The absence of accessible vitronectin receptors in differentiated tissue hinders adenoviral-mediated gene transfer to the intestinal epithelium in vitro

Firewalls Prevent Systemic Dissemination of Vectors Derived from Human Adenovirus Type 5 and Suppress Production of Transgene-Encoded Antigen in a Murine Model of Oral Vaccination

To define the bottlenecks that restrict antigen expression after oral administration of viral-vectored vaccines, we tracked vectors derived from the human adenovirus type 5 at whole body, tissue, and cellular scales throughout the digestive tract in a murine model of oral delivery. After intragastric administration of vectors encoding firefly luciferase or a model antigen, detectable levels of transgene-encoded protein or mRNA were confined to the intestine, and restricted to delimited anatomical zones. Expression of luciferase in the form of multiple small bioluminescent foci in the distal ileum, cecum, and proximal colon suggested multiple crossing points. Many foci were unassociated with visible Peyer's patches, implying that transduced cells lay in proximity to villous rather than follicle-associated epithelium, as supported by detection of transgene-encoded antigen in villous epithelial cells. Transgene-encoded mRNA but not protein was readily detected in Peyer's patches, suggesting that post-transcriptional regulation of viral gene expression might limit expression of transgene-encoded antigen in this tissue. To characterize the pathways by which the vector crossed the intestinal epithelium and encountered sentinel cells, a fluorescent-labeled vector was administered to mice by the intragastric route or inoculated into ligated intestinal loops comprising a Peyer's patch. The vector adhered selectively to microfold cells in the follicle-associated epithelium, and, after translocation to the subepithelial dome region, was captured by phagocytes that expressed CD11c and lysozyme. In conclusion, although a large number of crossing events took place throughout the intestine within and without Peyer's patches, multiple firewalls prevented systemic dissemination of vector and suppressed production of transgene-encoded protein in Peyer's patches.

Targeting the gastrointestinal tract with viral vectors: state of the art and possible applications in research and therapy

While there is a large body of preclinical data on the use of viral vectors in gene transfer, relatively little is known about viral gene transfer in the gastrointestinal tract. Viral vector technology is especially underused in the field of neurogastroenterology when compared to brain research. This review provides an overview of the studies employing viral vectors-in particular retroviruses, adenoviruses and adeno-associated viruses-to transduce different cell types in the intestine. Early work mainly focused on mucosal transduction, but had limited success due to the harsh luminal conditions in the gastrointestinal tract and the high turnover rate of enterocytes. More recently, several studies have successfully employed viral gene transfer to target the enteric nervous system and its progenitors. Although several hurdles still need to be overcome, in particular on how to augment transduction efficiency and specific cell targeting, viral vector technology holds strong potential not only as a valid research tool in fundamental gastroenterological research but also as a therapeutic agent in translational (bio)medical research.

Efficient Adenovirus Gene Transfer Methods in Human Colonic Caco-2 Epithelial Cells Using Capric Acid

Adenovirus (Ad) vectors are widely used in gene therapy and in vitro/in vivo gene transfer. However, Ad-mediated gene transfer in epithelial cells shows low efficiency, because Ad fiber cannot bind to the primary receptor, the coxsackievirus and adenovirus receptor (CAR), present in tight junctions. Caco-2 monolayer cells cultured on Transwell-chamber plates for approximately 2 weeks are widely used for drug membrane permeation studies, but Ad-mediated gene transfer is difficult in Caco-2 monolayer cells. First, we examined the efficiency of gene transfer into Caco-2 monolayer cells. Luciferase production in cultured Caco-2 cells transduced with Ad vectors was 20-fold lower on day 12 than on day 1. In contrast, the expression of CAR protein in Caco-2 cells gradually increased along with the duration of culture. For efficient gene transfer into Caco-2 monolayer cells, the binding ability of Ad vectors with CAR was found to be important. Capric acid (C10), a medium-chain fatty acid is a tight-junction modulator used as a pharmaceutical agent. We found that a novel gene transfer method using transduction with Ad vectors in the presence of C10 led more efficiently to LacZ expression in Caco-2 monolayer cells than Ad vectors alone. The results of the present study indicate that C10 could be very useful for Ad-mediated gene transfer in human colonic Caco-2 epithelial cells.

