Adenovirus type 5 and 7 capsid chimera: fiber replacement alters receptor tropism without affecting primary immune neutralization epitopes

Adenovirus encoding soluble tumor necrosis factor alpha receptor immunoglobulin prolongs gene expression of a cotransfected reporter gene in rat lung

OBJECTIVE

Because almost all pulmonary diseases are not caused by one gene, multiple gene transfection is required for current gene therapy. Adenovirus is an important gene therapy vector, but a short duration and the inability of repeated administration remain limitations. The aims of this study were to evaluate whether adenoviral vector encoding soluble tumor necrosis factor alpha receptor immunoglobulin and beta-galactosidase cotransfection prolongs gene expression and facilitates repeated vector administration to investigate the feasibility of a cotransfection strategy.

METHODS

F344 rats received intratracheal administration of 1 x 10(9) plaque-forming units of adenoviral vector encoding beta-galactosidase or both adenoviral vector encoding beta-galactosidase and adenoviral vector encoding soluble tumor necrosis factor alpha receptor immunoglobulin. In the expression study beta-galactosidase gene expression in the lung was examined by means of enzyme-linked immunosorbent assay on days 2, 7, 14, 28, and 56 (n = 4/day). In the repeated transfection study, soluble tumor necrosis factor alpha receptor immunoglobulin and beta-galactosidase were readministered once (7 days after the first adenovirus administration) or twice (on days 7 and 14; n = 4/day). A 2-way factorial analysis of variance was used for statistical analysis.

RESULTS

Soluble tumor necrosis factor alpha receptor immunoglobulin and beta-galactosidase cotransfection prolonged the duration of beta-galactosidase expression. However, antiadenovirus antibody production was significantly increased in the cotransfection group. In addition, there was no increase in beta-galactosidase expression after readministration of soluble tumor necrosis factor alpha receptor immunoglobulin and beta-galactosidase.

CONCLUSION

Adenoviral vector encoding soluble tumor necrosis factor alpha receptor immunoglobulin and beta-galactosidase cotransfection prolongs beta-galactosidase expression but does not increase beta-galactosidase expression after repeated administration. These results suggest that tumor necrosis factor alpha is one of the most important factors in regulating the duration of gene expression. The cotransfection approach is feasible, but the increase of antiadenovirus antibodies might make repeated cotransfection unfeasible.

Characterization of in vitro and in vivo gene transfer properties of adenovirus serotype 35 vector

We have recently developed a replication-defective, recombinant adenovirus (Ad) vector composed of the whole Ad serotype 35 (Ad35), a member of subgroup B. We describe herein the in vitro and in vivo gene transfer properties of Ad35 vector in comparison with Ad serotype 5 (Ad5) and the Ad5F35 vector, which is a fiber-substituted Ad5 vector containing Ad35 fiber proteins. In vitro, Ad35 vector efficiently transduced not only human CAR-positive cells but also CAR-negative cells. Following intravenous administration into mice, both Ad5 and Ad35 vectors were rapidly cleared from the bloodstream with a half-life of approximately 3 min. Ad5 vector-mediated transgene expression predominantly occurred in liver parenchymal cells, although the Ad5 vector was delivered to both liver parenchymal and nonparenchymal cells. In contrast, Ad35 vector was efficiently taken up by liver nonparenchymal cells and mediated transduction efficiency in the liver on a level 4 log orders lower than the Ad5 vector. These findings demonstrate that Ad35 vector is an attractive vehicle for gene transfer into human cells, while the biodistribution profile of Ad35 vector in mice is much different from that of the Ad5 vector.

Human adenovirus type 35: nucleotide sequence and vector development

In this report, we describe the complete 34,794 base pair genomic sequence of the human adenovirus serotype 35 (Ad35) Holden strain. The viral genome exhibits a compact organization similar to other adenoviral serotypes, with overlapping genes on both strands. In all, 47 open reading frames (ORFs) were identified, including early (E1, 2, 3, 4) and late (L1, 2, 3, 4, 5) regions conserved among the adenoviridae family. In addition, 14 ORFs were identified that do not encode known adenoviral genes. Comparison of the predicted translational products of the conserved genes with those of other adenoviruses revealed that Ad35 has high homology to Ad7, Ad3, Ad21, Ad17, and simian Ads25. Based on the complete Ad35 DNA sequence, E3-, E1-, and E1/E3-deleted Ad35-based vector systems were developed. An HEK293-derived cell line was established for the propagation of the E1-deleted Ad35 vector, avoiding the emergence of replication-competent adenovirus. Moreover, production of the E1-deleted recombinant Ad35 vector was achieved by transient transduction of a plasmid encoding the Ad35 E1B gene in HEK293 cells. Testing showed that the Ad35-based vector efficiently infects both human and rhesus macaque dendritic cells. Our novel Ad35-based vectors and their corresponding packaging cell lines will provide a versatile and powerful system for DNA-based vaccine development and gene therapy applications.

Structural and phylogenetic analysis of adenovirus hexons by use of high-resolution x-ray crystallographic, molecular modeling, and sequence-based methods

A major impediment to the use of adenovirus as a gene therapy vector and for vaccine applications is the host immune response to adenovirus hexon-the major protein component of the icosahedral capsid. A solution may lie in novel vectors with modified or chimeric hexons designed to evade the immune response. To facilitate this approach, we have distinguished the portion of hexon that all serotypes have in common from the hypervariable regions that are responsible for capsid diversity and type-specific immunogenicity. The common hexon core-conserved because it forms the viral capsid-sets boundaries to the regions where modifications can be made to produce nonnative hexons. The core has been defined from the large and diverse set of known hexon sequences by an accurate alignment based on the newly refined crystal structures of human adenovirus types 2 (Ad2) and Ad5 hexon. Comparison of the two hexon models, which are the most accurate so far, reveals that over 90% of the residues in each have three-dimensional positions that closely match. Structures for more distant hexons were predicted by building molecular models of human Ad4, chimpanzee adenovirus (AdC68), and fowl adenovirus 1 (FAV1 or CELO). The five structures were then used to guide the alignment of the 40 full-length (>900 residues) hexon sequences in public databases. Distance- and parsimony-based phylogenetic trees are consistent and reveal evolutionary relationships between adenovirus types that parallel those of their animal hosts. The combination of crystallography, molecular modeling, and phylogenetic analysis defines a conserved molecular core that can serve as the armature for the directed design of novel hexons.

Shortening adenovirus type 5 fiber shaft decreases the efficiency of postbinding steps in CAR-expressing and nonexpressing cells

The coxsackie B virus and adenovirus receptor (CAR) functions as an attachment receptor for multiple adenovirus serotypes. It has been shown that apart from virus-cellular receptor interactions, the fiber shaft length also influences viral tropism. We therefore generated Ad5FbDelta639 virus with 8beta-repeats in the shaft, instead of the 22beta-repeats present in the wild-type. Here, we show that the extent of attachment of the virus with shortened fiber to CAR-expressing cells was three- to fivefold lower than that of the wild-type. Transduction studies, however, clearly showed that infection of CAR-expressing cells with Ad5FbDelta639 was strongly impaired by comparison with the wild-type virus. Since this impairment was not linked to a proportional reduction in binding to cells, it appeared to be linked to subsequent/later events in infection. A similar decrease in efficacy of postbinding steps was also evidenced in cells that did not express CAR.

Corneal IL-8 expression following adenovirus infection is mediated by c-Src activation in human corneal fibroblasts

Emerging evidence indicates that intracellular signaling cascades mediate entry of pathogenic adenoviruses into target host cells as well as some of the undesirable inflammatory responses to adenoviral gene vectors. We found that Ad19 infection of cultured human corneal fibroblasts induced IL-8 gene transcription independently of IL-1beta, TNF-alpha, and viral gene expression, suggesting that intracellular signaling events might mediate early inflammatory events in adenovirus keratitis. Heat but not UV light inactivation of the virus abrogated the effect of infection on IL-8 mRNA and protein levels, consistent with a viral binding-mediated mechanism. The tyrosine kinase inhibitor herbimycin blocked Ad19-induced IL-8 expression. Western blot analysis revealed tyrosine phosphorylation of the functionally related kinases c-Src and extracellular signal-regulated kinase (ERK) 1/2 in corneal fibroblasts within 15 min after infection. Respective inhibitors of these kinases, PP2 and PD98059, also blocked Ad19-induced IL-8 mRNA and protein expression. Application of inhibitors to Src and ERK kinase assays suggested an upstream relationship of c-Src to ERK. Finally, DNA microarray studies performed 1 h after Ad19 or mock infection of corneal fibroblasts in the presence or absence of the Src-specific inhibitor PP2 confirmed a relationship between c-Src and IL-8 expression in Ad19-infected corneal cells. c-Src may act as a global regulator of early proinflammatory host responses to Ad19 infection of the human cornea.

