Efficient oncolysis by a replicating adenovirus (ad) in vivo is critically dependent on tumor expression of primary ad receptors

Replicating adenoviruses (Ads) are designed to replicate in and destroy cancer cells, generating viral progeny that spread within the tumor. To address the importance of the primary cellular receptor for Ads, the coxsackievirus and Ad receptor (CAR), in permitting intratumoral spread of a replicating Ad, we have used a pair of tumor cell lines differing only in the expression of a primary receptor for Ad5. This novel system thus allowed the first direct evaluation of the relationship between the efficacy of a replicating Ad and the primary receptor levels of the host cell without the confounding influence of other variable cellular factors. We demonstrate that the absence of the primary cellular receptor on the tumor cells restricts the oncolytic potency of a replicating Ad both in vitro and in vivo. Based on these findings, it is apparent that the potential therapeutic advantages afforded by viral replication would be negated by poor intratumoral spread of the viral progeny due to the failure to infect neighboring tumor cells. Because a number of studies have reported that primary cancer cells express only low levels of CAR, our results suggest that strategies to redirect Ads to achieve CAR-independent infection will be necessary to realize the full potential of replicating Ads in the clinical setting.

Advanced generation adenoviral vectors possess augmented gene transfer efficiency based upon coxsackie adenovirus receptor-independent cellular entry capacity

Adenoviral (Ad) vectors have been widely used in the context of cancer gene therapy approaches. Their utility in these contexts, however, has frequently been limited by tumor cell resistance to Ad infection. The basis of this resistance has been defined recently as resulting from a deficiency of the primary adenovirus receptor, coxsackie adenovirus receptor. As a means to circumvent this limitation, a variety of tropism modification strategies have allowed coxsackie adenovirus receptor-independent gene delivery via the Ad vector. These advanced generation adenovirus vectors exhibit enhanced infectivity, which can allow direct therapeutic gain. Such vectors may allow improvements in efficacy in the context of ongoing human clinical gene therapy approaches for cancer.

A targetable, injectable adenoviral vector for selective gene delivery to pulmonary endothelium in vivo

Adenoviral (Ad) vectors are promising gene therapy vehicles due to their in vivo stability and efficiency, but their potential utility is compromised by their restricted tropism. Targeting strategies have been devised to improve the efficacy of these agents, but specific targeting following in vivo systemic administration of vector has not previously been demonstrated. The distinct aim of the current study was to determine whether an Ad-targeting strategy could maintain fidelity upon systemic vascular administration. We used a bispecific antibody to target Ad infection specifically to angiotensin-converting enzyme (ACE), which is preferentially expressed on pulmonary capillary endothelium and which may thus enable gene therapy for pulmonary vascular disease. Cell-specific gene delivery to ACE-expressing cells was first confirmed in vitro. Administration of retargeted vector complex via tail vein injection into rats resulted in at least a 20-fold increase in both Ad DNA localization and luciferase transgene expression in the lungs, compared to the untargeted vector. Furthermore, targeting led to reduced transgene expression in nontarget organs, especially the liver, where the reduction was over 80%. Immunohistochemical and immunoelectron microscopy analysis confirmed that the pulmonary transgene expression was specifically localized to endothelial cells. Enhancement of transgene expression in the lungs as a result of the ACE-targeting strategy was also confirmed using a new noninvasive imaging technique. This study shows that a retargeting approach can indeed specifically modify the gene delivery properties of an Ad vector given systemically and thus has encouraging implications for the further development of targetable, injectable Ad vectors.

