Identification of therapeutic targets for quiescent, chemotherapy-resistant human leukemia stem cells

CD37 regulates the self-renewal of leukemic stem cells via integrin-mediated signaling in acute myeloid leukemia

Leukemic stem cells (LSCs) are a small subset of leukemia cells that drive leukemia initiation and maintenance. Herein, we report that CD37, a member of transmembrane 4 superfamily (TM4SF), regulates the survival of acute myeloid leukemia (AML) cells as well as the self-renewal of AML LSCs. The downregulation of CD37 retarded proliferation and increased apoptosis in human AML cell lines THP-1 and OCI-AML2. Deficiency of CD37 in vivo had a minimal effect on normal hematopoiesis but significantly impeded leukemia maintenance and propagation, which led to increased apoptosis and decreased cell cycle entry in AML blasts as well as impaired colony formation and declined frequency of AML LSCs in the serial transplantation. Furthermore, CD37 interacted with integrin α4β7 and activated the phosphatidylinositol 3-kinase (PI3K)-AKT pathway mediated by integrin signaling. Our study provides novel insights for targeted therapy of AML, indicating CD37 as a safe and effective target for immunotherapy.

From Chemotherapy to Targeted Therapy: Unraveling Resistance in Acute Myeloid Leukemia Through Genetic and Non-Genetic Insights

Acute myeloid leukemia (AML) is a devastating disease characterized by extensive inter-patient and intra-patient heterogeneity. Despite the introduction of intensive chemotherapy in the 1970s as the standard treatment, the development of mechanism-based targeted therapies since 2017 has been broadening the therapeutic landscape. However, both chemotherapy and targeted therapies continue to face the challenges of primary and secondary resistance. This review summarizes the mechanisms underlying resistance to chemotherapy and targeted therapies in AML and discusses the opportunities and challenges brought by the transition from chemotherapy to precision medicine.

Preclinical targeting of leukemia-initiating cells in the development future biologics for acute myeloid leukemia

INTRODUCTION

Leukemia-initiating cells (LICs) are a critical subset of cells driving acute myeloid leukemia (AML) relapse and resistance to therapy. They possess unique properties, including metabolic, epigenetic, and microenvironmental dependencies, making them promising therapeutic targets.

AREAS COVERED

This review summarizes preclinical advances in targeting AML LICs, including strategies to exploit metabolic vulnerabilities, such as the reliance on oxidative phosphorylation (OXPHOS), through the use of mitochondrial inhibitors; target epigenetic regulators like DOT1L (Disruptor of Telomeric Silencing 1-like) to disrupt LIC survival mechanisms; develop immunotherapies, including CAR (chimeric antigen receptor) T-cell therapy, and bispecific antibodies; and disrupt LIC interactions with the bone marrow microenvironment by inhibiting supportive niches.

EXPERT OPINION

LIC-targeted therapies hold significant promise for revolutionizing AML treatment by reducing relapse rates and improving long-term outcomes. However, challenges such as LIC heterogeneity, therapy resistance, and associated toxicity persist. Recent studies have illuminated the distinct biological characteristics of LICs, advancing our understanding of their behavior and vulnerabilities. These insights offer new opportunities to target LICs at earlier disease stages and to explore combination therapies with other targeted treatments, ultimately enhancing therapeutic efficacy and improving patient outcomes.

Cancer stem cells: Masters of all traits

Cancer is a heterogeneous disease, which contributes to its rapid progression and therapeutic failure. Besides interpatient tumor heterogeneity, tumors within a single patient can present with a heterogeneous mix of genetically and phenotypically distinct subclones. These unique subclones can significantly impact the traits of cancer. With the plasticity that intratumoral heterogeneity provides, cancers can easily adapt to changes in their microenvironment and therapeutic exposure. Indeed, tumor cells dynamically shift between a more differentiated, rapidly proliferating state with limited tumorigenic potential and a cancer stem cell (CSC)-like state that resembles undifferentiated cellular precursors and is associated with high tumorigenicity. In this context, CSCs are functionally located at the apex of the tumor hierarchy, contributing to the initiation, maintenance, and progression of tumors, as they also represent the subpopulation of tumor cells most resistant to conventional anti-cancer therapies. Although the CSC model is well established, it is constantly evolving and being reshaped by advancing knowledge on the roles of CSCs in different cancer types. Here, we review the current evidence of how CSCs play a pivotal role in providing the many traits of aggressive tumors while simultaneously evading immunosurveillance and anti-cancer therapy in several cancer types. We discuss the key traits and characteristics of CSCs to provide updated insights into CSC biology and highlight its implications for therapeutic development and improved treatment of aggressive cancers.

TIM-3 marks measurable residual leukemic stem cells responsible for relapse after allogeneic stem cell transplantation

In this study, we investigated the measurable residual leukemic stem cell (MR-LSC) population after allogeneic stem cell transplantation (allo-SCT) for high-risk acute myeloid leukemia (AML), utilizing T-cell immunoglobulin mucin-3 (TIM-3) expression as a functional marker of AML leukemic stem cells (LSCs). Analysis of the CD34+CD38- fraction of bone marrow cells immediately after achievement of engraftment revealed the presence of both TIM-3+LSCs and TIM-3- donor hematopoietic stem cells (HSCs) at varying ratios. Genetic analysis confirmed that TIM-3+ cells harbored patient-specific mutations identical to those found in AML clones, whereas TIM-3- cells did not, indicating that TIM-3+CD34+CD38- cells represent residual AML LSCs. In 92 allo-SCT occasions involving 83 AML patients, we enumerated the frequencies of TIM-3+LSCs immediately after achieving hematologic complete remission with complete donor cell chimerism. Notably, only 22.2% of patients who achieved a TIM-3+MR-LSClow status (<60%) experienced relapse, with a median event-free survival (EFS) of 1581 days (median follow-up duration was 2177 days among event-free survivors). Conversely, 87.5% of patients with TIM-3+MR-LSCint/high (≥60%) relapsed, with a median EFS of 140.5 days. Furthermore, MR-LSC status emerged as a significant independent risk factor for relapse (hazard ratio, 8.56; p < 0.0001), surpassing the impact of patient disease status prior to allo-SCT, including failure to achieve complete remission (hazard ratio, 1.98; p = 0.048). These findings suggest that evaluating TIM-3+ MR-LSCs immediately after engraftment, which reflects the competitive reconstitution of residual TIM-3+ LSCs and donor HSCs, may be valuable for predicting outcomes in AML patients undergoing allo-SCT.

