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101 Myeloproliferative Neoplasm (MPN) Blastic Transformation Occurs at the Level of Hematopoietic Stem Cells

Program: Oral and Poster Abstracts
Type: Oral
Session: 635. Myeloproliferative Syndromes: Basic Science: Mechanisms of Development and Progression
Hematology Disease Topics & Pathways:
AML, Diseases, Biological Processes, MPN, Myeloid Malignancies, pathogenesis
Saturday, December 1, 2018: 10:30 AM
Room 7B (San Diego Convention Center)

Xiaoli Wang, PhD1, Cing Siang Hu2*, Joseph Tripodi2*, Vesna Najfeld, PhD3, Bruce Petersen, MD2, Raajit K. Rampal, MD, PhD4, Noushin Farnoud5*, Christopher Famulare, MS5*, John Mascarenhas, MD6 and Ronald Hoffman, MD7

1Division of Hematology/Medical Oncology/Pathology, The Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai; Myeloproliferative Neoplasm Research Consortium (MPN-RC), Rego Park, NY
2Division of Hematology/Medical Oncology/Pathology, The Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York, NY
3Division of Hematology/Medical Oncology/Pathology, The Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai; Myeloproliferative Neoplasm Research Consortium (MPN-RC), New York, NY
4Leukemia Service, Department of Medicine, Memorial Sloan Kettering Cancer Center; Myeloproliferative Neoplasm Research Consortium (MPN-RC), New York, NY
5Leukemia Service, Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, NY
6Icahn School of Medicine at Mount Sinai, New York, NY
7Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York, NY

Myeloproliferative neoplasm-blast phase (MPN-BP) and de novo acute myeloid leukemia (AML) each have distinct mutational patterns and clinical courses. MPN-BP patients have a particularly dismal prognosis with a median survival of less than 6 months with currently available therapies. So far, the cellular hierarchy that characterizes MPN-BP and the evolution of various leukemia-initiating clones (LIC) in MPN-BP have not been well delineated. We therefore established an in vivo MPN-BP xenograft model to address these questions.

Among the 22 patients with MPN-BP studied 11 were cytogenetically normal while the remainder had multiple chromosomal abnormalities including del(5), del(20q), del(14), +1q, del(17p). 86% of the patients had at least 2 myeloid malignancy gene mutations including JAK2, ASXL1, TET2, MPL, SF3B1, RUNX1, U2AF1, PTPN11, IDH1/2, SRSF2 and TP53. These findings indicate that MPN-BP is characterized by multiple mutational events and cytogenetic abnormalities. T cell-depleted mononuclear cells from 8 of 14 patients engrafted in NSG mice {>0.5% hCD45+ cells in bone marrow (BM)}. Among them, samples from 6 patients resulted in a high degree of hCD45+ cell chimerism (34.6±6.4% in BM) and recapitulated numerous aspects of MPN-BP within 4 months, including the presence of at least 20% hCD45dimCD33+ cells or hCD34+ cells, or at least 20% blasts as detected by morphological examination of the marrow and leukemia cell dissemination to the spleen and PB. These mice had a 2.8±0.6- fold increase in splenic weight as compared to mice receiving PBS alone. The leukemic mice were characterized by reduced blood counts, suggesting that MPN-BP cells suppressed normal murine hematopoiesis, or led to cytopenias due to hyper-splenism. Moreover, the greater degrees of blast cell chimerism and the higher frequency of leukemia initiating cells as determined by limiting dilution analyses correlated with a shorter time to leukemia initiation and an inferior clinical outcome of the transplanted NSG mice. Grafts from each of these 6 MPN-BP patients produced a large number of donor-derived myeloid cells and a smaller number of lymphoid cells (mostly CD3+ and few CD19+). Cells belonging to each of these lineages and leukemic cells in primary recipients produced from Pts 4, 5, 6 and 11 had an identical proportion of chromosomally abnormal and mutated cells as primary cells [Pt 4: JAK2V617F, TET2 and PHF6; Pt 5 and 11: Del (20q), +8; Pt 6: +1q, del(17p)], except that a small proportion of T cells from Pts 5 and 11 lacked chromosomal abnormalities. Furthermore, the degree of MPN-BP engraftment and leukemic cell burden increased with the subsequent 3 serial transplantations even when the recipients received progressively smaller numbers of MPN-BP cells from the prior recipient. Primary Pt 6 originally had a JAK2V617F+ PV but lost JAK2V617F at the time the MPN-BP occurred at which time there were two clonal cell populations, one with +1q (12%) and the other del(17p) (80%), the site of the TP53 gene, as well as normal cells (8%). In the primary recipient NSG the donor derived cells were JAK2V617F- but contained +1q (1%) and del(17p) (98.5%) and cytogenetically normal (0.5%). +1q and JAK2V617F were not observed, while cells containing the TP53 deletion alone were detected in donor derived leukemic cells, mature myeloid and T cells in the secondary and subsequent serial recipients. Furthermore, del(17p) was found in phenotypically isolated HSCs, MPPs, MLPs, CMPs, GMPs, MEPs, and mature T cells within the CD33 cell fraction as well as CD45dimCD33+ AML blasts selected from primary MPN-BP cells from Pt6. However, +1q was found exclusively in purified MLPs and MEP. These observations establish that cytogenetic and mutational events that lead to MPN-BP occur at different stages along the developmental HSC hierarchy and that a small population of normal HSCs persist. Furthermore, in JAK2V617F+ MPNs that develop MPN-BP and lose JAK2V617F, additional cytogenetic events occur at different stages along the JAK2V617F- MPN-BP-stem cell hierarchy. Our ability to serially transplant the LIC from these patients has allowed us to create the first MPN-BP PDX model that will not only extend our understanding of MPN-BP stem cell biology but might also prove useful for screening drugs to treat MPN-BP.

Disclosures: Rampal: Jazz: Consultancy, Honoraria; Incyte: Honoraria, Research Funding; Stemline: Research Funding; Constellation: Research Funding; Celgene: Honoraria. Mascarenhas: Incyte: Membership on an entity's Board of Directors or advisory committees, Research Funding; CTI Biopharma: Membership on an entity's Board of Directors or advisory committees, Research Funding; Merck: Research Funding; Roche: Research Funding; Novartis: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees; Promedior: Research Funding; Janssen: Research Funding. Hoffman: Formation Biologics: Research Funding; Summer Road: Research Funding; Merus: Research Funding; Incyte: Research Funding; Janssen: Research Funding.

*signifies non-member of ASH