Viral IL-10-mediated immune regulation in pancreatic islet transplantation

Newer therapeutic approaches towards the management of diabetes mellitus: an update

Diabetes mellitus is a chronic metabolic condition characterized by an elevation of blood glucose levels, resulting from defects in insulin secretion, insulin action, or both. The prevalence of the disease has been rapidly rising all over the globe at an alarming rate. Despite advances in the management of diabetes mellitus, it remains a growing epidemic that has become a significant public health burden due to its high healthcare costs and its complications. There is no cure has yet been found for the disease, however, treatment modalities include insulin and antidiabetic agents along with lifestyle modifications are still the mainstay of therapy for diabetes mellitus. The treatment spectrum for the management of diabetes mellitus has rapidly developed in recent years, with new class of therapeutics and expanded indications. This article focused on the emerging therapeutic approaches other than the conventional pharmacological therapies, which include stem cell therapy, gene therapy, siRNA, nanotechnology and theranostics.

Adiponectin gene therapy prevents islet loss after transplantation

Significant pancreatic islet dysfunction and loss shortly after transplantation to the liver limit the widespread implementation of this procedure in the clinic. Nonimmune factors such as reactive oxygen species and inflammation have been considered as the primary driving force for graft failure. The adipokine adiponectin plays potent roles against inflammation and oxidative stress. Previous studies have demonstrated that systemic administration of adiponectin significantly prevented islet loss and enhanced islet function at post‐transplantation period. In vitro studies indicate that adiponectin protects islets from hypoxia/reoxygenation injury, oxidative stress as well as TNF‐α‐induced injury. By applying adenovirus mediated transfection, we now engineered islet cells to express exogenous adiponectin gene prior to islet transplantation. Adenovirus‐mediated adiponectin transfer to a syngeneic suboptimal islet graft transplanted under kidney capsule markedly prevented inflammation, preserved islet graft mass and improved islet transplant outcomes. These results suggest that adenovirus‐mediated adiponectin gene therapy would be a beneficial clinical engineering approach for islet preservation in islet transplantation.

Clustered regularly interspaced short palindromic repeats, a glimpse - impacts in molecular biology, trends and highlights

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) is a novel molecular tool. In recent days, it has been highlighted a lot, as the Nobel prize was awarded for this sector in 2020, and also for its recent use in Covid-19 related diagnostics. Otherwise, it is an eminent gene-editing technique applied in diverse medical zones of therapeutics in genetic diseases, hematological diseases, infectious diseases, etc., research related to molecular biology, cancer, hereditary diseases, immune and inflammatory diseases, etc., diagnostics related to infectious diseases like viral hemorrhagic fevers, Covid-19, etc. In this review, its discovery, working mechanisms, challenges while handling the technique, recent advancements, applications, alternatives have been discussed. It is a cheaper, faster technique revolutionizing the medicinal field right now. However, their off-target effects and difficulties in delivery into the desired cells make CRISPR, not easily utilizable. We conclude that further robust research in this field may promise many interesting, useful results.

Towards a Functional Cure for Diabetes Using Stem Cell-Derived Beta Cells: Are We There Yet?

Diabetes mellitus is a pandemic metabolic disorder that results from either the autoimmune destruction or the dysfunction of insulin-producing pancreatic beta cells. A promising cure is beta cell replacement through the transplantation of islets of Langerhans. However, donor shortage hinders the widespread implementation of this therapy. Human pluripotent stem cells, including embryonic stem cells and induced pluripotent stem cells, represent an attractive alternative beta cell source for transplantation. Although major advances over the past two decades have led to the generation of stem cell-derived beta-like cells that share many features with genuine beta cells, producing fully mature beta cells remains challenging. Here, we review the current status of beta cell differentiation protocols and highlight specific challenges that are associated with producing mature beta cells. We address the challenges and opportunities that are offered by monogenic forms of diabetes. Finally, we discuss the remaining hurdles for clinical application of stem cell-derived beta cells and the status of ongoing clinical trials.