Unveiling the potential of CLL-1: a promising target for AML therapy

Acute myeloid leukemia (AML) remains a formidable blood cancer, despite recent advances in treatment. A significant challenge persists in improving patient outcomes, particularly in addressing relapse and treatment resistance. Identifying new therapeutic targets is critical for advancing AML therapy. C-type lectin-like molecule-1 (CLL-1) has emerged as a promising therapeutic target in AML. This cell surface receptor is highly expressed on AML blasts and demonstrates stable expression throughout disease progression. CLL-1's consistent presence makes it an ideal candidate for monitoring minimal residual disease (MRD), which is a critical indicator for predicting relapse. Beyond its utility as a diagnostic marker, CLL-1 offers exciting potential in the development of immunotherapies. Emerging strategies, such as CAR-T-cell therapy and antibody-drug conjugates (ADCs), are being investigated to leverage the immune system against CLL-1-expressing AML cells. This review examines the structure, function, and expression patterns of CLL-1 in AML and other hematologic malignancies, providing insights into its role in disease pathogenesis and treatment potential. Exploring CLL-1 as a target for diagnosis, MRD monitoring, and immunotherapy opens new avenues for AML treatment. A deeper understanding of its relationship with AML pathogenesis will aid in the development of targeted therapies, offering hope for improved patient outcomes in the future.

Advances in DNA/RNA Sequencing and Their Applications in Acute Myeloid Leukemia (AML)

Acute myeloid leukemia (AML) is an aggressive malignancy that poses significant challenges due to high rates of relapse and resistance to treatment, particularly in older populations. While therapeutic advances have been made, survival outcomes remain suboptimal. The evolution of DNA and RNA sequencing technologies, including whole-genome sequencing (WGS), whole-exome sequencing (WES), and RNA sequencing (RNA-Seq), has significantly enhanced our understanding of AML at the molecular level. These technologies have led to the discovery of driver mutations and transcriptomic alterations critical for improving diagnosis, prognosis, and personalized therapy development. Furthermore, single-cell RNA sequencing (scRNA-Seq) has uncovered rare subpopulations of leukemia stem cells (LSCs) contributing to disease progression and relapse. However, widespread clinical integration of these tools remains limited by costs, data complexity, and ethical challenges. This review explores recent advancements in DNA/RNA sequencing in AML and highlights both the potential and limitations of these techniques in clinical practice.

Immunophenotypic features of early haematopoietic and leukaemia stem cells

Many tumours are organised in a hierarchical structure with at its apex a cell that can maintain, establish, and repopulate the tumour-the cancer stem cell. The haematopoietic stem cell (HSC) is the founder cell for all functional blood cells. Like HSCs, the leukaemia stem cells (LSC) are hypothesised to be the leukaemia-initiating cells, which have features of stemness such as self-renewal, quiescence, and resistance to cytotoxic drugs. Immunophenotypically, CD34+CD38- defines HSCs by adding lineage negativity and CD90+CD45RA-. At which stage of maturation the further differentiation is blocked, determines the type of leukaemia, and determines the immunophenotype of the LSC specific to the leukaemia type. No apparent LSC phenotype has been described in lymphoid leukaemia, and it is debated if a specific acute lymphocytic leukaemia-initiating cell is present, as all cells are capable of engraftment in a secondary mouse model. In chronic lymphocytic leukaemia, a B-cell clone is responsible for uncontrolled proliferation, not a specific LSC. In chronic and acute myeloid leukaemia, LSC is described as CD34+CD38- with the expression of a marker that is aberrantly expressed (LSC marker), such as CD45RA, CD123 or in the case of chronic myeloid leukaemia CD26. In acute myeloid leukaemia, the LSC load had prognostic relevance and might be a biomarker that can be used for monitoring and as an addition to measurable residual disease. However, challenges such as the CD34-negative immunophenotype need to be explored.

Slow-replicating leukemia cells represent a leukemia stem cell population with high cell-surface CD74 expression

Persistence of quiescent leukemia stem cells (LSCs) after treatment most likely contributes to chemotherapy resistance and poor prognosis of leukemia patients. Identification of this quiescent cell population would facilitate eradicating LSCs. Here, using a cell-tracing PKH26 (PKH) dye that can be equally distributed to daughter cells following cell division in vivo, we identify a label-retaining slow-cycling leukemia cell population from AML1-ETO9a (AE9a) leukemic mice. We find that, compared with cells not maintaining PKH-staining, a higher proportion of PKH-retaining cells are in G0 phase, and PKH-retaining cells exhibit increased colony formation ability and leukemia initiation potential. In addition, PKH-retaining cells possess high chemo-resistance and are more likely to be localized to the endosteal bone marrow region. Based on the transcriptional signature, HLA class II histocompatibility antigen gamma chain (Cd74) is highly expressed in PKH-retaining leukemia cells. Furthermore, cell surface CD74 was identified to be highly expressed in LSCs of AE9a mice and CD34+ human leukemia cells. Compared to Lin-CD74- leukemia cells, Lin-CD74+ leukemia cells of AE9a mice exhibit higher stemness properties. Collectively, our findings reveal that the identified slow-cycling leukemia cell population represents an LSC population, and CD74+ leukemia cells possess stemness properties, suggesting that CD74 is a candidate LSC surface marker.

Identification of leukemia stem cell subsets with distinct transcriptional, epigenetic and functional properties

The leukemia stem cell (LSC) compartment is a complex reservoir fueling disease progression in acute myeloid leukemia (AML). The existence of heterogeneity within this compartment is well documented but prior studies have focused on genetic heterogeneity without being able to address functional heterogeneity. Understanding this heterogeneity is critical for the informed design of therapies targeting LSC, but has been hampered by LSC scarcity and the lack of reliable cell surface markers for viable LSC isolation. To overcome these challenges, we turned to the patient-derived OCI-AML22 cell model. This model includes functionally, transcriptionally and epigenetically characterized LSC broadly representative of LSC found in primary AML samples. Focusing on the pool of LSC, we used an integrated approach combining xenograft assays with single-cell analysis to identify two LSC subtypes with distinct transcriptional, epigenetic and functional properties. These LSC subtypes differed in depth of quiescence, differentiation potential, repopulation capacity, sensitivity to chemotherapy and could be isolated based on CD112 expression. A majority of AML patient samples had transcriptional signatures reflective of either LSC subtype, and some even showed coexistence within an individual sample. This work provides a framework for investigating the LSC compartment and designing combinatorial therapeutic strategies in AML.