Adenoviral vectors targeted to CD40 enhance the efficacy of dendritic cell-based vaccination against human papillomavirus 16-induced tumor cells in a murine model

Dendritic cells (DCs) represent a unique junction from which to initiate antigen-specific immunity. One of the most challenging obstacles for DC-based immunotherapy has been the means by which to convey tumor antigen-encoding genes to DCs. In this study, we show that adenoviral (or adenovirus, Ad) vectors targeted to CD40 by means of bispecific antibodies can enhance gene transfer to murine DCs. Moreover, we illustrate that this vector initiates phenotypic changes characteristic of DC maturation. To explore the in vivo potential of this strategy, we coupled this targeting approach with an Ad vector carrying the gene for a tumor antigen. In particular, the human papillomavirus (HPV) E7 antigen represents an attractive target for antigen-specific immunity of cervical cancer. Relative to DCs infected by untargeted Ad, DCs infected by AdE7 targeted to the receptor CD40 enhanced protection against HPV-16-induced tumor cells in a murine model. We have further established that this protection was both antigen specific and CD8+ T-cell dependent. Illustrating that Ad-modified DCs may be used in repeated vaccination, we report that preimmunization of animals with Ad infected DCs prior to E7 vaccination only moderately reduced vaccine efficacy. Finally, we have observed that CD40-targeted AdE7 can initiate partial therapeutic immunity in mice bearing established tumors. These findings suggest that gene-based vaccination of DCs with tumor antigens can elicit productive antitumoral immunity and that enhancements in gene transfer efficacy and/or DC maturation may facilitate this process.

Development and evaluation of a rapid dipstick assay for serodiagnosis of acute human brucellosis

A dipstick assay for the detection of brucella-specific immunoglobulin M antibodies was evaluated with 707 sera from 247 laboratory-confirmed brucellosis patients and 342 control sera from brucellosis-free individuals. These sera were collected from six different countries. The assay was found to be highly sensitive and specific. In addition, the test is easy to use and does not require specialized training or equipment, and the components are stable without a requirement for refrigeration. All of these factors make the test ideal for developing countries and rural settings.

Selective gene delivery to head and neck cancer cells via an integrin targeted adenoviral vector

In vivo cancer gene therapy approaches for squamous cell carcinoma of the head and neck (SCCHN) based on adenoviral vector-mediated gene delivery have been limited by the suboptimal efficacy of gene transfer to tumor cells. We hypothesized that this issue was due to deficiency of the primary adenoviral receptor, the coxsackie-adenovirus receptor (CAR), on the tumor targets. Studies of CAR levels on SCCHN cell lines confirmed that their relative refractoriness to the adenoviral vector was based on this deficiency. To circumvent this deficiency, we applied an adenoviral vector targeted to a tumor cell marker characteristic of SCCHN. In this regard, integrins of the alpha2beta1 and alpha3beta1 class are frequently overexpressed in SCCHN. Furthermore, these integrins recognize the RGD peptide motif. On this basis, we applied an adenoviral vector genetically modified to contain such a peptide within the HI loop of the fiber protein as a means to alter viral tropism. Studies confirmed that the CAR-independent gene delivery achieved via this strategy allowed enhanced gene transfer efficiencies to SCCHN tumor cells. Importantly, this strategy could achieve preferential augmentation of gene transfer in tumor cells compared with normal cells. The ability to achieve enhanced and specific gene transfer to tumor cells via adenoviral vectors has important implications for gene therapy strategies for SCCHN and for other neoplasms in general.

Retargeting to EGFR enhances adenovirus infection efficiency of squamous cell carcinoma

BACKGROUND

Adenovirus-mediated gene therapy has been used for squamous cell carcinoma of the head and neck (SCCHN), but the in vivo efficacy has been limited by a lack of tissue specificity and low infection efficiency. We are interested in improving cancer gene therapy strategies using targeted adenovirus vectors.

OBJECTIVE

To determine if the infection efficiency of adenovirus-mediated gene transfer to SCCHN cells could be enhanced by retargeting to the epidermal growth factor receptor (EGFR), which is known to be overexpressed in these tumors.

DESIGN

Epidermal growth factor receptor retargeting in SCCHN cells was accomplished with a bispecific antibody that recognized the knob domain of adenovirus as well as EGFR. Using this retargeting schema, we compared the infection efficiency and specificity of unmodified and EGFR-retargeted adenovirus.

