Changing the surface of a virus shell fusion of an enzyme to polyoma VP1

Anticancer Activity of Reconstituted Ribonuclease S-Decorated Artificial Viral Capsid

Ribonuclease S (RNase S) is an enzyme that exhibits anticancer activity by degrading RNAs within cancer cells; however, the cellular uptake efficiency is low due to its small molecular size. Here we generated RNase S-decorated artificial viral capsids with a size of 70-170 nm by self-assembly of the β-annulus-S-peptide followed by reconstitution with S-protein at neutral pH. The RNase S-decorated artificial viral capsids are efficiently taken up by HepG2 cells and exhibit higher RNA degradation activity in cells compared with RNase S alone. Cell viability assays revealed that RNase S-decorated capsids have high anticancer activity comparable to that of standard anticancer drugs.

Construction of protein-functionalized virus-like particles of parvovirus B19

Decoration of virus-like particles (VLPs) expands the repertory of functions these particles can display. In the last years, VLPs have successfully been used as scaffolds to present different molecules, frequently through the specific reaction of chemical groups on the surface of the particles, or by protein engineering when the presentation of peptides or proteins is the primary goal. VLPs of parvovirus B19 (B19V), have been previously produced in vitro and its stability and ability to assemble into hybrid particles composed of wild-type and chimeric proteins evidenced their potential as research tools. Herein, we report the presentation of functional proteins on the surface of B19V VLPs, through the fusion of the gene coding for the heterologous protein within the gene coding for the structural protein VP2. Two model proteins were used for the construction of chimeras, a lipase from Bacillus pumilus (BplA) and the enhanced green fluorescent protein (EGFP). Both chimeras were folded and successfully assembled in vitro into VLPs. While the BplA chimera exhibited esterase activity, the chimera of EGFP showed no fluorescence. We replaced the EGFP by its fast-folding derivative "super folder GFP" (sfGFP) flanked by larger linkers to increase its movement freedom, which resulted in fluorescent protein able to assemble fluorescent VLPs. These results expand the toolbox for VLP decoration as well as for the construction of new nanobiomaterials.

Platform technologies for modern vaccine manufacturing

Improved understanding of antigenic components and their interaction with the immune system, as supported by computational tools, permits a sophisticated approach to modern vaccine design. Vaccine platforms provide an effective tool by which strategically designed peptide and protein antigens are modularized to enhance their immunogenicity. These modular vaccine platforms can overcome issues faced by traditional vaccine manufacturing and have the potential to generate safe vaccines, rapidly and at a low cost. This review introduces two promising platforms based on virus-like particle and liposome, and discusses the methodologies and challenges.

Synthetic biology design to display an 18 kDa rotavirus large antigen on a modular virus-like particle

Virus-like particles are an established class of commercial vaccine possessing excellent function and proven stability. Exciting developments made possible by modern tools of synthetic biology has stimulated emergence of modular VLPs, whereby parts of one pathogen are by design integrated into a less harmful VLP which has preferential physical and manufacturing character. This strategy allows the immunologically protective parts of a pathogen to be displayed on the most-suitable VLP. However, the field of modular VLP design is immature, and robust design principles are yet to emerge, particularly for larger antigenic structures. Here we use a combination of molecular dynamic simulation and experiment to reveal two key design principles for VLPs. First, the linkers connecting the integrated antigenic module with the VLP-forming protein must be well designed to ensure structural separation and independence. Second, the number of antigenic domains on the VLP surface must be sufficiently below the maximum such that a "steric barrier" to VLP formation cannot exist. This second principle leads to designs whereby co-expression of modular protein with unmodified VLP-forming protein can titrate down the amount of antigen on the surface of the VLP, to the point where assembly can proceed. In this work we elucidate these principles by displaying the 18.1 kDa VP8* domain from rotavirus on the murine polyomavirus VLP, and show functional presentation of the antigenic structure.

