Efficient gene transfer into human CD34(+) cells by a retargeted adenovirus vector

Localization of regions in CD46 that interact with adenovirus

A variety of pathogens use CD46, a ubiquitously expressed membrane protein that regulates complement activation, as a cellular attachment receptor. While the CD46 binding sites of several pathogens, including measles virus, Neisseria gonorrhea, and human herpesvirus 6, have been described, the region of CD46 responsible for adenovirus binding has not been determined. In this study, we used competition experiments with known CD46 ligands, CD46-specific antibodies, and a set of CD46 mutants to localize the binding domain for the group B adenovirus serotype 35 (Ad35). Our results show that Ad35 competes with measles virus for binding to CD46 but not with complement protein C3b. We further show that this interaction is a protein-protein interaction and that N glycosylations do not critically contribute to infection with Ad35 fiber-containing Ad vectors. Our data demonstrate that the native conformation of the CCP2 domain is crucial for Ad35 binding and that the substitution of amino acids at positions 130 to 135 or 152 to 156 completely abolishes the receptor function of CD46. These regions localize to the same planar face of CD46 and likely form an extended adenovirus binding surface, since no single amino acid substitution within these areas eliminates virus binding. Finally, we demonstrate that the infection with a virus possessing human group B serotype Ad11 fibers is also mediated by the CCP2 domain. This information is important to better characterize the mechanisms of the receptor recognition by adenovirus relative to other pathogens that interact with CD46, and it may help in the design of antiviral therapeutics against adenovirus serotypes that use CD46 as a primary cellular attachment receptor.

Optimization of adenovirus serotype 35 vectors for efficient transduction in human hematopoietic progenitors: comparison of promoter activities

Adenoviral gene transfer to hematopoietic stem cells (HSCs)/progenitors would provide a new approach to the treatment of hematopoietic diseases and study of the hematopoietic system. We have previously reported that an adenovirus (Ad) vector composed of whole Ad serotype 35 (Ad35), which belongs to subgroup B, shows efficient gene transfer into human bone marrow CD34+ cells. However, Ad35 vector-mediated transduction into human HSCs/progenitors has not yet been fully optimized. In the present study, we have systematically examined promoter activity in the context of Ad35 vectors in human bone marrow CD34+ cells and primitive CD34+ subsets to optimize the transduction efficiency in human hematopoietic stem/progenitor cells. In the first of the transduction experiments, the improved in vitro ligation method was applied to Ad35 vector construction to allow for simple and efficient production of an E1/E3-deleted Ad35 vector. Using this method, we constructed a series of Ad35 vectors encoding the enhanced green fluorescence protein (GFP) under the control of a variety of strong viral and cellular promoters. Of the six types of promoters tested, significantly higher transduction efficiencies were achieved with the human elongation factor 1alpha promoter (EF1alpha promoter), the human cytomegalovirus (CMV) immediate-early 1 gene enhancer/beta-actin promoter with beta-actin intron (CA promoter), and the CMV promoter/enhancer with the largest intron of CMV (intron A) (CMVi promoter) in the human CD34+ cells and the immature subsets (CD34+ CD38(low/-) and CD34+ AC133+ subsets). In particular, the CA promoter was found to allow for the highest transduction efficiencies in both the whole human CD34+ cells and the immature hematopoietic subsets. Furthermore, the CA promoter-mediated GFP-expressing cells differentiated into progenitor cells of all lineages. These results indicate the construction of an optimized Ad35 vector backbone for efficient transduction into HSCs/progenitors.

Adenovirus binding to blood factors results in liver cell infection and hepatotoxicity

Adenoviruses (Ad) are efficient vehicles for gene delivery in vitro and in vivo. Therefore, they are a promising tool in gene therapy, particularly in the treatment of cancer and cardiovascular diseases. However, preclinical and clinical studies undertaken during the last decade have revealed a series of problems that limit both the safety and efficacy of Ad vectors, specifically after intravenous application. Major obstacles to clinical use include innate toxicity and Ad sequestration by nontarget tissues. The factors and mechanisms underlying these processes are poorly understood. The majority of intravenously injected Ad particles are sequestered by the liver, which in turn causes an inflammatory response characterized by acute transaminitis and vascular damage. Here, we describe a novel pathway that is used by Ad for infection of hepatocytes and Kupffer cells upon intravenous virus application in mice. We found that blood factors play a major role in targeting Ad vectors to hepatic cells. We demonstrated that coagulation factor IX and complement component C4-binding protein can bind the Ad fiber knob domain and provide a bridge for virus uptake through cell surface heparan sulfate proteoglycans and low-density lipoprotein receptor-related protein. An Ad vector, Ad5mut, which contained mutations in the fiber knob domain ablating blood factor binding, demonstrated significantly reduced infection of liver cells and liver toxicity in vivo. This study contributes to a better understanding of adenovirus-host interactions for intravenously applied vectors. It also provides a rationale for novel strategies to target adenovirus vector to specific tissues and to reduce virus-associated toxicity after systemic application.

RNA interference of PPARgamma using fiber-modified adenovirus vector efficiently suppresses preadipocyte-to-adipocyte differentiation in 3T3-L1 cells

The peroxisome proliferator-activated receptor (PPAR) gamma is regarded as a "master regulator" of adipocyte differentiation and is abundantly expressed in adipose. To understand the biological role of PPARgamma in adipose, RNA interference (RNAi) of PPARgamma should be a powerful tool. 3T3-L1 cell line serves an excellent model to investigate the mechanism of preadipocyte-to-adipocyte differentiation. However, this cell line is difficult to transfect by plasmid vectors and viral vectors. We optimized the transduction of both 3T3-L1 preadipocytes and adipocytes by means of fiber-modified adenovirus (Ad) vectors. Among the various vectors tested, polylysine modification of the C-terminal of the fiber knob most markedly improved the transduction efficiency in both 3T3-L1 preadipocytes and adipocytes. Then, we examined whether fiber-modified Ad vectors with polylysine peptides expressing the small interfering RNA (siRNA) for PPARgamma inhibit the differentiation of 3T3-L1 preadipocytes into adipocytes. Oil red O staining and measurement of glycerol-3-phosphate dehydrogenase (GPDH) activity indicated that the vectors effectively suppressed the differentiation of 3T3-L1 preadipocytes to adipocytes. These results suggested that the combination of fiber-modified Ad vectors containing polylysine peptides and RNAi is an effective tool for the study of the biological and physiological mechanism of adipogenesis in adiposity and diabetes using 3T3-L1 models. Ad vector-mediated RNAi for PPARgamma should also be useful to clarify the biological role of the PPARgamma pathway in various tissues in addition to adipose and for therapeutic application to a variety of diseases, including adiposity and diabetes.

