Identification of a DNA encapsidation sequence for human polyomavirus pseudovirion formation

Copy Number Heterogeneity of JC Virus Standards

Quantitative PCR is a diagnostic mainstay of clinical virology, and accurate quantitation of viral load among labs requires the use of international standards. However, the use of multiple passages of viral isolates to obtain sufficient material for international standards may result in genomic changes that complicate their use as quantitative standards. We performed next-generation sequencing to obtain single-nucleotide resolution and relative copy number of JC virus (JCV) clinical standards. Strikingly, the WHO international standard and the Exact v1/v2 prototype standards for JCV showed 8-fold and 4-fold variation in genomic coverage between different loci in the viral genome, respectively, due to large deletions in the large T antigen region. Intriguingly, several of the JCV standards sequenced in this study with large T antigen deletions were cultured in cell lines immortalized using simian virus 40 (SV40) T antigen, suggesting the possibility of transcomplementation in cell culture. Using a cutoff 5% allele fraction for junctional reads, 7 different rearrangements were present in the JC virus sequences present in the WHO standard across multiple library preparations and sequencing runs. Neither the copy number differences nor the rearrangements were observed in a clinical sample with a high copy number of JCV or a plasmid control. These results were also confirmed by the quantitative real-time PCR (qPCR), droplet digital PCR (ddPCR), and Sanger sequencing of multiple rearrangements. In summary, targeting different regions of the same international standard can result in up to an 8-fold difference in quantitation. We recommend the use of next-generation sequencing to validate standards in clinical virology.

Inhibition of human diffuse large B-cell lymphoma growth by JC polyomavirus-like particles delivering a suicide gene

Background

Diffuse large B-cell lymphoma (DLBCL) is one of the most common types of aggressive B-cell non-Hodgkin lymphoma. About one-third of patients are either refractory to the treatment or experience relapse afterwards, pointing to the necessity of developing other effective therapies for DLBCL. Human B-lymphocytes are susceptible to JC polyomavirus (JCPyV) infection, and JCPyV virus-like particles (VLPs) can effectively deliver exogenous genes to susceptible cells for expression, suggesting the feasibility of using JCPyV VLPs as gene therapy vectors for DLBCL.

Methods

The JCPyV VLPs packaged with a GFP reporter gene were used to infect human DLBCL cells for gene delivery assay. Furthermore, we packaged JCPyV VLPs with a suicide gene encoding thymidine kinase (TK) to inhibit the growth of DLBCL in vitro and in vivo.

Results

Here, we show that JCPyV VLPs effectively entered human germinal center B-cell-like (GCB-like) DLBCL and activated B-cell-like (ABC-like) DLBCL and expressed the packaged reporter gene in vitro. As measured by the MTT assay, treatment with tk-VLPs in combination with gancyclovir (GCV) reduced the viability of DLBCL cells by 60%. In the xenograft mouse model, injection of tk-VLPs through the tail vein in combination with GCV administration resulted in a potent 80% inhibition of DLBCL tumor nodule growth.

Conclusions

Our results demonstrate the effectiveness of JCPyV VLPs as gene therapy vectors for human DLBCL and provide a potential new strategy for the treatment of DLBCL.

Production and biomedical applications of virus-like particles derived from polyomaviruses

Virus-like particles (VLPs), aggregates of capsid proteins devoid of viral genetic material, show great promise in the fields of vaccine development and gene therapy. These particles spontaneously self-assemble after heterologous expression of viral structural proteins. This review will focus on the use of virus-like particles derived from polyomavirus capsid proteins. Since their first recombinant production 27 years ago these particles have been investigated for a myriad of biomedical applications. These virus-like particles are safe, easy to produce, can be loaded with a broad range of diverse cargoes and can be tailored for specific delivery or epitope presentation. We will highlight the structural characteristics of polyomavirus-derived VLPs and give an overview of their applications in diagnostics, vaccine development and gene delivery.

