Efficiency of cytokine gene transfer in corneal endothelial cells and organ-cultured corneas mediated by liposomal vehicles and recombinant adenovirus

Control of TNF-induced dendritic cell maturation by hybrid-type N-glycans

The activity of α-1,2-mannosidase I is required for the conversion of high-mannose to hybrid-type (ConA reactive) and complex-type N-glycans (Phaseolus vulgaris-leukoagglutinin [PHA-L] reactive) during posttranslational protein N-glycosylation. We recently demonstrated that α-1,2-mannosidase I mRNA decreases in graft-infiltrating CD11c(+) dendritic cells (DCs) prior to allograft rejection. Although highly expressed in immature DCs, little is known about its role in DC functions. In this study, analysis of surface complex-type N-glycan expression by lectin staining revealed the existence of PHA-L(low) and PHA-L(high) subpopulations in murine splenic conventional DCs, as well as in bone marrow-derived DC (BMDCs), whereas plasmacytoid DCs are nearly exclusively PHA-L(high). Interestingly, all PHA-L(high) DCs displayed a strongly reduced responsiveness to TNF-α-induced p38-MAPK activation compared with PHA-L(low) DCs, indicating differences in PHA-L-binding capacities between DCs with different inflammatory properties. However, p38 phosphorylation levels were increased in BMDCs overexpressing α-1,2-mannosidase I mRNA. Moreover, hybrid-type, but not complex-type, N-glycans are required for TNF-α-induced p38-MAPK activation and subsequent phenotypic maturation of BMDCs (MHC-II, CD86, CCR7 upregulation). α-1,2-mannosidase I inhibitor-treated DCs displayed diminished transendothelial migration in response to CCL19, homing to regional lymph nodes, and priming of IFN-γ-producing T cells in vivo. In contrast, the activity of α-1,2-mannosidase I is dispensable for LPS-induced signaling, as well as the DCs' general capability for phenotypic and functional maturation. Systemic application of an α-1,2-mannosidase I inhibitor was able to significantly prolong allograft survival in a murine high-responder corneal transplantation model, further highlighting the importance of N-glycan processing by α-1,2-mannosidase I for alloantigen presentation and T cell priming.

Genetic manipulation of corneal endothelial cells: transfection and viral transduction

The corneal endothelium plays a key role in the physiology of the cornea, maintaining its transparency by regulating corneal hydration. Moreover, corneal endothelial cells play the central role in irreversible corneal graft rejection as human corneal endothelial cells are predominantly postmitotic, and destroyed cells cannot be replaced. Therefore, gene transfer to the corneal endothelium to modify the corneal immune response for prophylaxis of corneal endothelial rejection has become a fast-developing research field. An addition pivotal advantage of gene transfer to the cornea is the possibility of ex vivo transfection during organ culturing, minimizing the risk of systemic spread of the vector or the transgene expression. A wide variety of vectors has been found suitable for gene transfer to the corneal endothelium, and therapeutic efficacy has been demonstrated in some experimental models of corneal disease. However, the transfection efficiency varies widely among the different vectors, and the optimal transfection efficiency to provoke a desired effect is still unclear. Moreover, it certainly depends on the biological function of the chosen transgene (cytokine, growth factor, etc.). As a consequence, relatively few studies have been able to demonstrate significant prolongation of corneal allograft survival after gene transfer to the endothelium, and the ideal transfer strategy has not been found. In contrast, different transfer strategies compete today, each with its special advantages and disadvantages. Physical, viral, and nonviral techniques have been used to transfer transgenes into endothelial cells. In the introduction of this chapter, a short overview of the different gene transfer strategies for endothelial cells is given; the materials and methods sections describe in detail the most widely used viral gene transfer technique (adenoviral) and an important nonviral alternative technique (liposomal transfection) to endothelial cells.

Expression of the chemokine antagonist vMIP II using a non-viral vector can prolong corneal allograft survival

BACKGROUND

The expression of chemokines is central to the recruitment of inflammatory cells for graft rejection, and modulation of chemokine action is of potential in preventing graft rejection. We have examined chemokine expression in a murine model of corneal allograft rejection, and also determined the effect of expressing a broad acting chemokine antagonist, viral macrophage inflammatory protein II (vMIP II), on graft survival.

METHOD

The expression of chemokines in a murine model of corneal transplantation was determined by real time RT-PCR and, in the case of regulated on activation normal T-cell expressed and secreted, by ELISA. The plasmid encoding the virally derived chemokine antagonist, vMIP II, was introduced into the corneal endothelial cells using a non-viral vector consisting of liposomes and transferrin. The expression and activity of vMIP II was determined by ELISA and functional assays, and the effect on graft survival noted.

