Cloning and expression of the VP1 major capsid protein of diabetogenic encephalomyocarditis (EMC) virus and prevention of EMC virus-induced diabetes by immunization with the recombinant VP1 protein

Developing a vaccine for type 1 diabetes by targeting coxsackievirus B

INTRODUCTION

Virus infections have long been considered as a possible cause of type 1 diabetes (T1D). One virus group, enteroviruses (EVs), has been studied extensively, and clinical development of a vaccine against T1D-associated EV types has started.

AREAS COVERED

Epidemiological studies have indicated an association between EVs and T1D. These viruses have a strong tropism for insulin-producing β-cells; the destruction of these cells leads to T1D. The exact mechanisms by which EVs could cause T1D are not known, but direct infection of β-cells and virus-induced inflammation may play a role. Recent studies have narrowed down the epidemiological association to a subset of EVs: group B coxsackieviruses (CVBs). These findings have prompted efforts to develop vaccines against CVBs. Prototype CVB vaccines have prevented both infection and CVB-induced diabetes in mice. This review summarizes recent progress in the field and the specifics of what could constitute the first human vaccine developed for a chronic autoimmune disease.

EXPERT COMMENTARY

Manufacturing of a clinical CVB vaccine as well as preclinical studies are currently in progress in order to enable clinical testing of the first CVB vaccine. Ongoing scientific research projects can significantly facilitate this effort by providing insights into the mechanisms of the CVB-T1D association.

Developing a vaccine for Type 1 diabetes through targeting enteroviral infections

Type 1 diabetes (T1D) is a chronic disease caused by the destruction of insulin producing β-cells in the pancreas. Studies carried out during the past decades have implied that enteroviruses could be an important causative agent. These findings have generated efforts aiming at developing vaccines against these viruses and testing their efficacy against T1D in clinical trials. Extensive work has been carried out to define the serotype of enteroviruses which are linked to T1D and which should be included in the vaccine, and experimental vaccines have been shown to be effective and safe in mouse models. Large-scale studies are currently in progress to increase the confidence in the scientific concept of the enterovirus-diabetes association, paralleling the efforts aimed at starting the clinical development of the vaccine. This review summarizes recent progress in this field and the scenarios regarding this development process.

Protective immune response in mice vaccinated with a recombinant adenovirus containing capsid precursor polypeptide P1, nonstructural protein 2A and 3C protease genes (P12A3C) of encephalomyocarditis virus

Encephalomyocarditis virus (EMCV) infection can cause acute myocarditis and sudden death in pre-weaned piglets as well as severe reproductive failure in sows. In this study, two recombinant adenoviruses containing capsid precursor polypeptide P1 alone (Ad-P1) and P1 plus nonstructural protein 2A and 3C protease coding regions (Ad-P12A3C) of EMCV were respectively constructed using replication-defective human adenovirus serotype 5 as vector, and their antibody responses and protective efficacies against a lethal EMCV challenge were evaluated in mice. Both Ad-P1 and Ad-P12A3C were confirmed to be capable of expressing VP1 protein in BHK21 cells by immunoperoxidase monolayer assay (IPMA). The results showed that mice vaccinated once or twice with Ad-P1 and Ad-P12A3C generated specific antibody response against VP1 protein of EMCV. Although Ad-P1 induced higher antibody titers, virus-neutralizing antibody response was considerably less (p<0.05), compared to that of Ad-P12A3C. Upon challenging with a virulent EMCV strain, Ad-P12A3C elicited efficacious protection (100% for both vaccination once and twice) in the vaccinated mice; whereas the mice immunized with Ad-P1 showed a lower protection (12.5% for vaccination once and 75% for twice). Our work suggests that the recombinant adenovirus (Ad-P12A3C) containing the capsid precursor polypeptide coding region (P1) plus nonstructural protein 2A and 3C protease genes have an excellent potential to be used as a vaccine that can provide sufficient protective efficacy against EMCV infection in animals.