Adenoviral transduction of enterocytes and M-cells using in vitro models based on Caco-2 cells: the coxsackievirus and adenovirus receptor (CAR) mediates both apical and basolateral transduction

Understanding virus-cell interaction is a key to the design of successful gene delivery vectors. In the present study we investigated Ad5 transduction of enterocytes and M-cells utilizing differentiated Caco-2 cells and cocultures of Caco-2 cells with lymphocytes. Transduction inhibition studies showed that CAR is the major receptor mediating apical and basolateral virus entry in differentiated Caco-2 cells. Integrins and heparan sulfate glycosaminoglycans do not appear to play a significant role. Immunofluorescence localized CAR to sites of cell-cell contact, with staining mostly observed on the cell perimeter. Staining was observed even in nonpermeabilized monolayers, suggesting apical accessibility of the receptor. Cocultures with mouse Peyer's patch lymphocytes or Raji B human lymphocytes were more susceptible to transduction than Caco-2 cells, and the effects were dose-dependent. Similar to Caco-2 cells, CAR and not integrins mediated apical transduction. In conclusion, contrary to other epithelial cell lines, both apical and basolateral transduction of absorptive enterocytes and M-cells is mediated by binding to CAR. The coculture system can be used to study the interactions between M-cells and gene delivery vectors.

Delivery of human immunodeficiency virus vaccine vectors to the intestine induces enhanced mucosal cellular immunity

Effective vaccines for human immunodeficiency virus type 1 (HIV-1) will likely need to stimulate protective immunity in the intestinal mucosa, where HIV-1 infection causes severe CD4(+) T-cell depletion. While replication-competent recombinant adenovirus (rAd) vectors can stimulate adenovirus-specific mucosal immunity after replication, oral delivery of replication-defective rAd vectors encoding specific immunogens has proven challenging. In this study, we have systematically identified barriers to effective gut delivery of rAd vectors and identified sites and strategies to induce potent cellular and humoral immunity. Vector-mediated gene transfer by rAd5 was susceptible to low-pH buffer, gastric and pancreatic proteases, and extracellular mucins. Using ex vivo organ explants, we found that transduction with rAd5 was highest in the ileum and colon among all intestinal segments. Transgene expression was 100-fold higher after direct surgical introduction into the ileum than after oral gavage, with rAd5 showing greater potency than the rAd35 or the rAd41 vector. A single immunization of rAd5 encoding HIV-1 gp140B to the ileum stimulated potent CD8(+) T-cell responses in the intestinal and systemic compartments, and these responses were further enhanced by intramuscular rAd5 boosting. These studies suggest that induction of primary immune responses by rAd5 gut immunization and subsequent systemic boosting elicits potent antigen-specific gut mucosal responses.

Restituting intestinal epithelial cells exhibit increased transducibility by adenoviral vectors

BACKGROUND AND AIMS

While mature enterocytes are resistant to transduction by adenovirus type 5 (Ad5) vectors, undifferentiated cells are transduced much more efficiently. Our purpose was to study enterocyte transduction in models of intestinal wound healing.

METHODS

Transduction was studied ex vivo using cultures of endoscopic biopsies and in vitro utilizing Caco-2 cells in models of mucosal wound healing. Vectors carried either the LacZ or the luciferase gene. CAR (coxsackievirus and adenovirus receptor) and integrins were studied with transduction inhibition and immunofluorescent staining.

RESULTS

Increased transduction efficiency was observed for a subset of enterocytes with a flattened de-differentiated phenotype present at the edge of cultured biopsies. In the in vitro systems, expanding Caco-2 cell monolayers exhibited increased transducibility that was time- and dose-dependent, reaching virtually 100% in cells along the leading edge at high viral load. Bioluminescence activity of transduced expanding monolayers was up to 3-fold greater than that of non-expanding monolayers ('fence' system, 48 h, MOI 1000, p < 0.05). Mitomycin C pre-treatment did not affect levels of transduction in expanding monolayers. At the highest viral load tested, CAR or integrin blocking prior to virus application resulted in 39.4% and 45.4% reduction in transduction levels (p < 0.05). Immunofluorescence revealed altered expression of CAR on the migrating edge of the Caco-2 cultures and the expression of CAR on the apical membrane of biopsy enterocytes.

CONCLUSIONS

Increased CAR and integrin accessibility in migrating enterocytes mediates increased transduction by Ad5 vectors. This subset of enterocytes provides a target for the delivery of genes of interest for both research and gene therapy applications.

