Immunogenicity of human embryonic stem cells: can we achieve tolerance?

Human embryonic stem cells are unique in their capacity to propagate without losing pluripotency, and at the same time may readily differentiate to various cell types of the three embryonic germ layers. It is widely accepted today that differentiated human embryonic stem cells may in the future enable repair of vital tissues of the body. Detailed differentiation protocols need to be developed and safety issues associated with cellular therapeutics must be examined. One of the greatest hurdles facing transplantation is the development of immune rejection processes towards non-autologous cells. Profiling of histocompatibility antigens expressed on the cells reveals that they might be subjected to immune response. Here we describe the routes of immune recognition that can identify these antigens and the proposed ways for overcoming the rejection of human embryonic stem cell derivatives.