The HOX11 protein plays an important role in the initiation of T-cell lymphoblastic leukemia (T-ALL). Our research group has generated mice that develop terminal lymphoma as a result of an inappropriate expression of this protein in lymphocytes. We have successfully used these mice to identify how HOX11 converts normal lymphocytes to malignant cells. Our current studies will provide additional information on the regulation of HOX11 and its role in the development of T-ALL. They may also lead to the development of new diagnostic tools or new therapies for the treatment of T-ALL.