Our immune system protects us from abnormal (cancer) cells and a key component is the natural killer (NK) cell. However, tumour cells can inhibit the activity of NK cells, rendering them inactive and allowing tumours to grow. We have a strategy to create NK cells that are not inactivated by the tumour. We will use mouse NK cells and mouse melanoma cells as a model to test our hypothesis that NK cells can be engineered to overcome the tumour’s inhibition and continue to kill tumour cells.