Abstract PR09: Single-cell transcriptional profiling of acute myeloid leukemia identifies self-renewing stem cells
Authors: Noble-Orcutt Klara E. , Sachs Karen , Navis Connor , Hillesheim Alexandria , Nykaza Ian , LaRue Rebecca S. , Hansen Conner , Ha Ngoc , Linden Michael A. , Largaespada David A. , Sachs Zohar 
Published: August 2018

Abstract
Acute myeloid leukemia (AML) is a lethal cancer with a survival of less than 50%. Standard cytotoxic therapies frequently induce complete remission, but patients frequently relapse and die of their disease. Leukemia stem cells (LSCs) are the leukemia cells with self-renewal potential and ability to recapitulate the disease. Most anticancer therapies are designed to inhibit proliferation. Yet, in hematopoietic stem cells, the mechanisms of proliferation are distinct from self-renewal (Li et al. Nature 2013). Consequently, targeting proliferation may explain the failure of traditional chemotherapy to target LSCs and eradicate AML. Our goal is define the self-renewing LSCs in order to develop therapeutics that target them and eliminate AML relapse. We previously showed that activated NRAS (NRASG12V) facilitates self-renewal in the LSC-enriched subpopulation of a transgenic mouse model of AML (Mll-AF9/NRASG12V) (Sachs et al. Blood 2014; Kim et al. Blood 2009). We hypothesize that self-renewal capacity and the NRAS-activated pathways required for self-renewal are limited to a subpopulation of LSCs.
We used single-cell RNA sequencing to identify the self-renewing cells among the LSC-enriched subgroup in this model (Mac1LowKit+Sca1+, “MKS”). We identified three discrete transcriptional profiles among the LSC-enriched subpopulation and found that that two of these profiles (Profile 1 and Profile 2) are NRASG12V-dependent. These two profiles can be differentiated by CD36 and CD69 expression. We sorted the MKS LSCs based on CD36 and CD69 expression. Sorted LSC subsets were transplanted into recipient mice to compare their ability to transfer leukemia as a measure of their self-renewal capacity. We found that MKS-CD36-CD69+ cells (consistent with Profile 1) rapidly transferred leukemia with high penetrance in 20 of 22 mice. In contrast, MKS-CD36+CD69- cells (Profile 2) failed transfer leukemia in most mice; only 2 of 25 of these mice developed AML (p &lt; 0.004).
In our previous work, we demonstrated that the NRASG12V-activated self-renewal gene expression profile that we identified in our murine model was expressed in human AML, suggesting that the gene expression behavior of LSCs from this model may recapitulate the gene expression behavior of human LSCs (Sachs et al. Blood 2014). In order to determine if the single-cell transcriptional profiles of our murine AML can be found in primary human AML precursors, we performed single-cell RNA sequencing on CD34+ human AML cells obtained from a diagnostic bone marrow specimen. Analogous to our murine model, we found that these human AML cells express 2 distinct single-cell transcriptional profiles and they differentially express RAS-activated gene expression profiles and profiles of hematopoietic differentiation. Next, we used our murine single-cell self-renewal transcriptional profile to define a 96-gene panel consisting of 88 genes from this profile and 8 housekeeping genes. We sorted primary, diagnostic human AML cells for leukemia stem and progenitor cells (CD34+CD38-) and performed single-cell qPCR on these cells using our 96-gene panel. We found that a subset of these cells preferentially expresses Profile 1, the self-renewal gene expression profile that we identified in our murine model, and another subset preferentially expresses Profile 2 (the profile associated with no leukemia-reconstituting capacity).
In these experiments, we use a murine model of AML to define the LSC self-renewal gene expression profile at the single-cell level and functionally validate this profile in vivo. Analogous to the murine model, a subset of human AML stem and progenitor cells expresses this LSC self-renewal gene expression profile at the single-cell level. These data suggest that single-cell gene expression profiling can delineate leukemia cells with true self-renewal capacity.
This abstract is also being presented as Poster 43.
Citation Format: Klara E. Noble-Orcutt, Karen Sachs, Connor Navis, Alexandria Hillesheim, Ian Nykaza, Rebecca S. LaRue, Conner Hansen, Ngoc Ha, Michael A. Linden, David A. Largaespada, Zohar Sachs. Single-cell transcriptional profiling of acute myeloid leukemia identifies self-renewing stem cells [abstract]. In: Proceedings of the Second AACR Conference on Hematologic Malignancies: Translating Discoveries to Novel Therapies; May 6-9, 2017; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(24_Suppl):Abstract nr PR09.