A mosaic adenovirus possessing serotype Ad5 and serotype Ad3 knobs exhibits expanded tropism

The efficiency of cancer gene therapy with recombinant adenoviruses based on serotype 5 (Ad5) has been limited partly because of variable, and often low, expression by human primary cancer cells of the primary cellular-receptor which recognizes the knob domain of the fiber protein, the coxsackie and adenovirus receptor (CAR). As a means of circumventing CAR deficiency, Ad vectors have been retargeted by utilizing chimeric fibers possessing knob domains of alternate Ad serotypes. We have reported that ovarian cancer cells possess a primary receptor for Ad3 to which the Ad3 knob binds independently of the CAR-Ad5 knob interaction. Furthermore, an Ad5-based chimeric vector, designated Ad5/3, containing a chimeric fiber proteins possessing the Ad3 knob, demonstrates CAR-independent tropism by virtue of targeting the Ad3 receptor. Based on these findings, we hypothesized that a mosaic virus possessing both the Ad5 knob and the Ad3 knob on the same virion could utilize either primary receptor, resulting in expanded tropism. In this study, we generated a dual-knob mosaic virus by coinfection of 293 cells with Ad5-based and Ad5/3-based vectors. Characterization of the resultant virions confirmed the incorporation of both Ad5 and Ad3 knobs in the same particle. Furthermore, this mosaic virus was able to utilize either receptor, CAR and the Ad3 receptor, for virus attachment to cells. Enhanced Ad infectivity with the mosaic virus was shown in a panel of cell lines, with receptor profiles ranging from CAR-dominant to Ad3 receptor-dominant. Thus, this mosaic virus strategy may offer the potential to improve Ad-based gene therapy approaches by infectivity enhancement and tropism expansion.

Generation of fiber-modified adenovirus vectors containing heterologous peptides in both the HI loop and C terminus of the fiber knob

BACKGROUND

Fiber-modified adenovirus (Ad) vectors can be effective in overcoming the limitations of conventional Ad vectors, specifically their inefficient gene transfer into cells lacking the primary receptor, the coxsackievirus and adenovirus receptor (CAR). Several types of fiber-modified Ad vectors have been developed. In this study, we evaluated the functionality of several fiber-modified Ad vectors.

METHODS

We developed a simple method based on in vitro ligation to construct Ad vectors containing heterologous foreign peptides in both the HI loop and C terminus of the fiber knob. A functional comparison of Ad vectors containing RGD and/or K7 (KKKKKKK) peptide in the HI loop or C terminus of the fiber knob was performed in several types of human, mouse, and rat cells, including CAR-positive and -negative cells, and tumor cells in mice in vivo.

RESULTS

In the case of the in vitro experiment, Ad vectors containing RGD peptide in the HI loop of the fiber knob showed a higher level of gene transfer than vectors containing RGD peptide at the C terminus of the fiber knob. Ad vectors containing K7 peptide at the C terminus of the fiber knob showed levels of gene transfer similar to those of Ad vectors containing RGD peptide in the HI loop of the fiber knob, depending on the cell type. Ad vectors containing both peptides in the HI loop or C terminus of the fiber knob showed the highest levels of gene transfer and a broader tropism. For gene transfer into tumor cells in vivo, the Ad vectors containing RGD peptide were the most efficient.

CONCLUSIONS

In the experiment using cultured cells, Ad vectors containing both RGD and K7 peptides were the most efficient with a broader tropism. In contrast, in the experiment in vivo, Ad vectors containing RGD peptide in the HI loop of the fiber knob were more efficient than the vectors containing K7 peptide (including double-modified vectors containing both the RGD and K7 peptides). These comparative analyses could provide a systemic reference for the use of fiber-modified Ad vectors. Our simple method, in which the peptide of interest can be expressed in Ad vectors in either the HI loop or the C terminus of the fiber knob, or both, could be a powerful tool for gene transfer into mammalian cells in studies of gene function as well as in gene therapy.

Current and future strategies for the treatment of malignant brain tumors

Glioblastoma (GB) is the most common subtype of primary brain tumor in adults. These tumors are highly invasive, very aggressive, and often infiltrate critical neurological areas within the brain. The mean survival time after diagnosis of GB has remained unchanged during the last few decades, in spite of advances in surgical techniques, radiotherapy, and also chemotherapy; patients' survival ranges from 9 to 12 months after initial diagnosis. In the same time frame, with our increasing understanding and knowledge of the physiopathology of several cancers, meaningful advances have been made in the treatment and control of several cancers, such as breast, prostate, and hematopoietic malignancies. Although a number of the genetic lesions present in GB have been elucidated and our understanding of the progressions of this cancer has increased dramatically over the last few years, it has not yet been possible to harness this information towards developing effective cures. In this review, we will focus on the classical ways in which GB is currently being treated, and will introduce a novel therapeutic modality, i.e., gene therapy, which we believe will be used in combination with classical treatment strategies to prolong the life-span of patients and to ultimately be able to control and/or cure these brain tumors. We will discuss the use of several vector systems that are needed to introduce the therapeutic genes within either the tumor mass, if these are not resectable, or the tumor bed, after successful tumor resection. We also discuss different therapeutic modalities that could be exploited using gene therapy, i.e., conditional cytotoxic approach, direct cytotoxicity, immunotherapy, inhibition of angiogenesis, and the use of pro-apoptotic genes. The advantages and disadvantages of each of the current vector systems available to transfer genes into the CNS are also discussed. With the advances in molecular techniques, both towards the elucidation of the physiopathology of GB and the development of novel, more efficient and less toxic vectors to deliver putative therapeutic genes into the CNS, it should be possible to develop new rationale and effective therapeutic approaches to treat this devastating cancer.

Generation of an adenoviral vector containing an addition of a heterologous ligand to the serotype 3 fiber knob

As an initial assessment of the feasibility of employing the adenovirus serotype 3 (Ad3) fiber knob as a locale for introducing a tropism-modifying motif, we generated an adenoviral vector containing a six-histidine tag genetically fused to the carboxy-terminus of the Ad3 fiber knob. The heterologous tag proved to be accessible for binding in the context of the virion and, moreover, had rendered the modified vector capable of mediating gene transfer through an artificial, non-Ad3 receptor.

Reduction of natural adenovirus tropism to the liver by both ablation of fiber-coxsackievirus and adenovirus receptor interaction and use of replaceable short fiber

The initial recognition and binding of adenovirus vector to the host cell surface is mediated by interaction between the adenovirus fiber knob protein and its receptor, the coxsackievirus and adenovirus receptor (CAR). This natural tropism of adenovirus vector needs to be ablated in order to achieve targeted gene transfer. To this end, we noted that adenovirus serotype 40 (Ad40) contains two distinct long and short fibers; the short fiber is unable to recognize CAR, while the long fiber binds CAR. We generated adenovirus serotype 5-based mutants with chimeric Ad40-derived fibers, which were composed of either long or short shafts together with CAR binding or nonbinding knobs. The capacity of these adenovirus mutants for in vitro and in vivo gene transfer to liver cells was examined. In the case of primary human hepatocytes displaying a high expression level of CAR and alphav integrin, both CAR binding ability and fiber shaft length played important roles in efficient transduction. Most significantly, the high transduction efficiency observed in the liver and spleen following intravenous administration of adenovirus vector was dramatically reduced by both ablation of fiber-CAR interaction and the use of replaceable short fiber. In other tissues displaying a low level of transduction, no significant differences in transduction efficiency were observed among adenovirus vector mutants. Furthermore, incorporation of a 7-lysine-residue motif at the C-terminal end of CAR-nonbinding short fiber efficiently achieved transduction of target cells via the heparan-containing receptor. Our results demonstrated that the natural tropism of adenovirus in vivo is influenced not only by fiber-CAR interaction but also by fiber shaft length. Furthermore, our strategy may be useful for retargeting adenovirus to particular tumors and tissue types with specific receptors.