Development and assessment of human adenovirus type 11 as a gene transfer vector

Adenovirus vectors based on human serotype 5 (Ad5) have successfully been used as gene transfer vectors in many gene therapy-based approaches to treat disease. Despite their widespread application, many potential therapeutic applications are limited by the widespread prevalence of vector-neutralizing antibodies within the human population and the inability of Ad5-based vectors to transduce important therapeutic target cell types. In an attempt to circumvent these problems, we have developed Ad vectors based on human Ad serotype 11 (Ad11), since the prevalence of neutralizing antibodies to Ad11 in humans is low. E1-deleted Ad11 vector genomes were generated by homologous recombination in 293 cells expressing the Ad11-E1B55K protein or by recombination in Escherichia coli. E1-deleted Ad11 genomes did not display transforming activity in rodent cells. Transduction of primary human CD34+ hematopoietic progenitor cells and immature dendritic cells was more efficient with Ad11 vectors than with Ad5 vectors. Thirty minutes after intravenous injection into mice that express one of the Ad11 receptors (CD46), we found, in a pattern and at a level comparable to what is found in humans, Ad11 vector genomes in all analyzed organs, with the highest amounts in liver, lung, kidney, and spleen. Neither Ad11 genomes nor Ad11 vector-mediated transgene expression were, however, detected at 72 h postinfusion. A large number of Ad11 particles were also found to be associated with circulating blood cells. We also discovered differences in in vitro transduction efficiencies and in vivo biodistributions between Ad11 vectors and chimeric Ad5 vectors possessing Ad11 fibers, indicating that Ad11 capsid proteins other than fibers influence viral infectivity and tropism. Overall, our study provides a basis for the application of Ad11 vectors for in vitro and in vivo gene transfer and for gaining an understanding of the factors that determine Ad tropism.

Targeted adenovirus vectors

Recombinant adenovirus (Ad) vectors continue to be the preferred vectors for gene therapy and the study of gene function because they are relatively easy to construct, can be produced at high titer, and have high transduction efficiency. However, in some applications gene transfer with Ad vectors is less efficient because the target cells lack expression of the primary receptor, coxsackievirus and adenovirus receptor (CAR). Another problem is the wide biodistribution of vector in tissue following in vivo gene transfer because of the relatively broad tissue expression of CAR. To overcome these limitations, various approaches have been developed to modify Ad tropism. In one approach, the capsid proteins of Ad are modified, such as with the addition of foreign ligands or the substitution of the fiber with other types of Ad fiber, in combination with the ablation of native tropism. In other approaches, Ad vectors are conjugated with adaptor molecules, such as antibody and fusion protein containing an anti-Ad single-chain antibody (scFv) or the extracellular domain of CAR with the targeting ligands, or chemically modified with polymers containing the targeting ligands. In this paper, we review advances in the development of targeted Ad vectors.

Approaches to improving the kinetics of adenovirus-delivered genes and gene products

Adenovirus (Ad) vectors have been expected to play a great role in gene therapy because of their extremely high transduction efficiency and wide tropism. However, due to the intrinsic deficiency of their immunogenic toxicities, Ad vectors are rapidly cleared from the host, transgene expression is transient, and readministration of the same serotype Ad vectors is problematic. As a result, Ad vectors are continually undergoing refinement to realize their potential for gene therapy application. Even after 1999, when a patient fatally succumbed to the toxicity associated with Ad vector administration at a University of Pennsylvania (U.S.) experimental clinic, enthusiasm of gene therapists for Ad vectors has not waned. With great efforts from various research groups, significant advances have been achieved through comprehensive approaches to improving the kinetics of Ad vector-delivered genes and gene products.

Cellular vehicles for cancer gene therapy: current status and future potential

Cancer is a difficult target for any therapeutic strategy; therefore, there is a continuous search for new therapeutic modalities, for application either alone or in combination. In this regard, gene-based therapy is a new approach that offers hope of improved control of tumors. Intensive research to apply gene therapy for cancer treatment has led to identification of the most important technical and theoretical barriers that need to be overcome for clinical success. One of the central unresolved challenges remains the issue of specific and efficient delivery of genes to target cells or tissues, emphasizing the importance of the gene carrier. Along with different viral and non-viral vector systems, mammalian cells have also been considered as vehicles for delivery of anti-cancer therapeutics. The cell-based delivery approach was introduced as the first attempt to apply gene therapy to cancer treatment, and in general, has followed most of the ups and downs of gene therapy applications, progressing alongside new knowledge gained in this field. As a result, significant progress has been made in some aspects of the cell-based approach, while the development of other essential issues is only just gaining speed. It appears that the initial phase of development of cell-based protocols - the achievement of efficient ex vivo cell loading with therapeutics - has largely been fulfilled. However, the desired efficacy of cell-based strategies in general has not yet been reached, and specificity of tumor homing needs to be improved considerably. There is hope that advances in related scientific fields will promote the utilization of cells as powerful and versatile vehicles for cancer gene therapy.

Deletion of penton RGD motifs affects the efficiency of both the internalization and the endosome escape of viral particles containing adenovirus serotype 5 or 35 fiber knobs

Adenovirus (Ad) vectors are widely used for gene delivery in vitro and in vivo. A solid understanding of the biology of this virus is imperative for the development of novel, effective, and safe vectors. For the group C adenovirus serotypes 2 and 5 that use CAR as a primary attachment receptor, it is known that the penton base RGD motifs interact with cellular integrins and that this interaction promotes virus internalization. However, the RGD motif's impact on the efficiency of postinternalization steps, such as the escape of the virus particle from the endosome, is less defined. Furthermore, the role of penton-integrin interactions remains unknown for new vectors possessing group B Ad fiber knobs that use CD46 as a primary virus attachment receptor. In this study, we used vectors with the RGD motif deleted that contained Ad5 and B-group Ad35 fiber knobs and long fiber shafts and studied the role of RGD-integrin interactions in virus internalization and endosome escape. The deletion of the RGD motif in the penton base did not affect virus attachment, regardless of the type of cellular receptor used for attachment. RGD motif deletion, however, significantly reduced the rate of virus internalization for both the Ad5 and Ad35 fiber knob-containing vectors. This study also demonstrates the role of penton RGD motifs in facilitating the endosome escape step of virus infection and indicates that penton-integrin interactions are involved in internalization of capsid-chimeric CD46-interacting Ads with long fiber shafts.

Human hematopoietic (CD34+) stem cells possess high-affinity receptors for adenovirus type 11p

Gene transfer into human hematopoietic stem cells using Ad5 is inefficient due to lack of the primary receptor CAR and the secondary receptors alphavbeta3 integrin and alphavbeta5 integrin, and due to the high seroprevalence of Ad5 antibodies in most adults, resulting in diminished gene transduction. In the present study, we screened six species (species A-F) of adenovirus, displaying different tropisms for interaction with CD34+ cells, at the level of virus attachment and expression. Virus particles were biotinylated and their binding capacity was determined by FACS analysis using streptavidin-FITC. Ad11p, Ad35, and Ad3 (species B) showed high binding affinity, while Ad7, Ad11a (species B), and Ad37 (species D) displayed intermediate affinity. Virions of Ad4 (species E), Ad5 (species C), Ad31 (species A), and Ad41 (species F) hardly bound to hematopoietic progenitor cells. Using a double-labeling system, we demonstrated that adenoviruses bind to quiescent CD34+ cells. Ad11p virions showed the highest affinity among the adenoviruses detected. We further confirmed that virus fiber-specific receptors were present on the hematopoietic progenitor cell surface, because both recombinant fiber of Ad11p and specific antiserum against rfiber could block virus attachment. The ability of the adenoviruses to infect hematopoietic cells was studied by immunofluorescence staining. The adenoviruses from species B and Ad37 showed higher infectivity than Ad31, Ad5, Ad4, and Ad41. Among the studied species B adenoviruses, Ad11p manifested a superior infectivity. Thus, we have confirmed that these cells have high-affinity receptors for species B:2 human adenovirus, Ad11p, and this virus may be used as candidate vector to target therapeutic genes to hematopoietic stem cells.

