The current knowledge of immune privilege in stem cells

Immune privilege as an active defensive mechanism guards cells and tissues against foreign antigens. Developing tumors and adult stem cells are believed to be immune privileged, since they have the ability to avoid rejection after implantation. Allograft rejection of transplanted tissues and organs occurs because of allelic differences between graft and host at polymorphic loci, which give rise to histocompatibility antigens; unless immunosuppressive therapy is given. This obstacle also exists when using human embryonic stem cell for cell transplantation, rising challenges in cell therapy and in regenerative medicine. Therefore, to better understand the mechanisms underlying in immune privilege and to obtain strategies which can mimic the naturally immune privileged cells, is of utmost significance in transplantation and regenerative medicine.