Subgroup B and F fiber chimeras eliminate normal adenovirus type 5 vector transduction in vitro and in vivo

Altering adenovirus vector (Ad vector) targeting is an important goal for a variety of gene therapy applications and involves eliminating or reducing the normal tropism of a vector and retargeting through a distinct receptor-ligand pathway. The first step of Ad vector infection is high-affinity binding to a target cellular receptor. For the majority of adenoviruses and Ad vectors, the fiber capsid protein serves this purpose, binding to the coxsackievirus and adenovirus receptor (CAR) present on a variety of cell types. In this study we have explored a novel approach to altering Ad type 5 (Ad5) vector targeting based on serotypic differences in fiber function. The subgroup B viruses bind to an unidentified receptor that is distinct from CAR. The subgroup F viruses are the only adenoviruses that express two distinct terminal exons encoding fiber open reading frames. We have constructed chimeric fiber adenoviruses that utilize the tandem fiber arrangement of the subgroup F genome configuration. By taking advantage of serotypic differences in fiber expression, fiber shaft length, and fiber binding efficiency, we have developed a tandem fiber vector that has low binding efficiency for the known fiber binding sites, does not rely on an Ad5-based fiber, and can be grown to high titer using conventional cell lines. Importantly, when characterizing these vectors in vivo, we find the subgroup B system and our optimal tandem fiber system demonstrate reduced liver transduction by over 2 logs compared to an Ad5 fiber vector. These attributes make the tandem fiber vector a useful alternative to conventional strategies for fiber manipulation of adenovirus vectors.

There are two different species B adenovirus receptors: sBAR, common to species B1 and B2 adenoviruses, and sB2AR, exclusively used by species B2 adenoviruses

Unlike most adenovirus (Ad) serotypes, the species B Ads do not use the coxsackie-adenovirus receptor as an attachment receptor. The species B attachment receptor(s) has not yet been identified and is also poorly characterized. Species B Ads can be further divided into species B1 and B2 Ads, and these display different organ tropisms, suggesting a difference in receptor usage. We have studied the receptor interactions of the species B1 serotypes 3p and 7p and the species B2 serotypes 11p and 35 and characterized the properties of the species B receptor(s). Reciprocal blocking experiments using unlabeled Ad11p or Ad3p virions to block the binding to A549 cells of (35)S-labeled 3p, 7p, 11p, and 35 showed that only Ad11p virions efficiently blocked the binding of all the species B Ads studied (> or =70%). Thus, there is apparently a common species B Ad receptor (sBAR). However, Ad3p virions only partially (< or =30%) blocked the binding of Ad11p and Ad35 to A549 cells. Binding experiments after trypsin treatment of the cells confirmed that the species B2 serotypes address at least two different receptors on A549 and J82 cells, since sBAR is trypsin sensitive but the species B2 Ad receptor (sB2AR) is not. Both receptors are proteins or glycoproteins, since binding of all species B serotypes was abolished after proteinase K or subtilisin treatment of A549 or J82 cells. Furthermore, binding of the species B serotypes to sBAR was abolished with EDTA and restored with Ca(2+), whereas the binding of Ad11p and Ad35 to SB2AR was independent of divalent cations.

In vivo transduction of photoreceptors or ciliary body by intravitreal injection of pseudotyped adenoviral vectors

Strategies for retargeting adenoviral (Ad) vectors have been developed, but their in vivo efficacy remains to be demonstrated. Gene delivery to specific ocular cell types represents an approach to treating many diseases that cause irreversible blindness. One of these cell types, the photoreceptor (PR), is not infected by standard Ad5-based vectors. We evaluated gene delivery after intraocular injection of Ads pseudotyped with three different fiber proteins and found three distinct patterns of infection. An intravitreally injected Ad5 vector readily infected the iris, corneal endothelium, and ciliary body, while few cells in the retina expressed transgene product. In contrast, an Ad3-pseudotyped virus selectively transduced ciliary body, of interest for treating diseases such as glaucoma. A vector pseudotyped with the fiber protein of Ad37 transduced PRs as well as ciliary body. This finding has potential application to the treatment of retinal degenerative or neovascular diseases. These studies demonstrate cell type-selective gene delivery in vivo with retargeted Ads, provide information about the cellular tropisms of several Ad serotypes, and should lead to improved strategies for preserving vision.

Genetic manipulations of adenovirus type 5 fiber resulting in liver tropism attenuation

The development of genetically modified adenoviral vectors capable of specifically transducing a given cell population requires the addition and functional presentation of particular tropism determinants within the virus capsid, together with the abrogation of the molecular determinants that dictate their natural tropism in vivo. The human adenovirus serotype 5 (Ad5) first attaches to the cell surface following high-affinity binding of the C-terminal knob of the fiber capsid protein to the coxsackie and adenovirus receptor (CAR). Here we have assessed whether genetic shortening of the fiber shaft (virus BS1), or replacing the Ad5 fiber shaft and knob with their Ad3 counterparts (virus DB6), could cripple this interaction in vitro and in vivo. A 10-fold decrease in the binding of the modified capsids to soluble CAR was evidenced, which correlated with a similar reduction of their ability to transduce CAR-positive cells in vitro. The ability of BS1 to interact with cellular integrins was also impaired, suggesting that the penton base and the short-shafted fiber when embedded in the capsid preclude each other from efficiently interacting with their cognate cell surface receptors (CAR and integrins respectively). BS1 and DB6 intravenous injections in mice further supported a profound impairment of the ability of the capsid-modified viruses to transduce the liver as demonstrated by a 10-fold reduction of intracellular viral DNA and transgene expression. Interestingly enough, the host humoral response was also specifically weakened in BS1- and DB6-inoculated animals. Taken together, these observations indicate that (i) fiber shortening and (ii) pseudo-typing of Ad5-based vectors with the shaft and knob from non-CAR-binding serotypes constitute two promising strategies to successfully attenuate their native tropism in vitro and most importantly in vivo.

Construction and characterization of adenovirus serotype 5 packaged by serotype 3 hexon

Adenovirus serotype 5 (Ad5) has great potential for gene therapy applications. A major limitation, however, is the host immune response against Ad5 infection that often prevents the readministration of Ad5 vectors. In this regard, the most abundant capsid protein, hexon, has been implicated as the major target for neutralizing antibodies. In this study, we sought to escape the host neutralization response against Ad5 via hexon replacement. We constructed a chimeric adenovirus vector, Ad5/H3, by replacing the Ad5 hexon gene with the hexon gene of Ad3. The chimeric viruses were successfully rescued in 293 cells. Compared to that for the control Ad5/H5, the growth rate of Ad5/H3 was significantly slower and the final yield was about 1 log order less. These data indicate that the Ad3 hexon can encapsidate the Ad5 genome, but with less efficiency than the Ad5 hexon. The gene transfer efficacy of Ad5/H3 in HeLa cells was also lower than that of Ad5/H5. Furthermore, we tested the host neutralization responses against the two viruses by using C57BL/6 mice. The neutralizing antibodies against Ad5/H3 and Ad5/H5 generated by the immunized mice did not cross-neutralize each other in the context of in vitro infection of HeLa cells. Preimmunization of C57BL/6 mice with one of the two types of viruses also did not prevent subsequent infection of the other type. These data suggest that replacing the Ad5 hexon with the Ad3 hexon can circumvent the host neutralization response to Ad5. This strategy may therefore be used to achieve the repeated administration of Ad5 in gene therapy applications.

Adenovirus type 37 binds to cell surface sialic acid through a charge-dependent interaction

Most adenoviruses use the coxsackie-adenovirus receptor (CAR) as a major cellular receptor. We have shown recently that adenovirus types 8, 19a, and 37, which are the major causes of epidemic keratoconjunctivitis, use sialic acid rather than CAR as a major cellular receptor. The predicted isoelectric point of the receptor-interacting knob domain in the adenovirus fiber protein is unusually high (9.0-9.1) in type 8, 19a, and 37. The pKa of sialic acid is low, 2.6, implying a possible involvement of charge in fiber knob-sialic acid interactions. Here we show that (i) positively charged adenovirus knobs require sialic acid for efficient cell membrane interactions; (ii) viral and knob interactions with immobilized sialic acid or cell-surface sialic acid are sensitive to increased ionic strength; (iii) negatively charged molecules such as sulfated glycosaminoglycans inhibit the binding of virions to target cells in a nonspecific, charge-dependent manner; and that (iv) the ability of adenovirus knobs to interact with sialic acid correlates with the overall charge on the top surface of the respective knobs as predicted by homology modeling. Taken together, the results presented provide strong evidence for a charge mechanism during the interaction between the Ad37 fiber knob and sialic acid.