Efficient gene transfer using the human JC virus-like particle that inhibits human colon adenocarcinoma growth in a nude mouse model

The JC virus (JCV) may infect human oligodendrocytes and consequently cause progressive multifocal leukoencephalopathy (PML) in patients with immune deficiency. In addition, the virus has also been detected in other human tissues, including kidney, B lymphocytes, and gastrointestinal tissue. The recombinant major structural protein, VP1, of JCV is able to self-assemble to form a virus-like particle (VLP). It has been shown that the VLP is capable of packaging and delivering exogenous DNA into human cells for gene expression. However, gene transfer is not efficient when using in vitro DNA packaging methods with VLPs. In this study, a novel in vivo DNA packaging method using the JCV VLP was used to obtain high efficiency gene transfer. A reporter gene, the green fluorescence protein, and a suicide gene, the herpes simplex virus thymidine kinase (tk), were encapsidated into VLPs in Escherichia coli. The VLP was used to specifically target human colon carcinoma (COLO-320 HSR) cells in a nude mouse model. Intraperitoneal administration of ganciclovir in the tk-VLP-treated mice greatly reduced tumor volume. These findings suggest that it will be possible to develop the JCV VLP as a gene delivery vector for human colon cancer therapy in the future.

Inhibition of simian virus 40 large tumor antigen expression in human fetal glial cells by an antisense oligodeoxynucleotide delivered by the JC virus-like particle

Human JC virus (JCV) is a neurotropic virus, and the etiological agent of progressive multifocal leukoencephalopathy (PML), a fatal neurological disease. Because of its natural infection tropism, it is possible to use the JCV capsid as a gene-transducing vector for therapeutic purposes in neurological disorders. In the current study, a recombinant JCV virus-like particle (VLP) was generated and purified from yeast. VLP was able to accommodate and protect DNA molecules of up to approximately 2000 bp in length. VLP was able to package and deliver an antisense oligodeoxynucleotide (AS-ODN) against simian virus 40 (SV40) large tumor antigen (LT) into SV40-transformed human fetal glial (SVG) cells in order to inhibit expression of the oncoprotein. Subsequently, apoptosis of VLP-AS-ODN-treated cells was demonstrated after the blocking of LT expression. In addition, JCV VLP was able to deliver ODN into human astrocytoma, neuroblastoma, and glioblastoma cells with high efficiency. In vivo delivery of ODN into a human neuroblastoma tumor nodule by VLP was also demonstrated. These findings suggest that JCV VLP is a gene delivery vector with potential therapeutic use for human neurological disorders.

Analysis of DNA-binding activity of the JC virus minor capsid protein VP2

To investigate the DNA binding activity of the JC virus minor capsid protein, VP2, both wild-type and mutant VP2 were cloned and expressed in Escherichia coli. Southwestern blotting was employed for the DNA-binding assay. The results showed that VP2 was able to bind to DNA, except when either the last 13 or the last 29 amino acids were truncated. The results indicate that the DNA-binding domain of VP2 is located within the last 13 amino acids. Furthermore, we also demonstrated that Lys(332) and Lys(336) within the DNA-binding domain are crucial for DNA binding. The findings may provide further information for understanding the mechanism of virion assembly of the JC virus.

Analysis of minimal sequences on JC virus VP1 required for capsid assembly

Human JC virus (JCV) belongs to the family of Polyomaviridae. The viral capsid is composed of 72 capsomeres. Five VP1 molecules make up a capsomere structure. To investigate the minimal sequences on JCV VP1 polypeptide required for capsid assembly, the first 12 (Delta N12) and 19 (Delta N19) amino acids at the N-terminus and the last 16 (Delta C16), 17 (Delta C17), and 31 (Delta C31) amino acids at the C-terminus of VP1 were truncated and expressed in E. coli. The VP1 proteins of Delta N12 and Delta C16 were able to self-assemble into a virus-like particle similar to that of wild-type (WT) VP1. However, the mutant proteins of Delta N19, Delta C17, and Delta C31 formed a pentameric capsomere structure as demonstrated by a 10-50% sucrose gradient centrifugation and electron microscopy. These results suggest that the 12 amino-terminal and 16 carboxy-terminal amino acids of VP1 are dispensable for the formation of virus-like particles, and further truncation at either end of VP1 leads to the loss of this property.