Many diseases are based around insufficient energy production of ATP in your cells.
Researchers at the Zhejiang University School of Medicine decided to try and correct for this by genetically synthesizing a mature cell that can photosynthesize despite the disorder (in this case, osteoarthritis in mouse chondrocyte cells).
Where might we go from here? The ability to resolve ATP insufficiencies is huge, but how to properly apply a solution involving photosynthesis, especially on a multi-cellular level is still a question for the future.