Murine models based on acute myeloid leukemia-initiating stem cells xenografting

Acute myeloid leukemia(AML) is an aggressive malignant disease defined by abnormal expansion of myeloid blasts. Despite recent advances in understanding AML pathogenesis and identifying their molecular subtypes based on somatic mutations, AML is still characterized by poor outcomes, with a 5-year survival rate of only 30%-40%, the majority of the patients dying due to AML relapse. Leukemia stem cells(LSC) are considered to be at the root of chemotherapeutic resistance and AML relapse. Although numerous studies have tried to better characterize LSCs in terms of surface and molecular markers, a specific marker of LSC has not been found, and still the most universally accepted phenotypic signature remains the surface antigens CD34+CD38- that is shared with normal hematopoietic stem cells. Animal models provides the means to investigate the factors responsible for leukemic transformation, the intrinsic differences between secondary post-myeloproliferative neoplasm AML and de novo AML, especially the signaling pathways involved in inflammation and hematopoiesis. However, AML proved to be one of the hematological malignancies that is difficult to engraft even in the most immunodeficient mice strains, and numerous ongoing attempts are focused to develop "humanized mice" that can support the engraftment of LSC. This present review is aiming to in-troduce the field of AML pathogenesis and the concept of LSC, to present the current knowledge on leukemic blasts surface markers and recent attempts to develop best AML animal models.

Intra-heterogeneity in transcription and chemoresistant property of leukemia-initiating cells in murine Setd2^(-/-) acutemyeloid leukemia

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 Nras^(G12S) and Braf^(K520E).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 doxorubicinresistant 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 treatmentwithDAand 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 inmurine Setd2^(-/-)-AML and disclosed the transcriptional and functional heterogeneity of LICs,revealing that the coexistence of different types of LICs in thismodel brings about diverse drug response.