing immune processes, such as active infections, and long-term immune memory, for example imprinted by infections that have been cleared a long time ago or by vaccinations. We tested the hypothesis that the secretion of granzyme B, as detected in ex vivo ELISPOT assays, permits this distinction. We studied EBV-, flu- and CMV-specific CD8(+) cells in healthy individuals, Vaccinia virus-reactive CD8(+) cells in the course of vaccination, and HIV-specific CD8(+) cells in HIV-infected individuals. Antigen-specific ex vivo GzB production was detected only transiently after Vaccinia immunization, and in HIV-infected individuals. Our data suggest that ex vivo ELISPOT measurements of granzyme B permit the identification of actively ongoing CD8(+) cell responses-a notion that is pertinent to the immune diagnostic of infections, transplantation, allergies, autoimmune diseases, tumors and vaccine development.

Granzyme H induces apoptosis of target tumor cells characterized by DNA fragmentation and Bid-dependent mitochondrial damage

Natural killer (NK) cells are the effectors of innate immunity to act as the first line of defense against viruses and tumors. Granzyme H (GzmH) is predicted to evolve from GzmB and constitutively expressed at a high level in human NK cells. It indicates GzmH plays a pivotal role in NK cell mediated cytolysis. However GzmH is defined as an orphan granzyme and its function has less been defined. Here we demonstrate GzmH can induce rapid apoptosis of target cells, which is dependent on caspase activation and mitochondrial damage. GzmH-induced death is characterized by phophatidylserine externalization, nuclear condensation, DNA fragmentation, caspase activation and cytochrome c release that are hallmarks of typical apoptosis. GzmH can directly cleave ICAD to unleash CAD for DNA fragmentation. Moreover, GzmH directly processes Bid to produce the active form tBid leading to cytochrome c release. Therefore, GzmH may play an essential role in caspase-dependent pathogen clearance in the innate immunity that may complement the proapoptotic function of GzmB in human NK cells.

Cloning of pig serine proteinase inhibitor 9 and its use in protecting against apoptosis

The activity of granzyme B, a main effector molecule of natural killer (NK) cells and cytotoxic T lymphocytes, is regulated by the intracellular serine proteinase inhibitor 9 (PI-9). Pig PI-9 was first cloned, and the sequences that encode pig PI-9, including the start codon and stop codon, were identified. The cDNA was inserted into the cloning site of pCXN2 (chicken beta actin promoter and cytomegalovirus enhancer), transfected into pig endothelial cells (PEC), and several stable PEC clones were established. An NK cell-mediated cytolysis test was next applied to the PEC clones, using YT cells (an NK-like cell line). The PEC transfectants with pig PI-9 had a significant inhibitory effect on NK cell-mediated PEC lysis. The overexpression of the anti-apoptotic molecule, pig PI-9, has the potential for use in protecting graft cells from human NK cells.

A study of T cell tolerance to the tumor-associated antigen MDM2: cytokines can restore antigen responsiveness, but not high avidity T cell function

Background

Most tumor-associated antigens (TAA) currently used for immunotherapy of cancer are also expressed in normal tissues, which may induce tolerance and impair T cell-mediated immunity. However, there is limited information about how physiological expression in normal tissues alters the function of TAA-specific T cells.

Methodology/Principal Findings

We used a T cell receptor transgenic model to study how MDM2 expression in normal tissues affects the function of T cells specific for this TAA that is found at high levels in many different types of tumors. We found that some MDM2-specific T cells escaped thymic deletion and persisted in the peripheral T cell pool. When stimulated with antigen, these T cells readily initiated cell division but failed to proliferate and expand, which was associated with a high rate of apoptosis. Both IL-2 and IL-15 efficiently rescued T cell survival and antigen-specific T cell proliferation, while IL-7 and IL-21 were ineffective. Antigen-stimulated T cells showed impaired expression of the effector molecules CD43, granzyme-B and IFN-γ, a defect that was completely restored when T cells were stimulated in the presence of IL-2. In contrast, IL-15 and IL-21 only restored the expression of CD43 and granzyme-B, but not IFN-γ production. Finally, peptide titration experiments with IL-2 rescued T cells indicated that they were of lower avidity than non-tolerant control T cells expressing the same TCR.

Conclusions/Significance

These data indicate that cytokines can rescue the antigen-specific proliferation and effector function of MDM2-specific T cells, although this does not lead to the recovery of high avidity T cell function. This study sheds light on possible limitations of immunotherapy approaches that target widely expressed TAA, such as MDM2.

Lung epithelial cell apoptosis during acute lung injury in infancy

CONTEXT

Apoptosis of lung epithelial cells is implicated in the pathogenesis of acute lung injury. Most research on this subject has focused on adults. Very little is known about a potential interaction of this process with lung development in children.