Improved gene delivery to intestinal mucosa by adenoviral vectors bearing subgroup B and d fibers

A major obstacle to successful oral vaccination is the lack of antigen delivery systems that are both safe and highly efficient. Conventional replication-incompetent adenoviral vectors, derived from human adenoviruses of subgroup C, are poorly efficient in delivering genetic material to differentiated intestinal epithelia. To date, 51 human adenovirus serotypes have been identified and shown to recognize different cellular receptors with different tissue distributions. This natural diversity was exploited in the present study to identify suitable adenoviral vectors for efficient gene delivery to the human intestinal epithelium. In particular, we compared the capacities of a library of adenovirus type 5-based vectors pseudotyped with fibers of several human serotypes for transduction, binding, and translocation toward the basolateral pole in human and murine tissue culture models of differentiated intestinal epithelia. In addition, antibody-based inhibition was used to gain insight into the molecular interactions needed for efficient attachment. We found that vectors differing merely in their fiber proteins displayed vastly different capacities for gene transfer to differentiated human intestinal epithelium. Notably, vectors bearing fibers derived from subgroup B and subgroup D serotypes transduced the apical pole of human epithelium with considerably greater efficiency than a subgroup C vector. Such efficiency was correlated with the capacity to use CD46 or sialic acid-containing glycoconjugates as opposed to CAR as attachment receptors. These results suggest that substantial gains could be made in gene transfer to digestive epithelium by exploiting the tropism of existing serotypes of human adenoviruses.

Increased transduction of human intestinal epithelial cells by adenoviral vectors in inflammatory bowel disease

BACKGROUND

Delivery of genes encoding anti-inflammatory proteins has been proposed as a strategy for the treatment of inflammatory bowel disease (IBD). The goal of this study was to assess the ability of a standard adenoviral vector to transfect epithelial cells in intestinal explants from patients with IBD compared with controls.

METHODS

Endoscopic colon biopsies obtained from patients with no history of IBD and endoscopically normal colon (n = 4), patients with a history of ulcerative colitis (UC; n = 5), and patients with a history of Crohn's disease (CD; n = 3) were placed in explant culture and exposed to an adenoviral vector carrying the nuclear targeted beta-galactosidase reporter gene.

RESULTS

X-Gal staining showed that the total number of transduced cells per square millimeter was greater in UC explants than in controls (mean, 11.3 versus 0.9 blue nuclei/mm, respectively; P < 0.02) and that the frequency of epithelial cell transduction was greater in UC explants than in controls (86% versus 47% of explants, respectively; P = 0.01). Transduction of mature columnar surface epithelial cells occurred exclusively in UC and CD explants and was not seen in controls. Attenuated epithelial cells at sites of tissue damage or ulceration showed increased transduction compared with mature columnar epithelial cells (62% versus 19% of occurrences, respectively; P < 0.0001).

CONCLUSIONS

We conclude that intestinal epithelial cells from IBD patients are more readily transfected by standard adenoviral vectors than are those from control patients. These results suggest that targeting genes to inflamed intestine through the luminal route may be possible.

Gene therapy for esophageal carcinoma: the use of an explant model to test adenoviral vectors ex vivo

Adenoviral gene therapy might be a promising therapeutic strategy for esophageal carcinoma. However, adenoviral transduction efficacy in vivo is still limited. This efficacy can be improved by the insertion of an Arg-Gly-Asp (RGD) peptide in the HI-loop of the viral fiber knob. Indeed in established esophageal cell lines, we observed an up to six-fold improved transduction using the RGD-targeted adenovirus. Established cell lines, however, are easily transformed and do not represent the more complex in vivo histology and anatomy. Therefore, we set up an esophageal explant model using esophageal biopsies from patients. Viability is a limiting factor for this system. Cultured squamous epithelium, intestinal metaplasia and squamous cell carcinoma had a sufficient viability to study adenoviral transduction. Viability of the cultured adenocarcinoma biopsies was poor. Adenoviral transduction in the explant model was poor and was localized in particular cells. The transduction of the nontargeted and RGD-targeted adenovirus was similar in localization and efficacy. In conclusion, we established an esophageal explant system to test the transduction of adenoviral vectors ex vivo. The transduction was limited and localized in specific cells. RGD-targeted adenovirus did not show an improved transduction in this system.

Mechanistic studies on nonviral gene delivery to the intestine using in vitro differentiated cell culture models and an in vivo rat intestinal loop

PURPOSE

To identify factors influencing nonviral vector transfection in differentiated CaCo-2 and mucus-secreting coculture, CaCo-2: Ht29GlucH, cell culture models and to compare these in vitro results with in vivo transfection efficiency in rat intestine.

METHODS

A range of nonviral vectors including DOTAP, Lipofectin, Superfect, PEI, and polylysine were investigated. CaCo-2 and a mucus-secreting coculture were used at 21 days. Transfection efficiency was assessed using pCMVluc (firefly luciferase) plasmid, and radio-labeled plasmid was used to determine the binding and internalization of plasmid DNA. The in vivo model used was a ligated rat intestinal loop.