Engineering designer beta cells with a CRISPR-Cas9 conjugation platform

Genetically fusing protein domains to Cas9 has yielded several transformative technologies; however, the genetic modifications are limited to natural polypeptide chains at the Cas9 termini, which excludes a diverse array of molecules useful for gene editing. Here, we report chemical modifications that allow site-specific and multiple-site conjugation of a wide assortment of molecules on both the termini and internal sites of Cas9, creating a platform for endowing Cas9 with diverse functions. Using this platform, Cas9 can be modified to more precisely incorporate exogenously supplied single-stranded oligonucleotide donor (ssODN) at the DNA break site. We demonstrate that the multiple-site conjugation of ssODN to Cas9 significantly increases the efficiency of precision genome editing, and such a platform is compatible with ssODNs of diverse lengths. By leveraging the conjugation platform, we successfully engineer INS-1E, a β-cell line, to repurpose the insulin secretion machinery, which enables the glucose-dependent secretion of protective immunomodulatory factor interleukin-10.

Cas9 fusions partners are often limited to natural polypeptide chains at the Cas9 termni. Here the authors present a platform for site-specific and multiple-site conjugation to both termini and internal sites of Cas9, and they apply this platform to efficiently engineer insulin-producing β cells.

Viral Vector Mediated Interleukin-10 Gene Transfer in Skin Allograft

BACKGROUND

Expression of genes with immunoregulatory capacity can potentially decrease rejection of allograft. According to recent studies, viral interleukin (IL)-10 can reduce immune response during allotransplantation and is one of the most promising methods for the prevention of rejection. Our study aimed to analyze the immunosuppressive potential of recombinant adenovirus-mediated rat IL-10 in rat skin allograft.

METHODS

We performed skin graft surgery 1 hour after infecting the donated skin with adenovirus-mediated rat IL-10. On day 7 postoperatively, the skin allografts were harvested, and acute rejection was graded histologically.

RESULTS

Viral IL-10 gene transfer into rat skin allografts improved graft survival and reduced acute rejections.

CONCLUSION

The results of our study suggest that the therapeutic potential of graft viral IL-10 gene transfer is an effective immunosuppressive method for preventing skin allograft rejection.

microRNA-7 upregulates death receptor 5 and primes resistant brain tumors to caspase-mediated apoptosis

Background

MicroRNAs (miRs) are known to play a pivotal role in tumorigenesis, controlling cell proliferation and apoptosis. In this study, we investigated the potential of miR-7 to prime resistant tumor cells to apoptosis in glioblastoma (GBM).

Methods

We created constitutive and regulatable miR-7 expression vectors and utilized pharmacological inhibition of caspases and genetic loss of function to study the effect of forced expression of miR-7 on death receptor (DR) pathways in a cohort of GBM with established resistance to tumor necrosis factor apoptosis inducing ligand (TRAIL) and in patient-derived primary GBM stem cell (GSC) lines. We engineered adeno-associated virus (AAV)-miR-7 and stem cell (SC) releasing secretable (S)-TRAIL and utilized real time in vivo imaging and neuropathology to understand the effect of the combined treatment of AAV-miR-7 and SC-S-TRAIL in vitro and in mouse models of GBM from TRAIL-resistant GSC.

Results

We show that expression of miR-7 in GBM cells results in downregulation of epidermal growth factor receptor and phosphorylated Akt and activation of nuclear factor-kappaB signaling. This leads to an upregulation of DR5, ultimately priming resistant GBM cells to DR-ligand, TRAIL-induced apoptotic cell death. In vivo, a single administration of AAV-miR-7 significantly decreases tumor volumes, upregulates DR5, and enables SC-delivered S-TRAIL to eradicate GBM xenografts generated from patient-derived TRAIL-resistant GSC, significantly improving survival of mice.

Conclusions

This study identifies the unique role of miR-7 in linking cell proliferation to death pathways that can be targeted simultaneously to effectively eliminate GBM, thus presenting a promising strategy for treating GBM.

Herpesviral capture of immunomodulatory host genes

Herpesviruses have acquired numerous genes from their hosts. Although these homologs are not essential for viral replication, they often have important immunomodulatory functions that ensure viral persistence in the host. Some of these viral molecules are called virokines as they mimic cellular cytokines of their host such as interleukin-10 (cIL-10). In recent years, many viral homologs of IL-10 (vIL-10s) have been discovered in the genome of members of the order Herpesvirales. For some, gene and protein structure as well as biological activity and potential use in the clinical context have been explored. Besides virokines, herpesviruses have also captured genes encoding membrane-bound host immunomodulatory proteins such as major histocompatibility complex (MHC) molecules. These viral MHC mimics also retain many of the functions of the cellular genes, in particular directly or indirectly modulating the activity of natural killer cells. The mechanisms underlying capture of cellular genes by large DNA viruses are still enigmatic. In this review, we provide an update of the advances in the field of herpesviral gene piracy and discuss possible scenarios that could explain how the gene transfer from host to viral genome was achieved.

