NOTCH1 and acute lymphoblastic leukemia: It was further shown that human Tspan33 promotes γ-secretase cleavage of Notch and that depletion of Tspan33 might be a potential target in T-ALL, a rare yet aggressive form of lymphoblastic leukemia, which is associated with activating mutations of Notch1 (Weng et al., 2004; Dunn et al., 2010).