Ocular gene transfer may provide a means for arresting the retinal degeneration characteristic of many inherited causes of blindness, including retinitis pigmentosa (RP). Previously, we have shown in immunodeficient animals that recombinant adeno-associated virus (rAAV) mediates transduction of photoreceptors as well as the retinal pigment epithelium (RPE) following subretinal injection. In this study we extend these observations and show that highly purified recombinant AAV vectors encoding the reporter gene LacZ transduce photoreceptors in an immunocompetent mouse strain following subretinal injection and efficiently transduce ganglion cells after intravitreal injection. Levels of transduction increase over time. Sublethal gamma-irradiation is shown to facilitate this process.

In order to investigate the immunological consequences of that the eye is not normally immune-privileged with respect gene transfer to the eye using viral vectors, adenovirus carto viral vectors. Inflammatory cells were detected in the vitrying a lacZ reporter gene (AV.LacZ) was injected either reous after anterior chamber injection and in the retina after subretinally, subconjunctivally or into the anterior chamber subretinal injection of adenovirus. The presence of both of three groups of adult mice: immunocompetent or transi-CD4 + and CD8 + T cells was established by immunophenoently immunosuppressed BALB/c mice and congenic typing. Reinjection of BALB/c mice resulted in rapid decline immunodeficient nude mice. Adenovirally mediated lacZ in reporter gene expression, but successful readminisexpression persisted for approximately 3 weeks following tration was possible in the case of immunodeficient nude injection of the vector into the anterior chamber, retina or mice. However, after transient depletion of T cells, achieextra ocular tissues of the conjuctiva of BALB/c mice. It ved by intraperitoneal injection of both CD8-and CD4-speappears that T cell-mediated immune responses limit the cific antibodies, the duration of expression in BALB/c mice duration of AV-mediated ocular gene expression in adult was longer in the eye (at least 12 weeks, again with mice since lacZ gene expression was detected for at least decrease in level over time), than in extra-ocular tissues (8 15 weeks in T cell-deficient BALB/c nude mice, although weeks) provided the animal was not reinjected with virus, the level of transgene expression decreased with time.raising the possibility of partial ocular immune-privilege Since intra-ocular AV-mediated gene expression was not after transient immunosuppression. significantly longer than extra-ocular expression, it appears

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Conclusion-An immune response to vector and transgene products is able to slow degeneration in the rd mouse. This phenomenon should be taken into account when analysing the degeneration in the rd mouse following gene transfer. (Br J Ophthalmol 2001;85:341-344)

There is growing interest in gene delivery to the eye in describes a strategy for prolonging gene expression by order to develop gene therapy for the many ocular disblocking the B7-CD28 interactions between antigen orders which may be amenable to this approach. To date, presenting cells (APC) and T cells in order to prevent the recombinant adenoviruses (AV) have been the main vector costimulatory signals required for T cell survival and proused for gene delivery to anterior and posterior segments liferation. This was achieved by the co-injection of AV in animal models. As with delivery to other organs, immune encoding a secreted immunomodulatory molecule (CTLA4-responses to vector and transgene limit the duration of Ig) which consists of the extra-cellular domain of mouse expression in the eye. Using an E1-deleted adenoviral vec-CTLA4 fused to the Fc region of human IgG. Subretinal cotor carrying a lacZ reporter gene, we have previously deminjection of AV encoding ␤ galactosidase with AV encoding onstrated that a T cell-mediated immune response reduces CTLA4-Ig results in prolonged expression in retinal cells the level of intra-ocular transgene expression over time compared with subretinal injection of only adenovirus and limits it to around 3 weeks in mice. This report encoding ␤ galactosidase. Keywords: gene therapy; immune response; photoreceptor; eyeThere is growing interest in gene transfer into various tissues of the eye since there are many ocular disorders which may be amenable to gene therapy. 1 Of these, there is particular interest in developing gene therapy for inherited retinal degenerations, some of which are due to single gene defects in photoreceptor-specific genes. These disorders may ultimately be treated by gene replacement strategies which require gene transfer to photoreceptors or by strategies which prevent these cells entering the apoptotic pathway. The latter might be achieved, for instance, by the delivery of genes encoding neurotrophic growth factors to the adjacent retinal pigment epithelium (RPE) cells or to cells in the anterior chamber. A number of vectors, including those based on herpes simplex virus (HSV), 2 lentivirus 3 and adeno-associated virus (AAV) [4][5][6][7] have been used for ocular gene transfer but, to date, the most widely reported system is that based on adenoviral (AV) vectors. [8][9][10][11][12][13][14][15][16][17][18][19] Studies in either the rabbit or more often the mouse, using these AV vectors carrying a lacZ reporter gene, have demonstrated that cells in the anterior segment, including the corneal endothelium, iris pigment epithelium, ciliary body, trabecular meshwork and Schlemms canal, may be efficiently transduced by intra-cameral injection. Subretinal injection is required for efficient targeting of the RPE and also results in the transduction of a small proportion of photoreceptors. Host immune responses to vector and transgene currently present a general problem for long-term gene delivery. There has been particular concern about the immunogenicity of A...