OBJECTIVE

To summarize the current literature on lung epithelial cell apoptosis and common causes of acute lung injury in infants and young children and to identify new areas of research.

DESIGN

A Medline-based literature search.

RESULTS AND CONCLUSIONS

Few studies have focused on lung epithelial cell apoptosis during common causes of acute lung injury in children. Nevertheless, the limited literature suggests that this may be an important mechanism during respiratory distress syndrome of infants and viral respiratory tract infection. Apoptosis is an essential process during lung development and maturation. Insufficient attention has been paid to potential consequences of this for the short- and long-term outcomes of acute lung injury.

The major human and mouse granzymes are structurally and functionally divergent

Approximately 2% of mammalian genes encode proteases. Comparative genomics reveals that those involved in immunity and reproduction show the most interspecies diversity and evidence of positive selection during evolution. This is particularly true of granzymes, the cytotoxic proteases of natural killer cells and CD8+ T cells. There are 5 granzyme genes in humans and 10 in mice, and it is suggested that granzymes evolve to meet species-specific immune challenge through gene duplication and more subtle alterations to substrate specificity. We show that mouse and human granzyme B have distinct structural and functional characteristics. Specifically, mouse granzyme B is 30 times less cytotoxic than human granzyme B and does not require Bid for killing but regains cytotoxicity on engineering of its active site cleft. We also show that mouse granzyme A is considerably more cytotoxic than human granzyme A. These results demonstrate that even "orthologous" granzymes have species-specific functions, having evolved in distinct environments that pose different challenges.

Perforin-mediated target-cell death and immune homeostasis

The granule exocytosis pathway of cytotoxic lymphocytes is crucial for immune surveillance and homeostasis. The trafficking of granule components, including the membrane-disruptive protein perforin, to the immunological synapse leads to the delivery of granule proteases (granzymes) into the target cell and its destruction through apoptosis. Several independent molecular abnormalities associated with defects of either granule trafficking or perforin function can cause cytotoxic lymphocyte dysfunction. In humans, inherited perforin mutations result in severe immune dysregulation that manifests as familial haemophagocytic lymphohistiocytosis. This Review describes recent progress in defining the structure, function, biochemistry and cell biology of perforin.

Infective, neoplastic, and homeostatic sequelae of the loss of perforin function in humans

Perforin, a pore-forming protein toxin synthesized and stored in the cytoplasmic vesicles of cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells, is secreted when these effector lymphocytes encounter virus-infected or neoplastic cells. Perforin is encoded by a single-copy gene and is critical for immune homeostasis and defense of the organism against intracellular sepsis. A complete deficiency of perforin expression in either mice or humans is associated with a syndrome of immune insufficiency and severely deregulated lymphoid homeostasis. Humans who inherit inactivating mutations of perforin or defects in various parts of the cellular machinery that delivers perforin to the target cell suffer from familial hemophagocytic lymphohistiocytosis (FHL), a fatal condition necessitating bone marrow transplantation, usually in infancy. In mice, a high incidence of spontaneous B cell lymphoma has also been noted as the animals age. Across human populations, a number of polymorphisms that result in measurable, but suboptimal CTL activity have been noted, and some of these predispose to attenuated FHL or susceptibility to infectious disease, but in many cases, to no discernible disease predisposition. This chapter discusses the significance of human perforin polymorphisms, particularly those associated with diseases other than FHL, and recent advances in our understanding of perforin biology and function.

Mouse and human granzyme B have distinct tetrapeptide specificities and abilities to recruit the bid pathway

Granzyme B is an important mediator of cytotoxic lymphocyte granule-induced death of target cells, accomplishing this through cleavage of Bid and cleavage and activation of caspases as well as direct cleavage of downstream substrates. Significant controversy exists regarding the primary pathways used by granzyme B to induce cell death, perhaps arising from the use of different protease/substrate combinations in different studies. The primary sequence of human, rat, and mouse granzymes B is well conserved, and the substrate specificity and crystal structure of the human and rat proteases are extremely similar. Although little is known about the substrate specificity of mouse granzyme B, recent studies suggest that it may differ significantly from the human protease. In these studies we show that the specificities of human and mouse granzymes B differ significantly. Human and mouse granzyme B cleave species-specific procaspase-3 more efficiently than the unmatched substrates. The distinct specificities of human and mouse granzyme B highlight a previously unappreciated requirement for Asp(192) in the acquisition of catalytic activity upon cleavage of procaspase-3 at Asp(175). Although human granzyme B efficiently cleaves human or mouse Bid, these substrates are highly resistant to cleavage by the mouse protease, strongly indicating that the Bid pathway is not a major primary mediator of the effects of mouse granzyme B. These studies provide important insights into the substrate specificity and function of the granzyme B pathway in different species and highlight that caution is essential when designing and interpreting experiments with different forms of granzyme B.

