Homing of endogenous stem/progenitor cells for in situ tissue regeneration: Promises, strategies, and translational perspectives.

Stem cell-based therapy has been one of the best documented approaches in regenerative medicine, promising cures for a multitude of diseases and disorders. However, the ex vivo expansion of stem cells and their in vivo delivery are restricted by the limited availability of stem cell sources, the excessive cost of commercialization, and the anticipated difficulties of clinical translation and regulatory approval. An alternative to adoptively transferred stem cells are cell populations already present in a patient's body, including stem/progenitor cells, which can be actively attracted to sites of injury. This technique, known as endogenous cell homing, has the potential to provide new therapeutic options for in situ tissue regeneration. Such options would be less costly and complex than approaches that require substantial ex vivo cell manipulation and that use artificial vehicles for cell delivery. Tissue regeneration methods that rely on endogenous stem/progenitor cell homing, local tissue responses, and functional stimulation thus offer new insights into in vivo tissue engineering and hold great promise for the future of translational medicine. Although such methods that take advantage of the latent endogenous regenerative potential of the patient are promising for the repair of damaged tissue, they are in need of further experimental support before application in late-stage diseases or severe tissue injury. This review is not meant to be exhaustive but gives a brief outlook on the promises, strategies, and current applications of endogenous stem cell homing for in situ tissue regeneration, with particular emphasis placed upon pharmacological means based on cell-instructive scaffolds and release technology to direct cell mobilization and recruitment. In the future these exciting paradigms are likely to help reconcile the clinical and commercial pressures in regenerative medicine.