Genetically engineered human islets protected from CD8-mediated autoimmune destruction in vivo

Islet transplantation is a promising therapy for type 1 diabetes, but graft function and survival are compromised by recurrent islet autoimmunity. Immunoprotection of islets will be required to improve clinical outcome. We engineered human β cells to express herpesvirus-encoded immune-evasion proteins, "immunevasins." The capacity of immunevasins to protect β cells from autoreactive T-cell killing was evaluated in vitro and in vivo in humanized mice. Lentiviral vectors were used for efficient genetic modification of primary human β cells without impairing their function. Using a novel β-cell-specific reporter gene assay, we show that autoreactive cytotoxic CD8(+) T-cell clones isolated from patients with recent onset diabetes selectively destroyed human β cells, and that coexpression of the human cytomegalovirus-encoded US2 protein and serine proteinase inhibitor 9 offers highly efficient protection in vitro. Moreover, coimplantation of these genetically modified pseudoislets with β-cell-specific cytotoxic T cells into immunodeficient mice achieves preserved human insulin production and C-peptide secretion. Collectively, our data provide proof of concept that human β cells can be efficiently genetically modified to provide protection from killing mediated by autoreactive T cells and retain their function in vitro and in vivo.

Adenovirus-mediated viral interleukin-10 gene transfer prevents concanavalin A-induced liver injury

BACKGROUND AND AIM

Liver injury is closely associated with immune inflammation. Lacking immunostimulatory functions, viral interleukin-10 (vIL-10), a cellular IL-10 homologue, has been an attractive molecule for immunomodulatory therapy. We aimed to reveal a protective effect of the gene transfer of an adenoviral vector encoding vIL-10 on liver injury induced by concanavalin A.

METHODS

C57BL/6J mice were intravenously injected with adenoviral vector encoding vIL-10 before concanavalin A challenge. Liver injury was assessed. Interferon-γ and interleukin-4 levels were measured by ELISA. The activation of splenic and hepatic immune cells was analysed using an MTT assay.

RESULTS

Adenoviral vector encoding vIL-10 pretreatment significantly decreased concanavalin A-mediated elevations in serum alanine aminotransaminase and aspartate aminotransaminase activity, and necrotic area in liver tissues. The protective effect of adenoviral vector encoding vIL-10 was attributed to its inhibition of T cell activation, and production of interferon-γ and interleukin-4 by the immune cells. Recombinant mouse IL-10, a high homologous cytokine to vIL-10, effectively downregulated interferon-γ and interleukin-4 release by hepatic mononuclear cells.

CONCLUSION

Adenovirus vector-mediated vIL-10 gene transfer can prevent concanavalin A-induced hepatic injury, minimise pro-inflammatory cytokine release, and inhibit the activation of T lymphocytes.

Gene and cell therapy based treatment strategies for inflammatory bowel diseases

Inflammatory bowel diseases (IBD) are a group of chronic inflammatory disorders most commonly affecting young adults. Currently available therapies can result in induction and maintenance of remission, but are not curative and have sometimes important side effects. Advances in basic research in IBD have provided new therapeutic opportunities to target the inflammatory process involved. Gene and cell therapy approaches are suitable to prevent inflammation in the gastrointestinal tract and show therefore potential in the treatment of IBD. In this review, we present the current progress in the field of both gene and cell therapy and future prospects in the context of IBD. Regarding gene therapy, we focus on viral vectors and their applications in preclinical models. The focus for cell therapy is on regulatory T lymphocytes and mesenchymal stromal cells, their potential for the treatment of IBD and the progress made in both preclinical models and clinical trials.

