After a transplant – and to assure that the new organ is not rejected - patients are put on life-long therapy to suppress their immune system (IS), which, nevertheless, needs to be left intact enough to be able to defend the body against all kinds of disease. A tricky balance as the many rejected organs attest. But a discovery by Maria Monteiro and Luis Graça, two Portuguese scientists, could change all this, at least for the liver. Their work, just out in the Journal of Immunology (1), describes how they found a new type of white blood cell – baptised NKTreg (reg from regulatory) – that, once activated, migrate into the liver and suppress any immune response in its vicinity. What is most remarkable is that the immune system elsewhere is left intact. And the implications do not end in better liver transplants as, once these cells create an “immune tolerant organ”, we can graft any type of tissue or express any gene that the body might need into it, knowing that it would be safe from the IS. The potential of the discovery is such that a patent by Monteiro and Graça for the production and therapeutic use of NKTreg cells in humans has already been accepted.