RESULTS

Squamous cell carcinoma of the head and neck cell lines were shown to be infected by adenovirus with low efficiency, which is likely because of the low level of adenovirus receptor expressed in the SCCHN cells. Epidermal growth factor receptor retargeting markedly enhanced transduction in both SCCHN cell lines and primary tumor tissue, as indicated by the elevated levels of reporter gene expression. Furthermore, retargeting enhanced infection of tumor tissue compared with normal tissue from the same patient.

CONCLUSIONS

Epidermal growth factor receptor retargeting enhanced adenovirus infection of SCCHN cells and, in doing so, augments the potency of the vector. This modification makes the vector potentially more valuable in the clinical setting.

Reduction of ischemia-reperfusion injury of the liver by in vivo adenovirus-mediated gene transfer of the antiapoptotic Bcl-2 gene

OBJECTIVE

To examine the possibility of reducing ischemia-reperfusion injury (I/R injury) to the mouse liver by in vivo adenovirus-mediated gene transfer of the antiapoptotic human Bcl-2 gene.

SUMMARY BACKGROUND DATA

Ischemia-reperfusion injury has been demonstrated in a number of clinically relevant diseases such as myocardial infarction, cerebrovascular disease, sepsis, peripheral vascular disease, and organ transplantation. In this regard, apoptosis plays a central role.

METHODS

Normal C57BL/6 mice were used. An adenovirus (deltaE1) vector containing the human Bcl-2 gene was developed in the authors' laboratory. An adenovirus vector encoding an irrelevant gene (beta-galactosidase, AdCMVLacZ) was used as a control. Taking advantage of the hepatotropic properties of adenovirus vectors, gene transfer was performed with 1 x 10(9) plaque-forming units by intravenous tail injection, 48 hours before the ischemic injury. Ischemic-reperfusion injury was induced by temporal and segmental occlusion of hepatic blood flow. Aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase activity was measured using standard assays. Liver biopsies were obtained before and 6 hours after I/R injury for morphologic assessment, and apoptosis was determined in situ with a histochemical assay.

RESULTS

The expression of AdCMVhBcl-2 vector was confirmed by reverse transcription-polymerase chain reaction and functionally validated in apoptotic studies in endothelial cells. Expression of the Bcl-2 gene protects against I/R injury, as shown by a significant decrease in transaminases (p < 0.05) and necrosis and apoptosis (p < 0.001), and permanent survival (p < 0.0001), compared with sham-operated animals and animals treated with AdCMVLacZ.

CONCLUSIONS

Genetic modification of the liver to induce cytoprotection has potential applications to prevent I/R injury to the liver in surgical interventions, including liver transplantation.

Fibroblast growth factor 2 retargeted adenovirus has redirected cellular tropism: evidence for reduced toxicity and enhanced antitumor activity in mice

Adenovirus (Ad) have been used as vectors to deliver genes to a wide variety of tissues. Despite achieving high expression levels in vivo, Ad vectors display normal tissue toxicity, transient expression, and antivector immune responses that limit therapeutic potential. To circumvent these problems, several retargeting strategies to abrogate native tropism and redirect Ad uptake through defined receptors have been attempted. Despite success in cell culture, in vivo results have generally not shown sufficient selectivity for target tissues. We have previously identified (C. K. Goldman et al., Cancer Res., 57: 1447-1451, 1997) the fibroblast growth factor (FGF) ligand and receptor families as conferring sufficient specificity and binding affinity to be useful for targeting DNA in vivo. In the present studies, we retargeted Ad using basic FGF (FGF2) as a targeting ligand. Cellular uptake is redirected through high-affinity FGF receptors (FGFRs) and not the more ubiquitous lower-affinity Ad receptors. Initial in vitro experiments demonstrated a 10- to 100-fold increase in gene expression in numerous FGFR positive (FGFR+) cell lines using FGF2-Ad when compared with Ad. To determine whether increased selectivity could be detected in vivo, FGF2-Ad was administered i.v. to normal mice. FGF2-Ad demonstrates markedly decreased hepatic toxicity and liver transgene expression compared with Ad treatment. Importantly, FGF2-Ad encoding the herpes simplex virus thymidine kinase (TK) gene transduces Ad-resistant FGFR+ tumor cells both ex vivo and in vivo, which results in substantially enhanced survival (180-260%) when the prodrug ganciclovir is administered. Because FGFRs are up-regulated on many types of malignant or injured cells, this broadly useful method to redirect native Ad tropism and to increase the potency of gene expression may offer significant therapeutic advantages.