Effect of acyl chain length and unsaturation on physicochemical properties and transfection efficiency of N-acyl-substituted low-molecular-weight chitosan

The effects of acyl chain length and unsaturation on physicochemical characteristics and transfection efficiency of novel nanomicelles of N-acyl-substituted low-molecular-weight chitosan (N-acyl LMWC) were studied. After transfection optimization, 18-carbon chain length grafts were selected, and N-acyl LMWCs were prepared with increasing unsaturation (18:1-18:3 carbon acyl grafts). N-acyl LMWCs were characterized using infrared spectroscopy and elemental analysis. The effect of DNA addition on size and zeta potential of N-acyl LMWCs was determined by dynamic light scattering. N-acyl LMWC-plasmid DNA (pDNA) polyplex stability was confirmed using gel electrophoresis. Transfection efficiency of the derivative polymers was visualized in human embryonic kidney cells using a plasmid encoding green fluorescent protein by confocal fluorescence microscopy and was quantified using therapeutic plasmids encoding for interleukin-4 and interleukin-10. N-acyl LMWCs could form cationic nanomicelles with average hydrodynamic size between 73 and 132 nm. DNA addition to nanomicelles led to minimal increase in the size. N-acyl LMWC-pDNA polyplexes showed excellent stability on storage and could protect DNA from enzymatic degradation. The transfection efficiencies of N-acyl LMWCs with 18:1 and 18:2 grafts were comparable with FuGENE® HD but were approximately eightfold and 35-fold greater as compared with LMWC and naked DNA, respectively.

Genetic vaccination for re-establishing T-cell tolerance in type 1 diabetes

Type 1 diabetes (T1D) is a T-cell mediated autoimmune disease resulting in the destruction of the insulin-secreting β cells. Currently, there is no established clinical approach to effectively suppress long-term the diabetogenic response. Genetic-based vaccination offers a general strategy to reestablish β-cell specific tolerance within the T-cell compartment. The transfer of genes encoding β-cell autoantigens, anti-inflammatory cytokines and/or immunomodulatory proteins has proven to be effective at preventing and suppressing the diabetogenic response in animal models of T1D. The current review will discuss genetic approaches to prevent and treat T1D with an emphasis on plasmid DNA- and adeno-associated virus-based vaccines.

Autoantigens plus interleukin-10 suppress diabetes autoimmunity

BACKGROUND

Recombinant vaccinia virus (rVV) strains expressing the immunomodulatory cholera toxin B subunit (CTB) fused to the autoantigen glutamic acid decarboxylase (GAD) or the immunosuppressive cytokine interleukin-10 (IL-10) were independently able to generate only low levels of immune suppression of type 1 diabetes mellitus (T1DM). Here we suggest that a vaccinia virus (VV)-mediated combination of CTB::GAD fusion and IL-10 proteins promises a effective and durable immunotherapeutic strategy for T1DM.

METHODS

To explore this hypothesis, a CTB::GAD fusion gene was co-delivered with a gene encoding IL-10 by rVV infection (rVV-CTB::GAD + rVV-IL10) into 5-7-week-old non-obese diabetic (NOD) mice. The mice were assessed for vaccine protection against development of hyperglycemia from 12 to 64 weeks of age by assessment of pancreatic inflammation (insulitis) and splenocyte-secreted interferon-gamma and IL-10 cytokine levels.

RESULTS

By 36 weeks of age, from 54% to 80% of the mice in the negative control animal groups (either mock-infected or inoculated with unrelated plasmid or VV) had developed hyperglycemia. Similarly, no statistically significant improvement in protection against diabetes onset was achieved by inoculation with VV expressing CTB::GAD or IL-10 independently. Surprisingly, only 20% of mice co-inoculated with rVV-CTB::GAD + rVV-IL10 developed hyperglycemia by 28 weeks of age. Other treatment groups developed hyperglycemia by 32-36 weeks. After 36 weeks, diabetes incidence no longer increased in any groups until the end of experiment at 64 weeks of age. Histological analysis of pancreatic tissues of hyperglycemic mice revealed high levels of intra-islet insulitis. Analysis of insulitis at termination of the experiment showed that euglycemic mice co-inoculated with VV expressing CTB::GAD and IL-10 had more effectively reduced inflammation in comparison with the other groups.

CONCLUSIONS

A combinatorial vaccination strategy based on VV co-delivery of genes encoding the immunoenhanced autoantigen CTB::GAD and the anti-inflammatory cytokine IL-10 can maintain effective and durable euglycemia and immunological homeostasis in NOD mice with prediabetes.