Strategies for muscle-specific targeting of adenoviral gene transfer vectors

Currently, adenoviral transfer of therapeutic genes such as dystrophin is hampered by low transduction efficiency of adult skeletal muscle. This is largely due to the lack of appropriate virus attachment receptors on the myofiber surface. Recent studies in transgenic mice revealed that upregulation of Coxsackie- and adenovirus receptor improves gene transfer efficiency by approximately ten-fold. Conversely, the vector load that needed to be administered to achieve sufficient gene transfer could be lowered significantly. Reduced viral vector loads may help to control virally mediated toxicity and immunogenicity. To date, there are no drugs or methods known to increase Coxsackie- and adenovirus receptor expression in skeletal muscle that would be easily applicable in humans. However, alternative strategies such as vector retargeting are currently being investigated that may allow for an increase in binding of adenoviral vectors to skeletal muscle. Recent experiments have shown that directed mutagenesis of the adenoviral fiber knob allows for a significant reduction in Coxsackie- and adenovirus receptor binding and for introduction of a new binding domain. Therefore, vector retargeting towards efficient and specific infection of skeletal muscle may be achieved by directed genetic alteration of adenoviral capsid proteins.

A p5 integration efficiency element mediates Rep-dependent integration into AAVS1 at chromosome 19

Adeno-associated virus (AAV) undergoes site-specific integration into human chromosome 19 through a deletion-substitution mechanism at the well characterized AAVS1 site. We have shown previously that a cis element within the left end of the AAV genome enhances the efficiency of Rep-mediated site-specific integration into chromosome 19 when present in inverted terminal repeat-containing recombinant AAV (rAAV) plasmids. We now demonstrate that a 138-bp cis element, the p5 integration efficiency element (p5IEE), mediates efficient integration. The p5IEE is not only required for efficient site-specific integration, it is also sufficient. Integration mediated by the p5IEE occurs in the absence of the AAV inverted terminal-repeat elements. The data presented in this study demonstrate that the p5IEE is a multifunctional element, serving as the highly regulatable Rep promoter and the primary substrate for targeted integration.

Adenovirus type 37 uses sialic acid as a cellular receptor on Chang C cells

Epidemic keratoconjunctivitis (EKC) is a severe eye infection caused mainly by adenovirus type 8 (Ad8), Ad19, and Ad37. We have shown that the EKC-causing adenoviruses use sialic acid as a cellular receptor on A549 cells instead of the coxsackie-adenovirus receptor, which is used by most adenoviruses. Recently, Wu et al. (Virology 279:78-89, 2001) proposed that Ad37 uses a 50-kDa protein as a receptor on Chang C conjunctival cells and that this interaction is independent of sialic acid. According to the American Type Culture Collection, this cell line carries HeLa cell markers and should be considered to be a genital cell line. This prompted us to investigate the function of sialic acid as a cellular receptor for Ad37 in Chang C cells. In this study, we demonstrate that enzymatic removal or lectin-mediated blocking of cell surface sialic acid inhibits the binding of Ad37 virions to Chang C cells, as does soluble, virion-interacting sialic acid-containing substances. The binding was Ca2+ or Mg2+ ion independent and mediated by the knob domain of the trimeric viral fiber polypeptide. Moreover, Ad37 virions infected Chang C cells and two other genital cell lines (HeLa and SiHa) as well as a corneal cell line in a strictly sialic acid-dependent manner. From these results, we conclude that Ad37 uses sialic acid as a major receptor in cell lines derived from both genital and corneal tissues.

Insertion of an exogenous domain in the adenovirus type 2 fiber globular region

Adenoviruses have been used for gene therapy or immunization due to their ability to efficiently infect a broad range of cells and tissues. These applications as well as specificity could be improved further by redirecting binding of the virus to specific cell types. In this regard, modification of viral genes encoding coat proteins is an option to achieve improvement in retargeting. In this report, we describe a substitution in the adenovirus type 2 fiber globular region by the 44 amino acid C4 domain of human immunodeficiency virus type 1 gp120. In vitro translation analysis and immunoprecipitation assays show that the incorporation of the C4 domain into the fiber protein does not ablate its trimerization property and demonstrates the availability of the C4 epitope for interaction with monoclonal anti-C4 antibody. The recombinant adenovirus containing this modified fiber was also characterized by immunoprecipitation with the same antibody, showing the viability of such kind of modification.

Fiber shaft extension in combination with HI loop ligands augments infectivity for CAR-negative tumor targets but does not enhance hepatotropism in vivo

Recent studies demonstrate that the fiber shaft length, which ranges from six beta-repeats to 23 beta-repeats in human adenoviruses (Ads), influences viral tropism. We have previously shown that artificial extension of the shaft length inhibits infectivity in CAR (coxsackievirus and Ad receptor)-positive cell lines, but does not affect infectivity in a CAR-independent, integrin-dependent cell entry pathway. On the basis of these findings, we hypothesized that Ad vectors with shaft extension might display lower infectivity in liver, which expresses high levels of CAR. We also postulated that infectivity of Ad vectors with shaft extension in CAR-negative tumors could be increased by exploiting a CAR-independent cell entry by incorporation of an RGD4C motif into the fiber knob HI-loop. We thus compared gene transfer efficiencies of our Ad serotype 5 (Ad5) capsid-based 'longer-shafted' Ad vector with or without an RGD4C motif in the HI-loop of the fiber knob (Ad5long and Ad5RGDlong, 32 beta-repeats) to wild-type Ad vector (Ad5, 22 beta-repeats) in vitro and in vivo. In this study, Ad5long showed similar infectivity in CAR-negative tumors (69.7%, P = 0.098), but significantly reduced infectivity in CAR-positive tumors (19.1%, P = 0.000038) and in liver (12.5%, P = 0.0047) compared with Ad5. On the other hand, Ad5RGDlong demonstrated similar infectivity in CAR-positive tumors (70.5%, P = 0.012) and in liver (83.4%, P = 0.51), but significantly increased infectivity in CAR-negative tumors (327%, P = 0.0000042) compared with Ad5. Importantly, Ad5RGDlong demonstrated an augmented gene transfer capacity for CAR negative tumors, but no enhanced hepatotropism in vivo. We suggest that Ad vectors with artificial fiber shaft extension in combination with HI loop ligands may be useful for gene therapy applications.

Adenovirus mediated gene transfer to skeletal muscle

Transfer of therapeutic genes into muscle tissue has promise for the treatment of a variety of muscular dystrophies. Various vectors have been used to deliver genes to skeletal muscle but their application has faced several major limitations including: (1) the lack of transgene persistence caused by the immune rejection of transduced myofibers and/or vector toxicity, and (2) the maturation dependence of viral transduction. While the immunorejection and/or cytotoxic problems are being overcome with the development of new vectors, maturation-dependent viral transduction is still a major hurdle in gene transfer to skeletal muscle. Poor adenoviral transduction in mature myofibers has been attributed to: (1) the extracellular matrix of mature myofibers may form a physical barrier and prevent the passage of large viral particles; (2) viral receptors are down-regulated with muscle maturation; and (3) loss of myoblasts with muscle maturation, which serve as intermediaries in the viral transduction. In this review, we will focus on recent developments in overcoming those hurdles of gene therapy in skeletal muscle, especially to adenovirus (Ad), including: (1) new mutant vectors lacking all viral genes to decrease immunogenicity, and hence, improve persistence of transgene expression in muscle in vivo; (2) using tissue specific promoters to evade immunorejection; (3) permeabilization of the extracellular matrix; (4) modifying the viral receptors in mature myofibers; and (5) myoblast or muscle stem cell mediated ex vivo gene transfer.