RESULTS

After allotransplantation, there was up-regulation of all 11 chemokines examined. After gene delivery, there was expression of active vMIP II for more than 14 days and considerable prolongation of graft survival. This was associated with a decrease in leukocyte infiltration of the stroma of the cells.

CONCLUSION

As expected there was considerable up-regulation of chemokines during allograft rejection. The expression of vMIP II showed considerable prolongation of graft survival. This is the first time we have observed prolongation of graft survival after a non-viral (as opposed to viral) means of gene delivery and indicates the potential of interfering with chemokine action to prevent corneal graft failure.

Corneal gene therapy

Gene therapy to the cornea can potentially correct inherited and acquired diseases of the cornea. Factors that facilitate corneal gene delivery are the accessibility and transparency of the cornea, its stability ex vivo and the immune privilege of the eye. Initial corneal gene delivery studies characterized the relationship between intraocular modes of administration and location of reporter gene expression. The challenge of achieving effective topical gene transfer, presumably due to tear flow, blinking and low penetration of the vector through epithlelial tight junctions left no alternative but invasive administration to the anterior chamber and corneal stroma. DNA vaccination, RNA interference and gene transfer of cytokines, growth factors and enzymes modulated the corneal microenvironment. Positive results were obtained in preclinical studies for prevention and treatment of corneal graft rejection, neovascularization, haze and herpetic stromal keratitis. These studies, corneal gene delivery systems and modes of administration, and considerations regarding the choice of animal species used are the focus of this review. Opportunities in the field of corneal gene therapy lie in expanding the array of corneal diseases investigated and in the implementation of recent designs of safer vectors with reduced immunogenicity and longer duration of gene expression.

Corneal epithelium as a platform for secretion of transgene products after transfection with liposomal gene eyedrops

BACKGROUND

The first objective of the study was to evaluate the transfection of corneal epithelium with non-viral vectors to secrete transgene products into the tear fluid and aqueous humor. The second goal was to evaluate the differentiated corneal epithelial cell culture for transfection studies.

METHODS

The human corneal epithelial (HCE) cell line was cultured to different stages of differentiation and transfected with complexes of pCMV-SEAP2 with DOTAP/DOPE, DOTAP/DOPE/protamine sulfate (PS) and polyethylenimine (PEI). The complexes of DOTAP/DOPE with plasmid (CMV-SEAP2 or pCMV-Luc4) were subsequently applied topically to the rabbit eyes. Secreted alkaline phosphatase (SEAP) was analyzed using chemiluminescent assay. Luciferase (Luc) was detected at the mRNA level in cornea and conjunctiva using a qRT-PCR.

RESULTS

The transfection levels decreased with differentiation of HCE cells. PEI was effective in transfecting both the dividing and partly differentiated cells, but ineffective in differentiated cells. DOTAP/DOPE showed high activity in differentiated cell cultures, while added PS did not improve transfection. Significant SEAP expression was observed for three days after in vivo transfection in the tear fluid and aqueous humor. The luciferase mRNA was found both in the cornea and conjunctiva. The rates of SEAP secretion from both the basolateral side of differentiated HCE cells and cornea in vivo were within the same range.

CONCLUSIONS

Corneal epithelium can be transfected topically to secrete gene products to the tear fluid and aqueous humor. The differentiated HCE model is a useful tool in the evaluation of non-viral carriers for corneal transfection.

Effects of local and systemic viral interleukin-10 gene transfer on corneal allograft survival

In this study, we explored the immunomodulatory effects of viral interleukin (IL) IL-10 after ex vivo and in vivo gene transfer in experimental corneal transplantation. Wistar-Furth rats were used as donors and major histocompatibility complex class I/II-disparate Lewis rats served as recipients. For ex vivo gene therapy donor corneas were either transfected with liposome/vIL-10 plasmid DNA mixtures or transduced with a vIL-10 expressing adenovirus vector (AdvIL-10). For in vivo studies, recipients were treated with AdvIL-10 intraperitoneally 1 day before transplantation. Graft survival was analysed using the Kaplan-Meier survival method. To monitor the efficacy of the therapy messenger RNA (mRNA) cytokine expression profiles in grafts and draining lymph nodes were analysed by quantitative real-time reverse transcription-polymerase chain reaction. Moreover, anti-adenovirus immunity was also investigated. Neither ex vivo liposome-mediated vIL-10 gene transfer nor ex vivo AdvIL-10 gene transfer led to prolonged corneal allograft survival. In contrast, corneal allograft survival was significantly prolonged in animals receiving systemic AdvIL-10 gene transfer. Moreover, only systemic vIL-10 gene therapy modulated the cytokine mRNA expression profile in draining lymph nodes. Interestingly, systemic AdvIL-10 gene transfer could not inhibit the generation of anti-adenovirus antibodies. Our data indicate systemic expression of the vIL-10 gene is required to modulate the cytokine expression profile in the draining lymph nodes, which might be a pre-requisite for the success of cytokine gene therapy.

