Use of herpes simplex virus type 1-based amplicon vector for delivery of small interfering RNA

Silencing of gene expression by small interfering RNAs (siRNAs) is rapidly becoming a powerful tool for genetic analysis of mammalian cells. The use of DNA-based plasmid vectors to achieve transient and stable expression of siRNA has been developed to avoid the problems of double-stranded oligonucleotides transfection. These vectors direct the transcription of small hairpin RNAs (shRNAs) from a polymerase-III (H1 or U6)-RNA gene promoter. However, numerous disadvantages remain, including low transfection efficiency and difficulty in transfecting primary cells. To overcome some of these problems, the use of viral vectors for siRNA delivery has been described. Retroviral, adenoviral, adeno-associated and herpes viral shRNAs delivery systems have been successfully used to silence genes, in vitro and in vivo. The use of a herpes simplex virus type 1 (HSV-1)-based amplicon vector for siRNA delivery into mammalian cells, using human polyomavirus BK (BKV)-transformed cells as a model system is described. The results demonstrate the ability of amplicon vectors to inhibit the expression of BKV T-Ag and tumorigenicity of BKV-transformed cells. We show that the use of the amplicon vector is highly efficient for the delivery of siRNA molecules. The unique ability of these vectors to deliver multiple copies of siRNA may provide a useful tool in the development of novel anticancer therapy.

Characterization of herpes simplex virus type 1 recombinants that express and incorporate high levels of HCV E2-gC chimeric proteins

We report the construction of two HSV-1 recombinants encoding chimeric forms of the E2 glycoprotein of HCV-1a composed of the ectodomain of E2 (aa384-611 or 384-711) fused to different parts of the transmembrane and cytoplasmic domain of the HSV-1 gC glycoprotein (gC). The parental HSV-1, known as KgBpK(-)gC(-), is deleted for gC and the main heparan sulphate (HS) binding domain of gB, and it exhibits impaired binding (ca. 80%) to HS compared to the wild type virus KOS [Laquerre, S., Argnani, R., Anderson, D.B., Zucchini, S., Manservigi, R., Glorioso, J.C., 1998. Heparan sulphate proteoglycan binding by herpes simplex virus type 1 glycoproteins B and C, which differ in their contributions to virus attachment, penetration, and cell-to-cell spread. J. Virol. 72, 6119-6130]. We show that gC:E2 proteins are efficiently expressed and transported to the cell surface. We also demonstrate that HSV-1 can incorporate both gC:E2 chimeric proteins into particles and show that incorporation of both chimeric molecules in the viral envelope partially restored binding (ca. 20%) of the HSV-1 recombinants to heparan sulphate. Finally, we showed that the gC:E2ScaI chimeric glycoprotein was able to bind a recombinant form of hCD81 and virion-expressed gC:E2ScaI permitted the binding of the HSV-1 recombinant virus to the hCD81 molecule.

Cationic liposomes as potential carriers for ocular administration of peptides with anti-herpetic activity

In the present study the preparation, characterization and activity of cationic liposomes containing the secretory form of herpes simplex virus type 1 (HSV-1) glycoprotein B (gB1s) or two related polylysine rich peptides, namely DTK1 and DTK2, were described. The immunotherapeutic potential of these HSV antigens containing liposomes was examined with a rabbit ocular model of HSV-1 infection. Our study indicates that the liposomes (i) are able to encapsulate quantitatively gB1s and around 30% the DTK peptides, (ii) are characterized by dimensions compatible with ocular applications and (iii) can release the peptide comparably to the free solution. In addition, neutralization studies demonstrated that an anti-DTK specific polyclonal antiserum can inhibit HSV-1 infection, indicating that such peptides could be a good immunogen/antigen in an anti-HSV vaccine formulation. Although the vaccination protocol did not induce protection against the eye disease, a significative protection against a lethal ocular challenge was detectable together with the absence of reactivation episodes from latency on the survived animals. In this respect, the use of cationic liposomes coupled to gB1s and DTK peptides, as a local ocular vaccine, could represent an interesting approach in order to obtain a possible efficacy in protecting animals against a subsequent HSV-1 ocular challenge.

