The concept of “self” is critically important in the immune system. Each of our cells present a unique set of molecules on their outer walls which signal to our wandering immunity police that they belong (“your papers, please”). Any other cells not presenting the same combination are considered foreign invaders and are attacked (“your papers are not in order!”). This works great for resisting infection but is a major impediment to transplant surgery. Even “tissue matching” is inexact, requiring recipients to have their immune system forever after repressed in order to maintain the graft. Finding a way to allow for a graft of desirable foreign tissue but also maintain a robust immune system is a therefore a major goal.
A stem cell research grant by theCalifornia Institute of Regenerative Medicine has a quite novel approach: regenerating the thymus, the “police academy” where the immunity cells learn to recognize the body’s own cells from foreign invaders. The thymus atrophies in adulthood, so regenerating it from stem cells from an appropriate HLA line might trick the immune system into accepting the graft with the same HLA type.
Quite a clever approach, and yet another reason that I am glad to have voted in favor of forming CIRM (ironically shortly before I was diagnosed with ALS).