A system for the propagation of adenoviral vectors with genetically modified receptor specificities

The development of genetically modified adenovirus (Ad) vectors with specificity for a single cell type will require both the introduction of novel tropism determinants and the ablation of endogenous tropism. Consequently, it will not be possible to exploit the native cellular entry pathway in the propagation of these targeted Ad vectors. Based on the concept that Ad enters cells by a two-step process in which a primary receptor serves as a high affinity binding site for the Ad fiber knob, with subsequent internalization mediated by alpha v integrins, we designed two artificial primary receptors. The extracellular domain of one of these synthetic receptors was derived from a single-chain antibody (sFv) with specificity for Ad5 knob, while the second receptor consisted of an icosapeptide identified by biopanning a phage display library against Ad5 knob. Expression of either of these artificial virus-binding receptors in fiber receptor-negative cells possessing alpha v integrins conferred susceptibility to Ad infection. We then created a novel mechanism for cell binding by genetically modifying both the vector and the target cell. In this approach, six histidine (His) residues were incorporated at the C-terminal of the Ad fiber protein. The resultant Ad vector was able to infect nonpermissive cells displaying the cognate artificial receptor, containing an anti-His sFv. This strategy, comprising a genetically engineered Ad virion and a modified cell line, should be useful in the propagation of targeted Ad vectors that lack the ability to bind the native fiber receptor.

Retrospective analysis of the Beijing family of Mycobacterium tuberculosis in preserved lung tissues

Direct repeat spoligotyping of 85 paraffin-embedded lung biopsies was used to investigated the occurrence around Beijing of the Beijing family of Mycobacterium tuberculosis. Samples ranged in time from 1956 to 1990. Hybridization patterns were found with 49 (58%) samples, and 45 (92%) produced typical Beijing family patterns extending over the 34-year period.

Differential susceptibility of primary and established human glioma cells to adenovirus infection: targeting via the epidermal growth factor receptor achieves fiber receptor-independent gene transfer

Adenovirus (Ad) vectors are promising for gene therapy of glioma due to their ability to achieve efficient gene transfer upon intratumoral administration. Yet in this context, Ad mediates widespread gene transfer to both tumor and surrounding parenchyma. Ad entry is dependent upon the expression of fiber receptors, such as coxsackie/adenovirus receptor, and alpha(v) integrins on the target cells for binding and internalization, respectively. We hypothesized that the susceptibility of human gliomas to Ad would likely be heterogeneous due to variable expression of these receptors. It was found that established human glioma cell lines exhibited differential susceptibility to Ad-mediated gene transfer, which correlated directly with the level of radiolabeled Ad binding and with the expression of coxsackie/adenovirus receptor but not with the expression of alpha(v) integrins. To circumvent the lack of fiber receptors and to target Ad gene transfer specifically to tumor cells, we used a bispecific antibody conjugate to ablate Ad binding to fiber receptors and retarget binding to the epidermal growth factor receptor (EGFR), a tumor-associated marker negligibly expressed in normal, mitotically quiescent neural tissues. The results demonstrate that EGFR-targeted Ad gene transfer was EGFR specific and independent of fiber-fiber receptor interactions. Furthermore, EGFR targeting significantly enhanced Ad gene delivery to 7 of 12 established glioma cell lines and to 6 of 8 cultured primary gliomas. Interestingly, EGFR-targeted Ad gene transfer did not correlate with EGFR expression across cell lines, suggesting the importance of other factors. This study establishes that fiber receptor expression limits the utility of Ad vectors for gene transfer to glioma cells and suggests that targeting Ad via EGFR may prove valuable for tumor-specific gene transfer to high-grade gliomas. These findings have key relevance in the context of Ad vector-based approaches for glioma gene therapy.

