In situ tissue regeneration through host stem cell recruitment

The field of tissue engineering has made steady progress in translating various tissue applications. Although the classical tissue engineering strategy, which involves the use of culture-expanded cells and scaffolds to produce a tissue construct for implantation, has been validated, this approach involves extensive cell expansion steps, requiring a lot of time and laborious effort before implantation. To bypass this ex vivo process, a new approach has been introduced. In situ tissue regeneration utilizes the body’s own regenerating capacity by mobilizing host endogenous stem cells or tissue-specific progenitor cells to the site of injury. This approach relies on development of a target-specific biomaterial scaffolding system that can effectively control the host microenvironment and mobilize host stem/progenitor cells to target tissues. An appropriate microenvironment provided by implanted scaffolds would facilitate recruitment of host cells that can be guided to regenerating structural and functional tissues. A review of strategies for mobilizing the body's stem cell reservoirs documents steady progress in accelerating the repair of damaged tissues. Foreign tissue grafts can treat disease and injury, but carry the risk of host rejection. Treatments using a patient's cultured stem cells circumvent rejection, but such procedures are complex and laborious. James Yoo and colleagues at Wake Forest School of Medicine, USA, explored a promising alternative: biodegradable implants that recruit local pools of stem cells for tissue repair. Such implants typically consist of non-toxic scaffold materials that support cell growth at the site of injury. These are accompanied by signaling factors that ‘awaken’ dormant stem cells, typically given by injection or released directly from the scaffold. Early results in muscle and bone show promise, but further research is required before in situ tissue regeneration becomes clinical reality.