Natural killer cells in viral infection: more than just killers

Innate immunity was believed originally to serve simply as the first-line defense against infection and malignancy, with adaptive immunity imposing specificity and ensuring that appropriate responses are mounted against chronic or reoccurring challenges. In this model of immunity, innate and adaptive immune responses are sequential, essentially non-overlapping, and interactions between components of each response limited or non-existent. Over the last 5 years, it has become increasingly evident that interactions between elements of the innate and adaptive immune systems are common. Indeed, it is now clear that the generation and maintenance of effective immunity require an extensive array of interactions between multiple components of the immune system. This review discusses recent advances in this area with particular emphasis on the role of natural killer cells in shaping the adaptive immune response to viral infection.

Increased granzyme A expression in type II pneumocytes of patients with severe chronic obstructive pulmonary disease

RATIONALE

Chronic obstructive pulmonary disease (COPD) is associated with increased numbers of CD8(+) cytotoxic T lymphocytes (CTLs) in the lung, but the functional activity of CTLs remains unknown. Granzyme A (GrA) and B (GrB) are serine proteases considered to be important effector molecules of CTLs and natural killer cells.

OBJECTIVE

To investigate protein and mRNA expression of GrA and GrB in peripheral lung tissue from patients with COPD and control subjects with normal lung function.

METHODS

Paraffin-embedded sections of surgical lung specimens from 22 patients with COPD (FEV(1), 22% predicted; GOLD stage 4) and 15 control subjects (FEV(1), 108% predicted) were immunostained for GrA and GrB, and semiquantified on a 3-point scale. Messenger RNA expression in total lung, specific cell types enriched for by laser capture microdissection, and freshly isolated primary cells were determined by reverse transcriptase-polymerase chain reaction.

MEASUREMENTS AND MAIN RESULTS

GrA and GrB immunoreactivity was observed in CD8(+) CTLs and CD57(+) natural killer cells, but also in type II pneumocytes and alveolar macrophages in both groups. Bronchiolar epithelium stained positive for GrA, but negative for GrB. These observations were confirmed by reverse transcriptase-polymerase chain reaction on total lung, laser capture microdissection-enriched specific cell types and freshly isolated primary type II pneumocytes. The scores of GrA-expressing type II pneumocytes were significantly higher in patients with COPD versus control subjects.

CONCLUSIONS

GrA and GrB mRNA and protein are detectable in human lung tissue. GrA expression is increased in type II pneumocytes of patients with very severe COPD. These results indicate that GrA may be important in the development of COPD.

Enhancement of CD8 T-cell function through modifying surface glycoproteins in young and old mice

Previous work from our laboratory has shown that modifying cell surface glycosylation with either a Clostridium perfringens-derived sialidase (CP-Siase), or an O-linked glycoprotein endopeptidase (OSGE) can enhance the function of CD4 T cells from both young and old mice at multiple levels. Here we have re-assessed the effect of age on CD8 T-cell function, and examined the outcome of enzymatic treatment with CP-Siase and OSGE on its different aspects. Pre-treatment of CD8 T cells with either CP-Siase or OSGE led to a significant increase in anti-CD3-mediated Ca2+ response in both young and old mice. Pre-treated CD8 T cells from both age groups also displayed a significant increase in activation-induced CD69 and CD25 expression, and produced significantly higher amounts of interleukin-2 and interferon-gamma in comparison to their untreated counterparts. Furthermore, pretreatment with either enzyme enhanced granzyme B expression in CD8 T cells, and increased their cytolytic activity in vitro. These data support the notion that glycosylated surface proteins hinder CD8 T-cell activation and function in both young and old mice, and raise the possibility of significantly improving CD8 T cell function in older individuals through enzymatic alteration of surface glycoproteins.

Perforin and Granzymes Have Distinct Roles in Defensive Immunity and Immunopathology

Successful control of viral infection requires the host to eliminate the infecting pathogen without causing overt immunopathology. Here we showed that perforin (Prf1) and granzymes (Gzms) have distinct roles in defensive immunity and immunopathology in a well-established model of viral infection. Both Prf1 and Gzms drastically affected the outcome of murine cytomegalovirus (MCMV) infection. Viral titres increased markedly in both Prf1(-/-) and Gzma(-/-)Gzmb(-/-) mice, but Gzma(-/-)Gzmb(-/-) mice recovered and survived infection, whereas Prf1(-/-) mice did not. Indeed, infected Prf1-deficient hosts developed a fatal hemophagocytic lymphohistiocytosis (HLH)-like syndrome. This distinction in outcome depended on accumulation of mononuclear cells and T cells in infected Prf1(-/-) mice. Importantly, blocking experiments that clearly identified tumor necrosis factor-alpha (TNF-alpha) as the principal contributor to the lethality observed in infected Prf1(-/-) mice provided support for the clinical potential of such an approach in HLH patients whose disease is triggered by viral infection.