Gene transfer to ovarian cancer versus normal tissues with fiber-modified adenoviruses

Adenovirus serotype 5 (Ad5) displays unparalleled gene transfer efficacy to cells with high coxsackie-adenovirus receptor (CAR) expression. Unfortunately, cells isolated from clinical human cancers, both ovarian and other types, express highly variable and often low levels of CAR. Fortunately, native Ad5 tropism can be modified to circumvent CAR deficiency and to enhance infectivity. Ad5/3luc1 incorporates the serotype 3 fiber knob and binds to a receptor distinct from CAR, while the fiber of Ad5lucRGD is modified with an RGD-4C motif, allowing CAR-independent binding to integrins. We studied the liver tropism and blood clearance of these viruses after intravenous (i.v.) injection, and biodistribution after intraperitoneal (i.p.) injection to tumor-bearing mice. To estimate efficacy, we assessed gene transfer to purified human primary ovarian cancer cells, and in a mouse model of ovarian cancer. Ad5/3luc1 achieved improved gene transfer over Ad5lucRGD, and both infectivity-enhanced viruses were superior to the isogenic control with an unmodified Ad5 capsid. In the presence of malignant ascites, gene transfer was improved with both Ad5/3luc1 and Ad5lucRGD. Thus, retargeting to the Ad3 receptor enhances gene transfer to clinically relevant ovarian cancer substrates, while the mouse toxicity and biodistribution profile of both fiber-modified Ad vectors is comparable to Ad5.

Targeted adenoviral vectors

Replication-defective vectors based on human adenovirus serotypes 2 and 5 (Ad2 and Ad5) possess a number of attributes which favor their use as gene delivery vehicles in gene therapy applications. However, the widespread distribution of the primary cellular receptor for Ad, the coxsackievirus and adenovirus receptor (CAR), allows Ad vectors to infect a broad range of cells in the host. Conversely, a number of tissues which represent important targets for gene therapy, such as the airway epithelium and cancer cells, are refractory to Ad infection due a paucity of CAR. Thus, there is a strong rationale for the development of CAR-independent Ad vectors capable of enhanced specificity and efficiency of gene transfer to target cells. In this article we review the approaches which have been employed to generate tropism-modified Ad vectors. These targeting strategies have led to improvements in the safety and efficacy of Ad vectors and have the potential to yield an increased therapeutic benefit in the human clinical context.

Infectious virions produced from a human papillomavirus type 18/16 genomic DNA chimera

The organotypic raft culture system has allowed the study of the differentiation-dependent aspects of the human papillomavirus (HPV) life cycle. However, genetic strategies to more completely understand the HPV life cycle are limited. The generation of chimeric viruses has been a useful tool in other virus systems to analyze infection and replication. To investigate the specificity of the interaction of nonstructural genes of one HPV type with the structural genes of another HPV type, we have replaced the L2 and L1 open reading frames (ORFs) of HPV type 18 (HPV18) with the L2 and L1 ORFs of HPV type 16 (HPV16). The resulting HPV18/16 chimeric construct was introduced into primary keratinocytes, where it was stably maintained episomally at a range of 50 to 100 copies of HPV genomic DNA, similar to that typically found in HPV-infected cells in vivo. The integrity of the HPV18/16 genomic DNA chimera was demonstrated. Upon differentiation in raft cultures, late viral functions, including viral DNA amplification, capsid gene expression, and virion morphogenesis, occurred. Chimeric HPV18/16 virions were purified from the raft cultures and were capable of infecting keratinocytes in vitro. Additionally, infection was specifically neutralized with human HPV16 virus-like particle (VLP)-specific antiserum and not with human HPV18 VLP-specific antiserum. Our data demonstrate that the nonstructural genes of HPV18 functionally interact with the structural genes of HPV16, allowing the complete HPV life cycle to occur. We believe that this is the first report of the propagation of chimeric HPV by normal life cycle pathways.

Human adenoviruses of subgenera B, C, and E with various tropisms differ in both binding to and replication in the epithelial A549 and 293 cells

Adenoviruses of six subgenera, namely, adenovirus 31 (Ad31) (subgenus A), Ad3, Ad7, Ad11p, Ad11a, and Ad35 (subgenus B), Ad5v and Ad5p (subgenus C), Ad37 (subgenus D), Ad4 (subgenus E), and Ad41 (subgenus F), were studied. The relative binding properties of different adenoviruses to 293 (human kidney embryonic cells) and A549 (human lung carcinoma cells) cells were compared by flow cytometry. All analyzed adenoviruses bound to cells in a dose-dependent manner. The binding capacity showed that Ad11p, Ad35 (subgenus B:2) with kidney tropism, and Ad4 (subgenus E), which can cause adenopharyngoconjunctivitis, bound strongly to both A549 and 293 cells. The other members of subgenus B and Ad37 of subgenus D manifested an intermediate binding capacity. The analyzed adenoviruses of subgenera A, C, and F manifested a low affinity. Adenoviruses of subgenera B:2 and E manifested high binding affinity to preparations of cell membranes from the epithelial cell lines. Reciprocal competition experiments using Ad11p and Ad4 demonstrated that the two viruses did not block each other. Antibodies against alphavbeta3 and alphavbeta5 reduced the binding of Ad5v virions and slightly impaired the binding of Ad4 but did not affect Ad11p binding to the A549 cell surface. Recombinant fiber proteins of Ad11p and Ad35 reciprocally blocked the binding of both viruses to the epithelial cells but they could not block Ad4. The hexon protein expression of Ad11p and Ad4 was 100 times more efficient than that of the Ad5 vector (pFG140), whereas the infectivity of Ad11p and Ad4 was 40- to 200-fold that of the commonly used Ad5v vector. Taken together, our findings demonstrate that Ad11p and Ad4 bind different receptor molecules and that the fibers of these two viruses provide the predominant high degree of binding, which obviously is a requirement for subsequent internalization and efficacious expression.

Adenovirus vectors containing chimeric type 5 and type 35 fiber proteins exhibit altered and expanded tropism and increase the size limit of foreign genes

Adenovirus (Ad) fiber proteins are responsible for the initial attachment of the virion to the cell membrane. Most Ad vectors currently in use are based on the Ad type 5 (Ad5), which belong to subgroup C, and use the coxsackievirus and adenovirus receptors (CAR) as the initial receptor. Ad35, which belongs to subgroup B, recognizes unknown receptor(s) other than CAR. In this study, the feasibility of the Ad vector containing Ad5/35 chimeric fiber protein was examined in a wide variety of cell types, such as CAR-positive or -negative human tumor cells, rodent cells, and blood cells (a total of 20 cell types), and in mice in vivo. Transduction data suggested that the Ad vectors containing the Ad5/35 chimeric fiber protein exhibited altered and expanded tropism when compared with the Ad5-based vector. The chimeric vector also allows the packaging of larger foreign DNAs than the conventional Ad5-based vector, which can package approximately 8.1-8.2 kb of foreign DNA. The chimeric vector containing approximately 8.8 kb of foreign DNA was generated without affecting the viral growth rate and titer. These results suggested that inclusion of the Ad35 fiber protein into the Ad5-based vector could lead to an improved efficiency in gene therapy and in gene transfer experiments, especially for the cells lacking in sufficient CAR expression.

Feline hyperthyroidism: advances towards novel molecular therapeutics

Feline hyperthyroidism is the most common endocrine disorder of the elderly cat. Traditionally, the disease is treated by surgical thyroidectomy, medical management with antithyroid drugs or radiation therapy using iodine-131. However, none of these treatments is ideal and molecular therapeutics may offer novel methods of treating the disease. This article reviews the background of, and preliminary investigations into, the development of a transcriptionally targeted somatic gene therapy strategy for the treatment of this feline condition.

Artificial extension of the adenovirus fiber shaft inhibits infectivity in coxsackievirus and adenovirus receptor-positive cell lines

Recent studies demonstrate that virus-cellular receptor interactions are not the sole determinants of adenovirus (Ad) tropism. It has been shown that the fiber shaft length, which ranges from 6 to 23 beta-repeats in human Ads, also influences viral tropism. However, there is no report that investigates whether artificial extension of the shaft alters the infectivity profile of Ad. Therefore, we constructed Ad serotype 5 (Ad5) capsid-based longer-shafted Ad vectors by incorporating Ad2 shaft fragments of different lengths into the Ad5 shaft. We show that "longer-shafted" Ad vectors (up to 32 beta-repeats) could be rescued. We also show that longer-shafted Ad vectors had no impact on knob-CAR (coxsackievirus and Ad receptor) interaction compared to wild-type Ad. Nevertheless, gene transfer efficiencies of longer-shafted Ad vectors were lower in CAR-positive cell lines compared to wild-type Ad. We suggest that artificial extension of the shaft can inhibit infectivity in the context of CAR-positive cell lines without modification of knob-CAR interaction.

