Nude Mouse is able to accept Xeno-Graft because they lack:

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 Nude Mouse: A model deficient T-cell function A nude mouse is a laboratory mouse from a strain with a genetic mutation of the FOXN1 gene. The Foxn1 gene is the single most impoant gene for the thymic organogenesis for development of thymic epithelial cells. Because they lack a thymus, nude mice cannot generate mature T lymphocytes. Therefore they are unable to mount many types of adaptive immune responses, including antibody formation that requires CD4+ helper T cell; cell-mediated immune responses, which require CD4+ and/or CD8+ T cells; delayed-type hypersensitivity responses (require CD4+ T cells); killing of virus-infected or malignant cells (requires CD8+ cytotoxic cells); graft rejection (requires both CD4+ and CD8+ T cells) These mice possess a vestigial thymus which is incapable of producing mature T-cells as shown by a decreased lymphocyte population carrying the theta antigen and depleted &;thymus-dependent&; areas in their peripheral lympoid organs. However, they have T-cell prescursors in their bone marrow. Nude mice lack &;Thymosin&;, a factor secreted by the epithelial cells of the thymus. 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. Ref: Ananthanarayana and Paniker 9th edition Pgno: 98