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.

Quantitative characterization of virus-like particles by asymmetrical flow field flow fractionation, electrospray differential mobility analysis, and transmission electron microscopy

Here we characterize virus-like particles (VLPs) by three very distinct, orthogonal, and quantitative techniques: electrospray differential mobility analysis (ES-DMA), asymmetric flow field-flow fractionation with multi-angle light scattering detection (AFFFF-MALS) and transmission electron microscopy (TEM). VLPs are biomolecular particles assembled from viral proteins with applications ranging from synthetic vaccines to vectors for delivery of gene and drug therapies. VLPs may have polydispersed, multimodal size distributions, where the size distribution can be altered by subtle changes in the production process. These three techniques detect subtle size differences in VLPs derived from the non-enveloped murine polyomavirus (MPV) following: (i) functionalization of the surface of VLPs with an influenza viral peptide fragment; (ii) packaging of foreign protein internally within the VLPs; and (iii) packaging of genomic DNA internally within the VLPs. These results demonstrate that ES-DMA and AFFFF-MALS are able to quantitatively determine VLP size distributions with greater rapidity and statistical significance than TEM, providing useful technologies for product development and process analytics.

Advanced antigen delivery of murine survivin: chimeric virus-like particles in cancer vaccine research

Success in cancer immunotherapy depends on the identification and efficient targeting of specific tumor-associated antigens. Two pivotal strategies to prime patients' immune system against malignant cells are tumor-specific adoptive T-cell therapy and tumor-specific vaccination. Here, we will focus on immunotherapeutic vaccination and discuss the advantages and disadvantages of different strategies to deliver tumor-specific T-cell epitopes. A particular focus will be put on virus-like particles (VLPs) as vehicle to deliver tumor-specific epitopes in the context of full-length proteins, as multi-epitope constructs or as individual tumor-associated T-cell epitopes. VLPs represent non-infectious and non-replicating antigen delivery systems devoid of any nucleic acid. They constitute innovative immunotherapeutic agents against cancer due to their superior, adjuvant-like antigenicity. We will present various tumor-associated antigens currently in different stages of development including survivin, as promising candidates for targeted tumor therapies.

Development of a vaccine marker technology: Display of B cell epitopes on the surface of recombinant polyomavirus-like pentamers and capsoids induces peptide-specific antibodies in piglets after vaccination

Highly immunogenic capsomers (pentamers) and virus-like particles (VLPs) were generated through insertion of foreign B cell epitopes into the surface-exposed loops of the VP1 protein of murine polyomavirus and via heterologous expression of the recombinant fusion proteins in E. coli. Usually, complex proteins like the keyhole limpet hemocyanin (KLH) act as standard carrier devices for the display of such immunogenic peptides after chemical linkage. Here, a comparative analysis revealed that antibody responses raised against the carrier entities, KLH or VP1 pentamers, did not significantly differ up to 18 weeks, demonstrating the highly immunogenic nature of VP1-based particulate structures. The carrier-specific antibody response was reproducibly detected in the meat juice after processing. More importantly, chimeric VP1 pentamers and VLPs carrying peptides of 12 and 14 amino acids in length, inserted into the BC2 loop, induced a strong and long-lasting humoral immune response against VP1 and the inserted foreign epitope. Remarkably, the epitope-specific antibody response was only moderately decreased when VP1 pentamers were used instead of VLPs. In conclusion, we identified polyomavirus VP1-based structures displaying surface-exposed immunodominant B cell epitopes as being an efficient carrier system for the induction of potent peptide-specific antibodies. The application of this approach in vaccine marker technology in livestock holding and the meat production chain is discussed.