DNA vaccine-mediated immune responses in Coxsackie virus B3-infected mice

DNA immunizations with the major structural protein VP1 of Coxsackie virus B3 (CVB3) have been previously found to protect BALB/c mice from lethal challenge. Here we report that the other CVB3 capsid proteins, VP2, VP3, and VP4, were less effective at preventing CVB3-caused disease. The application of pCMV/VP1 as a vaccine caused decreased myocyte destruction, reduced viral load in the heart tissue, accelerated antibody induction, and an early cytokine expression in heart tissue. In summary, our results indicate that the induction of B cell and/or T cell memory in vaccinated mice prior to challenge is responsible for the protection observed.

Oral administration of branched chain amino acids improves virus-induced glucose intolerance in mice

We investigated the therapeutic effect of branched chain amino acids (BCAA) on mice with glucose intolerance induced by encephalomyocarditis virus (EMCV). Male DBA/2 mice were divided into three groups: treated with BCAA, (such as valine, leucine, and isoleucine), untreated, and control. BCAA-treated and -untreated groups were inoculated intraperitoneally with the NDK25 variant of EMCV at 200 plaque-forming units per mouse. The BCAA-treated group was administered orally 0.9 g/kg/day of each BCAA from the day after viral inoculation. The control group neither received virus inoculation nor was treated with BCAA. One week after inoculation, oral glucose tolerance tests (OGTT) were performed. After the glucose loading at 1.5 g/kg of body weight, blood glucose levels in the untreated group were 92.0+/-10.0 mg/dl at baseline, 224.6+/-10.9 mg/dl at 30 min, and 169.4+/-21.4 mg/dl at 60 min, which were significantly (P<0.05) higher than those in the control group (62. 7+/-3.6 mg/dl, 167.2+/-16.4, and 83.8+/-6.0 mg/dl, respectively). Blood glucose levels in the BCAA-treated group were 54.5+/-3.7 mg/dl at baseline, 145.2+/-8.7 mg/dl at 30 min, and 128.7+/-18.3 mg/dl at 60 min after the glucose loading, which were not significantly higher than those in the control group. Immunoreactive insulin levels at 30 min after the glucose loading were lower in the untreated group than in the control group at 1 week after virus inoculation. Histological investigations showed that the grade of insulitis in the pancreas of mice of the BCAA-treated group was lower than that of the mice of the untreated group. These results suggest that oral administration of BCAA is able to improve glucose intolerance induced by EMCV.

Gain or loss of diabetogenicity resulting from a single point mutation in recombinant encephalomyocarditis virus

Molecular pathogenic mechanisms for virus-induced disease have received considerable attention. Encephalomyocarditis (EMC) virus-induced diabetes in mice has been extensively studied to elucidate the cellular and molecular mechanisms involved in the development of this disease. In this study, we report for the first time that a single point mutation at nucleotide position 3155 or 3156 of the recombinant EMC viral genome, located on the major capsid protein VP1, which causes an amino acid change, results in the gain or loss of viral diabetogenicity. A G base at nucleotide position 3155 (alanine at amino acid position 776 of the EMC virus polyprotein [Ala776]; GCC) results in viral diabetogenicity, whereas the substitution of other bases at the same or next position results in a loss of viral diabetogenicity. This finding provides clear evidence that a point mutation at a critical site in a viral genome affects the ability of the virus to cause a cell-specific disease.

Autoimmunity and the highway to diabetes

Insulin-dependent diabetes mellitus (IDDM) is an immunopathological condition involving loss of beta cell function, but views of how this arises are confusing and contradictory. For example, studies with non-obese diabetic mice implicate abnormal cytokine production in disease pathogenesis, but give little insight into how this arises. Many genetic and environmental risk factors have been described, but no single factor predicts the development of disease. Moreover, the prevalence of auto-antibodies suggests an autoimmune aetiology, but no antigen is recognized by all individuals. As an aid to understanding how IDDM develops, this review considers the risk factors as distinct starting points on a journey, and reviews current literature in search of the point where the roads from each origin merge into a highway to diabetes.