The use of recombinant viral techniques to deliver and express genes of therapeutic value to ocular tissue is likely to be the most important and direct interface between basic science and clinical ophthalmology in the next decade. There are several reasons for this: 1. A growing number of genes responsible for presently incurable ocular diseases or for adverse side effects of surgical procedures have been or are being identified. They provide a multitude of viable genetic strategies for ocular therapy; 2. The eye’s accessibility, immune and physical containment and often rapid biological response make it one of the most likely targets for successful gene therapy intervention in the near future; 3. There are multiple strains of animals that either mimic or are the exact genetic counterpart of ocular disease in humans; 4. Behavioral and physiological assessment of visual function (visual acuity tests, visual field analysis, electroretinograms) have been extremely well established for many decades in literally millions of patients. This provides a robust set of criteria for evaluating the success of clinical trials. Three labs at the University of Florida are actively engaged in ocular gene delivery experiments: William Hauswirth-retina, John Guy-optic nerve, and Gregory Schultz-cornea. Two of the laboratories will use adeno-associated virus (AAV) as the vector for gene delivery and this will be done in collaboration with Gene Therapy Vector Core Lab and N. Muzyczka. Preliminary experiments by W. Hauswirth and N. Muzyczka in rats, guinea pigs and mice have demonstrated that AAV recombinant vectors carrying the gene for beta galactosidase under the control of either a tissue specific opsin promoter or the CMV promoter can transduce the retinal epithelial and sensory nerve cell layers of the eye at high frequency. Expression has been found to continue for up to three months. This result has suggested a variety of applications for hereditary retinopathies and age related ocular degenerative diseases.
Dr. Hauswirth will be attempting rhodopsin gene therapy in the pro23-his transgenic mouse, an exact model of one form of human retinitis pigmentosa (RP). Dr. Hauswirth is also collaborating with three laboratories outside the University that are interested in ocular gene therapy. With Drs. Matt Lavail and Roy Steinberg of UCSF, recombinant AAV containing various opsin promoter/ neurotrophin constructs are being tested for use as photoreceptor survival-promoting agents in animal models of degenerative retinal diseases. Using a rat photoreceptor light damage model which mimics human photoreceptor degeneration, expression of protective levels of human neurotrophins could lead to human protocols in 2-4 years. With Dr. John Flannery at UC Berkeley, recombinant AAV containing opsin promoter/b subunit of cyclic GMP phosphodiesterase constructs are being provided for use in somatic gene therapy of retinal degeneration in the rd mouse, the major animal model for recessive human RP. If successful, human trials could begin in 3-5 years for human RP caused by b-PDE genetic defects. Finally, with Dr. Debra Faber at UCLA, recombinant AAV containing opsin promoter/reporter genes are being provided for expression testing in retinoblastoma cells in culture as an initial assay of its utility in treating ocular tumors. Potential human trials with this intervention are at least 5 years away. The HAL facility on the GCRC will be essential in producing clinical grade vectors for each of these protocols.
References
- Muzyczka N. Use of AAV as a general transduction vector for mammalian cells. In: Curr. Top. Micro. Imm. Viral Expression Vectors (Muzyczka, N., ed), Springer Verlag, Berlin, vol 158, pp. 97-129.
- DesJardin LE, Timmers AM, Hauswirth WW. Transcription of photoreceptor genes during fetal retinal development: Evidence for positive and negative regulation. J Biol Chem 268:6953-6960, 1993.
- Van Ginkel PR, Hauswirth WW. Parallel regulation of fetal gene expression in different photoreceptor cell types. J Biol Chem 269:4986-4992, 1994