The invention provides an ex-vivo method, i.e. an in vitro method, for genetically modifying cells of a vascularised tissue, which can be an organ, during normothermic or subnormothermic perfusion without damaging the tissue or its cells due to oxygen undersupply. The method enables keeping the vascularised tissue at normothermic or subnormothermic conditions over a sufficient period of time to genetically modify the cells e.g. with viral vectors.