Replication-competent herpes simplex vectors: design and applications

Replication-competent vectors are derived from attenuated viruses whose genes, that are nonessential for replication in cultured cells in vitro, are either mutated or deleted. The removal of one or more nonessential genes may reduce pathogenicity without requiring a cell line to complement growth. Herpes simplex viruses (HSV) are potential vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous systems, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases, and targeted infection to specific tissues or organs. This review highlights the progress in creating attenuated genetically engineered HSV vectors.

Effects of defective herpes simplex vectors expressing neurotrophic factors on the proliferation and differentiation of nervous cells in vivo

Neurotrophic factors (NTFs) are known to govern the processes involved in central nervous system cell proliferation and differentiation. Thus, they represent very attractive candidates for use in the study and therapy of neurological disorders. We constructed recombinant herpesvirus-based-vectors capable of expressing fibroblast growth factor-2 (FGF-2) and ciliary neurotrophic factor (CNTF) alone or in combinations. In vitro, vectors expressing FGF-2 and CNTF together, but not those expressing either NTF alone, caused proliferation of O-2A progenitors. Furthermore, based on double-labeling experiments performed using markers for neurons (MAP-2), oligodendrocytes (CNPase) and astrocytes (GFAP), most of the new cells were identified as astrocytes, but many expressed neuronal or oligodendrocytic markers. In vivo, vectors have been injected in the rat hippocampus. At 1 month after inoculation, a highly significant increase in BrdU-positive cells was observed in the dentate gyrus of animals injected with the vector expressing FGF-2 and CNTF together, but not in those injected with vectors expressing the single NTFs. Furthermore, double-labeling experiments confirmed in vitro data, that is, most of the new cells identified as astrocytes, some as neurons or oligodendrocytes. These data show the feasibility of the vector approach to induce proliferation and differentiation of neurons and/or oligodendrocytes in vivo.

Mice genetic immunization with plasmid DNA encoding a secreted form of HSV-1 gB induces a protective immune response against herpes simplex virus type 1 infection

Intramuscularly (i.m.) delivered plasmid DNA encoding a secreted form of glycoprotein B of herpes simplex virus type 1 (HSV-1 gB1s) was evaluated for the ability to elicit a protective immune response in Balb/c mice. Animals received three i.m. injections of a gB1s expression plasmid (pRP-RSV-gB1s) or of a wild-type transmembrane gB1 coding plasmid (pRP-RSV-gB1), while control mice were injected with the vector alone (pRP-RSV). A specific antibody response was observed in almost all immunized animals, and in most cases antibodies were also detected after 1 month in the absence of further vaccine boosts. Serum antibodies mostly displayed neutralizing activity against HSV-1. Glycoprotein B1s DNA immunization was also effective in protecting animals against the primary infection induced by a subsequent HSV-1 challenge and limited HSV-1 infection of sensitive ganglia.

Local and systemic inoculation of DNA or protein gB1s-based vaccines induce a protective immunity against rabbit ocular HSV-1 infection

A secreted form of gB1 (gB1s), previously shown to protect rabbits against HSV-1 ocular infection when inoculated systemically, was delivered to rabbit periocular area to evaluate its vaccine efficacy upon local administration. The efficacy of local or systemic inoculation of a gB1s-DNA-based vaccine in the rabbit model of ocular HSV-1 infection was assessed in parallel flow. Rabbits received four inoculations of the different immunogens, then immune responses and clinical symptoms were evaluated. Both the local protein and the systemic DNA administration elicited a neutralizing antibody response, reduced ocular symptoms with respect to controls (P<0.01), and completely prevented the death of rabbits from encephalitis. Conversely, local DNA vaccination did not induce any detectable antibody response, and could only partially protect rabbits from the development of encephalitis and severe ocular infection.

