The Immune Response to Allogeneic Differentiated Mesenchymal Stem Cells in the Context of Bone Tissue Engineering.

The use of allogeneic differentiated mesenchymal stem cells (MSCs) to mediate bone formation may be a potential alternative to the current gold standards of bone repair. Although it is known that undifferentiated MSCs are immunomodulatory and weakly immunogenic, the host immune reaction to differentiated MSCs is less known. Implantation of allogeneic osteogenic or chondrogenically differentiated MSC pellets may be a promising route to induce bone repair via the processes of intramembranous and endochondral ossification. This review summarizes the current literature surrounding the immune response to these allogeneic differentiated stem cells in the context of bone repair and replacement. Although there have been great developments in researching the effects of allogeneic differentiated cells on the host immune system, lack of standardized preclinical assays has limited their progression to the clinics. Future investigations are required to identify the host immune cells having a positive or negative effect on bone formation mediated by these allogeneic differentiated MSCs to move the use of these cells toward future clinical bone repair therapies.