Ablating adenovirus type 5 fiber-CAR binding and HI loop insertion of the SIGYPLP peptide generate an endothelial cell-selective adenovirus

Adenovirus type 5 (Ad) based vectors transduce vascular endothelial cells (EC) and have been widely used for vascular gene transfer. However, many cell types express the Ad receptor (cox-sackievirus adenovirus receptor; CAR), preventing selective EC infection and precluding clinical use. We previously isolated the human EC-binding peptides SIGYPLP and LSNFHSS by phage display and demonstrated by means of a bispecific antibody that SIGYPLP directs efficient, high-level, EC-selective Ad-mediated gene transfer. We now generate genetically modified Ad fiber proteins with selective EC tropism by engineering these peptides into the HI loop of the Ad fiber. SIGYPLP, but not LSNFHSS, enhanced EC selectivity, demonstrating maintenance of peptide-cell binding fidelity upon incorporation into virions. Combining fiber mutations that block CAR binding (detargeting) with SIGYPLP insertion (retargeting) generated a novel Ad vector, AdKO1SIG, in a single component system. AdKO1SIG demonstrated efficient and selective tropism for EC compared with control Ad vectors. This is the first demonstration of genetic incorporation of a novel, mammalian, cell-selective ligand that retains its targeting fidelity in the Ad fiber HI loop, in combination with point mutations that abolish fiber-CAR interaction. This study demonstrates the potential for improving the cell-selectivity and safety of adenoviral vectors.

Replication-defective vector based on a chimpanzee adenovirus

An adenovirus previously isolated from a mesenteric lymph node from a chimpanzee was fully sequenced and found to be similar in overall structure to human adenoviruses. The genome of this virus, called C68, is 36,521 bp in length and is most similar to subgroup E of human adenovirus, with 90% identity in most adenovirus type 4 open reading frames that have been sequenced. Substantial differences in the hexon hypervariable regions were noted between C68 and other known adenoviruses, including adenovirus type 4. Neutralizing antibodies to C68 were highly prevalent in sera from a population of chimpanzees, while sera from humans and rhesus monkeys failed to neutralize C68. Furthermore, infection with C68 was not neutralized from sera of mice immunized with human adenovirus serotypes 2, 4, 5, 7, and 12. A replication-defective version of C68 was created by replacing the E1a and E1b genes with a minigene cassette; this vector was efficiently transcomplemented by the E1 region of human adenovirus type 5. C68 vector transduced a number of human and murine cell lines. This nonhuman adenoviral vector is sufficiently similar to human serotypes to allow growth in 293 cells and transduction of cells expressing the coxsackievirus and adenovirus receptor. As it is dissimilar in regions such as the hexon hypervariable domains, C68 vector avoids significant cross-neutralization by sera directed against human serotypes.

Targeting of high-capacity adenoviral vectors

High-capacity adenoviral (HC-Ad) vectors contain only the noncoding termini of the viral genome, can deliver large DNA fragments of up to 36 kb into target cells, and feature reduced toxicity and prolonged transgene expression in vivo. To enhance the potential of HC-Ad vectors to transduce specific cell types, we constructed a versatile infectious new helper virus plasmid that can be used readily to introduce peptide ligands into the HI loop of the fiber knob domain of Ad5-based HC-Ad vectors. Helper viruses with a 6x-His epitope or Arg-Gly-Asp (RGD) peptide insertion retained the full infectivity of the wild-type helper virus. The RGD-modified helper virus was used for production of a capsid-modified HC-Ad vector expressing beta-galactosidase. The RGD HC-Ad vector transduced the ovarian carcinoma cell lines SK-OV-3 and OVCAR-3 with 4- to 20-fold higher efficiency, compared to unmodified vectors. Transduction of both primary vascular smooth muscle cells as well as primary human endothelial cells was increased up to 15-fold with the RGD-modified vector. Competition experiments with recombinant knob protein and different RGD peptides indicated that the RGD-mediated transduction was Coxsackie and Adenovirus receptor (CAR)-independent and involved integrin alpha(v)beta(5). The use of fiber-modified helper viruses in the last amplification step of HC-Ad vector production allows for convenient and efficient targeting of these vectors towards different cell types. Targeting strategies will increase the spectrum of applications for HC-Ad vectors and will further add to their safety.

Efficient infection of primitive hematopoietic stem cells by modified adenovirus

Almost all studies of adenoviral vector-mediated gene transfer have made use of the adenovirus type 5 (Ad5). Unfortunately, Ad5 has been ineffective at infecting hematopoietic progenitor cells (HPC). Chimeric Ad5/F35 vectors that have been engineered to substitute the shorter-shafted fiber protein from Ad35 can efficiently infect committed hematopoietic cells and we now show highly effective gene transfer to primitive progenitor subsets. An Ad5GFP and Ad5/F35GFP vector was added to CD34(+) and CD34(-)lineage(-) (lin(-)) HPC. Only 5-20% of CD34(+) and CD34(-)lin(-) cells expressed GFP after Ad5 exposure. In contrast, with the Ad5/F35 vector, 30-70% of the CD34(+), 50-70% of the CD34(-)lin(-) and up to 60% of the CD38(-) HPC expressed GFP and there was little evident cellular toxicity. Because of these improved results, we also analyzed the ability of Ad5/F35 virus to infect the hoechst negative 'side population' (SP) of marrow cells, which appear to be among the very earliest multipotent HPC. Between 51% and 80% of marrow SP cells expressed GFP. The infected populations retained their ability to form colonies in two short-term culture systems, with no loss of viability. We also studied the transfer and expression of immunomodulatory genes, CD40L (cell surface expression) and interleukin-2 (secreted). Both were expressed at immunomodulatory levels for >5 days. The ability of Ad5/F35 to deliver transgenes to primitive HPC with high efficiency and low toxicity in the absence of growth factors provides an improved means of studying the consequences of transient gene expression in these cells.

Rapid assessment of adenovirus serum neutralizing antibody titer based on quantitative, morphometric evaluation of capsid binding and intracellular trafficking: population analysis of adenovirus capsid association with cells is predictive of adenovirus infectivity

Neutralizing antiviral antibodies are typically detected on the basis of inhibition of viral function, such as propagation of a viral infection or inhibition of viral gene expression. Evidence is presented that anti-adenovirus neutralizing antibodies can be evaluated by analysis of cell-associated capsids or by analysis of intracellular trafficking of the capsids within 1 h after infection. Quantitative analyses of these morphologic parameters represent rapid, broadly applicable, functional assays for the detection of anti-adenovirus neutralizing antibodies.

Adenovirus serotype 7 retention in a late endosomal compartment prior to cytosol escape is modulated by fiber protein

The intracellular trafficking of adenovirus (Ad) subgroup B (e.g., Ad7) differs from that of subgroup C (e.g., Ad5) in that Ad5 rapidly escapes from endocytic compartments following infection whereas Ad7 accumulates in organelles. To assess the hypothesis that Ad7 is targeted to the lysosomal pathway, Ad7 and Ad5 were conjugated with fluorophores and their trafficking in A549 epithelial cells was analyzed by fluorescence microscopy. Within 1 h after infection, Ad7, but not Ad5, accumulated in the cytoplasm of A549 cells. The pH in the environment of Ad5 was nearly neutral (pH 7), while Ad7 occupied acidic compartments (pH 5) over the first 2 h with a gradual shift toward neutrality by 8 h. Ad7 partially colocalized with alpha(2)-macroglobulin and late endosomal and lysosomal marker proteins, including Rab7, mannose-6-phosphate receptor, and LAMP-1. The pH optimum for membrane lysis by Ad7, as well as a chimeric Ad5 capsid that expressed the Ad7 fiber (Ad5fiber7), was pH 5.5, while that for lysis by Ad5 was pH 6.0. Thus, the native trafficking pathway for Ad7 involves residence in late endosomes and lysosomes, with information encoded in the Ad7 fiber acting as a pH-dependent trigger for membrane lysis and escape to the cytosol.

