The article discusses the chimeric nature of transplanted organs, particularly the liver, and its implications for graft acceptance and rejection. The authors, including Thomas E. Starzl and colleagues, first observed this phenomenon in 1969 when they found that hepatocytes and endothelial cells in orthotopic hepatic allografts retained donor specificity, while the macrophage system was replaced by recipient cells. Recent studies have confirmed the presence of donor cells in clinically stable patients, even years after liver replacement, through anatomical and molecular techniques. These donor cells have been shown to play a role in processes such as enzyme transfer and immune system regulation, contributing to the resistance of the liver to cellular and humoral rejection. The authors also explore the concept of mixed allogeneic chimerism in other organs, such as the intestine and bone marrow, and its potential role in graft acceptance. They highlight the importance of cell migration and repopulation in organ transplantation, suggesting that this process is a common early event in graft acceptance. The article discusses the implications of this chimerism for understanding graft tolerance and the potential for improving treatment strategies, such as perioperative infusion of bone marrow or other immunocompetent cells. The authors conclude that the chimeric state, characterized by the presence of both donor and recipient immune cells, may be a key factor in the success of solid organ transplants, and that this understanding could inform future research and clinical practices.The article discusses the chimeric nature of transplanted organs, particularly the liver, and its implications for graft acceptance and rejection. The authors, including Thomas E. Starzl and colleagues, first observed this phenomenon in 1969 when they found that hepatocytes and endothelial cells in orthotopic hepatic allografts retained donor specificity, while the macrophage system was replaced by recipient cells. Recent studies have confirmed the presence of donor cells in clinically stable patients, even years after liver replacement, through anatomical and molecular techniques. These donor cells have been shown to play a role in processes such as enzyme transfer and immune system regulation, contributing to the resistance of the liver to cellular and humoral rejection. The authors also explore the concept of mixed allogeneic chimerism in other organs, such as the intestine and bone marrow, and its potential role in graft acceptance. They highlight the importance of cell migration and repopulation in organ transplantation, suggesting that this process is a common early event in graft acceptance. The article discusses the implications of this chimerism for understanding graft tolerance and the potential for improving treatment strategies, such as perioperative infusion of bone marrow or other immunocompetent cells. The authors conclude that the chimeric state, characterized by the presence of both donor and recipient immune cells, may be a key factor in the success of solid organ transplants, and that this understanding could inform future research and clinical practices.