T cell responses in experimental viral retinitis: Mechanisms, peculiarities and implications for gene therapy with viral vectors

Potential Sources and Roles of Adaptive Immunity in Age-Related Macular Degeneration: Shall We Rename AMD into Autoimmune Macular Disease?

Age-related macular degeneration (AMD) is the leading cause of vision loss in the elderly throughout the industrialized world. Its most prominent pathologic features are lesions involving the retinal pigment epithelium (RPE) the Bruch's membrane, the degeneration of photoreceptors, and, in the most aggressive cases, choroidal neovascularization. Genetic associations between the risk of developing AMD and polymorphism within components of the complement system, as well as chemokine receptors expressed on microglial cells and macrophages, have linked retinal degeneration and choroidal neovascularization to innate immunity (inflammation). In addition to inflammation, players of the adaptive immunity including cytokines, chemokines, antibodies, and T cells have been detected in animal models of AMD and in patients suffering from this pathology. These observations suggest that adaptive immunity might play a role in different processes associated with AMD such as RPE atrophy, neovascularization, and retinal degeneration. To this date however, the exact roles (if any) of autoantibodies and T cells in AMD remain unknown. In this review we discuss the potential effects of adaptive immune responses in AMD pathogenesis.

Measuring the intravitreal mobility of nanomedicines with single-particle tracking microscopy

Aim: To develop a robust assay to evaluate and compare the intravitreal mobility of nanoparticles in the intact vitreous body. Materials & methods: Excised bovine eyes were prepared to preserve the fragile structure of the vitreous humor, while permitting high-resolution fluorescence microscopy and single-particle tracking analysis of intravitreally injected nanoparticles. This assay was validated by analyzing polystyrene beads and further employed to evaluate gene nanomedicines composed of poly(amido amine)s and plasmid DNA. Results: The assay was able to distinguish immobilized cationic nanoparticles from mobile PEGylated nanoparticles. PEGylation of the polyplexes resulted in a drastic improvement of their mobility. Conclusion: An ex vivo eye model is presented for studying nanoparticle mobility in intact vitreous humor by single-particle tracking microscopy. These results give important guidelines for developing gene- and drug-delivery nanomedicines that are compatible with intravitreal administration.

Original submitted 20 April 2012; Revised submitted 22 November 2012

Therapeutic margins in a novel preclinical model of retinitis pigmentosa

The third-most common cause of autosomal recessive retinitis pigmentosa (RP) is due to defective cGMP phosphodiesterase-6 (PDE6). Previous work using viral gene therapy on PDE6-mutant mouse models demonstrated photoreceptors can be rescued if administered before degeneration. However, whether visual function can be rescued after degeneration onset has not been addressed. This is a clinically important question, as newly diagnosed patients exhibit considerable loss of rods and cones in their peripheral retinas. We have generated and characterized a tamoxifen inducible Cre-loxP rescue allele, Pde6b(Stop), which allows us to temporally correct PDE6-deficiency. Whereas untreated mutants exhibit degeneration, activation of Cre-loxP recombination in early embryogenesis produced stable long-term rescue. Reversal at later time-points showed partial long-term or short-lived rescue. Our results suggest stable restoration of retinal function by gene therapy can be achieved if a sufficient number of rods are treated. Because patients are generally diagnosed after extensive loss of rods, the success of clinical trials may depend on identifying patients as early as possible to maximize the number of treatable rods.

Rd8 mutation in the Crb1 gene of CD11c-eYFP transgenic reporter mice results in abnormal numbers of CD11c-positive cells in the retina

There has been considerable debate about whether dendritic cells (DCs), which are potent antigen-presenting cells pivotal to adaptive immune responses, are present in CNS parenchyma. In studies aimed at answering this issue, we discovered that while the neural retina of young naive transgenic C57BL/6 CD11c-eYFP reporter mice contained more than 800 CD11c-positive cells/retina, these cells were virtually absent in C57BL/6 CD11c-DTR/GFP mice. Clinical fundus examination, confocal imaging of retinal whole mounts, and sections revealed colocalization of CD11c-positive cells with classic mild to severe retinal dystrophic lesions. Immunophenotypic analysis revealed that CD11c-positive cells in the neural retina of these mice had the characteristic profile of activated microglia and not DCs. Genotypic analysis confirmed that the cause of the retinal dystrophic lesions in CD11c-eYFP transgenic mice was the occurrence of the Crb1(rd8) mutation, which affects all mice of the C57BL/6N strain but not the C57BL/6J strain. Comparison of 2 different types of CD11c reporter transgenic mice revealed that a mutation in the Crb1 gene leads to retinal degeneration resulting in the activation of large numbers of local microglia that could be readily mistaken for CD11c-positive putative DCs.

Gene therapy for noninfectious uveitis

Noninfectious intraocular inflammatory disease remains a significant cause of visual loss, even with current systemic immunosuppression. Alternative novel treatments are thus required, particularly for severe forms of posterior uveitis. Encouraging results from several phase I/II clinical trials of gene therapy for monogenic retinal disorders have paved the way for the development of this approach for other ocular conditions. Gene therapy for uveitis offers the possibility of potent, self-regulating, long-term disease control following a single treatment and without systemic side effects. To date, gene therapy approaches using interleukin-10, interleukin-1 receptor antagonist, interferon-alpha, soluble TNF-alpha receptors, and alpha-MSH gene transfer have been used successfully to attenuate experimental animal models of uveitis. This review evaluates these preclinical studies, considers the route to clinical application, and explores future targets and approaches.