A tumor-targeted and conditionally replicating oncolytic adenovirus vector expressing TRAIL for treatment of liver metastases

We have constructed a new capsid-modified adenovirus (Ad) vector that specifically replicates in tumor cells and expresses TNF-related apoptosis-inducing ligand (TRAIL). The Ad capsid contains short-shafted fibers derived from Ad serotype 35, which allow for efficient infection of malignant tumor cells, and largely avoids innate toxicity after intravenous application. Replication-dependent homologous recombination in Ad genomes was used to achieve tumor-specific expression of Ad E1a (to mediate viral replication) and TRAIL (to mediate apoptosis and enhance release of progeny virus from infected cells). We demonstrated that our oncolytic vector (Ad5/35.IR-E1A/TRAIL) induced apoptosis in human tumor cell lines derived from colorectal, lung, prostate, and liver cancer. Both in vitro and in vivo tumor models showed efficient intratumoral spread of this vector. In a model for metastatic colon cancer, tail vein infusion of Ad5/35.IR-E1A/TRAIL resulted in elimination of preestablished liver metastases. Intravenous injection of this vector caused a transient elevation of serum glutamic pyruvic transaminase in tumor-bearing mice, which we attributed to factors released from apoptotic tumor cells. Liver histology analyzed at day 14 after virus injection did not show signs of hepatocellular damage. This new oncolytic vector represents a potentially efficient means for gene therapy of metastatic cancer.

Adenoviral Serotype 5 Vectors Pseudotyped with Fibers from Subgroup D Show Modified TropismIn VitroandIn Vivo

Adenovirus (Ad5) serotype 5 vectors are commonly used for gene transfer. Preclinical studies have shown that their application to systemic gene delivery, however, is limited by their highly efficient uptake in the liver, principally mediated by receptor-binding sites on the fiber shaft and knob domain. Using Ad to target other sites in vivo requires vectors that lack hepatic tropism. We therefore sought to exploit Ad family diversity to isolate vectors that possessed poor hepatic tropism. We pseudotyped the fibers from Ad16 (subgroup B; Ad5/16), Ad19p (subgroup D; Ad5/19p), and Ad37 (subgroup D; Ad5/37) onto Ad5 capsids and assessed infectivity profiles in vitro in multiple cell types and in vivo in rats. In rat, mouse, and human hepatocytes, Ad5/19p and Ad5/37 both possessed a striking lack of hepatic cell infectivity compared with Ad5. Both vectors were, however, able to transduce human vascular endothelial and smooth muscle cells with efficiencies equal to or greater than that of nonmodified Ad5. We evaluated liver uptake in 12-week-old male rats after intravenous injection. In contrast to a vector with the wild-type Ad5 fiber, Ad5, both Ad5/19p and Ad5/37 produced significantly less virion accumulation (measured at 1 hr and 5 days) and transgene expression in the liver. Thus, Ad5/19p and Ad5/37 may be useful platforms for the development of targeted Ad vectors.

Conserved CTL epitopes on the adenovirus hexon protein expand subgroup cross-reactive and subgroup-specific CD8+ T cells

Adenoviruses often cause lethal infections in immunocompromised individuals. Adoptive transfer of immune T cells offers a therapeutic option, but this strategy has been hindered by the paucity of information on molecular targets of cellular immunity and by the immunologic heterogeneity of the 51 human adenoviruses, which are grouped from A to F on the basis of genome size, composition, homology, and organization. Clonal analysis of the adenovirus-specific cytotoxic T lymphocyte (CTL) responses of seropositive individuals identified 5 novel CD8+ T-cell epitopes, all located in conserved regions of the capsid protein hexon. Reactive T cells were cross-reactive between 2 to 4 groups, while no T cells specific for a single subgroup were detected. Thus, by exploiting these peptide targets, it is possible to prepare a T-cell population capable of reacting with most adenoviruses that cause disease in immunocompromised patients.

Functionally distinct subpopulations of cord blood CD34+ cells are transduced by adenoviral vectors with serotype 5 or 35 tropism

Adenovirus serotype 5 (Ad5)-based vectors can be retargeted with fiber receptor specificity of serotype 35 adenovirus (Ad5F35) and thereby bypass the paucity of the coxsackie and adenovirus receptor (CAR) on hematopoietic cells by utilizing CD46 as cellular receptor. The gene transfer efficiency into NOD/SCID repopulating cells by an Ad5F35-GFP vector was investigated in comparison with its corresponding Ad5-GFP vector. Cord blood CD34+ cells were transduced following overnight culture under serum-free conditions supported by early acting cytokines. In agreement with previous findings, the Ad5F35-GFP vector showed significant superiority to the Ad5-GFP vector in gene transfer into cells with primitive immunophenotype. However, the Ad5F35-GFP vector allowed efficient gene transfer into both dividing and nondividing CD34+ cells, whereas the Ad5-GFP vector preferentially allowed gene transfer into dividing cells expressing lower levels of CD34 antigen, which correlated with high levels of CAR expression. The sorted GFP+ cells following Ad5F35-GFP transduction at relatively low multiplicity of infection consistently reconstituted the NOD/SCID mouse bone marrow with multilineage differentiation. In contrast, the GFP+ cells following Ad5-GFP transduction were nearly devoid of reconstitution capacity. Thus, Ad5F35 vectors encoding functional genes can facilitate transient genetic manipulation of human NOD/SCID repopulating cells.

Genome size and structure determine efficiency of postinternalization steps and gene transfer of capsid-modified adenovirus vectors in a cell-type-specific manner

Adenovirus serotype 5 (Ad5) vectors containing Ad B-group fibers have become increasingly popular as gene transfer vectors because they efficiently transduce human cell types that are relatively refractory to Ad5 infection. So far, most B-group fiber-containing vectors have been first-generation vectors, deleted of E1 and/or E3 genes. Transduction with these vectors, however, results in viral gene expression and is associated with cytotoxicity and immune responses against transduced cells. To circumvent these problems, we developed fiber-chimeric Ad vectors devoid of all viral genes that were produced either by the homologous recombination of first-generation vectors or by using the Cre/lox-based helper virus system. In this study we compared early steps of infection between first-generation (35-kb genome) and Ad vectors devoid of all viral genes with genome sizes of 28 kb and 12.6 kb. All vectors possessed an Ad35-derived fiber knob domain, which uses CD46 as a primary attachment receptor. Using immortalized human hematopoietic cell lines and primary human CD34-positive hematopoietic cells, we found that the Ad genome size did not affect the efficiency of virus attachment to and internalization into cells. Furthermore, independently of the genome length and structure, all vectors migrated to the nucleus through late endosomal and lysosomal cellular compartments. However, the vector containing the short 12.6-kb genome was unable to efficiently escape from endosomes and deliver its DNA into the nucleus. Moreover, compared to other vectors, these Ad particles were less stable and had an abnormal capsid protein composition, including a lack of capsid-stabilizing protein IX. Our data indicate that the size and structure of the packaged viral genomes can affect the integrity of Ad particles, which in turn results in lower infectivity of Ad vectors.

Model of unidirectional transluminal gene transfer

Gene transfer assays in vitro are poor indicators of transduction efficacy observed in vivo. We designed and optimized an intermediate model for assessing and quantifying unidirectional transduction ex vivo. The model enables simultaneous transmucosal evaluation of up to 96 different variables under the same tissue conditions. We show that the model is versatile and suitable for use with different vectors (adenovirus and AAV), different reporter genes (beta-galactosidase and green fluorescent protein), and viscera with various tissue features such as peritoneum and urothelium. Ex vivo transduction assays may correlate better with in vivo gene transfer results. Because the experimental model described here can be performed in small samples, it may enable translational applications in tissues of human origin.