[Comparison of several viral vectors for gene therapy of corneal endothelial cells]

AIM

In this paper we compare the transduction efficiency, toxicity, and safety of retroviral vectors [equine infectious anemia virus (EIAV), human immunodeficiency virus-1 (HIV-1), human foamy virus (PFV] and adenovirus (Ad) for potential use in gene therapy of corneal endothelial cells.

METHOD

Murine corneal endothelial cells were transduced with EIAV, HIV-1, PFV, and Ad, resulting in the overexpression of a green fluorescent protein (eGFP) transgene marker. The transduction efficiency was assessed by flow cytometry, while cytotoxicity and apoptosis rate were detected by annexin V/propidium iodide (PI) stain.

RESULTS

Ad had the highest transduction efficiency with 99% of the cells expressing the transgene, followed by EIAV (95%), HIV-1 (75%), and PFV (43%). However, the high transduction efficiency of Ad also resulted in the highest apoptosis rate (25%) in the corneal endothelial cells. There was no detectable difference in the toxicity between PFV and HIV-1 (10%). EIAV transduction had the lowest cytotoxicity, with only 3% of the cells being annexin V/PI positive.

CONCLUSION

Compared to other vectors EIAV exhibited high transduction efficiency combined with low toxicity to corneal endothelial cells. Therefore, it is a powerful tool for gene therapy applications in selected corneal endothelial diseases.

Gene therapy in the cornea

Technological advances in the field of gene therapy has prompted more than three hundred phase I and phase II gene-based clinical trials for the treatment of cancer, AIDS, macular degeneration, cardiovascular, and other monogenic diseases. Besides treating diseases, gene transfer technology has been utilized for the development of preventive and therapeutic vaccines for malaria, tuberculosis, hepatitis A, B and C viruses, AIDS, and influenza. The potential therapeutic applications of gene transfer technology are enormous. The cornea is an excellent candidate for gene therapy because of its accessibility and immune-privileged nature. In the last two decades, various viral vectors, such as adeno, adeno-associated, retro, lenti, and herpes simplex, as well as non-viral methods, were examined for introducing DNA into corneal cells in vitro, in vivo and ex vivo. Most of these studies used fluorescent or non-fluorescent marker genes to track the level and duration of transgene expression in corneal cells. However, limited studies were directed to evaluate prospects of gene-based interventions for corneal diseases or disorders such as allograft rejection, laser-induced post-operative haze, herpes simplex keratitis, and wound healing in animal models. We will review the successes and obstacles impeding gene therapy approaches used for delivering genes into the cornea.

In vitro adenovirus mediated gene transfer to the human cornea

BACKGROUND/AIMS

Replication deficient adenovirus is an efficient vector for gene transfer to the cornea. The aim was to optimise the transduction of human corneal endothelium with adenoviral vectors and to measure transgene production from transduced corneas.

METHODS

Adenoviral vectors (AdV) encoding enhanced green fluorescent protein (eGFP) or a transgenic protein (scFv) were used to transfect 34 human corneas. Reporter gene expression was assessed after 72-96 hours of organ culture. The kinetics of scFv production was monitored in vitro for 1 month by flow cytometric analysis of corneal supernatants.

RESULTS

Transduction of human corneas with high doses (5 x 10(7)-3 x 10(8) pfu) of AdV caused eGFP expression in 12-100% of corneal endothelial cells. Corneas were efficiently transduced following up to 28 days in cold storage. Very high AdV doses (2 x 10(9) pfu) reduced endothelial cell densities to 98 (SD 129) nuclei/mm(2) (compared to 2114 (716) nuclei/mm(2) for all other groups). Transgenic protein production peaked at 2.4 (0.9) microg/cornea/day at 2 weeks post-transduction, and decreased to 1.2 (0.4) microg/cornea/day by 33 days, at which time endothelial cell density had decreased to 431 (685) nuclei/mm(2).

CONCLUSION

Human corneas can be efficiently transduced by AdV following extended periods of cold storage, and transgene expression is maintained for at least 1 month in vitro.

