Immune recognition is the process by which the immune system differentiates between healthy cells and both abnormal cells and external pathogens.  This process is critical to effectively identify viruses, bacteria and cancers and effectively eradicate them. Immune tolerance is the process by which the immune system specifically turns itself off to avoid autoimmune diseases.  Immune tolerance is also critical after solid organ or bone marrow transplantation, such that a patient can avoid rejection of an organ or hematopoietic stem cells, and such that the newly transplanted cells can survive in the patient and not cause graft-versus-host disease (GVHD), which is the deadliest complication associated with bone marrow transplantation.
 
Unraveling immune tolerance will lead to new techniques that overcome transplant rejection and prevent GVHD. It will enable us to use bone marrow transplants to treat HIV and other complex diseases. It will increase our understanding of how best to prevent and treat autoimmune diseases. And it will inform our attempts to augment the immune system to treat diseases such as chronic infections and malignancies.