Hamster polyomavirus-derived virus-like particles are able to transfer in vitro encapsidated plasmid DNA to mammalian cells

The authentic major capsid protein 1 (VP1) of hamster polyomavirus (HaPyV) consists of 384 amino acid (aa) residues (42 kDa). Expression from an additional in-frame initiation codon located upstream from the authentic VP1 open reading frame (at position -4) might result in the synthesis of a 388 aa-long, amino-terminally extended VP1 (aa -4 to aa 384; VP1(ext)). In a plasmid-mediated Drosophila Schneider (S2) cell expression system, both VP1 derivatives as well as a VP1(ext) variant with an amino acid exchange of the authentic Met1Gly (VP1(ext-M1)) were expressed to a similar high level. Although all three proteins were detected in nuclear as well as cytoplasmic fractions, formation of virus-like particles (VLPs) was observed exclusively in the nucleus as confirmed by negative staining electron microscopy. The use of a tryptophan promoter-driven Escherichia coli expression system resulted in the efficient synthesis of VP1 and VP1(ext) and formation of VLPs. In addition, establishment of an in vitro disassembly/reassembly system allowed the encapsidation of plasmid DNA into VLPs. Encapsidated DNA was found to be protected against the action of DNase I. Mammalian COS-7 and CHO cells were transfected with HaPyV-VP1-VLPs carrying a plasmid encoding enhanced green fluorescent protein (eGFP). In both cell lines eGFP expression was detected indicating successful transfer of the plasmid into the cells, though at a still low level. Cesium chloride gradient centrifugation allowed the separation of VLPs with encapsidated DNA from "empty" VLPs, which might be useful for further optimization of transfection. Therefore, heterologously expressed HaPyV-VP1 may represent a promising alternative carrier for foreign DNA in gene transfer applications.

Virus-like particles derived from major capsid protein VP1 of different polyomaviruses differ in their ability to induce maturation in human dendritic cells

As polyomavirus major capsid protein VP1-derived virus-like particles (VLPs) have been demonstrated to be highly immunogenic, we studied their interaction with human dendritic cells (hDCs). Exposure of hDCs to VLPs originating from murine (MPyV) or hamster polyomavirus (HaPyV) induced hDC maturation. In contrast, exposure of hDCs to VLPs derived from human polyomaviruses (BK and JC) and simian virus 40 (SV40) only marginally induced DC maturation. The hDCs stimulated by HaPyV- or MPyV-derived VLPs readily produced interleukin-12 and stimulated CD8-positive T-cell responses in vitro. The highest frequencies of activated T cells were again observed after pulsing with HaPyV- and MPyV-derived VLPs. Monocyte-derived hDCs both bound and internalized the various tested polyomavirus VP1-derived VLPs with different levels of efficiency, partially explaining their individual maturation potentials. In conclusion, our data suggest a high variability in uptake of polyomavirus-derived VLPs and potency to induce hDC maturation.

ImmunoTrack®: The novel antibody-based technology for tracing in animal health

This paper describes a novel antibody-based livestock movement control tool and method of meat allocation, both in livestock husbandry as well as during the meat-processing chain. Immuno Track fulfills diverse prerequisites and meets regulatory demands which are substantial for a successful monitoring technology: (i) the induction of long-lasting antibody responses detectable onsite throughout the whole mast period of pigs, (ii) a single immunization injection with protein derivatives is sufficient to evoke a strong epitope-specific antibody response, and (iii) the complete degradation of the protein markers after the antibody response has been triggered in meatproducing animals such as cattle or pigs. There are diverse fields of application for the Immuno-Track marker technology, such as in quality meat programs, as compliance markers for animal vaccines or as a tool for verification of origin. Combination of this monitoring technology with the husbandry and identification databases for cattle and pigs within the European Community will lead to greater transparency in meat production, thereby regaining consumers' trust in concomitant structures of the meat-producing industry.