Sphingosine-1 phosphate receptor 1 (S1PR1) expression maintains stemness of acute myeloid leukemia stem cells

Acute myeloid leukemia (AML) arises from leukemia stem cells (LSCs) and is maintained by cells which have acquired features of stemness. We compared transcription profiles of AML cells with/without stem cell features defined as in vitro clonogenicity and serial engraftment in immune-deficient mice xenograft model. We used multi-parameter flow cytometry (MPFC) to separate CD34+ bone marrow-derived leukemia cells into sphingosine-1 phosphate receptor 1 (S1PR1)+ and S1PR1- fractions. Cells in the S1PR1+ fraction demonstrated significantly higher clonogenicity and higher engraftment potential compared with those in the S1PR1- fraction. In contrast, CD34+ bone marrow cells from normal samples showed reduced clonogenicity in the S1PR1+ fraction compared with the S1PR1- fraction. Inhibition of S1PR1 expression in an AML cell line reduced the colony-forming potential of KG1 cells. Transcriptomic analyses and rescue experiments indicated PI3K/AKT pathway and MYBL2 are downstream mediators of S1PR1-associated stemness. These findings implicate S1PR1 as a functional biomarker of LSCs and suggest its potential as a therapeutic target in AML treatment.

Genetic deletion of JAM-C in preleukemic cells rewires leukemic stem cell gene expression program in AML

ABSTRACT

The leukemic stem cell (LSC) score LSC-17 based on a stemness-related gene expression signature is an indicator of poor disease outcome in acute myeloid leukemia (AML). However, it is not known whether "niche anchoring" of LSC affects disease evolution. To address this issue, we conditionally inactivated the adhesion molecule JAM-C (Junctional Adhesion Molecule-C) expressed by hematopoietic stem cells (HSCs) and LSCs in an inducible mixed-lineage leukemia (iMLL)-AF9-driven AML mouse model. Deletion of Jam3 (encoding JAM-C) before induction of the leukemia-initiating iMLL-AF9 fusion resulted in a shift from long-term to short-term HSC expansion, without affecting disease initiation and progression. In vitro experiments showed that JAM-C controlled leukemic cell nesting irrespective of the bone marrow stromal cells used. RNA sequencing performed on leukemic HSCs isolated from diseased mice revealed that genes upregulated in Jam3-deficient animals belonged to activation protein-1 (AP-1) and tumor necrosis factor α (TNF-α)/NF-κB pathways. Human orthologs of dysregulated genes allowed to identify a score that was distinct from, and complementary to, the LSC-17 score. Substratification of patients with AML using LSC-17 and AP-1/TNF-α genes signature defined 4 groups with median survival ranging from <1 year to a median of "not reached" after 8 years. Finally, coculture experiments showed that AP-1 activation in leukemic cells was dependent on the nature of stromal cells. Altogether, our results identify the AP-1/TNF-α gene signature as a proxy of LSC anchoring in bone marrow niches, which improves the prognostic value of the LSC-17 score. This trial was registered at www.ClinicalTrials.gov as #NCT02320656.

Dormancy and awakening of cancer cells: the extracellular vesicle-mediated cross-talk between Dr. Jekill and Mr. Hyde

Cancer cell dormancy is a reversible process whereby cancer cells enter a quiescent state characterized by cell cycle arrest, inhibition of cell migration and invasion, and increased chemoresistance. Because of its reversibility and resistance to treatment, dormancy is a key process to study, monitor, and interfere with, in order to prevent tumor recurrence and metastasis and improve the prognosis of cancer patients. However, to achieve this goal, further studies are needed to elucidate the mechanisms underlying this complex and dynamic dual process. Here, we review the contribution of extracellular vesicles (EVs) to the regulation of cancer cell dormancy/awakening, focusing on the cross-talk between tumor and non-tumor cells in both the primary tumor and the (pre-)metastatic niche. Although EVs are recognized as key players in tumor progression and metastasis, as well as in tumor diagnostics and therapeutics, their role specifically in dormancy induction/escape is still largely elusive. We report on the most recent and promising results on this topic, focusing on the EV-associated nucleic acids involved. We highlight how EV studies could greatly contribute to the identification of dormancy signaling pathways and a dormancy/early awakening signature for the development of successful diagnostic/prognostic and therapeutic approaches.

Immunophenotypic characterization of leukemic stem cells in acute myeloid leukemia using single tube 10-colour panel by multiparametric flow cytometry: Deciphering the spectrum, complexity and immunophenotypic heterogeneity

INTRODUCTION

Despite extensive research, comprehensive characterization of leukaemic stem cells (LSC) and information on their immunophenotypic differences from normal haematopoietic stem cells (HSC) is lacking. Herein, we attempted to unravel the immunophenotypic (IPT) characteristics and heterogeneity of LSC using multiparametric flow cytometry (MFC) and single-cell sequencing.

MATERIALS AND METHODS

Bone marrow aspirate samples from patients with acute myeloid leukaemia (AML) were evaluated using MFC at diagnostic and post induction time points using a single tube-10-colour-panel containing LSC-associated antibodies CD123, CD45RA, CD44, CD33 and COMPOSITE (CLL-1, TIM-3, CD25, CD11b, CD22, CD7, CD56) with backbone markers that is, CD45, CD34, CD38, CD117, sCD3. Single-cell sequencing of the whole transcriptome was also done in a bone marrow sample.

RESULTS

LSCs and HSCs were identified in 225/255 (88.2%) and 183/255 (71.6%) samples, respectively. Significantly higher expression was noted for COMPOSITE, CD45RA, CD123, CD33, and CD44 in LSCs than HSCs (p < 0.0001). On comparing the LSC specific antigen expressions between CD34+ (n = 184) and CD34- LSCs (n = 41), no difference was observed between the groups. More than one sub-population of LSC was demonstrated in 4.4% of cases, which further revealed high concordance between MFC and single cell transcriptomic analysis in one of the cases displaying three LSC subpopulations by both methods.

CONCLUSION

A single tube-10-colour MFC panel is proposed as an easy and reproducible tool to identify and discriminate LSCs from HSCs. LSCs display both inter- and intra-sample heterogeneity in terms of antigen expressions, which opens the facets for single cell molecular analysis to elucidate the role of subpopulations of LSCs in AML progression.

Leukemic Stem Cells and Hematological Malignancies

The association between leukemic stem cells (LSCs) and leukemia development has been widely established in the context of genetic alterations, epigenetic pathways, and signaling pathway regulation. Hematopoietic stem cells are at the top of the bone marrow hierarchy and can self-renew and progressively generate blood and immune cells. The microenvironment, niche cells, and complex signaling pathways that regulate them acquire genetic mutations and epigenetic alterations due to aging, a chronic inflammatory environment, stress, and cancer, resulting in hematopoietic stem cell dysregulation and the production of abnormal blood and immune cells, leading to hematological malignancies and blood cancer. Cells that acquire these mutations grow at a faster rate than other cells and induce clone expansion. Excessive growth leads to the development of blood cancers. Standard therapy targets blast cells, which proliferate rapidly; however, LSCs that can induce disease recurrence remain after treatment, leading to recurrence and poor prognosis. To overcome these limitations, researchers have focused on the characteristics and signaling systems of LSCs and therapies that target them to block LSCs. This review aims to provide a comprehensive understanding of the types of hematopoietic malignancies, the characteristics of leukemic stem cells that cause them, the mechanisms by which these cells acquire chemotherapy resistance, and the therapies targeting these mechanisms.