RESULTS

Transfection levels decreased by over 1000-fold in differentiated models relative to nondifferentiated COS-7 cells and were related to reductions in luciferase production by individual cells. Active internalization of DNA by the differentiated cells decreased. Removal of mucus by the mucolytic agent N-acetylcysteine, from the coculture system significantly reduced (p < 0.05) transfection efficiency. In vivo the transfection efficiency of PEI proved superior to DOTAP.

CONCLUSIONS

Nonviral gene delivery to the hostile environment of the intestine is possible. Mechanistic studies using differentiated intestinal cell models aid identification of the rate-limiting steps to transfection and represent a more physiologically relevant approach to predict gene delivery to the intestine.

Adherence of yeast and filamentous forms of Candida albicans to cultured enterocytes

OBJECTIVE

Systemic candidiasis is a major cause of complicating infections in intensive care units. Morbidity and mortality are high, even in those who receive appropriate antifungal therapy. Because the intestinal tract is considered a major portal of entry for systemic candidiasis, experiments were designed to clarify the ability of yeast and filamentous forms, as well as the INT1 gene product, to influence adherence of Candida albicans to the intestinal epithelium.

DESIGN

Controlled.

SETTING

University teaching hospital research laboratory.

SUBJECTS

Mature Caco-2 and HT-29 cultured enterocytes.

INTERVENTIONS

C. albicans INT1 mutant strains, defective in filament production, were used to observe the ultrastructural surface interactions of C. albicans with cultured intestinal epithelial cells, namely Caco-2 and HT-29 cells. These mutant strains also were used to quantify the effect of the INT1 gene product on C. albicans adherence (yeast and filamentous forms) to cultured enterocytes. Ultrastructural surface interactions of C. albicans with cultured enterocytes were observed with high resolution scanning electron microscopy. C. albicans adherence to cultured enterocytes was quantified by using a colorimetric enzyme-linked immunosorbent assay.

MEASUREMENTS AND MAIN RESULTS

Both yeast and filamentous forms of C. albicans appeared tightly adherent to the apical surface of cultured enterocytes, and INT1 appeared to have little, if any, effect on these ultrastructural surface interactions. The distal ends of C. albicans filaments appeared to mediate adherence to enterocyte apical microvilli, and thigmotropism (contact guidance) appeared to play a role in C. albicans adherence. The absence of functional INT1 was associated with decreased adherence of C. albicans yeast forms to cultured enterocytes.

CONCLUSIONS

Although functional INT1 appeared to facilitate adherence of C. albicans yeast forms to cultured enterocytes, the role of INT1 in adherence of filamentous forms was unclear, and both yeast and filamentous forms could adhere to, and perhaps invade, the apical surface of cultured enterocytes.

Acute cytokine response to systemic adenoviral vectors in mice is mediated by dendritic cells and macrophages

We investigated the cellular basis for secretion of inflammatory cytokines in mice following intravenous administration of adenoviral vectors (Ad). Serum inflammatory cytokines including interleukin-6 (IL-6), IL-12, and tumor necrosis factor-alpha (TNF-alpha) were detected as early as 6 h following intravenous injection of Ad-expressing Escherichia coli beta-galactosidase (Ad-lacZ). Ad-lacZ readily accumulated in the splenic marginal zone 1 h after intravenous infusion, where both dendritic cells (DCs) and macrophages were transduced and activated within 6 h. Flow cytometric analyses showed that the expression of Ia and CD86 antigens was markedly enhanced on splenic DCs indicating their activation in vivo by Ad-lacZ. Upon ex vivo culture, these early-activated splenic DCs spontaneously produced high levels of IL-6 and IL-12. By contrast, activated splenic macrophages spontaneously secreted only IL-6. Elimination of tissue macrophages and splenic DCs in vivo considerably reduced the early release of IL-12, IL-6, and TNF-alpha and significantly blocked the specific cellular immune response to Ad and the transgene product in vivo. Our findings indicate that preferential activation of DCs and macrophages may account for Ad-triggered acute inflammatory response in vivo in mice. Moreover, DCs and macrophages may play different roles in this process in terms of their abilities to produce distinct patterns of inflammatory cytokines.

Integrin expression, enterocyte maturation, and bacterial internalization

BACKGROUND

Little is known about the molecular mechanisms involved in the translocation of enteric bacteria. Adhesion molecules mediate interactions between some enteric pathogens and mammalian cells, but no such interactions have been identified for enterocytes and normal enteric bacteria. Using enteric pathogens, adhesion molecule expression has been linked to bacterial internalization and to enterocyte differentiation. Therefore, experiments were designed to study enterocyte integrin expression and differentiation, as well as enterocyte internalization of Salmonella typhimurium, Proteus mirabilis, and Escherichia coli.

