Local Gene Transfer to Modulate Rat Corneal Allograft Rejection

Lentivirus-mediated PD-L1 overexpression in bone marrow-derived dendritic cells induces immune tolerance in a rat keratoplasty model

PURPOSE

The side effects of immune suppressants on immune rejection have become increasingly apparent after keratoplasty. To find out new alternative immunotherapy strategies, we studied the role of programmed death-1 (PD-1) and its ligand (PD-L1) co-stimulatory pathway in inducing immune tolerance of rat keratoplasty.

METHODS

The PD-L1 protein was constitutively overexpressed via lentiviral transduction in bone marrow-derived dendritic cells (BMDCs) from rats, then infused via the tail vein into rats before undergoing keratoplasty. Western blot analysis of PD-L1 protein confirmed the effectiveness of lentivirus-mediated. The phenotype of immature BMDC was confirmed by flow cytometry analysis with CD80, CD86, CD11c and MHC-II antibodies. To investigate the mechanism of the immune tolerance induced by BMDCs transfusion, PD-L1, IFN-γ and IL-17 in serum and cell culture supernatant were assessed by ELISA and qPCR.

RESULTS

After LPS stimulation, immature dendritic cells with over-expression of PD-L1 still showed high expression of PD-L1(p < 0.001), and low expression of IL-17 and IFN-γ (p < 0.001), which reduced neovascularization (p < 0.05), and prolonged the survival after corneal implants.

CONCLUSION

Immature DC cells with overexpression of PD-L1 have low ability to activate T cells，which is a potential treatment for avoiding graft rejection by promoting natural immunosuppression. This cellular treatment is expected to reduce the use of immune suppressants and the occurrence of side effects.

Gene-based Therapeutic Tools in the Treatment of Cornea Disease

BACKGROUND

As one of the main blinding ocular diseases, corneal blindness resulted from neovascularization that disrupts the angiogenic privilege of corneal avascularity. Following neovascularization, inflammatory cells are infiltrating into cornea to strengthen corneal injury. How to maintain corneal angiogenic privilege to treat corneal disease has been investigated for decades.

METHODOLOGY

Local administration of viral and non-viral-mediated anti-angiogenic factors reduces angiogenic protein expression in situ with limited or free of off-target effects upon gene delivery. Recently, Mesenchymal Stem Cells (MSCs) have been studied to treat corneal diseases. Once MSCs are manipulated to express certain genes of interest, they could achieve superior therapeutic efficacy after transplantation.

DISCUSSION

In the text, we first introduce the pathological development of corneal disease in the aspects of neovascularization and inflammation. We summarize how MSCs become an ideal candidate in cell therapy for treating injured cornea, focusing on cell biology, property and features. We provide an updated review of gene-based therapies in animals and preclinical studies in the aspects of controlling target gene expression, safety and efficacy. Gene transfer vectors are potent to induce candidate protein expression. Delivered by vectors, MSCs are equipped with certain characters by expressing a protein of interest, which facilitates better for MSC-mediated therapeutic intervention for the treatment of corneal disease.

CONCLUSION

As the core of this review, we discuss how MSCs could be engineered to be vector system to achieve enhanced therapeutic efficiency after injection.

Exogenous IL-10 induces corneal transplantation immune tolerance by a mechanism associated with the altered Th1/Th2 cytokine ratio and the increased expression of TGF-β

The aim of the present study was to examine the effect of exogenous IL-10 transfected rat dendritic cells (DCs) in corneal allografts. Rat lymphocyte separation medium and a cytokine induction method was used to extract and culture precursor cells of rat bone marrow-derived dendritic cells. A corneal transplant model was established, with Sprague-Dawley (SD) rats as the recipients and Wistar rats as the donors. Flow cytometry (FCM) was used to detect the expression of CD83, which indicates a mature dendritic cell, and a specific cell surface stimulatory molecule CD86. Western blot analysis was used to detect interleukin (IL)-10 protein expression and RT-PCR was used to detect cytokine IL-10, IL-2 and TGF-β mRNA expression in each group. Compared with the other groups, the survival time of corneal grafts in the IL-10-green fluorescent protein (GFP)-DC group was significantly prolonged and H&E staining demonstrated mild graft edema and inflammatory cell infiltration. There was a high expression of IL-10 and a low expression of the surface antigens, CD83 and CD86, with a lower proliferation of T lymphocytes in the IL-10-GFP-DC group. The expression of IL-10 and TGF-β in the IL-10-GFP-DC group was higher than that in the other groups, while the expression of IL-2 was lower. The transfection of the IL-10 gene inhibited dendritic cell maturation. IL-10 gene-modified immature dendritic cells (imDC) were able to inhibit corneal allograft rejection and induce immune tolerance to prolong the survival time of the corneal graft. The Th1/Th2 deviation and the high expression of TGF-β may lead to immune tolerance.