Cholesterol neutralized vemurafenib treatment by promoting melanoma stem-like cells via its metabolite 27-hydroxycholesterol

Vemurafenib has been used as first-line therapy for unresectable or metastatic melanoma with BRAFV600E mutation. However, overall survival is still limited due to treatment resistance after about one year. Therefore, identifying new therapeutic targets for melanoma is crucial for improving clinical outcomes. In the present study, we found that lowering intracellular cholesterol by knocking down DHCR24, the limiting synthetase, impaired tumor cell proliferation and migration and abrogated the ability to xenotransplant tumors. More importantly, administration of DHCR24 or cholesterol mediated resistance to vemurafenib and promoted the growth of melanoma spheroids. Mechanistically, we identified that 27-hydroxycholesterol (27HC), a primary metabolite of cholesterol synthesized by the enzyme cytochrome P450 27A1 (CYP27A1), reproduces the phenotypes induced by DHCR24 or cholesterol administration and activates Rap1-PI3K/AKT signaling. Accordingly, CYP27A1 is highly expressed in melanoma patients and upregulated by DHCR24 induction. Dafadine-A, a CYP27A1 inhibitor, attenuates cholesterol-induced growth of melanoma spheroids and abrogates the resistance property of vemurafenib-resistant melanoma cells. Finally, we confirmed that the effects of cholesterol on melanoma resistance require its metabolite 27HC through CYP27A1 catalysis, and that 27HC further upregulates Rap1A/Rap1B expression and increases AKT phosphorylation. Thus, our results suggest that targeting 27HC may be a useful strategy to overcome treatment resistance in metastatic melanoma.

Bone marrow inflammation in haematological malignancies

Tissue inflammation is a hallmark of tumour microenvironments. In the bone marrow, tumour-associated inflammation impacts normal niches for haematopoietic progenitor cells and mature immune cells and supports the outgrowth and survival of malignant cells residing in these niche compartments. This Review provides an overview of our current understanding of inflammatory changes in the bone marrow microenvironment of myeloid and lymphoid malignancies, using acute myeloid leukaemia and multiple myeloma as examples and highlights unique and shared features of inflammation in niches for progenitor cells and plasma cells. Importantly, inflammation exerts profoundly different effects on normal bone marrow niches in these malignancies, and we provide context for possible drivers of these divergent effects. We explore the role of tumour cells in inflammatory changes, as well as the role of cellular constituents of normal bone marrow niches, including myeloid cells and stromal cells. Integrating knowledge of disease-specific dynamics of malignancy-associated bone marrow inflammation will provide a necessary framework for future targeting of these processes to improve patient outcome.

Inhibition of mitochondrial folate metabolism drives differentiation through mTORC1 mediated purine sensing

Supporting cell proliferation through nucleotide biosynthesis is an essential requirement for cancer cells. Hence, inhibition of folate-mediated one carbon (1C) metabolism, which is required for nucleotide synthesis, has been successfully exploited in anti-cancer therapy. Here, we reveal that mitochondrial folate metabolism is upregulated in patient-derived leukaemic stem cells (LSCs). We demonstrate that inhibition of mitochondrial 1C metabolism through impairment of de novo purine synthesis has a cytostatic effect on chronic myeloid leukaemia (CML) cells. Consequently, changes in purine nucleotide levels lead to activation of AMPK signalling and suppression of mTORC1 activity. Notably, suppression of mitochondrial 1C metabolism increases expression of erythroid differentiation markers. Moreover, we find that increased differentiation occurs independently of AMPK signalling and can be reversed through reconstitution of purine levels and reactivation of mTORC1. Of clinical relevance, we identify that combination of 1C metabolism inhibition with imatinib, a frontline treatment for CML patients, decreases the number of therapy-resistant CML LSCs in a patient-derived xenograft model. Our results highlight a role for folate metabolism and purine sensing in stem cell fate decisions and leukaemogenesis.

Cellular hierarchy insights reveal leukemic stem-like cells and early death risk in acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) represents a paradigm for targeted differentiation therapy, with a minority of patients experiencing treatment failure and even early death. We here report a comprehensive single-cell analysis of 16 APL patients, uncovering cellular compositions and their impact on all-trans retinoic acid (ATRA) response in vivo and early death. We unveil a cellular differentiation hierarchy within APL blasts, rooted in leukemic stem-like cells. The oncogenic PML/RARα fusion protein exerts branch-specific regulation in the APL trajectory, including stem-like cells. APL cohort analysis establishes an association of leukemic stemness with elevated white blood cell counts and FLT3-ITD mutations. Furthermore, we construct an APL-specific stemness score, which proves effective in assessing early death risk. Finally, we show that ATRA induces differentiation of primitive blasts and patients with early death exhibit distinct stemness-associated transcriptional programs. Our work provides a thorough survey of APL cellular hierarchies, offering insights into cellular dynamics during targeted therapy.

High IL2RA/CD25 expression is a prognostic stem cell biomarker for pediatric acute myeloid leukemia without a core-binding factor

CD25 is an aberrant marker expressed on the leukemic stem cell (LSC) surface and an immunotherapy target in acute myeloid leukemia (AML). However, the clinical prevalence and significance of CD25 expression in pediatric AML are unknown. High IL2RA/CD25 expression in pediatric AML showed a stem cell-like phenotype, and elevated CD25 expression was associated with lower overall survival (p < .001) and event-free survival (p < .001) in the Japanese Pediatric Leukemia/Lymphoma Study Group AML-05 study. This finding was reproduced in AML without a core-binding factor in the Children's Oncology Group study cohort. High CD25 expression has prognostic significance in pediatric AML.

The relevance of the hematopoietic niche for therapy resistance in acute myeloid leukemia

The expansion of acute myeloid leukemia (AML) blasts not only suppresses normal hematopoiesis, but also alters the microenvironment. The interplay of different components of the bone marrow gives rise to altered metabolic states and activates signaling pathways which lead to resistance and impede effective therapy. Therefore, the underlying processes and mechanisms represent attractive therapeutic leverage points for overcoming therapy resistance in AML. Here, we briefly discuss resistance mechanisms based on cell interactions and secreted soluble factors in the hematopoietic niche and provide an overview of niche-related therapeutic targets currently undergoing preclinical and clinical investigation which may help improve the outcome in AML therapy.

Secondary acute myeloid leukemia and de novo acute myeloid leukemia with myelodysplasia-related changes - close or complete strangers?