Midkine promoter-driven suicide gene expression and -mediated adenovirus replication produced cytotoxic effects to immortalised and tumour cells

We examined possible application of a regulatory region of midkine (MK) gene, which is frequently upregulated in a number of human tumours but not in normal cells, to cancer gene therapy. We examined transcriptional activity of the MK genomic fragments in paired cell lines, immortalized cells and their parental normal fibroblasts, and found that the MK fragments activated a fused reporter or a suicide gene preferentially in the immortalized cells. Recombinant adenoviruses (Ad), in which the MK fragment was inserted upstream to the E1A gene (AdMK), replicated preferentially in the immortalized cells and were cytotoxie to them. Human hepatocellular carcinoma cells were significantly susceptible to AdMK compared with human normal fibroblasts in vitro and the replication of AdMK was less than that of wild-type Ad in the infected fibroblasts. Hepatocellular carcinoma cells infected with AdMK did not form tumours in immunocompromised mice and intratumoural injection of AdMK into the hepatocellular carcinoma developed in mice retarded the subsequent tumour growth. Expression of E1A and necrosis of tumours were detected in AdMK-injected but not control Ad-injected cases. The MK promoter-driven suicide gene therapy and -mediated replicative Ad can thereby produce cytotoxic effects to immortalized and tumour cells with minimal damage to normal cells.

Efficient internalization into low-passage glioma cell lines using adenoviruses other than type 5: an approach for improvement of gene delivery to brain tumours

There is a need for improvement of the commonly used adenovirus vectors based on serotype 5. This study was performed on three adenovirus serotypes with a CAR-binding motif (Ad4p, Ad5p and Ad17p) and three non-CAR-binding serotypes (Ad11p, Ad16p and Ad21p). The capacity of these alternative adenovirus vector candidates to deliver DNA into low-passage glioma cell lines from seven different donors was evaluated. The non-CAR-binding serotype Ad16p was the most efficient serotype with regard to import of its DNA, as well as initiation of hexon protein expression. Ad16p established hexon expression in 60–80 % of the cell population in gliomas from all donors tested. The other non-CAR-binding serotypes, Ad11p and Ad21p, showed hexon expression in 25–60 and 40–80 % of cells, respectively. The corresponding figure for the best CAR-binding serotype, Ad5p, was only 25–65 %, indicating greater variability between cells from different donors than serotype Ad16p had. The other CAR-binding serotypes, Ad4p and Ad17p, were refractory to some of the gliomas, giving a maximum of only 45 and 40 % hexon expression, respectively, in the most permissive cells. Interestingly, the transduction capacity of the CAR-binding serotypes was not correlated to the level of CAR expression on the cells.

Gene transfer into human T lymphocytes and natural killer cells by Ad5/F35 chimeric adenoviral vectors

OBJECTIVE

Genetic modification of effector lymphocytes, such as T cells and natural killer (NK) cells, is essential for many approaches to gene-based immunotherapy of cancer. However, transduction of lymphocytes has proven difficult by currently available gene transfer methods. Previous studies have shown that chimeric fiber-modified Ad5/F35 adenoviral vectors are able to efficiently transduce hematopoietic cells including immature progenitors. In this study, we examined the gene transfer into T lymphocytes and NK cells using Ad5/F35 compared with conventional Ad5 adenovectors.

METHODS

Primary T and NK cells were isolated from healthy donors' peripheral blood leukocytes by immunomagnetic selection. Cell lines and primary lymphocytes were transduced with replication-defective Ad5/F35 and Ad5, both containing a GFP reporter gene under the control of a CMV promoter. Transduction efficiencies were monitored by flow cytometry. The function of transduced lymphocytes was assessed by analysis of proliferative responses to mitogenic agents and in mixed leukocyte reactions.

RESULTS

Transgene expression was detected in up to 45% of primary CD3+ T lymphocytes and in up to 60% of primary NK cells using Ad5/F35. In contrast, conventional Ad5 transduced less than 8% and 5% of primary T cells and NK cells, respectively. Transduction efficiencies were similar in CD4+ and CD8+ T lymphocytes, and transgene expression could be detected for up to seven days. Activation of T cells significantly enhanced the efficiency of Ad5/F35-mediated gene transfer. Adenoviral transduction of lymphocytes did not result in any impairment of proliferative functions.

CONCLUSION

The results of this study demonstrate that both T lymphocytes and NK cells can be transduced by chimeric Ad5/F35 adenoviral vectors.

A soluble CAR-SCF fusion protein improves adenoviral vector-mediated gene transfer to c-Kit-positive hematopoietic cells

BACKGROUND

Although adenoviral vectors primarily derived from the adenovirus serotype 5 (Ad5) are widely used for many gene transfer applications, they cannot efficiently infect hematopoietic cells, since these cells do not express the coxsackie-adenoviral receptor (CAR).

METHODS

We have developed a soluble fusion protein that bridges adenoviral fibers and the c-Kit receptor to alter Ad5 tropism to immature hematopoietic cells. The CAR-SCF fusion protein consists of the extracellular domains of CAR and stem cell factor (SCF). The human megakaryoblastic leukemia cell lines UT-7 and M07e, human chronic myelogenous leukemia cell line K-562, and erythroleukemia cell line TF-1 were used to assess CAR-SCF-assisted Ad5-mediated gene transfer. Hematopoietic cell lines were infected with an Ad5 vector (Ad5-eGFP) or a fiber-mutant Ad5/F35 (Ad5/F35-eGFP) expressing the enhanced green fluorescent protein gene in the presence or absence of CAR-SCF.

RESULTS

Twenty-four hours after infection, more than 80% of M07e cells infected in the presence of CAR-SCF were eGFP-positive, compared with very few eGFP-positive cells following Ad5-eGFP infection in the absence of CAR-SCF. The enhancement of Ad5-eGFP infection by CAR-SCF was greater than that caused by Ad5/F35-eGFP (50%). The ability of CAR-SCF to enhance Ad5-eGFP infectivity was highly dependent on cellular c-Kit expression levels. Furthermore, CAR-SCF also enhanced Ad5-mediated gene transfer into human primary CD34(+) cells.

CONCLUSIONS

The CAR-SCF fusion protein assists Ad5-mediated transduction to c-Kit(+) CAR(-) hematopoietic cells. The use of this fusion protein would enhance a utility of Ad5-mediated hematopoietic cell transduction strategies.

An adenovirus vector with a chimeric fiber derived from canine adenovirus type 2 displays novel tropism

Many clinically relevant tissues are refractory to Ad5 transduction because of negligible levels of the primary Ad5 receptor, the coxsackie and adenovirus receptor (CAR). Thus, development of Ad vectors that display CAR-independent tropism could lead directly to therapeutic gain. The Toronto strain of canine adenovirus type 2 (CAV2) exhibits native tropism that is augmented by, but not fully dependent upon, CAR for cellular transduction. We hypothesized that an Ad5 vector containing the nonhuman CAV2 knob would provide expanded tropism and constructed Ad5Luc1-CK, an E1-deleted Ad5 vector encoding the fiber knob domain from CAV2. Ad5Luc1-CK gene delivery to CAR-deficient cells was augmented up to 30-fold versus the Ad5 control vector, and correlated with increased cell surface binding. Further, we confirmed the importance of cellular integrins to Ad5Luc1-CK transduction. Herein, we present the rationale, design, purification, and characterization of a novel tropism modified, infectivity-enhanced Ad vector.