Proteolysis of HIP during apoptosis occurs within a region similar to the BID loop

BID is an essential component of many apoptotic pathways. Cytosolic proteases cleave BID within an extended loop region, generating an active truncated fragment which synergizes with BAX and BAK to induce release of apoptogenic factors from mitochondria. To determine whether other proteins are cleaved in a similar manner as BID, we performed a database search for proteins which possess sequence similarity with the BID loop region. One of the proteins identified was the Hsc70-interacting protein (HIP). We analyzed the cleavage pattern of HIP using two known activators of BID: granzyme B and caspase-8. In in vitro cleavage assays using recombinant proteins, human and rat HIP were cleaved by granzyme B. Furthermore, the granzyme B-mediated cleavage site was mapped to the BID loop-like region of HIP by site-directed mutagenesis. This region was also the target for caspase-8-mediated cleavage in rat HIP. However, human HIP was not proteolyzed by caspase-8, which probably reflects sequence differences between human and rat HIP proteins at the P(1)' position of the caspase-8 recognition sequence. To determine whether HIP is cleaved during apoptosis, human Jurkat T cells were exposed to granzyme B and perforin. The results of these studies suggest that granzyme B-mediated loss of HIP expression occurs in vivo, and in a coordinate fashion with loss of BID, pro-caspase-8 and pro-caspase-3. These data implicate the Hsp70 co-chaperone HIP in the proteolytic cascade of some apoptotic pathways.

Granzyme K cleaves the nucleosome assembly protein SET to induce single-stranded DNA nicks of target cells

Although granzymes (Gzms) A- and B-induced cell death pathways have been defined, little is known about how other orphan Gzms function in CTL-mediated cytotoxicity. GzmK and A are tryptases among all the Gzms of humans and they are closely linked on the same chromosome. In this study, we showed that GzmK can be efficiently delivered into target cells with a cationic lipid protein transfection reagent Pro-Ject. We found human GzmK triggers rapid cell death independently of caspase activation. The features of death are characterized by rapid externalization of phosphatidylserine, nuclear morphological changes and single-stranded DNA nicks. GzmK hydrolyzes the nucleosome assembly protein SET in its recombinant and native forms or in intact cells. Cleavage of SET by GzmK abrogates its nucleosome assembly activity. After GzmK loading, SET and DNase NM23H1 rapidly translocate into the nucleus and SET is cleaved, where the nuclease activity of NM23H1 is activated to nick chromosomal DNA.

Identification of {alpha}-tubulin as a granzyme B substrate during CTL-mediated apoptosis

Cytotoxic lymphocytes induce target cell apoptosis via two major pathways: Fas/FasL and granule exocytosis. The latter pathway has largely been defined by the roles of the pore-forming protein perforin and by the serine proteinases granzymes A and B. Upon entry into target cells, the granzymes cleave substrates that ultimately result in cell death. To gain further insight into granzyme B function, we have identified novel substrates. SDS-PAGE analysis of S100 cell lysates identified a 51 kDa protein that was cleaved by granzyme B. Mass spectrometry analysis revealed that this fragment was the microtubule protein, alpha-tubulin, which was confirmed by western blotting. In addition, two-dimensional gel analysis showed that the truncated form of alpha-tubulin had a more basic isoelectric point than the full-length molecule, suggesting that granzyme B removed the acidic C-terminus. Site-directed mutagenesis within this region of alpha-tubulin revealed the granzyme B recognition site, which is conserved in a subset of alpha-tubulin isoforms. Significantly, we showed that alpha-tubulin was cleaved in target cells undergoing apoptosis as induced by cytotoxic T lymphocytes. Therefore, in addition to its role in the activation of mitochondria during apoptosis, these results suggest a role for granzyme B in the dismantling of the cytoskeleton.

Granzyme M Directly Cleaves Inhibitor of Caspase-Activated DNase (CAD) to Unleash CAD Leading to DNA Fragmentation

Granzyme (Gzm)M is constitutively highly expressed in NK cells that may play a critical role in NK cell-mediated cytolysis. However, the function of GzmM has been less defined. Just one report showed GzmM induces a caspase-independent death pathway. In this study, we demonstrate a protein transfection reagent Pro-Ject can efficiently transport GzmM into target cells. GzmM initiates caspase-dependent apoptosis with typical apoptotic nuclear morphology. GzmM induces DNA fragmentation, not DNA nicking. GzmM can directly degrade inhibitor of caspase-activated DNase to release the nuclease activity of caspase-activated DNase for damaging DNA. Furthermore, GzmM cleaves the DNA damage sensor enzyme poly(ADP-ribose) polymerase to prevent cellular DNA repair and force apoptosis.