AIM

To compare the main features of patients with secondary acute myeloid leukemias (AMLs) after post-myelodysplastic syndrome (AML-post-MDS) or post-myeloproliferative neoplasms (AML-post-MPN) and myeloid blast crisis of chronic myeloid leukemia (CML-BC) vs. de novoAMLs with myelodysplastic characteristics (dn-AML-MDS).

Hub genes and their key effects on prognosis of Burkitt lymphoma

BACKGROUND

Burkitt lymphoma (BL) is an exceptionally aggressive malignant neoplasm that arises from either the germinal center or post-germinal center B cells. Patients with BL often present with rapid tumor growth and require high-intensity multi-drug therapy combined with adequate intrathecal chemotherapy prophylaxis, however, a standard treatment program for BL has not yet been established. It is important to identify biomarkers for predicting the prognosis of BLs and discriminating patients who might benefit from the therapy. Microarray data and sequencing information from public databases could offer opportunities for the discovery of new diagnostic or therapeutic targets.

AIM

To identify hub genes and perform gene ontology (GO) and survival analysis in BL.

METHODS

Gene expression profiles and clinical traits of BL patients were collected from the Gene Expression Omnibus database. Weighted gene co-expression network analysis (WGCNA) was applied to construct gene co-expression modules, and the cytoHubba tool was used to find the hub genes. Then, the hub genes were analyzed using GO and Kyoto Encyclopedia of Genes and Genomes analysis. Additionally, a Protein-Protein Interaction network and a Genetic Interaction network were constructed. Prognostic candidate genes were identified through overall survival analysis. Finally, a nomogram was established to assess the predictive value of hub genes, and drug-gene interactions were also constructed.

RESULTS

In this study, we obtained 8 modules through WGCNA analysis, and there was a significant correlation between the yellow module and age. Then we identified 10 hub genes (SRC, TLR4, CD40, STAT3, SELL, CXCL10, IL2RA, IL10RA, CCR7 and FCGR2B) by cytoHubba tool. Within these hubs, two genes were found to be associated with OS (CXCL10, P = 0.029 and IL2RA, P = 0.0066) by survival analysis. Additionally, we combined these two hub genes and age to build a nomogram. Moreover, the drugs related to IL2RA and CXCL10 might have a potential therapeutic role in relapsed and refractory BL.

CONCLUSION

From WGCNA and survival analysis, we identified CXCL10 and IL2RA that might be prognostic markers for BL.

Cellular Composition and 5hmC Signature Predict the Treatment Response of AML Patients to Azacitidine Combined with Chemotherapy

Azacitidine (AZA) is a DNA methyltransferase inhibitor and epigenetic modulator that can be an effective agent in combination with chemotherapy for patients with high-risk acute myeloid leukemia (AML). However, biological factors driving the therapeutic response of such hypomethylating agent (HMA)-based therapies remain unknown. Herein, the transcriptome and/or genome-wide 5-hydroxymethylcytosine (5hmC) is characterized for 41 patients with high-risk AML from a phase 1 clinical trial treated with AZA epigenetic priming followed by high-dose cytarabine and mitoxantrone (AZA-HiDAC-Mito). Digital cytometry reveals that responders have elevated Granulocyte-macrophage-progenitor-like (GMP-like) malignant cells displaying an active cell cycle program. Moreover, the enrichment of natural killer (NK) cells predicts a favorable outcome in patients receiving AZA-HiDAC-Mito therapy or other AZA-based therapies. Comparing 5hmC profiles before and after five-day treatment of AZA shows that AZA exposure induces dose-dependent 5hmC changes, in which the magnitude correlates with overall survival (p = 0.015). An extreme gradient boosting (XGBoost) machine learning model is developed to predict the treatment response based on 5hmC levels of 11 genes, achieving an area under the curve (AUC) of 0.860. These results suggest that cellular composition markedly impacts the treatment response, and showcase the prospect of 5hmC signatures in predicting the outcomes of HMA-based therapies in AML.

The role of CD180 in hematological malignancies and inflammatory disorders

Toll-like receptors play a significant role in the innate immune system and are also involved in the pathophysiology of many different diseases. Over the past 35 years, there have been a growing number of publications exploring the role of the orphan toll-like receptor, CD180. We therefore set out to provide a narrative review of the current evidence surrounding CD180 in both health and disease. We first explore the evidence surrounding the role of CD180 in physiology including its expression, function and signaling in antigen presenting cells (APCs) (dendritic cells, monocytes, and B cells). We particularly focus on the role of CD180 as a modulator of other TLRs including TLR2, TLR4, and TLR9. We then discuss the role of CD180 in inflammatory and autoimmune diseases, as well as in hematological malignancies of B cell origin, including chronic lymphocytic leukemia (CLL). Based on this evidence we produce a current model for CD180 in disease and explore the potential role for CD180 as both a prognostic biomarker and therapeutic target. Throughout, we highlight specific areas of research which should be addressed to further the understanding of CD180 biology and the translational potential of research into CD180 in various diseases.

Characteristics and molecular mechanism of drug-tolerant cells in cancer: a review

Drug resistance in tumours has seriously hindered the therapeutic effect. Tumour drug resistance is divided into primary resistance and acquired resistance, and the recent study has found that a significant proportion of cancer cells can acquire stable drug resistance from scratch. This group of cells first enters the drug tolerance state (DT state) under drug pressure, and gradually acquires stable drug resistance through adaptive mutations in this state. Although the specific mechanisms underlying the formation of drug tolerant cells (DTCs) remain unclear, various proteins and signalling pathways have been identified as being involved in the formation of DTCs. In the current review, we summarize the characteristics, molecular mechanisms and therapeutic strategies of DTCs in detail.

Biomarkers as targets for CAR-T/NK cell therapy in AML

The most common kind of acute leukemia in adults is acute myeloid leukemia (AML), which is often treated with induction chemotherapy regimens followed by consolidation or allogeneic hematopoietic stem cell transplantation (HSCT). However, some patients continue to develop relapsed or refractory AML (R/R-AML). Small molecular targeted drugs require long-time administration. Not all the patients hold molecular targets. Novel medicines are therefore needed to enhance treatment outcomes. T cells and natural killer (NK) cells engineered with chimeric antigen receptors (CARs) that target antigens associated with AML have recently been produced and are currently being tested in both pre-clinical and clinical settings. This review provides an overview of CAR-T/NK treatments for AML.