Efficient delivery and stable gene expression in a hematopoietic cell line using a chimeric serotype 35 fiber pseudotyped helper-dependent adenoviral vector

Certain human cell populations have remained difficult to infect with human adenovirus (Ad) serotype 5 because of their lack of coxsackievirus B-adenovirus receptor (CAR). Native adenovirus fiber compositions, although diverse, cannot infect all tissue types. Recently, a chimeric Ad5/35 fiber was created, which displays an altered tropism from Ad5. We incorporated this chimeric fiber into a helper-dependent (HD) adenovirus vector system and compared HD to E1-deleted (E1Delta) vectors by transgene expression, cell transduction efficiency, and cytotoxicity. K562 cells were infected approximately 50 times more efficiently with the chimeric Ad5/35 fiber compared with the Ad5 fiber. Short-term transgene expression was sustained longer from HD Ad5/35 than E1Delta Ad5/35 vector after in vitro infection of actively dividing K562 cells. Rapid loss of transgene expression from E1Delta Ad5/35 infection was not due to the loss of vector genomes, as determined by quantitative real-time PCR (QRT-PCR), or cytotoxicity, but rather through a putative silencing mechanism.

Adenovirus type 5 pseudotyped with adenovirus type 37 fiber uses sialic acid as a cellular receptor

For purposes of gene therapy, the tropism of adenovirus (Ad) serotype 5 vectors can be altered with fibers derived from alternative serotypes. However, there is currently limited information available on the cellular receptors used by the approximately 51 known Ad serotypes. Recently, alpha(2-->3)-linked sialic acid (2,3-SA) has been implicated as the cellular receptor for wild-type Ad37. However, some studies have demonstrated that wild-type Ad37 uses a 50-kDa protein and not sialic acid as its primary receptor for binding of human conjunctival cells. The sialic acid receptor has also been shown not to play a major role in the infection of these cells by an Ad5 virion pseudotyped with Ad37 fiber (Ad5.GFP.DeltaF/37F). In this study, we demonstrate that a similar virus (Ad5F37) can indeed use alpha(2-->3)-linked sialic acid as a cellular receptor. We also find that the receptor used by Ad5F37 is sensitive to proteases and that Ad5F37 can use integrin more efficiently than sialic acid for cell entry. Unlike Ad5 vectors, Ad5F37 does not efficiently employ the coxsackie and adenovirus receptor (CAR) to infect cells. Similar to Ad5, Ad5F37 infection of cells that form tight junctions can be enhanced by ethylenediaminetetraacetic acid (EDTA). These results have implications in the design of pseudotyped adenovirus vectors for gene therapy and may have particular use in the treatment of diseases involving breakdown of the blood-retinal barrier.

Analysis of adenovirus sequestration in the liver, transduction of hepatic cells, and innate toxicity after injection of fiber-modified vectors

After intravenous administration, adenovirus (Ad) vectors are predominantly sequestered by the liver. Delineating the mechanisms for Ad accumulation in the liver is crucial for a better understanding of Ad clearance and Ad-associated innate toxicity. To help address these issues, in this study, we used Ad vectors with different fiber shaft lengths and either coxsackievirus-Ad receptor (CAR)-interacting Ad serotype 9 (Ad9) or non-CAR-interacting Ad35 fiber knob domains. We analyzed the kinetics of Ad vector accumulation in the liver, uptake into hepatocytes and Kupffer cells, and induction of cytokine expression and release in response to systemic vector application. Immediately after intravenous injection, all Ad vectors accumulated equally efficiently in the liver; however, only genomes of long-shafted Ads were maintained in the liver tissue over time. We found that Kupffer cell uptake of long-shafted Ads was mediated by the fiber knob domain and was CAR independent. The short-shafted Ads were unable to efficiently interact with hepatocellular receptors and were not taken up by Kupffer cells. Moreover, our studies indicated that Kupffer cells were not the major reservoir for the observed accumulation of Ads (used in this study) in the liver within the first 30 min after virus infusion. The lower level of liver cell transduction by short-shafted Ads correlated with a significantly reduced inflammatory anti-Ad response as well as liver damage induced by the systemic administration of these vectors. This study contributes to a better understanding of the biology of systemically applied Ad and will help in designing safer vectors that can efficiently transduce target tissues.

Targeted delivery of adenoviral vectors by cytotoxic T cells

Effective targeting of vectors to tumor cells that have metastasized to multiple different tissue sites remains a major challenge for gene therapy. Tumor-specific cytotoxic T lymphocytes (CTLs) have been shown in animal models and in humans to be able to cross tissue barriers and traffic to tumor cells. However, their capacity to eliminate malignancy has been limited by tumor immune evasion strategies. We now use a model of Epstein-Barr virus-mediated malignancy to show that human CTLs themselves may be modified to release therapeutic vectors following engagement of their antigen-specific receptors and that these vectors will effectively transduce and destroy tumor targets. We generated EBV-specific CTLs that were transgenic for the adenoviral E1 gene under the control of the cell activation-dependent CD40 ligand (CD40L) promoter. Following transduction with E1-deficient adenoviral vectors, these CTLs produced infectious virus when exposed to HLA-matched EBV-expressing targets, but not on exposure to major histocompatibility complex (MHC)-mismatched or otherwise irrelevant cells. This approach provides a means of delivering oncolytic/therapeutic vectors not only to locally accessible macroscopic tumors as is presently the case, but also to disseminated metastatic disease, while avoiding the risks associated with systemic administration of large doses of adenoviral vectors.

Abolition of hCAR-dependent cell tropism using fiber knobs of Atadenovirus serotypes

Most adenoviral vectors use in gene therapy protocols derive from species C. However, expression of the primary receptor (human Coxsackievirus and Adenovirus receptor, hCAR) for these AdV is variable on cancer cells. In vivo targeting of a therapeutic gene to specific cells has then become a major issue in gene therapy. The Ad fiber protein largely determines viral tropism through interaction with specific receptors. Hereto, we constructed a set of HAdV5 vectors carrying chimeric fibers with knob domains from nonhuman AdV, namely from the FAdV-1 (Aviadenovirus), DAdV-1, and BAdV-4 (Atadenovirus). Correspondents viruses were produced using an established new HEK293 cell line, which express the HAdV2 fiber. Recombinant HAdV harboring chimeric fibers constituted of the N-terminal domain of HAdV2, and knob domain of bovine adenovirus type 4 (BAdV-4) demonstrated the greatest reduction in fiber-mediated gene transfer into human cells expressing the hCAR. Moreover, this vector infects with a better efficiency than vector with wild-type fiber, the Chinese Hamster Ovarian (CHO) and SKOV3 cell lines, both from ovarian origin, hamster and human, respectively. These studies support the concept that changing the fiber knob domain to ablate hCAR interaction should result in a de- or retargeted adenoviral vector. The adenoviral vector with the chimeric HAdV2/BAdV-4 fiber lacking hCAR interaction and with an ovarian cell tropism could be a nice candidate to elaborate vectors for ovarian tumor therapy.

The human membrane cofactor CD46 is a receptor for species B adenovirus serotype 3

Many human adenovirus (Ad) serotypes use the coxsackie B virus-Ad receptor (CAR). Recently, CD46 was suggested to be a receptor of species B Ad serotype 11 (Ad11), Ad14, Ad16, Ad21, Ad35, and Ad50. Using Sindbis virus-mediated cDNA library expression, we identify here the membrane cofactor protein CD46 as a surface receptor of species B Ad3. All four major CD46 transcripts and one minor CD46 transcript expressed in nucleated human cells were isolated. Rodent BHK cells stably expressing the BC1 form of CD46 bound radiolabeled Ad3 with a dissociation constant of 0.3 nM, identical to that of CD46-positive HeLa cells expressing twice as many Ad3 binding sites. Pull-down experiments with recombinant Ad3 fibers and a soluble form of the CD46 extracellular domain linked to the Fc portion of human immunoglobulin G (CD46ex-Fc) indicated direct interactions of the Ad3 fiber knob with CD46ex-Fc but not CARex-Fc (Fc-linked extracellular domain of CAR). Ad3 colocalized with cell surface CD46 in both rodent and human cells at the light and electron microscopy levels. Anti-CD46 antibodies and CD46ex-Fc inhibited Ad3 binding to CD46-expressing BHK cells more than 10-fold and to human cells 2-fold. In CD46-expressing BHK cells, wild-type Ad3 and a chimeric Ad consisting of the Ad5 capsid and the Ad3 fiber elicited dose-dependent cytopathic effects and transgene expression, albeit less efficiently than in human cells. Together, our results show that all of the major splice forms of CD46 are predominant and functional binding sites of Ad3 on CD46-expressing rodent and human cells but may not be the sole receptor of species B Ads on human cells. These results have implications for understanding viral pathogenesis and therapeutic gene delivery.