Basic fibroblast growth factor enhancement of adenovirus-mediated delivery of the herpes simplex virus thymidine kinase gene results in augmented therapeutic benefit in a murine model of ovarian cancer

A number of preclinical and human clinical gene therapy trials using adenoviral vectors have shown that the number of viral particles necessary to give adequate levels of gene transfer can be associated with significant vector-related toxicity. In an effort to reduce the number of adenoviral particles required for a given level of gene transfer, we sought to redirect adenoviral infection via a receptor that is highly expressed on the target cells. By using basic fibroblast growth factor (FGF2) as the targeting ligand, adenovirus-mediated gene transfer to the human ovarian cancer cell line SKOV3.ip1 was significantly enhanced, permitting the transduction of a greater number of target cells to be achieved by a given dose of virus. In a murine model of human ovarian carcinoma, an FGF2-redirected adenoviral vector carrying the gene for herpes simplex virus thymidine kinase (AdCMVHSV-TK) was shown to result in a significant prolongation of survival compared with the same number of particles of unmodified AdCMVHSV-TK. In addition, equivalent survival rates were achieved with a 10-fold lower dose of the FGF2-redirected AdCMVHSV-TK compared with the unmodified vector. To our knowledge, this is the first report demonstrating that strategies to enhance the efficiency of in vivo transduction of adenoviral vectors will be of clinical utility.

Imaging and tissue biodistribution of 99mTc-labeled adenovirus knob (serotype 5)

Hepatic sequestration of systemically administered adenoviral vectors reduces the number of viral particles available for delivery to other tissues. The biological basis of this phenomenon was investigated using a new in vivo technique which permitted imaging in real time. Recombinant adenovirus serotype 5 knob (Ad5K) was radiolabeled with the gamma-emitter 99mTc (half-life = 6 h). Scatchard analysis of the 99mTc-Ad5K showed specific, high-affinity binding to U293 cells (Kd = 1.4 +/- 0.5 nM), demonstrating that the radiolabeling process had no effect on receptor binding. In vivo dynamic imaging with an Anger gamma camera revealed that the liver binding followed an exponential rise to maximum, with a measured 100% extraction efficiency. Initially, the liver binding capacity was 3.1 +/- 0.4 micrograms Ad5K, equivalent to approximately 17,000 Ad5K molecules per liver cell. Liver binding was blocked by preincubation of Ad5K with neutralizing anti-Ad5K antibody; a 50% reduction in liver uptake was demonstrated by imaging. Unlabeled Ad5K was more effective in blocking liver uptake of 99mTc-Ad5K, whereas irrelevant unlabeled Ad3K had no effect. Imaging data for the liver uptake studies were in agreement with biodistribution determined by removing and measuring tissues. These data demonstrated that in vivo imaging is a sensitive tool for measuring changes to liver tropism. Similar imaging techniques can be applied to adenovirus vectors to measure specific targeting for gene therapy.

The potential role of cell adhesion molecules in the pathogenesis of diabetic neuropathy

Cross-sectional studies have shown plasma cell adhesion molecules (CAMs) to be increased in patients with diabetes-related complications. In the first prospective study of CAMs, we have shown that plasma CAMs may be a predictor of the development of diabetic neuropathy. We followed up 28 diabetic patients (13 neuropathic) over a 5 year period, starting from 1991. All patients had peroneal nerve conduction velocity (PNCV), vibration perception threshold and plasma CAMs measured at baseline and follow-up. We found P-selectin and intercellular adhesion molecule-1 (ICAM-1) to be increased at baseline in patients with neuropathy compared to non-neuropathic patients. P-selectin and E-selectin were also found to be significantly higher at baseline in patients who at follow-up showed deterioration in PNCV of more than 3 m/s (p<0.05; p=0.01; respectively). P-selectin and ICAM-1 strongly correlated with PNCV. Univariate and multivariate regression analyses showed a significant inverse association between increasing log P-selectin, log E-selectin and log ICAM-1 with decreasing PNCV, and remained significant even after adjustment for glycaemic control. P-selectin and E-selectin, odds ratios of 8.8 (95% CI: 1.1-68.8; p=0.038) and 12.5 (95% CI: 1.2-132.1; p=0.036), respectively, were significantly associated with the risk of deterioration of PNCV after 5 years. This study suggests that plasma cell adhesion molecules may play an important role in the development and progression of peripheral neuropathy in diabetes mellitus.