Cancer Stem Cells are Actually Stem Cells with Disordered Differentiation: the Monophyletic Origin of Cancer

Cancer stem cells (CSCs) play an important role in cancer development. Based on advancements in CSC research, we propose a monophyletic model of cancer. This model is based on the idea that CSCs are stem cells with disordered differentiation whose original purpose was to repair damaged tissues. Inflammatory responses and damage repair signals are crucial for the creation and maintenance of CSCs. Normal quiescent stem cells are activated by environmental stimulation, such as an inflammatory response, and undergo cell division and differentiation. In the initial stage of cancer development, stem cell differentiation leads to heteromorphism due to the accumulation of gene mutations, resulting in the development of metaplasia or precancerosis. In the second stage, accumulated mutations induce poor differentiation and lead to cancer development. The monophyletic model illustrates the evolution, biological behavior, and hallmarks of CSCs, proposes a concise understanding of the origin of cancer, and may encourage a novel therapeutic approach.

Phenotypic characterization of disease-initiating stem cells in JAK2- or CALR-mutated myeloproliferative neoplasms

Myeloproliferative neoplasms (MPN) are characterized by uncontrolled expansion of myeloid cells, disease-related mutations in certain driver-genes including JAK2, CALR, and MPL, and a substantial risk to progress to secondary acute myeloid leukemia (sAML). Although behaving as stem cell neoplasms, little is known about disease-initiating stem cells in MPN. We established the phenotype of putative CD34+ /CD38- stem cells and CD34+ /CD38+ progenitor cells in MPN. A total of 111 patients with MPN suffering from polycythemia vera, essential thrombocythemia, or primary myelofibrosis (PMF) were examined. In almost all patients tested, CD34+ /CD38- stem cells expressed CD33, CD44, CD47, CD52, CD97, CD99, CD105, CD117, CD123, CD133, CD184, CD243, and CD274 (PD-L1). In patients with PMF, MPN stem cells often expressed CD25 and sometimes also CD26 in an aberrant manner. MPN stem cells did not exhibit substantial amounts of CD90, CD273 (PD-L2), CD279 (PD-1), CD366 (TIM-3), CD371 (CLL-1), or IL-1RAP. The phenotype of CD34+ /CD38- stem cells did not change profoundly during progression to sAML. The disease-initiating capacity of putative MPN stem cells was confirmed in NSGS mice. Whereas CD34+ /CD38- MPN cells engrafted in NSGS mice, no substantial engraftment was produced by CD34+ /CD38+ or CD34- cells. The JAK2-targeting drug fedratinib and the BRD4 degrader dBET6 induced apoptosis and suppressed proliferation in MPN stem cells. Together, MPN stem cells display a unique phenotype, including cytokine receptors, immune checkpoint molecules, and other clinically relevant target antigens. Phenotypic characterization of neoplastic stem cells in MPN and sAML should facilitate their enrichment and the development of stem cell-eradicating (curative) therapies.

Insights on hematopoietic cell kinase: An oncogenic player in human cancer

Hematopoietic cell kinase (Hck) is a member of the Src family and is expressed in hematopoietic cells. By regulating multiple signaling pathways, HCK can interact with multiple receptors to regulate signaling events involved in cell adhesion, proliferation, migration, invasion, apoptosis, and angiogenesis. However, aberrant expression of Hck in various hematopoietic cells and solid tumors plays a crucial role in tumor-related properties, including cell proliferation and epithelial-mesenchymal transition. In addition, Hck signaling regulates the function of immune cells such as macrophages, contributing to an immunosuppressive tumor microenvironment. The clinical success of various kinase inhibitors targeting the Src kinase family has validated the efficacy of targeting Src, and therapies with highly selective Hck kinase inhibitors are in clinical trials. This article reviews Hck inhibition as an emerging cancer treatment strategy, focusing on the expressions and functions of Hck in tumors and its impact on the tumor microenvironment. It also explores preclinical and clinical pharmacological strategies for Hck targeting to shed light on Hck-targeted tumor therapy.

Molecular Mechanisms in Murine Syngeneic Leukemia Stem Cells

Acute Myeloid Leukemia (AML) is a severe disease with a very high relapse rate. AML relapse may be attributable to leukemic stem cells (LSC). Notably, the "cancer stem cell" theory, which relates to LSCs, is controversial and criticized due to the technical peculiarities of the xenotransplant of human cells into mice. In this study, we searched for possible LSCs in an immunocompetent synergetic mice model. First, we found phenotypic heterogeneity in the ML23 leukemia line. We prospectively isolated a sub-population using the surface markers cKit⁺CD9^-CD48⁺Mac1^-/low, which have the potency to relapse the disease. Importantly, this sub-population can pass in syngeneic hosts and retrieve the heterogeneity of the parental ML23 leukemia line. The LSC sub-population resides in various organs. We present a unique gene expression signature of the LSC in the ML23 model compared to the other sub-populations. Interestingly, the ML23 LSC sub-population expresses therapeutic targeted genes such as CD47 and CD93. Taken together, we present the identification and molecular characterization of LSCs in a syngeneic murine model.

Chasing leukemia differentiation through induction therapy, relapse and transplantation

Despite rapid advances in our understanding of acute myeloid leukemia (AML), the disease remains challenging to treat with 5-year survival for adult patients 20 years or older estimated to be 26% (Cancer 2021). The use of new targeted therapies including BCL2, IDH1/IDH2, and FLT3 inhibitors has revolutionized treatment approaches but also changed the disease trajectory with unique modes of resistance. Recent studies have shown that stem cell maturation state drives expression level and/or dependence on various pathways, critical to determining drug response. Instead of anticipating these changes, we remain behind the curve chasing the next expanded clone. This review will focus on current approaches to treatment in AML, including defining the significance of blast differentiation state on chemotherapeutic response, signaling pathway dependence, metabolism, immune response, and phenotypic changes. We conclude that multimodal treatment approaches are necessary to target both the immature and mature clones, thereby, sustaining drug response.

From ecology to oncology: To understand cancer stem cell dormancy, ask a Brine shrimp (Artemia)

The brine shrimp (Artemia), releases embryos that can remain dormant for up to a decade. Molecular and cellular level controlling factors of dormancy in Artemia are now being recognized or applied as active controllers of dormancy (quiescence) in cancers. Most notably, the epigenetic regulation by SET domain-containing protein 4 (SETD4), is revealed as highly conserved and the primary control factor governing the maintenance of cellular dormancy from Artemia embryonic cells to cancer stem cells (CSCs). Conversely, DEK, has recently emerged as the primary factor in the control of dormancy exit/reactivation, in both cases. The latter has been now successfully applied to the reactivation of quiescent CSCs, negating their resistance to therapy and leading to their subsequent destruction in mouse models of breast cancer, without recurrence or metastasis potential. In this review, we introduce the many mechanisms of dormancy from Artemia ecology that have been translated into cancer biology, and herald Artemia's arrival on the model organism stage. We show how Artemia studies have unlocked the mechanisms of the maintenance and termination of cellular dormancy. We then discuss how the antagonistic balance of SETD4 and DEK fundamentally controls chromatin structure and consequently governs CSCs function, chemo/radiotherapy resistance, and dormancy in cancers. Many key stages from transcription factors to small RNAs, tRNA trafficking, molecular chaperones, ion channels, and links with various pathways and aspects of signaling are also noted, all of which link studies in Artemia to those of cancer on a molecular and/or cellular level. We particularly emphasize that the application of such emerging factors as SETD4 and DEK may open new and clear avenues for the treatment for various human cancers.

