Numerous mouse models of NOTCH1-induced T-cell leukemia have been described [13], where high levels of activated NOTCH1 in murine T-cell progenitor models impair T-cell maturation, leading to the accumulation of CD4+CD8+ double-positive (DP) cells, promoting thymic-independent T-cell development, and ultimately leading to T-cell leukemia closely resembling human T-ALL. The gene discussed is CD4; the disease is acute lymphoblastic leukemia.