In 1995, Dr. Warren J. Leonard of the National Heart, Lung, and Blood Institute (NHLBI), National Institutes of Health (NIH), reported the creation of an interleukin-2 receptor gamma chain (IL-2Rg) deficient mouse. His lab also demonstrated earlier that mutations in the gene encoding IL-2Rg result in X-linked severe combined immunodeficiency (XSCID) and that IL-2Rg is a subunit common to multiple cytokine receptors. The IL-2Rgdeficient mice created by Dr. Leonard provide a unique animal model, the first of its kind, to study XSCID and other immune deficiencies.