Present and Future Role of Immune Targets in Acute Myeloid Leukemia

It is now well known that the bone marrow (BM) cell niche contributes to leukemogenesis, but emerging data support the role of the complex crosstalk between AML cells and the BM microenvironment to induce a permissive immune setting that protects leukemic stem cells (LSCs) from therapy-induced death, thus favoring disease persistence and eventual relapse. The identification of potential immune targets on AML cells and the modulation of the BM environment could lead to enhanced anti-leukemic effects of drugs, immune system reactivation, and the restoration of AML surveillance. Potential targets and effectors of this immune-based therapy could be monoclonal antibodies directed against LSC antigens such as CD33, CD123, and CLL-1 (either as direct targets or via several bispecific T-cell engagers), immune checkpoint inhibitors acting on different co-inhibitory axes (alone or in combination with conventional AML drugs), and novel cellular therapies such as chimeric antigen receptor (CAR) T-cells designed against AML-specific antigens. Though dozens of clinical trials, mostly in phases I and II, are ongoing worldwide, results have still been negatively affected by difficulties in the identification of the optimal targets on LSCs.

Measurable residual disease by flow cytometry in acute myeloid leukemia is prognostic, independent of genomic profiling

Measurable residual disease (MRD) assessment provides a potent indicator of the efficacy of anti-leukemic therapy. It is unknown, however, whether integrating MRD with molecular profiling better identifies patients at risk of relapse. To investigate the clinical relevance of MRD in relation to a molecular-based prognostic schema, we measured MRD by flow cytometry in 189 AML patients enrolled in ECOG-ACRIN E1900 trial (NCT00049517) in morphologic complete remission (CR) (28.8 % of the original cohort) representing 44.4 % of CR patients. MRD positivity was defined as ≥ 0.1 % of leukemic bone marrow cells. Risk classification was based on standard cytogenetics, fluorescence-in-situ-hybridization, somatic gene analysis, and sparse whole genome sequencing for copy number ascertainment. At 84.6 months median follow-up of patients still alive at the time of analysis (range 47.0-120 months), multivariate analysis demonstrated that MRD status at CR (p = 0.001) and integrated molecular risk (p = 0.0004) independently predicted overall survival (OS). Among risk classes, MRD status significantly affected OS only in the favorable risk group (p = 0.002). Expression of CD25 (α-chain of the interleukin-2 receptor) by leukemic myeloblasts at diagnosis negatively affected OS independent of post-treatment MRD levels. These data suggest that integrating MRD with genetic profiling and pre-treatment CD25 expression may improve prognostication in AML.

Wilms tumor 1 gene expression in acute myeloid leukemia: prognostic significance and usefulness in minimal residual disease monitoring—a case–control study

Background

Minimal residual disease (MRD), which is characterized as leukemic cells at a level below morphologic detection, has been connected to the risk of relapse in acute myeloid leukemia. In 80–90% of acute myeloid leukemia (AML) patients, the Wilms tumor (WT1) gene is overexpressed at the mRNA level. In our prospective study, a total of 55 patients were enrolled in the study. Group I involved 40 AML patients and group II involved 15 patients healthy controls. WT1 gene expression was quantified using quantitative real-time PCR on bone marrow samples from AML patients at initial diagnosis and at day 28 after induction chemotherapy, and compared to 15 healthy controls in group II. Follow up of patients for prognosis evaluation was assessed. IBM SPSS software was used to capture and analyses the data.

Results

At diagnosis, the mean WT1 transcript value in AML patients was substantially higher than the expression observed in control patient’s Bone marrow. There was no statistically relevant relationship between the onset of relapse and WT1 expression. Patients with WT1 overexpression at diagnosis had a shorter overall survival than patients with negative WT1 expression.

Conclusions

Wilms tumor 1 gene expression was found to be significantly higher in AML patients than control cases, overall, our results confirmed the prognostic significance of WT1 overexpression in AML patients. Our findings support the application of MRD in AML patients based on WT1 overexpression.

Role of PARP Inhibitors in Cancer Immunotherapy: Potential Friends to Immune Activating Molecules and Foes to Immune Checkpoints

Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) induce cytotoxic effects as single agents in tumors characterized by defective repair of DNA double-strand breaks deriving from BRCA1/2 mutations or other abnormalities in genes associated with homologous recombination. Preclinical studies have shown that PARPi-induced DNA damage may affect the tumor immune microenvironment and immune-mediated anti-tumor response through several mechanisms. In particular, increased DNA damage has been shown to induce the activation of type I interferon pathway and up-regulation of PD-L1 expression in cancer cells, which can both enhance sensitivity to Immune Checkpoint Inhibitors (ICIs). Despite the recent approval of ICIs for a number of advanced cancer types based on their ability to reinvigorate T-cell-mediated antitumor immune responses, a consistent percentage of treated patients fail to respond, strongly encouraging the identification of combination therapies to overcome resistance. In the present review, we analyzed both established and unexplored mechanisms that may be elicited by PARPi, supporting immune reactivation and their potential synergism with currently used ICIs. This analysis may indicate novel and possibly patient-specific immune features that might represent new pharmacological targets of PARPi, potentially leading to the identification of predictive biomarkers of response to their combination with ICIs.

Preclinical Evaluation of the Multiple Tyrosine Kinases Inhibitor Anlotinib in Leukemia Stem Cells

Leukemia stem cells (LSCs) constitute the critical barrier to the cure of acute myeloid leukemia (AML) due to their chemoresistance and immune evasion property. Herein, the role of anlotinib, a multiple tyrosine kinase inhibitor, in killing LSCs and regulating chemoresistance and immune evasion was explored. Anlotinib treatment induced apoptosis of LSC-like cells as well as primary AML LSCs, while sparing the normal mononuclear cells in vitro. Moreover, anlotinib could impair the regeneration capacity of LSCs in the patient-derived leukemia xenograft mouse model. Mechanistically, anlotinib inhibited phosphorylation of c-kit, JAK2/STAT3, and STAT5, and downregulated STAT3 and STAT5 expression. In addition, anlotinib downregulated the anti-apoptotic proteins Bcl-2 and Bcl-xL, and upregulated Bax, thereby enhancing the sensitivity of LSCs to idarubicin in vitro. Intriguingly, anlotinib could also partially rescue the interferon-g production of T cells cocultured with LSCs by downregulating PD-L1 expression. In conclusion, anlotinib showed anti-LSC activity and the potential to enhance the sensitivity to idarubicin and inhibit the immunosuppressive feature of LSCs via JAK2/STAT signaling pathway downregulation in the preclinical study. Our results provided a rational basis for combinatory strategies involving anlotinib and chemotherapy or immunotherapy.