Polyomavirus EGFP-pseudocapsids: Analysis of model particles for introduction of proteins and peptides into mammalian cells

A vector for preparation of mouse polyomavirus capsid-like particles for transfer of foreign peptides or proteins into cells was constructed. Model pseudocapsids carrying EGFP fused with the C-terminal part of the VP3 minor protein (EGFP-VLPs) have been prepared and analysed for their ability to be internalised and processed by mouse cells and to activate mouse and human dendritic cells (DC) in vitro. EGFP-VLPs entered mouse epithelial cells, fibroblasts and human and mouse DC efficiently and were processed by both, lysosomes and proteasomes. Surprisingly, they did not induce upregulation of DC co-stimulation molecules or maturation markers in vitro; however, they did induce interleukin 12 secretion.

Virus-like particles: models for assembly studies and foreign epitope carriers

Virus‐like particles (VLPs), formed by the structural elements of viruses, have received considerable attention over the past two decades. The number of reports on newly obtained VLPs has grown proportionally with the systems developed for the expression of these particles. The chapter outlines the recent achievements in two important fields of research brought about by the availability of VLPs produced in a foreign host. These are: (1) The requirements for VLP assembly and (2) the use of VLPs as carriers for foreign epitopes. VLP technology is a rapidly advancing domain of molecular and structural biology. Extensive progress in VLP studies was achieved as the insect cell based protein production system was developed. This baculovirus expression system has many advantages for the synthesis of viral structural proteins resulting in the formation of VLPs. It allows production of large amounts of correctly folded proteins while also providing cell membranes that can serve as structural elements for enveloped viruses. These features give us the opportunity to gain insights into the interactions and requirements accompanying VLP formation that are similar to the assembly events occurring in mammalian cells. Other encouraging elements are the ability to easily scale up the system and the simplicity of purification of the assembled VLPs. The growing number of VLPs carrying foreign protein fragments on their surface and studies on the successful assembly of these chimeric molecules is a promising avenue towards the development of a new technology, in which the newly designed VLPs will be directed to particular mammalian cell types by exposing specific binding domains. The progress made in modeling the surface of VLPs makes them to date the best candidates for the design of delivery systems that can efficiently reach their targets.

Segments of Puumala Hantavirus Nucleocapsid Protein Inserted into Chimeric Polyomavirus-Derived Virus-Like Particles Induce a Strong Immune Response in Mice

Insertion of a short-sized epitope at four different sites of yeast-expressed hamster polyomavirus major capsid protein VP1 has been found to result in the formation of chimeric virus-like particles. Here, we demonstrate that the insertion of 45 or 120 amino acid-long segments from the N-terminus of Puumala hantavirus nucleocapsid protein into sites 1 (amino acids 80-89) and 4 (amino acids 288-295) of VP1 allowed the highly efficient formation of virus-like particles. In contrast, expression level and assembly capacity of fusions to sites 2 (amino acids 222-225) and 3 (amino acids 243-247) were drastically reduced. Immunization of BALB/c mice with chimeric virus-like particles induced a high-titered antibody response against the hantavirus nucleocapsid protein, even in the absence of any adjuvant. The strongest response was observed in mice immunized with virus-like particles harboring 120 amino acids of hantavirus nucleocapsid protein. According to the immunoglobulin subclass distribution of nucleocapsid protein-specific antibodies a mixed Th1/Th2 response was detected. The VP1 carrier itself also induced a mixed Th1/Th2 response, which was found to be reduced in mice immunized with virus-like particles harboring 120 amino acid-long inserts. In conclusion, hamster polyomavirus VP1 represents a promising carrier moiety for future vaccine development.