A 50-kDa membrane protein mediates sialic acid-independent binding and infection of conjunctival cells by adenovirus type 37

The ocular tropism of adenovirus type 37 (Ad37) does not correlate with the wide distribution of the 46-kDa coxsackievirus and adenovirus receptor (CAR), the major receptor for most adenovirus serotypes. We previously found that Ad37 infects and binds well to conjunctival cells (Chang C), but poorly to lung epithelial (A549) cells that express CAR and hypothesized that this serotype uses a distinct receptor that is selectively expressed on conjunctival cells. To test this, we produced particles of a fiber-deleted Ad5 vector containing the Ad37 fiber protein. The "pseudotyped" vector infected Chang C cells better than A549 cells using a CAR-independent pathway. Ad37 binding was calcium-dependent and was abolished by protease digestion of cell surface proteins. Using a virus overlay protein blot assay (VOPBA), we detected calcium-dependent Ad37 binding to 50- and 60-kDa membrane proteins on permissive Chang C cells. In contrast, calcium-dependent binding was detected with only the 60-kDa protein on nonpermissive A549 cells. Ad19p, a closely related serotype that failed to bind to conjunctival cells, recognized the 60-kDa, but not the 50-kDa, protein. Ad37 has been reported to use sialic acid instead of CAR as a cell receptor on A549 cells. Pretreatment of Chang C cells with neuraminidase abolished Ad37 binding to only the 60-kDa protein, suggesting that sialic acid mediates Ad37 binding to the 60-kDa protein. The pseudotyped Ad37 vector was also able to infect neuraminidase-treated Chang C cells. Thus, subgroup D adenoviral binding to the 50-kDa protein is calcium-dependent and cell type- and serotype-specific, whereas binding to the 60-kDa protein is not necessary for infection of conjunctival cells. Together, these data suggest that the 50-kDa protein is the major receptor for Ad37 on conjunctival cells.

Pseudopackaging of adenovirus type 5 genomes into capsids containing the hexon proteins of adenovirus serotypes B, D, or E

Adenoviruses (Ad) show promise as a vector system for gene delivery in vivo. However, a major challenge in the development of Ad vectors is the circumvention of the host immune responses to Ad infection, including both the host cytotoxic T-cell response and the humoral response resulting in neutralizing antibodies. One method to circumvent the effect of neutralizing antibodies against an Ad vector is to use different Ad serotypes to deliver the transgene of interest. This approach has been demonstrated with Ad genomes of highly related members of subgroup C. However, it is not known whether an Ad5-based vector DNA molecule can be packaged into capsids of evolutionarily more divergent adenoviruses. The aim of these studies was to determine if capsids containing hexon proteins from other Ad subgroups could package the Ad5 genome. A genetic approach utilizing an Ad5 temperature-sensitive (ts) mutant with a mutation in the hexon protein was used. When grown at the nonpermissive temperature, Ad5 ts147 replicates normally, providing a source of Ad5 DNA for virus assembly, but does not produce virus particles due to the hexon protein mutation. Coinfection of Ad5 ts147 with a wild-type virus of other Ad serotypes (Ad3, Ad4, or Ad9), which supply functional hexon proteins, resulted in the pseudopackaging of the Ad5 DNA genome. Furthermore, the pseudopackaged Ad5 DNA virions obtained in the coinfections were infectious. Therefore, switching hexons did not impair the infectivity or uncoating process of the pseudopackaged virion. Since hexon protein is a major antigenic determinant of the Ad capsid, this approach may prove useful to reduce the antigenicity of therapeutic Ad vectors and allow repeated vector administration.

Uptake of adenoviral vectors via fibroblast growth factor receptors involves intracellular pathways that differ from the targeting ligand

Target-specific delivery of adenoviral gene therapy vectors has been achieved by introducing basic fibroblast growth factor (FGF2) onto viral capsids. FGF2-retargeted vectors enter the cell through high-affinity FGF receptors while normal adenoviral receptor interactions are ablated. In addition, FGF2-mediated targeting permits a higher level of transgene expression and in vivo efficacy. We now present studies on the intracellular pathways and mechanisms of transduction by FGF2-retargeted adenovirus. FGF2 retargeting results in increased virion entry. Nuclear delivery is also increased, but to a level that is directly proportional to virion entry. In addition, after entry, the retargeted particle rapidly localizes to the nucleus in a time frame similar to that of adenovirus alone. Transgene expression is always enhanced with FGF2-mediated delivery, whether overall transduction of the population is increased, equivalent, or decreased relative to nontargeted adenoviral vectors. However, the increase in transgene expression does not correlate quantitatively with enhanced cellular entry, indicating that other factors may influence transgene expression levels. The increase in transgene expression occurs only when the FGF2-retargeting moiety is physically complexed with the adenoviral vector, indicating a requirement for a spatial link between the ligand and the virus particle. The FGF2-adenoviral complex activates the FGF receptor-mediated proliferative signaling cascade, but this signal transduction is not required for the enhanced level of gene expression observed after FGF2-mediated delivery. These findings emphasize that, in addition to altering receptor tropism, the influence of FGF2 retargeting extends to intracellular adenoviral trafficking pathways. Although the increased delivery of virions into the cell and nucleus contributes to the enhanced transgene expression observed with FGF2 retargeting, other as yet undefined cellular mechanisms also contribute to this process.

Functional and selective targeting of adenovirus to high-affinity Fcgamma receptor I-positive cells by using a bispecific hybrid adapter

Adenovirus (Ad) efficiently delivers its DNA genome into a variety of cells and tissues, provided that these cells express appropriate receptors, including the coxsackie-adenovirus receptor (CAR), which binds to the terminal knob domain of the viral capsid protein fiber. To render CAR-negative cells susceptible to Ad infection, we have produced a bispecific hybrid adapter protein consisting of the amino-terminal extracellular domain of the human CAR protein (CARex) and the Fc region of the human immunoglobulin G1 protein, comprising the hinge and the CH2 and CH3 regions. CARex-Fc was purified from COS7 cell supernatants and mixed with Ad particles, thus blocking Ad infection of CAR-positive but Fc receptor-negative cells. The functionality of the CARex domain was further confirmed by successful immunization of mice with CARex-Fc followed by selection of a monoclonal anti-human CAR antibody (E1-1), which blocked Ad infection of CAR-positive cells. When mixed with Ad expressing eGFP, CARex-Fc mediated an up to 250-fold increase of transgene expression in CAR-negative human monocytic cell lines expressing the high-affinity Fcgamma receptor I (CD64) but not in cells expressing the low-affinity Fcgamma receptor II (CD32) or III (CD16). These results open new perspectives for Ad-mediated cancer cell vaccination, including the treatment of acute myeloid leukemia.

Dependence of adenovirus infectivity on length of the fiber shaft domain

One of the objectives in adenovirus (Ad) vector development is to target gene delivery to specific cell types. Major attention has been given to modification of the Ad fiber knob, which is thought to determine virus tropism. However, among the human Ad serotypes with different tissue tropisms, not only the knob but also the length of the fiber shaft domain varies significantly. In this study we attempted to delineate the role of fiber length in coxsackievirus-adenovirus receptor (CAR)- and non-CAR-mediated infection. A series of Ad serotype 5 (Ad5) capsid-based vectors containing long or short fibers with knob domains derived from Ad5, Ad9, or Ad35 was constructed and tested in adsorption, internalization, and transduction studies. For Ad5 or Ad9 knob-possessing vectors, a long-shafted fiber was critical for efficient adsorption/internalization and transduction of CAR/alphav integrin-expressing cells. Ad5 capids containing short CAR-recognizing fibers were affected in cell adsorption and infection. In contrast, for the chimeric vectors possessing Ad35 knobs, which enter cells by a CAR/alphav integrin-independent pathway, fiber shaft length had no significant influence on binding or infectibility on tested cells. The weak attachment of short-shafted Ad5 or Ad9 knob-possessing vectors seems to be causally associated with a charge-dependent repulsion between Ad5 capsid and acidic cell surface proteins. The differences between short- and long-shafted vectors in attachment or infection were abrogated by preincubation of cells with polycations. This study demonstrates that the fiber-CAR interaction is not the sole determinant for tropism of Ad vectors containing chimeric fibers. CAR- and alphav integrin-mediated infections are influenced by other factors, including the length of the fiber shaft.

Virosomes: evolution of the liposome as a targeted drug delivery system

The drug delivery system (DDS) is attractive as a therapeutic method. Liposomes are of particular interest as a DDS because they can reduce drug toxicity, and offer promise as gene carriers. An evolution has occurred in the construction of liposomes in the effort to develop efficient vectors for in vivo use. To avoid uptake by the reticuloendothelial system (RES); Lipid components have been optimized. To enhance tissue targeting, liposome surface has been modified with antibodies or ligands recognized by specific cell types. To enhance the efficiency of gene delivery by the introduction of molecules directly into cells, virosomes have been developed by combining liposomes with fusiogenic viral envelope proteins. Liposomes are now being used in the treatment of intractable human diseases such as cancer and monogenic disorders. In the future, many medical procedures will be performed using liposomes.

