Immunological Barriers to Regenerative Medicine: Do They Matter?

Replacing damaged tissues using long-term repopulating stem cells remains the main overall aim of regenerative medicine. However, a number of obstacles have yet to be addressed. The generation of autologous stem cells is heavily compromised in older donors and the time required for their preparation is too long for emergency indications. Therefore, third-party stem cells are the only viable alternative but this represents a formidable barrier for the host immune system. More feasible strategies consist in improving the body's natural repair mechanisms by reprogramming the inflammatory milieu. Mesenchymal stromal cells (MSC) are probably amongst the most promising cell-based reagents for immunomodulation. In this chapter we review the principles of stem cell immunogenicity and immune privilege, and summarise the recent advances in approaches and mechanisms underlying endogenous tissue repair.