Formation of polyomavirus-like particles with different VP1 molecules that bind the urokinase plasminogen activator receptor

Icosahedral virus-like particles formed by the self-assembly of polyomavirus capsid proteins (Py-VLPs) can serve as useful nanostructures for delivering nucleic acids, proteins, and pharmaceuticals into animal cells and tissues. Four predominant surface-exposed loops in the VP1 structure offer potential sites to display sequences that might contribute new targeting specificities. Introduction into each of these loops of sequences derived from the amino-terminal fragment of urokinase plasminogen activator (uPA) or a related phage display peptide reduced the solubility of VP1 molecules when expressed in insect cells, and insertions into the EF loop reduced VP1 solubility least. Coexpression in insect cells of the uPA-VP1 molecules and VP1 containing a FLAG epitope in the HI loop permitted the formation of heterotypic Py-VLPs containing uPA-VP1 and FLAG-VP1. These heterotypic VLPs bound to uPAR on the surfaces of animal cells. Heterotypic Py-VLPs containing ligands for multiple cell surface receptors should be useful for targeting specific cells and tissues.

Chimeric bacteriophage fr virus-like particles harboring the immunodominant C-terminal region of hamster polyomavirus VP1 induce a strong VP1-specific antibody response in rabbits and mice

The late region of the hamster polyomavirus (HaPyV, former HaPV) genome encodes three structural proteins VP1, VP2, and VP3, where VP1 represents the major capsid protein of 384 amino acids. Screening of sera from HaPyV-infected papilloma-bearing and papilloma-free hamsters demonstrated the immunodominant features of all three capsid proteins. For both groups of hamsters in the C-terminal region of VP1 immunodominant B-cell epitopes were identified in the regions between amino acids 305 and 351 and amino acids 351 and 384. The high flexibility of the C-terminal region of VP1 was confirmed by the formation of chimeric virus-like particles based on the coat protein of the RNA bacteriophage fr which was previously found to tolerate only very short-sized foreign insertions. Phage fr coat protein-derived virus-like particles tolerated the N-terminal fusion of amino acids 333-384, 351-384, 351-374, and 364-384, respectively, of VP1. The induction of VP1-specific antibodies in rabbits and mice by immunization with chimeric virus-like particles harboring amino acids 333-384, 351-384, and 364-384, respectively, of VP1 suggested the immunodominant nature of the C-terminal region of VP1.

Cell-type specific targeting and gene expression using a variant of polyoma VP1 virus-like particles

The variant VP1-Z of the polyomavirus coat protein VP1 has been recently described as an engineered fusion protein of VP1 and the antibody binding domain protein Z. This construct is able to specifically bind and functionally present antibodies on the surface of virus-like particles of VP1-Z. Here we demonstrate that with the binding of Herceptin, an antibody directed against the receptor tyrosine kinase ErbB2, a cell type-specific targeting was established. ErbB2-positive cell lines were transduced with different plasmids encoding eGFP or beta-galactosidase. With both reporter systems functional gene expression in transduced cells could be observed. The transduction was strictly dependent on the use of a ternary complex formed of VLPs of VP1-Z, Herceptin, and the reporter plasmid DNA. The use of single components or ErbB2-negative cell lines did not result in functional gene transfer. The transduction was also completely dependent on the use of chloroquine, a lysosomotropic reagent. This indicates that the complex is internalized by ErbB2-mediated endocytosis.

Assessment of cell type specific gene transfer of polyoma virus like particles presenting a tumor specific antibody Fv fragment

Application of delivery systems in cancer therapy is restricted as a result of the lack of cell specificity of the respective vectors. Recently, a vector system based on virus-like particles (VLPs) of modified polyoma-VP1 was described which were able to bind specifically a tumor-specific antibody fragment, thus directing the vector system towards tumor cells. The functional gene transfer using the VP1 variant VP1-E8C, coupled with the antibody fragment of the tumor-specific antibody B3 is described in this paper. The specific targeting of the antigen expressing cells was highly efficient as determined by fluorescence microscopy. However, only a low percentage of these cells showed a functional gene transfer. This discrepancy could be accounted for by a rather low capacity of the virus like particles to transport DNA and the mechanism of their internalization by the target cells, which led to a lysosomal degradation of the particles. These limitations could be surmounted partially in cell culture experiments, and the principles suitable for applying this vector system in vivo are discussed.