Odorant Stimulation Enhances Survival of Olfactory Sensory Neurons via MAPK and CREB

Olfactory sensory neurons (OSNs) can be sensitized to odorants by repeated exposure, suggesting that an animal's responsiveness to olfactory cues can be enhanced at the initial stage of detection. However, because OSNs undergo a regular cycle of apoptosis and replacement by ostensibly naive, precursor-derived neurons, the advantage of sensitization would be lost in the absence of a mechanism for odorant-enhanced survival of OSNs. Using recombinant adenoviruses in conjunction with surgical and electrophysiological techniques, we monitored OSN survival and function in vivo and find that odorant exposure selectively rescues populations of OSNs from apoptosis. We further demonstrate that odorant stimuli rescue OSNs in a cAMP-dependent manner by activating the MAPK/CREB-dependent transcriptional pathway, possibly as a result of expression of Bcl-2.

The effect of sequestration by nontarget tissues on anti-tumor efficacy of systemically applied, conditionally replicating adenovirus vectors

Avoiding transduction of normal tissue after intravenous application of oncolytic adenoviruses (Ad) is an important strategy to improve the safety and efficacy of these vectors in gene therapy. As a model for a targeted vector, we used Ad vectors with type 35 fibers (Ad5/35), which efficiently transduce human cervical carcinoma cells but not liver cells. In an in vitro model of liver metastases, in which small nests of HeLa cells were surrounded by mouse hepatocytes, we showed that an Ad5/35-based conditionally replicating vector regulated by DNA replication-dependent recombination conferred increased gene transfer to tumor cells and enhanced viral replication and tumor cell lysis compared to the nontargeted Ad5 vector. Intravenous injection of Ad5/35 vectors into mice bearing liver metastases derived from HeLa cells caused markedly less hepatotoxicity than Ad5 vectors; however, it did not result in enhanced tumor cell transduction, viral replication, or oncolysis. Apparently, other factors, including the stability of virus in the blood, trapping within the liver sinusoids, transendothelial transfer, and/or vector diffusion of viral particles to tumor cells, limit tumor transduction, even if the vector is not taken up by liver cells.

Infection efficiency of human and mouse embryonic stem cells using adenoviral and adeno-associated viral vectors

Human and mouse embryonic stem (ES) cells have the capacity to differentiate into derivatives of all three germ layers, suggesting novel therapies for degenerative, metabolic, and traumatic disorders. ES-based regenerative medicine will be further advanced by the development of reliable methods for transgene introduction and expression. Here, we show infection of human and mouse embryonic stem (ES) cells with two of the most popular vectors in gene transfer, adenovirus type 5 (Ad5) and adeno-associated virus (AAV; serotypes 2, 4, and 5). All vectors express the nuclear-localized marker gene beta-galactosidase expressed from the Rous Sarcoma Virus long terminal repeat (RSV-LTR). Both Ad5 and AAV2 infected human and mouse ES cells and gave rise to beta-galactosidase expression. AAV4 and 5 did not yield detectable levels of beta-galactosidase expression. Quantitative PCR analysis of virally infected human and mouse ES cells revealed that only Ad5 and AAV2 are capable of transducing both cell-types. No viral DNA was detected in cells infected with either AAV4 or AAV5. Infection and subsequent differentiation of mouse and human ES cells with Ad5 showed that beta-galactosidase-expressing cells were restricted to cells in the interior of the embryoid body mass. No beta-galactosidase expression was observed in AAV-infected cells following differentiation. There was no difference in morphology or differentiation patterns between infected and noninfected differentiating mouse and human ES cells. Differentiation of hES cells prior to infection led to transduction of neuronally differentiated cells with good efficiency using all vectors. These data show that Ad5- and AAV2-based vectors are capable of infecting both human and mouse ES cells, in both their undifferentiated and differentiated states, whereas AAV4 and AAV5 can infect human and mouse ES cells only following differentiation.

Targeting of adenovirus via genetic modification of the viral capsid combined with a protein bridge

A potential barrier to the development of genetically targeted adenovirus (Ad) vectors for cell-specific delivery of gene therapeutics lies in the fact that several types of targeting protein ligands require posttranslational modifications, such as the formation of disulfide bonds, which are not available to Ad capsid proteins due to their nuclear localization during assembly of the virion. To overcome this problem, we developed a new targeting strategy, which combines genetic modifications of the Ad capsid with a protein bridge approach, resulting in a vector-ligand targeting complex. The components of the complex associate by virtue of genetic modifications to both the Ad capsid and the targeting ligand. One component of this mechanism of association, the Fc-binding domain of Staphylococcus aureus protein A, is genetically incorporated into the Ad fiber protein. The ligand is comprised of a targeting component fused with the Fc domain of immunoglobulin, which serves as a docking moiety to bind to these genetically modified fibers during the formation of the Ad-ligand complex. The modular design of the ligand solves the problem of structural and biosynthetic compatibility with the Ad and thus facilitates targeting of the vector to a variety of cellular receptors. Our study shows that targeting ligands incorporating the Fc domain and either an anti-CD40 single-chain antibody or CD40L form stable complexes with protein A-modified Ad vectors, resulting in significant augmentation of gene delivery to CD40-positive target cells. Since this gene transfer is independent of the expression of the native Ad5 receptor by the target cells, this strategy results in the derivation of truly targeted Ad vectors suitable for tissue-specific gene therapy.

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.

CD46 is a cellular receptor for group B adenoviruses

Group B adenoviruses, a subgenus of human Adenoviridae, are associated with a variety of often-fatal illnesses in immunocompromised individuals, including bone marrow transplant recipients and cancer and AIDS patients. Recently, group B adenovirus derivatives have gained interest as attractive gene therapy vectors because they can transduce target tissues, such as hematopoietic stem cells, dendritic cells and malignant tumor cells, that are refractory to infection by commonly used adenoviral vectors. Whereas many adenoviruses infect cells through the coxsackievirus and adenovirus receptor (CAR), group B adenoviruses use an alternate, as-yet-unidentified cellular attachment receptor. Using mass spectrometric analysis of proteins interacting with a group B fiber, we identified human CD46 as a cellular attachment receptor for most group B adenoviruses. We show that ectopic expression of human CD46 rendered nonhuman cells susceptible to infection with group B viruses in vitro and in vivo. In addition, both siRNA-mediated knockdown of CD46 and a soluble form of CD46 blocked infection of human cell lines and primary human cells. The discovery that group B adenoviruses use CD46, a ubiquitously expressed complement regulatory protein, as a cellular attachment receptor elucidates the diverse clinical manifestation of group B virus infections, and bears directly on the application of these vectors for gene therapy.

