Observation of GFP⁺ photoreceptors in host retinas following transplantation of GFP⁺ donor photoreceptor precursors was initially interpreted as evidence of integration of transplanted photoreceptors, but was later shown to actually reflect cytoplasmic transfer from donor to host. More recent studies reporting AAV-mediated reprogramming of Müller glia to photoreceptors or RGCs may instead reflect ectopic expression of glia-specific minipromoter constructs in retinal neurons. Finally, studies reporting rescue of photoreceptor function in rd1 mice following transplantation of fibroblasts treated with small molecules to induce expression of photoreceptor-specific genes may reflect neurotrophic effects of transplanted cells. ERG, electroretinogram.