Binding of external ligands onto an engineered virus capsid

The development of novel delivery systems for therapeutic substances includes targeting of the carriers to a specific site or tissue within the body of the recipient. This can be accomplished by appropriate receptor-binding domains and requires linking of these domains to the carrier. We have used recombinantly expressed polyomavirus-like particles as a model system and inserted the sequence of a WW domain into different surface loops of the viral capsid protein VP1. In one variant, the WW domain maintained its highly selective binding properties of proline-rich ligands and showed an increased affinity but also an accelerated association/dissociation equilibrium compared to the isolated WW domain, thus allowing a short-term coupling of external ligands onto the surface of the virus-like particles.

Conjugation of an antibody Fv fragment to a virus coat protein: cell-specific targeting of recombinant polyoma-virus-like particles

The development of cell-type-specific delivery systems is highly desirable for gene-therapeutic applications. Current virus-based vector systems show broad cell specificity, which results in the need to restrict the natural tropism of these viral systems. Here we demonstrate that tumour-cell-specific virus-like particles can be functionally assembled in vitro from recombinant viral coat protein expressed in Escherichia coli. The insertion of a negatively charged peptide in the HI loop of polyoma VP1 interferes with the binding of VP1 to the natural recognition site on mammalian cells and also serves as an adapter for the coupling of antibody fragments that contain complementary charged fusion peptides. A recombinant antibody fragment of the tumour-specific anti-(Lewis Y) antibody B3 could be coupled to the mutant VP1 by engineered polyionic peptides and an additional disulphide bond. With this system an entirely recombinant cell-specific delivery system assembled in vitro could be generated that transfers genes preferentially to cells presenting the tumour-specific antigen on the cell surface.

Coupling of antibodies via protein Z on modified polyoma virus-like particles

Therapeutic application of virus-based delivery systems often implies a change of the tropism of these vectors. This can be achieved by insertion of polypeptides (e.g., antibody fragments) in viral coat proteins. Such fusion proteins have only been used in viral vectors so far and, as part of a virus, they have not been available for a detailed biophysical characterization. We analyzed a fusion protein called VP1-Z, which is based on the polyoma virus coat protein VP1 and protein Z. Protein Z is an engineered antibody-binding domain derived from protein A from Staphylococcus aureus. The fusion VP1-Z was constructed by insertion of protein Z in the HI-loop of VP1. As wild-type VP1, VP1-Z formed pentameric capsomers and assembled to VLPs in vitro. The stability of these particles was very similar compared to that of VLPs of wild-type VP1. Protein Z was fully structured in the fusion protein and was still capable of binding antibodies on the surface of VLPs of VP1-Z. Using this fusion protein, we could change the tropism of polyoma VLPs toward cells presenting on their surface the antigen of the coupled antibody.

Formation of immunogenic virus-like particles by inserting epitopes into surface-exposed regions of hamster polyomavirus major capsid protein

We generated highly immunogenic virus-like particles that are based on the capsid protein VP1 of the hamster polyomavirus (HaPV-VP1) and harbor inserted foreign epitopes. The HaPV-VP1 regions spanning amino acids 81-88 (position 1), 222/223 (2), 244-246 (3), and 289-294 (4) were predicted to be surface exposed. An epitope of the pre-S1 region of the hepatitis B virus (designated S1; amino acid sequence DPAFR) was introduced into the predicted positions of VP1. All VP1/S1 fusion proteins were expressed in yeast and generated virus-like particles. Immunoassays using the S1-specific monoclonal antibody MA18/7 and immunization of C57Bl6 mice with different VP1/S1 constructs showed a pronounced reactivity and a strong S1-specific antibody response for particles carrying the insert in position 1, 2, 1+2, and 1+3. Our results suggest that HaPV-VP1 represents a highly flexible carrier moiety for the insertion of foreign sequences offering a broad range of potential uses, especially in vaccine development.