Spleen Is Indispensable for Lymphomagenesis in a Notch-Driven Acute T-Cell Lymphoblastic Leukemia/Lymphoma (T-ALL) Murine Model
Yi Ding, Huizhong Xiong, Juan J Lafaille. New York University Langone Medicial Center, New York, NY
Background: The notch pathway is an evolutionarily conserved signaling mechanism that regulates normal development and tissue homeostasis in a context- and dose-dependent manner. Deregulated Notch signaling has been implicated in many diseases and T-ALL is one of the most studied Notch-mediated cancers. Importantly, Notch1-activating mutations have been found in more than 50% of T-ALL patients.
Design: We set out to explore the molecular pathogenesis and to identify therapeutic targets in T-ALL. We developed a new murine T-ALL model (Tg8) which the Notch ligand Dll4 (Delta-like 4) is ectopically expressed in T cells, driven by TCRα regulatory elements. All Tg8 mice develop T cell lymphoma spontaneously and generally died within the first month after onset of palpable, enlarged lymph nodes. We investigated the state of the Notch pathway in Tg8 mice by evaluating the expression of surface and intracellular domain of Notch1 as well as the downstream Notch signaling targets Hes-1 and Deltex-1. The origin of the tumor causing CD4+CD8+ double positive (DP) T cells was determined by intra-thymical injection of biotin into wild type and Tg8 mice. Further, we tested if eliminating the notch pathway in T cells could stop lymphoma development by using shRNA to knockdown dll4 in hematopoietic stem cells of Tg8 mice. In order to assess if the spleen is required for T-ALL development, splenectomy was performed and tumor generation was monitored.
Results: Using the Tg8 mouse model, we showed that T cell-driven Dll4 expression promoted extra-thymic T cell development, which was restricted to the spleen. The spleen becomes a major organ of T cell development to generate double negative (DN) and DP cells. These splenic DP cells have a very high notch activity and give rise to T-ALL in all mice after a short latency. Blockade of the notch pathway in Tg8 mice impairs lymphoma development. Splenic DP T cells, but not thymic DP cells, circulated and populated other secondary lymphoid organs. Furthermore, these extra-thymic T cells originated the tumors, as animals undergoing splenectomy were protected from T-ALL.
Conclusions: We report here a new model of T-ALL in which ectopic expression of a notch ligand on T cells is sufficient to drive the lymphoma generation with a brief latency and 100% penetrance. Cancer occurs without any of the known notch pathway mutations. Remarkably, we demonstrated a novel mechanism of T-ALL pathogenesis through extra-thymic development of CD4+CD8+ DP cells in which the spleen plays a crucial and unique role.
Monday, March 19, 2012 9:30 AM
Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 282, Monday Morning