Strategies for local gene therapy of corneal allograft rejection

Penetrating keratoplasty is the most common type of tissue transplant in humans. Irreversible immune rejection leads to loss of vision and graft failure. This complex immune response further predisposes future corneal transplants to rejection and failure. A diverse armamentarium of surgical and pharmacologic tools is available to improve graft survival. In this review, we will discuss the various gene therapeutic strategies aimed at potentiating the anterior chamber-associated immune deviation to extend graft survival.

Antibody fragments, expressed by a fowl adenovirus vector, are able to neutralize infectious bursal disease virus

Single-chain variable fragments (scFv) contain the heavy and light chain variable domains of immunoglobulin, joined by a short peptide linker. Previously, our laboratory has produced neutralizing scFv to epitopes of infectious bursal disease virus (IBDV). The in vitro delivery and expression of one of these scFv with and without the C(H)2-C(H)4 Fc domain of chicken IgY attached (scFv-Fc) by a serotype 8 fowl adenovirus (FAdV-8) vector was investigated in the present study. A panel of FAdV-8 vectors was constructed, each containing a different transgene (scFv or scFv-Fc), a different promoter to drive scFv and scFv-Fc transcription (CMVie or the fowl adenovirus major late promoter), and a different sized, right-hand end genomic deletion (52 bp or 2.3 kb). This panel was used to establish what effect these variables had on protein production, viral replication and scFv transcription, as measured by enzyme-linked imunosorbent assay and real-time polymerase chain reaction. Our results showed that, using a FAdV-8 vector containing the optimal CMVie promoter/2.3 kb deletion combination, we successfully expressed a secreted form of both scFv and scFv-Fc that were able to neutralize IBDV both in vitro and in ovo. These studies indicate that the FAdV-8 vector may be a promising candidate to deliver and express therapeutic molecules such as scFv and scFv-Fc in vivo in poultry.

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 Graft Rejection

Penetrating keratoplasty is the most widely practiced type of transplantation in humans. Irreversible immune rejection of the transplanted cornea is the major cause of human allograft failure in the intermediate and late postoperative period. This immunological process causes reversible or irreversible damage to the grafted cornea in several cases despite the use of intensive immunosuppressive therapy. Corneal graft rejection comprises a sequence of complex immune responses that involves the recognition of the foreign histocompatibility antigens of the corneal graft by the host's immune system, leading to the initiation of the immune response cascade. An efferent immune response is mounted by the host immune system against these foreign antigens culminating in rejection and graft decompensation in irreversible cases. A variety of donor- and host-related risk factors contribute to the corneal rejection episode. Epithelial rejection, chronic stromal rejection, hyperacute rejection, and endothelial rejection constitute the several different types of corneal graft rejection that might occur in isolation or in conjunction. Corneal graft failure subsequent to graft rejection remains an important cause of blindness and hence the need for developing new strategies for suppressing graft rejection is colossal. New systemic pharmacological interventions recommended in corneal transplantation need further evaluation and detailed guidelines. Two factors, prevention and management, are of significant importance among all aspects of immunological graft rejection. Preventive aspects begin with the recipient selection, spread through donor antigenic activity, and end with meticulous surgery. Prevention of corneal graft rejection lies with reduction of the donor antigenic tissue load, minimizing host and donor incompatibility by tissue matching and suppressing the host immune response. Management of corneal graft rejection consists of early detection and aggressive therapy with corticosteroids. Corticosteroid therapy, both topical and systemic, is the mainstay of management. Addition of immunosuppressive to the treatment regimen helps in quick and long term recovery. Knowledge of the immunopathogenesis of graft rejection may allow a better understanding of the immunological process thus helping in its prevention, early detection and management.