A nude mouse is a laboratory mouse from a strain with a genetic mutation that causes a deteriorated or absent thymus, resulting in an inhibited immune system due to a greatly reduced number of T cells. The phenotype (main outward appearance) of the mouse is a lack of body hair, which gives it the "nude" nickname. The nude mouse is valuable to research because it can receive many different types of tissue and tumor grafts, as it mounts no rejection response. These xenografts are commonly used in research to test new methods of imaging and treating tumors. The genetic basis of the nude mouse mutation is a disruption of the FOXN1 gene.[1][2]