Metabolically biotinylated adenovirus for cell targeting, ligand screening, and vector purification

Development of cell-targeting vectors is an important focus for gene therapy. While some ligands can be genetically inserted into virus capsid proteins for cell targeting, for many ligands, this approach can disrupt either ligand function or vector function. To address this problem for adenovirus type 5 vectors, the fiber capsid protein was genetically fused to a biotin acceptor peptide (BAP). Adenovirus particles bearing this BAP were metabolically biotinylated during vector production by the endogenous biotin ligase in 293 cells to produce covalently biotinylated virions. The resulting biotinylated vector could be retargeted to new receptors by conjugation to biotinylated antibodies using tetrameric avidin (K(d) = 10(-15) M). The biotinylated vector could also be purified by biotin-reversible binding on monomeric avidin (K(d) = 10(-7) M). Finally, this vector was used as a ligand screening platform for dendritic cells in which a variety of structurally diverse protein, carbohydrate, and nucleic acid ligands were easily added to the vector using the biotin-avidin interaction. This work demonstrates the utility of metabolically biotinylated viruses for ligand screening, vector targeting, and virus purification applications.

Gene therapy with viral vectors

A key factor in the success of gene therapy is the development of gene delivery systems that are capable of efficient gene transfer in a broad variety of tissues, without causing any pathogenic effect. Currently, viral vectors based on many different viruses have been developed, and their performance and pathogenicity has been evaluated in animal models. The results of these studies form the basis for the first clinical trials for correcting genetic disorders using retroviral, adenoviral, and adeno-associated viral vectors. Even though the results of these trials are encouraging, vector development is still required to improve and refine future treatment of hereditary disorders.

Targeting of adenovirus to human renal cell carcinoma cells

OBJECTIVES

The use of recombinant adenoviruses in cancer gene therapy is limited by the widespread expression of the coxsackievirus and adenovirus receptor on normal human cells. Targeting adenoviral vectors to renal cell carcinoma (RCC) cells may improve their potential in cancer gene therapy of patients with metastatic RCC. The G250 protein, also known as the carbonic anhydrase IX protein, is membranously expressed in all cases of clear cell RCC, and clinical studies have demonstrated exceptional tumor targeting with a G250 monoclonal antibody.

METHODS

A recombinant bispecific single-chain antibody directed against the RCC-associated G250 protein and the adenovirus fiber knob domain was constructed and used to retarget recombinant adenovirus expressing the green fluorescent protein under control of the cytomegalovirus promoter. G250-specific adenoviral transduction of cells was examined by flow cytometric analysis of green fluorescent protein expression.

RESULTS

G250-positive RCC cells displayed enhanced susceptibility for transduction by the green fluorescent protein recombinant adenovirus complexed with the G250-directed bispecific single-chain antibody when compared with native adenovirus. This enhanced transduction was restricted to G250-positive RCC cells and could be abolished completely in the presence of excess G250 protein.

CONCLUSIONS

The results of this study demonstrate the feasibility of immunologic retargeting of adenovirus to RCC cells with the highly tumor-specific G250 protein as the target. This strategy may provide the possibility of improving cancer gene therapy for patients with RCC.

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.

Osteoinduction by ex vivo adenovirus-mediated BMP2 delivery is independent of cell type

The objective of the study was to analyze and compare the abilities of various human cell types with inherently dissimilar osteogenic potentials to induce heterotopic bone formation following ex vivo transduction with two distinct adenoviral vectors encoding bone morphogenetic protein type 2 (BMP2). The cells comprised primary human bone marrow mesenchymal stem cells (BM-MSCs), primary human skin fibroblasts (SFs), and a human diploid fetal lung cell line (MRC-5). The vectors included adenovirus type 5 or a chimeric adenovirus type 5 with the fiber gene of adenovirus type 35 (Ad5F35-BMP2), both demonstrating significantly different expression of BMP2 in vitro. The experimental groups consisted of the three human cell types transduced with each of the two adenoviral vectors. Using nonobese diabetic severe combined immunodeficiency (NOD/SCID) mice, the transduced cells were injected intramuscularly following ex vivo adenoviral transduction. The nature and extent of heterotopic bone formation were analyzed radiographically and histologically. At 14 days postinjection, abundant, highly mineralized bone was formed in mice injected with Ad5F35-BMP2-transduced cells irrespective of the cell type. There was no statistically significant difference in the amount of bone formed between BM-MSCs, SFs, and MRC-5 cells transduced with Ad5F35-BMP2, as assessed from bone surface area on biplanar plain radiography. Substantially lesser amounts or no bone could be detected in mice injected with cells transduced with Ad5-BMP2. Immunohistochemical analysis confirmed the presence of human cells in muscle as early as 2 days postdelivery; however, at 6-7 days after injection, the transduced cells could not be detected in surrounding muscle, or in the heterotopic bone, indicating the host origin of the newly formed bone. The results of the study demonstrate no significant difference in osteoinductive properties between BM-MSCs, SFs, and MRC-5 cells transduced ex vivo with the same type of adenovirus encoding BMP2. The level of BMP2 expression appears to be a crucial factor determining the extent of heterotopic bone formation and was significantly affected by the type of adenovirus used. In the cell types studied, Ad5F35-BMP2 was more efficacious than Ad5-BMP2 in providing adequate levels of BMP2 for efficient osteoinduction.

Development of adenovirus serotype 35 as a gene transfer vector

While 51 human adenoviral serotypes have been identified to date, the vast majority of adenoviral vectors designed for gene transfer have been generated in the adenovirus serotype 5 (Ad5) backbone. Viral infections caused by Ad5 are endemic in most human populations and the majority of humans carry preexisting humoral and/or cellular immunity to Ad5 which may severely limit the use of Ad5-based vectors for gene therapy applications. To circumvent this preexisting Ad5 immunity, we have identified Ad35 as an alternative adenoviral serotype to which the majority of humans do not have neutralizing antibodies. Importantly, Ad35 can be grown to high titers with a low particle-to-PFU ratio. As a prerequisite for the development of Ad35 for use as a gene transfer vector, a genome organization map was constructed using the available Ad35 sequence information, and E1a-deficient Ad35 vectors encoding marker genes were generated. Ad35 biodistribution in mice was assessed following intravenous administration and compared with that of Ad5. Extremely low levels of Ad35 were detected in all organs evaluated, including liver, lung, spleen, and bone marrow, while Ad5 displayed high transduction of these organs. Due to the lack of Ad35 liver tropism, minimal hepatotoxicity was observed in mice treated with Ad35. Furthermore, the half-life of Ad35 in mouse blood was found to be two to three times longer than that of Ad5. These data suggest that either mice do not express the Ad35 cell surface receptor or that Ad35 does not efficiently transduce mouse cells in vivo following systemic delivery. Therefore, to begin to elucidate the Ad35 cell entry mechanisms, in vitro competition studies were performed. These data demonstrated that Ad35 cell entry is CAR independent, and may involve protein(s) expressed on most human cells.

