Researchers used gene therapy to treat mice with retinitis pigmentosa, a condition where there is progressive degeneration of photoreceptors in the retina caused by lack of gene expression in any of over 80 genes. They administered the CX3CL1 gene and found that treatment prolonged the survival of cones.
S.K. Wang et al., “Soluble CX3CL1 gene therapy improves cone survival and function in mouse models of retinitis pigmentosa,” PNAS, doi:10.1073/pnas.1901787116, 2019.