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Myeloproliferative Neoplasm Stem Cells

Adam J. Mead and Ann Mullally

Abstract

Myeloproliferative neoplasms (MPN) arise in the hematopoietic stem cell (HSC) compartment as a result of the acquisition of somatic mutations in a single HSC that provide a selective advantage to mutant HSC over normal HSC and promote myeloid differentiation to engender a myeloproliferative phenotype. This population of somatically mutated HSC, which initiate and sustain MPN, are termed MPN stem cells. In greater than 95% of cases, mutations that drive the development of an MPN phenotype occur in a mutually exclusive manner in one of three genes: JAK2, CALR or MPL. The thrombopoietin receptor, MPL is the key cytokine receptor in MPN development and these mutations all activate MPL-JAK-STAT signaling in MPN stem cells. Despite common biological features, MPN display diverse disease phenotypes as a result of both constitutional and acquired factors that influence MPN stem cells, and likely also as a result of heterogeneity in the HSC in which MPN-initiating mutations arise. As the MPN clone expands it exerts cell-extrinsic effects on components of the bone marrow niche that can favor the survival and expansion of MPN stem cells over normal HSC, further sustaining and driving malignant hematopoiesis. Although developed as targeted therapies for MPN, current JAK2 inhibitors do not preferentially target MPN stem cells and as a result rarely induce molecular remissions in MPN patients. As the understanding of the molecular mechanisms underlying the clonal dominance of MPN stem cells advances, this will help facilitate the development of therapies that preferentially target MPN stem cells over normal HSC.

  • Submitted October 25, 2016.
  • Accepted November 22, 2016.