To address whether JDP2 is aberrantly expressed in T-ALL patients compared with normal thymocytes, we isolated human thymic subsets at various levels of differentiation and performed quantitative RT-PCR (qPCR) for JDP2. A brief wave of JDP2 expression was detected at the immature single-positive (ISP) and triple-negative stage of thymic maturation but was not detected in CD34+CD1a− ETPs or more mature thymocytes. Here, JDP2 is linked to acute lymphoblastic leukemia.