Background: Heterogeneity of leukemia-initiating cells (LICs) is a major obstacle in acute myeloid leukemia (AML) therapy. Accumulated evidence indicates that the coexistence of multiple types of LICs with different pathogenicity in the same individual is a common feature in AML. However, the functional heterogeneity including the drug response of coexistent LICs remains unclear. Therefore, this study aimed to clarify the intra-heterogeneity in LICs that can help predict leukemia behavior and develop more effective treatments. Methods: Spleen cells from the primary Setd2-/- -AML mouse were transplanted into C57BL/6 recipient mice to generate a transplantable model. Flow cytometry was used to analyze the immunophenotype of the leukemic mice. Whole-genome sequencing was conducted to detect secondary hits responsible for leukemia transformation. A serial transplantation assay was used to determine the self-renewal potential of Setd2-/- -AML cells. A limiting-dilution assay was performed to identify the LIC frequency in different subsets of leukemia cells. Bulk and single-cell RNA sequencing were performed to analyze the transcriptional heterogeneity of LICs. Small molecular inhibitor screening and in vivo drug treatment were employed to clarify the difference in drug response between the different subsets of LICs. Results: In this study, we observed an aged Setd2-/- mouse developing AML with co-mutation of NrasG12S and BrafK520E . Further investigation identified two types of LICs residing in the c-Kit+ B220+ Mac-1- and c-Kit+ B220+ Mac-1+ subsets, respectively. In vivo transplantation assay disclosed the heterogeneity in differentiation between the coexistent LICs. Besides, an intrinsic doxorubicin-resistant transcriptional signature was uncovered in c-Kit+ B220+ Mac-1+ cells. Indeed, doxorubicin plus cytarabine (DA), the standard chemotherapeutic regimen used in AML treatment, could specifically kill c-Kit+ B220+ Mac-1- cells, but it hardly affected c-Kit+ B220+ Mac-1+ cells. Transcriptome analysis unveiled a higher activation of RAS downstream signaling pathways in c-Kit+ B220+ Mac-1+ cells than in c-Kit+ B220+ Mac-1- cells. Combined treatment with DA and RAS pathway inhibitors killed both c-Kit+ B220+ Mac-1- and c-Kit+ B220+ Mac-1+ cells and attenuated disease progression. Conclusions: This study identified two cell subsets enriched for LICs in murine Setd2-/- -AML and disclosed the transcriptional and functional heterogeneity of LICs, revealing that the coexistence of different types of LICs in this model brings about diverse drug response. Keywords: Setd2−/− acute myeloid leukemia; drug response; heterogeneity; leukemia-initiating cell; single-cell RNA sequencing.

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乐备实（上海优宁维生物科技股份有限公司旗下全资子公司），是国内专注于提供高质量蛋白检测以及组学分析服务的实验服务专家，自2018年成立以来，乐备实不断寻求突破，公司的服务技术平台已扩展到单细胞测序、空间多组学、流式检测、超敏电化学发光、Luminex多因子检测、抗体芯片、PCR Array、ELISA、Elispot、PLA蛋白互作、多色免疫组化、DSP空间多组学等30多个，建立起了一套涵盖基因、蛋白、细胞以及组织水平实验的完整检测体系。

 
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