Use of a novel cross-linking method to modify adenovirus tropism

Recombinant adenovirus (Ad) vectors can accomplish efficient in vivo gene transfer and thus are important in the context of a variety of gene therapy approaches. The cellular receptor for the Ad fiber knob is prevalent on a number of normal tissues which undermines the targeting of Ad to specific tumor cells. Therefore, the ablation of native Ad tropism and the introduction of novel Ad tropism are both necessary to target Ad vectors specifically to tumors. In this study, we have developed a flexible method for cross-linking the Fab fragment of a neutralizing anti-knob monoclonal antibody (1D6.14) to a cell receptor ligand. The cross-linking moieties are complementary low molecular weight recognition units, similar in concept to the avidin-biotin system. For proof of concept, we cross-linked 1D6.14 Fab to the basic fibroblast growth factor (FGF2). The Fab and FGF2 conjugates were synthesized and characterized both structurally and functionally. The conjugates were then complexed with an adenovirus vector carrying firefly luciferase (AdCMVLuc) and the resulting complex used to show infection of a number of tumor cell lines expressing FGF receptors. This cross-linking system should provide a rapid and convenient method of conjugating various ligands to the Fab fragment for targeting Ad vectors to different types of tumors.

Epitope mapping of twelve monoclonal antibodies against the phenolic glycolipid-I of M. leprae

Epitope mapping of 12 monoclonal antibodies (MAbs) directed to the trisaccharide part of the phenolic glycolipid-I (PGL-I) of Mycobacterium leprae was carried out by using the set of chemically synthesized sugar-BSA conjugates. The results can be summarized as follows: mAb (1-21), mAb (1-24) and mAb (1-25) recognized the outer (nonreducing end) monosaccharide of the trisaccharide chain of PGL-I. However, the affinity of these MAbs to the outer monosaccharide was weak. They required the contributions of some parts of the second sugar for enough affinity. MAbs ml 6A12, ml 8A2, ml 8B2, and PG2 B8F recognized the outer disaccharide. MAb F47-21-3 recognized the outer disaccharide and some parts of the third sugar. MAb SF 1 recognized the trisaccharide of PGL-I. MAb 3D1-A9 recognized the phenol group and the structure around the branching point on the carrier protein in addition to the trisaccharide. MAbs DZ 1 and 2G3-A8 had unique characters which recognized the inner part of the sugar chain. MAb DZ 1 recognized the inner (reducing end) disaccharide. MAb 2G3-A8 recognized the inner monosaccharide, phenol group and the structure around the branching point on the carrier protein. All of the MAbs tested, except for ml 6A12, recognized the anomeric configurations in the sugar parts they recognized; ml 6A12 recognized the anomeric configuration only within the outer disaccharide. This set of MAbs, which were well defined on their binding specificity, promises to be an effective tool for the immunological study of PGL-I and the clinical assessment of leprosy.

Strategies to accomplish targeted gene delivery to muscle cells employing tropism-modified adenoviral vectors

We are developing strategies to modify the tropism of adenoviral vectors to accomplish targeted transduction of muscle cells for DMD gene therapy. In one approach, we have introduced targeting ligands into the adenovirus fibre, which mediates the binding of the virus Ad5 to the primary cellular receptor. In order to incorporate these fibre-ligand fusions into recombinant adenoviral vectors, we have employed a method based upon homologous DNA recombination between a fibre-deleted, propagation-defective rescue plasmid and a shuttle plasmid encoding a variant fibre. To date, we have generated an adenoviral vector containing chimeric fibres composed of the tail and shaft domains of adenovirus serotype 5 and the knob domain of serotype 3. This modification altered the receptor recognition profile of the virus containing the fibre chimera. In an alternative approach to the generation of a targeted adenoviral vector, we conjugated folate to the neutralising Fab fragment of an anti-fibre monoclonal antibody. This Fab-folate conjugate was shown to redirect adenoviral infection of target cells via the folate receptor at a high efficiency. These studies suggest that it will be possible to achieve our goal of deriving targeted adenoviral vectors for muscle cell-specific gene delivery in vivo.

