Abstract
Purpose::
Recent Phase I clinical trials indicate that adenovirus (Ad) vectors persist in human ocular tissues without adverse events and hence are a promising method of gene transfer to the retina. Ad vectors can accommodate up to 36 Kb of foreign DNA, making them useful for the inclusion of large upstream gene regulatory elements that are necessary for appropriate levels of transgene expression- a factor shown to be important in animal models of retinal degeneration. However, like lentivirus vectors, Ad vectors only transduce photoreceptors early during development and in adult mice transduce primarily the retinal pigment epithelium (RPE) upon subretinal delivery. Since the majority of mutant gene products that cause retinal degeneration are expressed in the photoreceptors, vectors with large capacity and tropism for fully developed photoreceptors are needed. While it has been shown previously that pseudotyping of Ad can allow for photoreceptor transduction in adult mice, the levels of transduction are low relative to other viral vectors such as adeno associated virus (AAV).
Methods::
To enhance photoreceptor transduction by Ad, we investigated the interaction between the RGD domain in Ad penton base and the RPE. We deleted the integrin-binding RGD domain in Ad penton and injected such Ad vectors expressing GFP into the subretinal space of adult mice. In addition, we constructed Ad vectors expressing cGMP beta phosphodiesterase or rhodopsin and injected these vectors into rd10 and rho -/- mice respectively at p18, a stage post photoreceptor development.
Results::
We found that deletion of the RGD domain permitted transgene expression in neural mouse retina approximately 700-fold more efficiently than with standard Ad5 vectors expressing GFP from the CMV promoter. By qualitative fluorescence microscopy, it appeared that virtually every photoreceptor expressed transgene product in the region of injection and high levels of photoreceptor transduction were achieved in approximately 65% of the retina. Two months after injection in rd10 and rho -/- mice, the latest time point examined thus far, ERG responses and histology indicated that these novel vectors rescue retinal function as well as morphology in these two mouse models of retinitis pigmentosa.
Conclusions::
Ad vectors with deletion in the RGD domain of penton base are efficient at delivering transgenes to photoreceptor cells. These vectors may be relevant for developing gene therapy approaches for individuals with retinal degeneration.
Keywords: gene transfer/gene therapy • retinal degenerations: hereditary • adenovirus