Replication-defective herpes simplex virus vectors for neurotrophic factor gene transfer in vitro and in vivo

We report here the construction and the use of two replication-defective herpes simplex virus vectors, SH FGF-2 and TH FGF-2, which efficiently transfer and express the cDNA for fibroblast-growth-factor-2 (FGF-2) in vitro and in vivo. One mutant was deleted in the immediate-early gene encoding ICP4; the other was deleted in ICP4, ICP22 and ICP27. FGF-2--or the control gene lacZ--were inserted in tk, under control of the human cytomegalovirus immediate-early promoter. Infection of Vero cells with SH FGF-2 induced a dramatic increase in FGF-2 protein levels in the first 2 days after infection, with a rapid return to baseline levels within day 4. In contrast, infection of Vero cells with TH FGF-2 displayed FGF-2 levels progressively increasing up to days 4-5, and slowly returning to baseline. Protein extracts of cells infected with TH FGF-2 induced neuronal differentiation of PC12 cells, indicating that the newly synthesized FGF-2 was biologically active. Robust transient transgene expression was also observed in the rat hippocampus after stereotaxical inoculation of TH FGF-2, but not of TH lacZ or of SH vectors. Enhanced gene expression both in vitro and in vivo by the triple immediate-early gene deletion mutant might be attributed to reduced vector cytotoxicity. The present data suggest that TH FGF-2 is suitable for studies of FGF-2 involvement in neurological disorders.

Heparan sulfate proteoglycan binding by herpes simplex virus type 1 glycoproteins B and C, which differ in their contributions to virus attachment, penetration, and cell-to-cell spread

Herpes simplex virus type 1 (HSV-1) mutants defective for envelope glycoprotein C (gC) and gB are highly impaired in the ability to attach to cell surface heparan sulfate (HS) moieties of proteoglycans, the initial virus receptor. Here we report studies aimed at defining the HS binding element of HSV-1 (strain KOS) gB and determining whether this structure is functionally independent of gB's role in extracellular virus penetration or intercellular virus spread. A mutant form of gB deleted for a putative HS binding lysine-rich (pK) sequence (residues 68 to 76) was transiently expressed in Vero cells and shown to be processed normally, leading to exposure on the cell surface. Solubilized gBpK- also had substantially lower affinity for heparin-acrylic beads than did wild-type gB, confirming that the HS binding domain had been inactivated. The gBpK- gene was used to rescue a KOS gB null mutant virus to produce the replication-competent mutant KgBpK-. Compared with wild-type virus, KgBpK- showed reduced binding to mouse L cells (ca. 20%), while a gC null mutant virus in which the gC coding sequence was replaced by the lacZ gene (KCZ) was substantially more impaired (ca. 65%-reduced binding), indicating that the contribution of gC to HS binding was greater than that of gB. The effect of combining both mutations into a single virus (KgBpK-gC-) was additive (ca. 80%-reduced binding to HS) and displayed a binding activity similar to that observed for KOS virus attachment to sog9 cells, a glycosaminoglycan-deficient L-cell line. Cell-adsorbed individual and double HS mutant viruses exhibited a lower rate of virus entry following attachment, suggesting that HS binding plays a role in the process of virus penetration. Moreover, the KgBpK- mutant virus produced small plaques on Vero cells in the presence of neutralizing antibody where plaque formation depended on cell-to-cell virus spread. These studies permitted the following conclusions: (i) the pK sequence is not essential for gB processing or function in virus infection, (ii) the lysine-rich sequence of gB is responsible for HS binding, and (iii) binding to HS is cooperatively linked to the process of efficient virus entry and lateral spread but is not absolutely required for virus infectivity.

Herpes simplex virus type 1 glycoprotein B requires a cysteine residue at position 633 for folding, processing, and incorporation into mature infectious virus particles

Herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) resides in the virus envelope in an oligomeric form and plays an essential role in virus entry into susceptible host cells. The oligomerizing domain is a movable element consisting of amino acids 626 to 653 in the gB external domain. This domain contains a single cysteine residue at position 633 (Cys-633) that is predicted to form an intramolecular disulfide bridge with Cys-596. In this study, we examined gB oligomerization, processing, and incorporation into mature virus during infection by two mutant viruses in which either the gB Cys-633 [KgB(C633S)] or both Cys-633 and Cys-596 [KgB(C596S/C633S)] residues were mutated to serine. The result of immunofluorescence studies and analyses of released virus particles showed that the mutant gB molecules were not transported to the cell surface or incorporated into mature virus envelopes and thus infectious virus was not produced. Immunoprecipitation studies revealed that the mutant gB molecules were in an oligomeric configuration and that these mutants produced hetero-oligomers with a truncated form of gB consisting of residues 1 to 43 and 595 to 904, the latter containing the oligomerization domain. Pulse-chase experiments in combination with endoglycosidase H treatment determined that the mutant molecules were improperly processed, having been retained in the endoplasmic reticulum (ER). Coimmunoprecipitation experiments revealed that the cysteine mutations resulted in gB misfolding and retention by the molecular chaperones calnexin, calreticulin, and Grp78 in the ER. The altered conformation of the gB mutant glycoproteins was directly detected by a reduction in monoclonal antibody recognition of two previously defined distinct antigenic sites located within residues 381 to 441 and 595 to 737. The misfolded molecules were not transported to the cell surface as hetero-oligomers with wild-type gB, suggesting that the conformational change could not be corrected by intermolecular interactions with the wild-type molecule. Together, these experiments confirmed that a disulfide bridge involving Cys-633 and Cys-596 is not essential for oligomerization but rather is required for proper folding and maintenance of a gB domain essential to complete posttranslational modification, transport, and incorporation into mature virus particles.

Red blood cells as delivery system for recombinant HSV-1 glycoprotein B: immunogenicity and protection in mice

The immunotherapeutic potential of autologous red blood cells (RBC) coupled to the secretory form of herpes simplex virus type 1 (HSV-1) glycoprotein B (gB1s) was examined with a mouse model of HSV-1 infection. C57BL/6 mice were immunized intraperitoneally with gB1s (0.05 microgram per dose) linked to RBC, or mixed with Freund's complete or bound to AlPO4 adjuvants (0.5 microgram per dose). Mice immunized with RBC coupled gB1s were protected against lethal and latent HSV-1 infection, and developed an anti-HSV antibody response, as measured by ELISA and HSV-1 neutralization assays, similar or higher than that elicited by the same antigen in Freund's complete adjuvant, which suggested that autologous RBC coupled to gB1s may provide an effective and safe method of immunization against HSV infection.

Expression of the herpes simplex virus type 1 glycoprotein E in human cells and in Escherichia coli: protection studies against lethal viral infection in mice

The objective of this study was to examine the protective efficacy of purified recombinant herpes simplex virus type 1 (HSV-1) glycoprotein E (gE-1) in the mouse lethal challenge model. A secreted form of gE-1 (hgE-1s) protein, containing amino acids 1-406, was produced in human cells by using the episomal replicating pRP-RSV expression vector. In addition, a portion of the gE-1 (bgE-1t) protein corresponding to amino acids 90-406, was expressed in Escherichia coli as a fusion protein with maltose binding protein using the pMAL-c2 expression vector. Mice vaccinated with hgE-1s developed high serum titres of HSV-1-neutralizing antibodies and were significantly protected from intraperitoneal lethal HSV-1 challenge, whereas mice vaccinated with bgE-1t exhibited only moderate levels of protective immunity. These results demonstrate that the expression of gE-1 in human cells has a strong impact on its protective efficacy and that most importantly the hgE-1s protein could be of values as a component of an HSV multi-subunit vaccine.

Herpes simplex virus type 1 (HSV-1) uracil-DNA glycosylase: functional expression in Escherichia coli, biochemical characterization, and selective inhibition by 6-(p-n-octylanilino)uracil

The Herpes simplex virus type 1 (HSV-1) uracil-DNA glycosylase (UDG) is encoded by the UL2 gene. The translation from the first putative start codon of UL2 predicts a polypeptide of 334 residues, while the translation from the second start codon predicts a polypeptide of 244 residues. We have cloned and expressed the two forms of UDG, by means of the prokaryotic expression vector pMAL-c2, and both of them were enzymatically active. Furthermore, the enzymatic properties of the recombinant UDGs and of the enzyme purified from HSV-1-infected cells were similar. The two UDG polypeptides have molecular weights of 27 and 37 kDa, respectively. The 37-kDa form of recombinant UDG is consistent with the reported molecular mass of 37 kDa for the enzyme purified from HSV-1-infected cells. Both recombinant UDGs were as sensitive as UDG purified from HSV-1-infected cells to 6-(p-n-octylanilino)uracil, the most potent of a series of uracil analogs that inhibit the viral enzyme.