MATERIALS AND METHODS

Relative expression of the alpha2, alpha3, and beta1 integrin subunits on Caco-2 and HT-29 enterocytes (mature and immature) was measured by ELISA. Bacteria-enterocyte surface interactions were observed by light and scanning electron microscopy. Bacterial internalization by enterocytes was quantified using the gentamicin protection assay.

RESULTS

Expression of the alpha2, alpha3, and beta1 integrin subunits was consistently increased in immature compared to mature Caco-2 enterocytes; however, compared to mature enterocytes, immature HT-29 enterocytes had similar expression of alpha3 and beta1 but decreased alpha2. Compared to untreated mature enterocytes, bacterial internalization was increased in immature enterocytes as well as mature enterocytes with lateral membranes artifactually exposed. However, there was no difference in bacterial internalization between immature enterocytes and mature enterocytes treated to expose the lateral membrane.

CONCLUSIONS

Bacterial internalization by enterocytes appeared to be due to factors other than integrin expression or enterocyte differentiation. Exposure of the lateral enterocyte membrane may play an important role in facilitating bacterial internalization by enterocytes.

Cationic lipid-mediated transfection of differentiated Caco-2 cells: a filter culture model of gene delivery to a polarized epithelium

PURPOSE

The use of rapidly dividing in vitro cell culture systems to assess the efficiency of gene delivery is now recognised as a poor indicator of in vivo success. We investigated whether differentiated Caco-2 cell filter-cultures would make a more suitable model for studying gene transfer to an epithelium.

METHODS

Caco-2 cells were cultured on semi-permeable membrane filters into differentiated polarised monolayers. Monolayer differentiation was assessed by monitoring the transport of taurocholic acid. Cells at different stages of differentiation were transfected with DNA/DOTAP lipoplexes and later analysed for reporter gene activity. The uptake of radiolabled DNA was also evaluated at various stages of differentiation.

RESULTS

Caco-2 cultures developed a resistance to lipoplex-mediated transfection as early as three days, when some cells were still dividing and undifferentiated. As cultures matured, expression of reporter gene progressively decreased partly due to reduced internalisation of DNA. The resistance to transfection could be overcome in part by pre-treatment of monolayers with calcium chelating agents or surfactants. However, transgene expression in treated monolayers was still significantly lower than that in dividing cultures.

CONCLUSIONS

Differentiated Caco-2 cells are a more appropriate model for gene-transfer studies to the intestinal epithelium because they demonstrate a resistance to transfection similar to that observed in vivo.

Overexpression of human intestinal oligopeptide transporter in mammalian cells via adenoviral transduction

PURPOSE

Our goals are to establish an in vitro screening system and to evaluate a new approach in improving oral absorption of peptides and peptide-like drugs by overexpression of the human intestinal oligopeptide transporter (hPepT1). This study characterizes the expression of hPepT1 in human intestinal Caco-2 cells, rat intestinal epithelial cells (IEC-18), and human cervix epithelial cells (Hela) after adenoviral transduction.

METHODS

A recombinant replication-deficient adenovirus carrying the hPepT1 gene was made and used as a vector for the expression of hPepT1. The increase in the uptake permeability of cephalexin and Gly-Sar was determined. The effects of time, dose, apical pH, and substrate specificity were evaluated.

RESULTS

A significant increase in the uptake permeability of Gly-Sar and cephalexin was found in all three cell lines after viral transduction. The increase of Gly-Sar permeability in Hela. IEC-18, and Caco-2 cells was 85-, 46-, and 15-fold respectively. Immunoblotting using an antibody against hPepT1 detected high levels of a 85-98-kDa protein in all three infected cell lines. Substrate permeability was dependent on time of infection, inward pH gradients, and multiplicity of infection (MOI). Decreased infectivity and lower hPepT1 expression were observed in differentiated Caco-2 cells. The uptake was inhibited by dipeptides and beta-lactam antibiotics but not amino acids.

CONCLUSIONS

Adenoviral infected Hela cells displayed a pronounced level of hPepT1 expression with a low background and high specificity to dipeptides. These features make this system a useful tool for screening of potential substrates. The success of overexpression of hPepT1 in Caco-2 and IEC-18 cells may lead to a novel approach in improving oral absorption of peptides and peptidornimetic drugs.