Specific strains of mice, such as BALB/c nude, non-obese diabetic severe combined immunodeficiency (NOD-SCID), and NOD-Prkdc scid IL2rg null (NCG) mice, are ideal candidates for xenograft studies because their immunodeficiency and other immune system features prevent the rejection of implanted human cancer cells or tissues. The gene discussed is IL2RG; the disease is cancer.