Gene therapy in transplantation

Gene therapy is an exciting and novel technology that offers the prospect of improving transplant outcomes beyond those achievable with current clinical protocols. This review explores both the candidate genes and ways in which they have been deployed to overcome both immune and non-immune barriers to transplantation success in experimental models. Finally, the major obstacles to implementing gene therapy in the clinic are considered.

How not to be seen: immune-evasion strategies in gene therapy

The development of efficient and safe vectors for gene delivery paved the way for evolution of gene therapy as a new modality for treatment of various inherited disorders and for cancer. The current vectors, viral and non-viral, have their limitations. Innate and adaptive immune responses to vector particles and components may restrict the efficiency of gene transfer and the persistence of expression of the transgene. Results from preclinical studies in animals and more recently data from clinical studies have demonstrated the potential impact of the cellular and the humoral immune response on the therapeutic efficacy. Not only the vector components, but also the transgene products may induce an immune response that negatively affects the therapeutic efficacy. The induction of a cytotoxic T-cell response to transgene-encoded peptides, as well as the production of antibodies directed against secreted proteins have been reported in preclinical and clinical studies, and these may thwart those applications that require long-term expression. Here we will review some of the options to blunt the acquired immune responses to transgene-encoded polypeptides.

The status of gene vectors for the treatment of diabetes

Diabetes mellitus type 1 (DM1) represents one of the most obvious targets for successful treatment by gene transfer. The disease provides targets and methods for therapy that include suppression of autoimmunity, restoration of insulin responsiveness, functional replacement of pancreatic islets, and correction of vascular and nerve damage associated with prolonged hyperglycemia. The pathogenesis of DM1 is well understood and gene sequences are known that would support these various approaches for genetic intervention. However, a key limitation at present is the availability of efficient and reliable methods for delivery and sustained expression of the transferred DNA. Most genetic vectors are derived from viruses, and recent improvements in adenovirus-derived, lentivirus-derived, and adeno-associated virus-derived vectors suggest that these will have successful application to diabetes in the future.

Ex vivo gene transfer of viral interleukin-10 to BB rat islets: no protection after transplantation to diabetic BB rats

Allogeneic and autoimmune islet destruction limits the success of islet transplantation in autoimmune diabetic patients. This study was designed to investigate whether ex vivo gene transfer of viral interleukin-10 (vIL-10) protects BioBreeding (BB) rat islets from autoimmune destruction after transplantation into diabetic BB recipients. Islets were transduced with adenoviral constructs (Ad) expressing the enhanced green fluorescent protein (eGFP), α-1 antitrypsin (AAT) or vIL-10. Transduction efficiency was demonstrated by eGFP-positive cells and vIL-10 production. Islet function was determined in vitro by measuring insulin content and insulin secretion and in vivo by grafting AdvIL-10-transduced islets into syngeneic streptozotocin (SZ)-diabetic, congenic Lewis (LEW.1 W) rats. Finally, gene-modified BB rat islets were grafted into autoimmune diabetic BB rats. Ad-transduction efficiency of islets increased with virus titre and did not interfere with insulin content and insulin secretion. Ad-transduction did not induce Fas on islet cells. AdvIL-10-transduced LEW.1 W rat islets survived permanently in SZ-diabetic LEW.1 W rats. In diabetic BB rats AdvIL-10-transduced BB rat islets were rapidly destroyed. Prolongation of islet culture prior to transplantation improved the survival of gene-modified islets in BB rats. Several genes including those coding for chemokines and other peptides associated with inflammation were down-regulated in islets after prolonged culture, possibly contributing to improved islet graft function in vivo. Islets transduced ex vivo with vIL-10 are principally able to cure SZ-diabetic rats. Autoimmune islet destruction in diabetic BB rats is not prevented by ex vivo vIL-10 gene transfer to grafted islets. Graft survival in autoimmune diabetic rats may be enhanced by improvements in culture conditions prior to transplantation.

