Despite many reports of putative stem-cell-based treatments in genetic and degenerative
disorders or severe injuries, the number of proven stem cell therapies has remained small.
In this Review, we survey advances in stem cell research and describe the cell types that are
currently being used in the clinic or are close to clinical trials. Finally, we analyse the
scientific rationale, experimental approaches, caveats and results underpinning the clinical
use of such stem cells.