Effect of ex vivo Gene Transfer with an Adenoviral Vector on Human Eye Bank Corneas

BACKGROUND

Ex vivo gene transfer to donor corneas using adenoviral vectors has gained increasing attention. This study investigates the effect of adenovirus-mediated gene transfer on endothelial cell (EC) count in human eye bank corneas.

METHODS

A replication-defective adenoviral vector containing the gene for green fluorescent protein was used to transduce organ-cultured normal human eye bank and porcine corneas. Transgene expression and EC count were assessed by light and fluorescence microscopy.

RESULTS

The transgene was expressed earlier by porcine EC (27% of all EC on day 2) than by human EC (6% on day 2), but the maximal number of EC finally expressing the transgene was higher in human than in porcine corneas (45 vs. 31% of all EC on day 12). Gene transfer caused considerably less EC loss in human than in porcine corneas (2 vs. 60% EC loss after 10 days).

CONCLUSIONS

Adenoviral vectors for ex vivo gene transfer are more efficient and less toxic in normal human eye bank corneas than in porcine corneas, but human EC require more time until expression of transgenic proteins.

Highly efficient ex vivo gene delivery into human corneal endothelial cells by recombinant adeno-associated virus

PURPOSE

Gene delivery at high efficiency is crucial for cornea endothelial cell gene therapy. This study investigated the efficiency of gene transfer by recombinant adeno-associated virus (rAAV) in an organ culture system.

METHODS

Human cornea tissue was exposed to rAAV delivering green fluorescent protein (ss-rAAV2-CMV-GFP) for one hour and then cultured at 31 degrees C for 2 weeks in a medium supplemented with growth factors. Endothelial cells expressing GFP gene were then identified.

RESULTS

High-efficiency gene transfer was found in over 90% of endothelial cells. Gene expression could be detected within 24 hours and remained stable up to 2 weeks in the organ culture system.

CONCLUSIONS

The high-delivery efficiency and rapid induction of gene expression indicate that rAAV is a promising vector for cornea endothelial cell gene therapy for ocular diseases. Organ culture at 31 degrees C using culture medium supplemented with growth factors significantly facilitates gene transfer into human corneal endothelium.

Gene therapy approaches to prolonging corneal allograft survival

Irreversible immunological rejection is the major cause of human corneal allograft failure and occurs despite the use of topical glucocorticoid immunosuppression. Systemic pharmacological interventions have not found widespread favour in corneal transplantation because of associated morbidities and inadequate demonstration of efficacy. Gene therapy offers tantalising prospects for improving corneal allograft survival, especially in those recipients at high risk of graft rejection. Donor corneas can be gene-modified ex vivo, while in storage prior to implantation, and the relative isolation of the transplanted cornea from the circulation decreases the risk of potential systemic complications. A wide variety of vectors have been found suitable for gene transfer to the cornea. The mechanisms involved in corneal graft rejection have been placed on a relatively secure footing over the past decade and in consequence a number of transgenes with promise for modulating rejection have been identified. However, relatively few studies have thus far demonstrated significant prolongation of corneal allograft survival after gene transfer to the donor cornea. In these instances, the therapeutic protein almost certainly acted at a proximal level in the afferent immune response, within the ocular environs.

Comparison of HIV-1 and EIAV-based lentiviral vectors in corneal transduction

In this study we compare the ability of self-inactivating Human Immunodeficiency Virus 1 (HIV-1) and Equine Infectious Anaemia Virus (EIAV)-based vectors to mediate gene transfer to rabbit and human corneas and to a murine corneal endothelial cell line. Both vectors were pseudotyped with vesicular stomatitis virus-G (VSV-G) envelope and contained marker transgenes under the control of an internal CMV promoter. For specificity of action, the heterologous promoter in the EIAV-vector was exchanged for an inducible E-Selectin promoter, previously shown to regulate gene-expression in a plasmid system. We show that EIAV is more efficient than HIV in transducing human and rabbit corneal endothelial cells. Rabbit corneal endothelial cells are transduced in higher quantity than human corneal endothelial cells. In the inducible system, however, we detected impairment between the vector and its internal E-Selectin promoter. Instead of controlled transgene expression or silencing of promoter activity, the U3-modified long-terminal-repeats (LTR) impaired the conditional activity of the E-Selectin promoter. Significant transgene expression was seen without stimulation of the inducible promoter. We show efficient transduction by lentiviruses of a corneal endothelial cell line and of full thickness corneas from different species, confirming that those vectors would be appropriate tools for gene therapy of selected corneal diseases. However, the modification within the U3-LTR did not adequately allow regulated transgene expression. These findings have important implications for vector design for diagnostic or therapeutic opportunities.