Organ rejection may be a thing of the past after a killer white blood cell was shown to protect against immune rejection during organ transplantation. The white blood cells suppress the immune response in the liver of experimental mice, but do not affect the work of the immune system elsewhere. Since the cells are also found in humans, it is expected to solve the problem of rejection that often occurs during organ transplantation. Marta Muntello, of the University of Lisbon, Portugal, and colleagues have been working on a study of the immune response in rats. Monteiro and colleagues studied natural killer T cells (NKT) in experimental mice. The researchers found that a class of NKT cells contains genes that control regulatory T cells, and that apoptotic T cells act to suppress the immune response in the organism. Unlike other regulatory T cells, this type of cell, called regulatory NKT, was reinjected into experimental mice directly into the liver and suppressed the liver’s immune response. Researcher Luis? Grassa said, “These new cells could allow us to achieve a smooth liver transplant without hindering the work of the rest of the immune system.”