JAK3 M511I has been previously described in T-PLL, SS, acute myeloid leukemia, and T-cell acute lymphoblastic leukemia (T-ALL), and has been characterized as an activating mutation, conferring cytokine independent growth to Ba/F3 cells and demonstrating transforming potential in murine hematopoietic progenitor cells [40–45]. Here, JAK3 is linked to T-cell acute lymphoblastic leukemia.