Inhibitory effect of cystic fibrosis sputum on adenovirus-mediated gene transfer in cultured epithelial cells

Effective gene transfer to the airway epithelial cells of individuals with cystic fibrosis (CF) requires gene therapy vectors to effectively penetrate the mucous lining of the airways of these patients. In this study, we examined the effects of the aqueous sol fraction of sputum recovered from CF patients (CF sol) on adenovirus (Ad)-mediated gene transfer to cultured epithelial cells. Sputum collected from patients with CF was separated into aqueous sol and gel fractions by ultracentrifugation and the sol fraction from different individuals was pooled. To determine if CF sol affects Ad-mediated transfection, Fisher rat thyroid (FRT) epithelial cells or normal human bronchial epithelial (NHBE) cells were infected with an Ad encoding beta-galactosidase (Ad2/betagal-2) in the presence or absence of the pooled CF sol. Transfection efficiency was determined by measuring beta-Gal activity. CF sol significantly inhibited Ad2-mediated gene transfer in a dose-dependent manner when the vector was incubated with CF sol prior to exposure to the cells. In contrast, preincubation of the cells with the sol was without effect. The inhibition of Ad-mediated gene transfer by CF sol was not related to its low pH, was abrogated by preadsorption with an Ad2 serotype vector, and was neutralized by heat treatment, but was not affected by treatment with protease inhibitors. Analysis of CF sol fractions from seven different individuals with CF showed inhibition of Ad-mediated gene transfer in four of the seven samples tested and, further, the inhibitory effect was correlated with the presence of Ad-specific antibodies. We conclude that preexisting adenovirus-specific antibodies present in some of the patient samples were the predominant factor inhibiting Ad-mediated gene transfer.

Ectodomain of coxsackievirus and adenovirus receptor genetically fused to epidermal growth factor mediates adenovirus targeting to epidermal growth factor receptor-positive cells

Human adenovirus (Ad) is extensively used for a variety of gene therapy applications. However, the utility of Ad vectors is limited due to the low efficiency of Ad-mediated gene transfer to target cells expressing marginal levels of the Ad fiber receptor. Therefore, the present generation of Ad vectors could potentially be improved by modification of Ad tropism to target the virus to specific organs and tissues. The fact that coxsackievirus and adenovirus receptor (CAR) does not play any role in virus internalization, but functions merely as the virus attachment site, suggests that the extracellular part of CAR might be utilized to block the receptor recognition site on the Ad fiber knob domain. We proposed to design bispecific fusion proteins formed by a recombinant soluble form of truncated CAR (sCAR) and a targeting ligand. In this study, we derived sCAR genetically fused with human epidermal growth factor (EGF) and investigated its ability to target Ad infection to the EGF receptor (EGFR) overexpressed on cancer cell lines. We have demonstrated that sCAR-EGF protein is capable of binding to Ad virions and directing them to EGFR, thereby achieving targeted delivery of reporter gene. These results show that sCAR-EGF protein possesses the ability to effectively retarget Ad via a non-CAR pathway, with enhancement of gene transfer efficiency.

Viral vectors for gene transfer: a review of their use in the treatment of human diseases

The efficient delivery of therapeutic genes and appropriate gene expression are the crucial issues for clinically relevant gene therapy. Viruses are naturally evolved vehicles which efficiently transfer their genes into host cells. This ability made them desirable for engineering virus vector systems for the delivery of therapeutic genes. The viral vectors recently in laboratory and clinical use are based on RNA and DNA viruses processing very different genomic structures and host ranges. Particular viruses have been selected as gene delivery vehicles because of their capacities to carry foreign genes and their ability to efficiently deliver these genes associated with efficient gene expression. These are the major reasons why viral vectors derived from retroviruses, adenovirus, adeno-associated virus, herpesvirus and poxvirus are employed in more than 70% of clinical gene therapy trials worldwide. Among these vector systems, retrovirus vectors represent the most prominent delivery system, since these vectors have high gene transfer efficiency and mediate high expression of therapeutic genes. Members of the DNA virus family such as adenovirus-, adeno-associated virus or herpesvirus have also become attractive for efficient gene delivery as reflected by the fast growing number of clinical trials using these vectors. The first clinical trials were designed to test the feasibility and safety of viral vectors. Numerous viral vector systems have been developed for ex vivo and in vivo applications. More recently, increasing efforts have been made to improve infectivity, viral targeting, cell type specific expression and the duration of expression. These features are essential for higher efficacy and safety of RNA- and DNA-virus vectors. From the beginning of development and utilisation of viral vectors it was apparent that they harbour risks such as toxicities, immunoresponses towards viral antigens or potential viral recombination, which limit their clinical use. However, many achievements have been made in vector safety, the retargeting of virus vectors and improving the expression properties by refining vector design and virus production. This review addresses important issues of the current status of viral vector design and discusses their key features as delivery systems in gene therapy of human inherited and acquired diseases at the level of laboratory developments and of clinical applications.

Initial interactions of subgenus D adenoviruses with A549 cellular receptors: sialic acid versus alpha(v) integrins

Selected members of the adenovirus family have been shown to interact with the coxsackie adenovirus receptor, alpha(v) integrins, and sialic acid on target cells. Initial interactions of subgenus D adenoviruses with target cells have until now been poorly characterized. Here, we demonstrate that adenovirus type 8 (Ad8), Ad19a, and Ad37 use sialic acid as a functional cellular receptor, whereas the Ad9 and Ad19 prototypes do not.

Ligand-mediated retargeting of recombinant adenovirus for gene transfer in vivo

The development of efficient and safe methods for in vivo gene transfer is central to the success of gene therapy. Recombinant adenoviral vectors, although highly efficient, are limited by the host immune response, potential safety hazards due to obligatory cotransfer of viral proteins, and their broad tissue tropism. Here, we demonstrate in an animal model that host range and tissue tropism of a recombinant adenovirus from a distant species can be modified by complexing adenovirus with a cell-specific ligand. Thus, a replication-deficient lacZ recombinant human adenovirus, which naturally does not infect avian cells, allowed highly efficient and specific gene transfer to the liver of ducks in vivo when complexed with N-acetylglucosamine, a ligand for the chicken hepatic lectin. This combination of ligand-mediated receptor targeting with adenoviral uptake and intracellular processing of a given gene represents a novel approach to gene therapy of inherited and acquired liver diseases.

Retroviral vector targeting to human immunodeficiency virus type 1-infected cells by receptor pseudotyping

We report the generation of retroviral vectors based on Moloney murine leukemia virus that specifically transduce cells infected with T-cell-tropic human immunodeficiency virus type 1 (HIV-1). This vector was pseudotyped with T-cell-tropic HIV-1 receptors CD4 and CXCR4. We demonstrate that transduction is contingent upon HIV-1 gp120 and gp41 expression.

Latest developments in gene transfer technology: achievements, perspectives, and controversies over therapeutic applications

Over the last decade, more than 300 phase I and phase II gene-based clinical trials have been conducted worldwide for the treatment of cancer and monogenic disorders. Lately, these trials have been extended to the treatment of AIDS and, to a lesser extent, cardiovascular diseases. There are 27 currently active gene therapy protocols for the treatment of HIV-1 infection in the USA. Preclinical studies are currently in progress to evaluate the possibility of increasing the number of gene therapy clinical trials for cardiopathies, and of beginning new gene therapy programs for neurologic illnesses, autoimmuno diseases, allergies, regeneration of tissues, and to implement procedures of allogeneic tissues or cell transplantation. In addition, gene transfer technology has allowed for the development of innovative vaccine design, known as genetic immunization. This technique has already been applied in the AIDS vaccine programs in the USA. These programs aim to confer protective immunity against HIV-1 transmission to individuals who are at risk of infection. Research programs have also been considered to develop therapeutic vaccines for patients with AIDS and generate either preventive or therapeutic vaccines against malaria, tuberculosis, hepatitis A, B and C viruses, influenza virus, La Crosse virus, and Ebola virus. The potential therapeutic applications of gene transfer technology are enormous. However, the effectiveness of gene therapy programs is still questioned. Furthermore, there is growing concern over the matter of safety of gene delivery and controversy has arisen over the proposal to begin in utero gene therapy clinical trials for the treatment of inherited genetic disorders. From this standpoint, despite the latest significant achievements reported in vector design, it is not possible to predict to what extent gene therapeutic interventions will be effective in patients, and in what time frame.