Table 2.

Reduced immunogenicity of cells. The table summarizes the likely reasons cells may be less immunogenic than tissues or organs or marrow. In bold we list the reasons why cell based therapy may be more immunogenic. The pathways for rejection are summarized in the first column to remind the non expert as to the different pathways that are activated in rejection

Rejection	PSC based cell transplant should be less immunogenic
• ABO blood group mediated	• Presumably no DC cells in most transplants
• Complement mediated	• Cell likely transplanted to immune privileged sites
• Adaptive immunity	• No ABO antigen response in most cases
• Innate immunity	• IPSC/ESC cells may have some tolerance themselves and MSC and other stem cells maybe immune modulatory
• Graft versus Host	• No vasculature or complement mediated rejection mechanisms
• Male vs. female	• Other antigen presenting cells (support cells) may not be present in the transplant

But: Fetal antigens may be present, Foreign protein may be present from culture, atypical antigens may be formed, silenced genes expressed, unknown therapeutic proteins may be present which may create rejection