Program: Oral and Poster Abstracts
Session: 635. Myeloproliferative Syndromes: Basic Science: Poster III
Results: Dimensionality reduction and clustering analysis by viSNE and SPADE identified multiple cell subsets outside the hematopoietic stem/progenitor cell (HSPC) compartment that exhibited overt thrombopoietin (TPO) sensitivity, while healthy controls had highly localized responses largely restricted to the HSPC compartment. Using Phenograph, ten sAML metaclusters were identified containing cells from six sAML patients analyzed. One of these metaclusters represented a distinct subpopulation of CD61+ CD34- CD38- CD45lo cells with variable CD90 and CD11b expression. This subpopulation of CD61+ cells was not identified by manual gating, and exhibited significantly greater STAT3/STAT5 phosphorylation in response to TPO than did lineage-negative CD34+ CD38- cells in five out of six (83%) AML patients examined. In addition, substantially elevated basal STAT3 phosphorylation in this population was hypersensitive to TPO and largely resistant to ex vivo ruxolitnib. The classify function of Phenograph was utilized to determine whether the cytokine hypersensitivity observed in the viSNE and SPADE analysis could be entirely accounted for by the aforementioned CD61+ CD34- CD38- CD45lo population. The signaling responses highly predictive of specific cell types were identified, which were used to assess the functional status of sAML cells compared to healthy Lin- CD34+ CD38- cells. By this approach, sAML cells were found to exhibit significant incongruity between surface cell type designation and functional designation. Furthermore, functionally primitive cells displayed a spectrum of myeloid surface markers, suggesting that restricting analysis to a subset of strictly surface-defined cells would potentially obscure populations of interest.
Conclusions: Our analysis revealed a distinct, previously undescribed population of CD61+ CD34- CD38- CD45lo cells in sAML. While the biological relevance of this population requires validation by functional assays, this result demonstrates that immunophenotypic changes in traditional surface-marker-defined populations may conceal important cell populations. These cells, and other functionally primitive but mature-designated cells could be relevant to studying sAML disease pathogenesis, progression, and/or response to therapy. This study further demonstrates the potential for mass cytometry to elucidate rare leukemic subpopulations in highly heterogeneous tumors.
Disclosures: Oh: Gilead: Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte Corporation: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Research Funding; CTI: Research Funding.
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