3079 - Thymic Precursor Cells Generate Acute Myeloid Leukemia in NUP98-PHF23/NUP98-HOXD13 Double Transgenic Mice

Abstract

Using Vav regulatory elements, we previously developed transgenic mice that expressed either a NUP98–PHF23 (NP23) or NUP98-HOXD13 (NHD13) fusion in the hematopoietic compartment. Both NP23 and NHD13 mice develop a wide variety of leukemias, including myeloid, erythroid, megakaryocytic and lymphoid, with an age of onset typically between 9 and 14 months. Remarkably, 100% of the NP23-NHD13 double transgenic mice developed acute myeloid leukemia (AML) within three months, characterized by almost complete replacement of the thymus with leukemic myeloblasts. Gene expression profiling indicated that Stefin A cluster genes, Hmga1 and Hist1h4b, Hist1h4d were uniquely overexpressed in the NP23/NHD13 myeloblasts compared to WT BM, NP23 and NHD13 single transgenic AML. The consistent, marked infiltration of the thymus, in many cases more so than bone marrow, led to the intriguing hypothesis that the AML generated in NP23-NHD13 mice arose in the thymus, as opposed to the bone marrow (BM). Transplantation of DN thymocytes from a young (5 wk old), non-leukemic NP23-NHD13 mouse showed that DN thymocytes could generate AML. Finally, we transplanted DN1, DN2, DN3 and DN4 thymocytes from a non-leukemic NP23-NHD13 mouse. DN1 and DN2, fractions transmitted AML. Further fractionation of the LSK population in the thymus demonstrated primarily MPP2 and MPP3 cells. To determine if signaling from normal thymic epithelial cells are required for the malignant transformation of NP23/NHD13 thymocytes, we crossed the NP23 and NHD13 transgenes onto a Nu/Nu background. Onset of AML was significantly delayed, but not prevented, in both the Nu/Nu and Nu/WT backgrounds. In vitro studies showed that DN thymocytes from non-leukemic NP23-NHD13 mice co-cultured on a OP9 stromal layer with cytokine support displayed a markedly enhanced ability to differentiate into Mac1+/Gr1+ myeloid cells compared to WT. These cells were transplanted; all recipients engrafted NP23-NHD13 myeloid cells with no evidence of T-cell differentiation. Taken together, these results show that the thymus of NP23-NHD13 mice acts as a reservoir for AML initiating cells.