Targeted gene delivery to Kaposi's sarcoma cells via the fibroblast growth factor receptor

Kaposi's sarcoma (KS) is a major AIDS-related malignancy associated with significant morbidity and mortality. Current chemotherapeutic regimens are associated with a dismal prognosis. In an effort to develop a new approach to KS treatment, we devised a gene therapy-based adenovirus retargeting schema that redirects the adenovirus to fibroblast growth factor receptors endogenously present on the cell surface of KS cells. By using a bifunctional conjugate consisting of a blocking antiadenoviral knob Fab linked to basic fibroblast growth factor, FGF2, the gene transduction of KS cells was enhanced 7.7-44 fold; recombinant adenoviruses encoding either the firefly luciferase reporter gene, or the herpes simplex thymidine kinase gene, demonstrated quantitative enhancement of expression in the KS cell lines. In this regard, two KS cell lines that were previously refractory to native adenovirus transduction could be successfully transduced by the addition of the conjugate. This study thus addresses the utility of adenoviral retargeting to the FGF receptor in KS cells that are ordinarily transduction refractory to standardized approaches and allows practical development of gene therapy approaches for the treatment of human KS.

Targeted gene delivery by tropism-modified adenoviral vectors

The utility of adenoviral vectors for gene therapy is currently limited due, in part, to the widespread distribution of the cellular receptor for the adenovirus fiber that precludes the targeting of specific cell types. In order to develop a targeted adenovirus, it is therefore necessary both to ablate endogenous viral tropism and to introduce novel tropism. We hypothesized that these two goals could be achieved by employing a neutralizing anti-fiber antibody, or antibody fragment, chemically conjugated to a cell-specific ligand. To test this concept, we chose to target the folate receptor, which is overexpressed on the surface of a variety of malignant cells. Therefore, we conjugated folate to the neutralizing Fab fragment of an anti-fiber monoclonal antibody. This Fab-folate conjugate was complexed with an adenoviral vector carrying the luciferase reporter gene and was shown to redirect adenoviral infection of target cells via the folate receptor at a high efficiency. Furthermore, when complexed with an adenoviral vector carrying the gene for herpes simplex virus thymidine kinase, the Fab-folate conjugate mediated the specific killing of cells that overexpress the folate receptor. This work thus represents the first demonstration of the retargeting of a recombinant adenoviral vector via a non-adenoviral cellular receptor.

Generation of recombinant adenovirus vectors with modified fibers for altering viral tropism

To expand the utility of recombinant adenovirus vectors for gene therapy applications, methods to alter native viral tropism to achieve cell-specific transduction would be beneficial. To this end, we are pursuing genetic methods to alter the cell recognition domain of the adenovirus fiber. To incorporate these modified fibers into mature virions, we have developed a method based on homologous DNA recombination between two plasmids. A fiber-deleted, propagation-defective rescue plasmid has been designed for recombination with a shuttle plasmid encoding a variant fiber gene. Recombination between the two plasmids results in the derivation of recombinant viruses containing the variant fiber gene. To establish the utility of this method, we constructed a recombinant adenovirus containing a fiber gene with a silent mutation. In addition, we generated an adenovirus vector containing chimeric fibers composed of the tail and shaft domains of adenovirus serotype 5 and the knob domain of serotype 3. This modification was shown to alter the receptor recognition profile of the virus containing the fiber chimera. Thus, this two-plasmid system allows for the generation of adenovirus vectors containing variant fibers. This method provides a rapid and facile means of generating fiber-modified recombinant adenoviruses. In addition, it should be possible to use this system in the development of adenovirus vectors with modified tropism to allow cell-specific targeting.