Suppression of hyperglycemia in NOD mice after inoculation with recombinant vaccinia viruses

In autoimmune (type 1) diabetes, autoreactive lymphocytes destroy pancreatic beta-cells responsible for insulin synthesis. To assess the feasibility of gene therapy for type 1 diabetes, recombinant vaccinia virus (rVV) vectors were constructed expressing pancreatic islet autoantigens proinsulin (INS) and a 55-kDa immunogenic peptide from glutamic acid decarboxylase (GAD), and the immunomodulatory cytokine interleukin (IL)-10. To augment the beneficial effects of recombinant virus therapy, the INS and GAD genes were fused to the C terminus of the cholera toxin B subunit (CTB). Five-week-old non-obese diabetic (NOD) mice were injected once with rVV. Humoral antibody immune responses and hyperglycemia in the infected mice were analyzed. Only 20% of the mice inoculated with rVV expressing the CTB::INS fusion protein developed hyperglycemia, in comparison to 70% of the mice in the uninoculated animal group. Islets from pancreatic tissues isolated from euglycemic mice from this animal group showed no sign of inflammatory lymphocyte invasion. Inoculation with rVV producing CTB::GAD or IL-10 was somewhat less effective in reducing diabetes. Humoral antibody isotypes of hyperglycemic and euglycemic mice from all treated groups possessed similar IgG1/IgG2c antibody titer ratios from 19 to 32 wk after virus inoculation. In comparison with uninoculated mice, 11-wk-old NOD mice injected with virus expressing CTB::INS were delayed in diabetes onset by more than 4 wk. The experimental results demonstrate the feasibility of using rVV expressing CTB::INS fusion protein to generate significant protection and therapy against type 1 diabetes onset and progression.

Quantitative micro positron emission tomography (PET) imaging for the in vivo determination of pancreatic islet graft survival

Islet transplantation is an attractive approach for treating type-1 diabetes, but there is a massive loss of transplanted islets. It is currently only possible to estimate islet mass indirectly, through measurement of circulating C-peptide and insulin levels. This type of estimation, however, is not sufficiently sensitive or reproducible for follow-up of individuals who have undergone islet transplantation. Here we show that islet graft survival could be assessed for 1 month in diabetic NOD mice using 9-(4-[(18)F]-fluoro-3-hydroxymethylbutyl)guanine ([(18)F]FHBG)-positron emission tomography (PET) technology, the PET signal reflecting insulin secretory capacity of transplanted islets. Expression of the gene encoding viral interleukin-10 (vIL-10), was measurable in real time with PET scanning. Additionally, we addressed the clinical potential of this approach by visualizing transplanted islets in the liver, the preferred clinical transplantation site. We conclude that quantitative in vivo PET imaging is a valid method for facilitating the development of protocols for prolonging islet survival, with the potential for tracking human transplants.

Cytoprotection of beta cells: rational gene transfer strategies

Gene transfer to pancreatic islets may prove useful in preventing islet cell destruction and prolonging islet graft survival after transplantation in patients with type 1 diabetes mellitus (T1DM). Potentially, a host of therapeutically relevant transgenes may be incorporated into an appropriate gene delivery vehicle and used for islet modification. An increasing understanding of the molecular pathogenesis of immune-mediated beta cell death has served to highlight molecules which have become suitable candidates for promoting islet cell survival in the face of oxidative stress. This review aims to give an overview of some conventional gene transfer strategies aimed at promoting islet cell survival in the face of cytokine onslaught. These strategies target three aspects of islet cell physiology: redox status and antioxidant defence, anti-apoptotic gene expression and mediators of cytokine signal transduction pathways.

Treatment of human disease by adeno-associated viral gene transfer

During the past decade, in vivo administration of viral gene transfer vectors for treatment of numerous human diseases has been brought from bench to bedside in the form of clinical trials, mostly aimed at establishing the safety of the protocol. In preclinical studies in animal models of human disease, adeno-associated viral (AAV) vectors have emerged as a favored gene transfer system for this approach. These vectors are derived from a replication-deficient, non-pathogenic parvovirus with a single-stranded DNA genome. Efficient gene transfer to numerous target cells and tissues has been described. AAV is particularly efficient in transduction of non-dividing cells, and the vector genome persists predominantly in episomal forms. Substantial correction, and in some instances complete cure, of genetic disease has been obtained in animal models of hemophilia, lysosomal storage disorders, retinal diseases, disorders of the central nervous system, and other diseases. Therapeutic expression often lasted for months to years. Treatments of genetic disorders, cancer, and other acquired diseases are summarized in this review. Vector development, results in animals, early clinical experience, as well as potential hurdles and challenges are discussed.