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// Alison K. Esser 1,* , Daniel A. Rauch 1,* , Jingyu Xiang 1 , John C. Harding 1 , Nicole A. Kohart 2 , Michael H. Ross 1 , Xinming Su 1 , Kevin Wu 1 , Devra Huey 2 , Yalin Xu 1 , Kiran Vij 1 , Patrick L. Green 2 , Thomas J. Rosol 2 , Stefan Niewiesk 2 , Lee Ratner 1 and Katherine N. Weilbaecher 1 1 Department of Medicine, Division of Oncology, Washington University School of Medicine, St. Louis, MO, USA 2 Department of Veterinary Biosciences, School of Veterinary Medicine, The Ohio State University, Columbus, OH, USA * Co-authors Correspondence to: Katherine N. Weilbaecher, email: // Keywords : HTLV-1, ATL, leukemia, HBZ, bone Received : June 10, 2017 Accepted : August 03, 2017 Published : August 27, 2017 Abstract Adult T-cell leukemia/lymphoma (ATL) is an aggressive T cell malignancy that occurs in HTLV-1 infected patients. Most ATL patients develop osteolytic lesions and hypercalcemia of malignancy, causing severe skeletal related complications and reduced overall survival. The HTLV-1 virus encodes 2 viral oncogenes, Tax and HBZ. Tax, a transcriptional activator, is critical to ATL development, and has been implicated in pathologic osteolysis. HBZ, HTLV-1 basic leucine zipper transcription factor, promotes tumor cell proliferation and disrupts Wnt pathway modulators; however, its role in ATL induced osteolytic bone loss is unknown. To determine if HBZ is sufficient for the development of bone loss, we established a transgenic Granzyme B HBZ (Gzmb-HBZ) mouse model. Lymphoproliferative disease including tumors, enlarged spleens and/or abnormal white cell counts developed in two-thirds of Gzmb-HBZ mice at 18 months. HBZ positive cells were detected in tumors, spleen and bone marrow. Importantly, pathologic bone loss and hypercalcemia were present at 18 months. Bone-acting factors were present in serum and RANKL, PTHrP and DKK1, key mediators of hypercalcemia and bone loss, were upregulated in Gzmb-HBZ T cells. These data demonstrate that Gzmb-HBZ mice model ATL bone disease and express factors that are current therapeutic targets for metastatic and bone resident tumors.