Efficient gene transfer into human CD34+ cells by an adenovirus type 35 vector

Efficient gene transfer into human hematopoietic stem cells (HSCs) is the most important requirement for gene therapy of hematopoietic disorders and for study of the hematopoietic system. An adenovirus (Ad) vector based on the Ad serotype 5 (Ad5) is known to transduce HSCs, including CD34(+) cells, with very low efficiency because of low-level expression of its primary receptor, coxsackievirus and adenovirus receptor (CAR). In the present study, we developed a recombinant Ad vector composed of the whole Ad serotype 35 (Ad35), which recognizes an unidentified receptor different from CAR for its infection. A transduction study showed that the Ad35-based vectors exhibit a higher transduction efficiency in human CD34(+) cells than the conventional Ad5 vectors and the Ad5F35 vectors, which are fiber-substituted Ad5 vectors containing Ad35 fiber proteins. The mean of fluorescence intensity in the CD34(+) cells transduced with the Ad35 vectors was 12-76 and 1.4-3 times higher than that in the cells transduced with the Ad5 and Ad5F35 vectors, respectively. The percentages of green fluorescent protein (GFP)-positive CD34(+) cells by transduction with Ad35, Ad5, and Ad5F35 vectors expressing GFP at 300 PFU/cell were 53%, 5%, and 52%, respectively, suggesting that Ad35 vectors mediate a more efficient gene transfer into human CD34(+) cells than Ad5 and Ad5F35 vectors, although the percentage of transduced cells was similar between Ad35 and Ad5F35 vectors. The Ad vector based on Ad35 could be very useful in gene therapy for blood disorders and gene transfer experiments using HSCs.

Large-scale expansion of dendritic cell-primed polyclonal human cytotoxic T-lymphocyte lines using lymphoblastoid cell lines for adoptive immunotherapy

Dendritic cells (DCs) have been shown to activate cytotoxic T-lymphocytes (CTLs) for many tumor and virus-associated antigens in vitro. In this study, the authors tested the feasibility of using DCs to expand polyclonal, cytomegalovirus (CMV)-specific CTL lines for adoptive immunotherapy. Two stimulations with DCs expressing pp65, the immunodominant antigen of CMV, effectively activated and expanded MHC-class I restricted, CMV-specific CTLs from peripheral blood mononuclear cells. However, limiting monocyte-derived DC numbers precluded the authors from expanding the CTLs to the numbers required for adoptive transfer protocols. Nonspecific stimulation methods failed to expand CTL lines specifically. However, the authors found that lymphoblastoid cell lines (LCLs) expressing pp65 expanded pp65-specific CTL lines without competition from EBV-specific CTLs. An unlimited source of antigen presenting cells that could present antigen in the appropriate MHC context emerged as a critical point for expansion of polyclonal, antigen-specific CTL lines.

Vectors for the treatment of autoimmune disease

Gene therapy has been applied in a variety of experimental models of autoimmunity with some success. In this article, we outline recent developments in gene therapy vectors, discuss advantages and disadvantages of each, and highlight their recent applications in autoimmune models. We also consider progress in vector targeting and components for regulating transgene expression, which will both improve gene therapy safety and empower gene therapy to fullfil its potential as a therapeutic modality. In conclusion, we consider candidate vectors that satisfy requirements for application in the principal therapeutic strategies in which gene therapy will be applied to autoimmune conditions.

Progress and problems with the use of viral vectors for gene therapy

Gene therapy has a history of controversy. Encouraging results are starting to emerge from the clinic, but questions are still being asked about the safety of this new molecular medicine. With the development of a leukaemia-like syndrome in two of the small number of patients that have been cured of a disease by gene therapy, it is timely to contemplate how far this technology has come, and how far it still has to go.

The complete nucleotide sequence, genome organization, and origin of human adenovirus type 11

The complete DNA sequence and transcription map of human adenovirus type 11 are reported here. This is the first published sequence for a subgenera B human adenovirus and demonstrates a genome organization highly similar to those of other human adenoviruses. All of the genes from the early, intermediate, and late regions are present in the expected locations of the genome for a human adenovirus. The genome size is 34,794 bp in length and has a GC content of 48.9%. Sequence alignment with genomes of groups A (Ad12), C (Ad5), D (Ad17), E (Simian adenovirus 25), and F (Ad40) revealed homologies of 64, 54, 68, 75, and 52%, respectively. Detailed genomic analysis demonstrated that Ads 11 and 35 are highly conserved in all areas except the hexon hypervariable regions and fiber. Similarly, comparison of Ad11 with subgroup E SAV25 revealed poor homology between fibers but high homology in proteins encoded by all other areas of the genome. We propose an evolutionary model in which functional viruses can be reconstituted following fiber substitution from one serotype to another. According to this model either the Ad11 genome is a derivative of Ad35, from which the fiber was substituted with Ad7, or the Ad35 genome is the product of a fiber substitution from Ad21 into the Ad11 genome. This model also provides a possible explanation for the origin of group E Ads, which are evolutionarily derived from a group C fiber substitution into a group B genome.

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.

Human adenovirus serotypes 4 and 11 show higher binding affinity and infectivity for endothelial and carcinoma cell lines than serotype 5

Adenoviruses are promising vectors for human cancer gene therapy. However, the extensively used adenoviruses serotypes 2 and 5 (Ad2 and Ad5) from species C have a major disadvantage in being highly prevalent; thus, most adults have an immunity against the two viruses. Furthermore, the expression of coxsackievirus and adenovirus receptors for Ad2 and Ad5 varies in different cells. This study aims to identify adenovirus serotypes with specific tropism for endothelial cells and epithelial tumour cells. Comparison of the binding affinities of Ad31, Ad11, Ad5, Ad37, Ad4 and Ad41, belonging to species A-F, respectively, to established cell lines of hepatoma (HepG2), breast cancer (CAMA and MG7), prostatic cancer (DU145 and LNCaP) and laryngeal cancer (Hep2), as well as to endothelial cells (HMEC), was carried out by flow cytometric analysis. Ad11 from species B showed markedly higher binding affinity than Ad5 for the endothelial cell line and all carcinoma cell lines studied. Ad4 showed a specific binding affinity for hepatoma cells and laryneal carcinoma cells. The ability of Ad11, Ad4 and Ad5 to be expressed in hepatoma, breast cancer and endothelial cell lines was studied by immunostaining and (35)S-labelling of viral proteins in infected cells. Ad11 and Ad4 manifested a higher proportion of infected cells and a higher degree of hexon expression than Ad5.

The interaction between the fiber knob domain and the cellular attachment receptor determines the intracellular trafficking route of adenoviruses

Most of the presently used adenovirus (Ad) vectors are based on serotype 5. However, the application of these vectors is limited by the native tropism of Ad5. To address this problem, a series of fiber chimeric vectors were produced to take advantage of the different cellular receptors used by Ad of different subgroups. In this study we utilize an Ad5-based chimeric vector containing sequences encoding the Ad35 fiber knob domain instead of the Ad5 knob (Ad5/35L) to analyze factors responsible for selection of intracellular trafficking routes by Ads. By competition analysis with recombinant Ad5 and Ad35 knobs we showed that the Ad5/35L vector infected cells through a receptor different from the Ad5 receptor. Intracellular trafficking of Ad5 and Ad5/35L viruses was analyzed in HeLa cells by tracking fluorophore-conjugated Ad particles, by immunostaining for capsid hexon protein, by electron microscopy, and by Southern blotting for viral DNA. These studies showed that the interaction with the Ad35 receptor(s) predestines Ad5/35L vector to intracellular trafficking pathways different from those of Ad5. Ad5 efficiently escaped from the endosomes early after infection. In contrast, Ad5/35L remained longer in late endosomal/lysosomal compartments and used them to achieve localization to the nucleus. However, a significant portion of Ad5/35L particles appeared to be recycled back to the cell surface. This phenomenon resulted in significantly less efficient Ad5/35L-mediated gene transfer compared to that of Ad5. We also demonstrated that the selection of intracellular trafficking routes was determined by the fiber knob domain and did not depend on the length of the fiber shaft. This study contributes to a better understanding of the mechanisms that govern the infection of retargeted, capsid-modified vectors which have potential application for hematopoietic stem cell and tumor gene therapy.