Single-cell multi-omics of human clonal hematopoiesis reveals that DNMT3A R882 mutations perturb early progenitor states through selective hypomethylation

Somatic mutations in cancer genes have been detected in clonal expansions across healthy human tissue, including in clonal hematopoiesis. However, because mutated and wild-type cells are admixed, we have limited ability to link genotypes with phenotypes. To overcome this limitation, we leveraged multi-modality single-cell sequencing, capturing genotype, transcriptomes and methylomes in progenitors from individuals with DNMT3A R882 mutated clonal hematopoiesis. DNMT3A mutations result in myeloid over lymphoid bias, and an expansion of immature myeloid progenitors primed toward megakaryocytic-erythroid fate, with dysregulated expression of lineage and leukemia stem cell markers. Mutated DNMT3A leads to preferential hypomethylation of polycomb repressive complex 2 targets and a specific CpG flanking motif. Notably, the hypomethylation motif is enriched in binding motifs of key hematopoietic transcription factors, serving as a potential mechanistic link between DNMT3A mutations and aberrant transcriptional phenotypes. Thus, single-cell multi-omics paves the road to defining the downstream consequences of mutations that drive clonal mosaicism.

Dissection of the MEF2D-IRF8 transcriptional circuit dependency in acute myeloid leukemia

Transcriptional dysregulation is a prominent feature in leukemia. Here, we systematically surveyed transcription factor (TF) vulnerabilities in leukemia and uncovered TF clusters that exhibit context-specific vulnerabilities within and between different subtypes of leukemia. Among these TF clusters, we demonstrated that acute myeloid leukemia (AML) with high IRF8 expression was addicted to MEF2D. MEF2D and IRF8 form an autoregulatory loop via direct binding to mutual enhancer elements. One important function of this circuit in AML is to sustain PU.1/MEIS1 co-regulated transcriptional outputs via stabilizing PU.1’s chromatin occupancy. We illustrated that AML could acquire dependency on this circuit through various oncogenic mechanisms that results in the activation of their enhancers. In addition to forming a circuit, MEF2D and IRF8 can also separately regulate gene expression, and dual perturbation of these two TFs leads to a more robust inhibition of AML proliferation. Collectively, our results revealed a TF circuit essential for AML survival.

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MEF2D is a context-specific vulnerability in IRF8^hi AML

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MEF2D and IRF8 form a transcriptional circuit via binding to each other’s enhancers

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MEF2D-IRF8 circuit supports PU.1’s chromatin occupancy and transcriptional output

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MEF2D and IRF8 can regulate separate gene expression programs alongside the circuit

CD93 promotes acute myeloid leukemia development and is a potential therapeutic target

CD93 is a transmembrane receptor belonging to the Group XIV C-Type lectin family. It is expressed in a variety of cellular types such as monocytes, neutrophils, platelets, microglia, and endothelial cells. CD93 has been reported to play important roles in cell proliferation, cell migration, and tumor angiogenesis. Here, we show CD93 is highly expressed in M4 and M5 subtypes of acute myeloid leukemia (AML) patients, and highly expressed in leukemia stem cells, AML progenitor cells, as well as more differentiated AML cells. We found that CD93 promotes AML cell proliferation, while CD93 deficient AML cells commit to differentiation. We further show that CD93 exerts its proliferative function through downstream SHP-2/Syk/CREB cascade in AML cells. Moreover, human AML cells treated with CD93 mAb combined with αMFc-NC-DM1 (an IgG Fc specific antibody conjugated to maytansinoid DM1), showed a striking reduction of proliferation. Our study revealed that CD93 is a critical participator of AML development and provides a potential therapeutic cell surface target. (160 words).

Flow Cytometric Identification of Hematopoietic and Leukemic Blast Cells for Tailored Clinical Follow-Up of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a myeloid malignancy that is characterized by the accumulation of leukemic blast cells, which originate from hematopoietic stem cells that have undergone leukemic transformation and/or are more mature progenitors that have gained stemness features. Currently, no consensus exists for the flow cytometric identification of normal blast cells and their leukemic counterparts by their antigenic expression profile. Differentiating between the benign cells and the malignant cells is crucial for the further deployment of immunophenotype panels for the clinical follow-up of AML patients. This review provides an overview of immunophenotypic markers that allow the identification of leukemic blast cells in the bone marrow with multiparameter flow cytometry. This technique allows the identification of hematopoietic blast cells at the level of maturing cells by their antigen expression profile. While aberrant antigen expression of a single immunophenotypic marker cell cannot be utilized in order to differentiate leukemic blast cells from normal blast cells, combinations of multiple immunophenotypic markers can enable the distinction of normal and leukemic blast cells. The identification of these markers has provided new perspectives for tailored clinical follow-up, including therapy management, diagnostics, and prognostic purposes. The immunophenotypic marker panels, however, should be developed by carefully considering the variable antigen marker expression profile of individual patients.

A Systems Biology- and Machine Learning-Based Study to Unravel Potential Therapeutic Mechanisms of Midostaurin as a Multitarget Therapy on FLT3-Mutated AML

Acute myeloid leukemia (AML), a hematologic malignancy that results in bone marrow failure, is the most common acute leukemia in adults. The presence of FMS-related tyrosine kinase 3 (FLT3) mutations is associated with a poor prognosis, making the evaluation of FLT3-inhibitors an imperative goal in clinical trials. Midostaurin was the first FLT3-inhibitor approved by the FDA and EMA for the treatment of FLT3-mutated AML, and it showed a significant improvement in overall survival for newly diagnosed patients treated with midostaurin, in combination with standard chemotherapy (RATIFY study). The main interest of midostaurin has been the FLT3-specific inhibition, but little is known about its role as a multikinase inhibitor and whether it may be used in relapse and maintenance therapy. Here, we used systems biology- and machine learning-based approaches to deepen the potential benefits of the multitarget activity of midostaurin and to better understand its anti-leukemic effect on FLT3-mutated AML. The resulting in silico study revealed that the multikinase activity of midostaurin may play a role in the treatment’s efficacy. Additionally, we propose a series of molecular mechanisms that support a potential benefit of midostaurin as a maintenance therapy in FLT3-mutated AML, by regulating the microenvironment. The obtained results are backed up using independent gene expression data.

Competitive inhibition of IL-2/IL-2R has a dual effect on HSC ex vivo expansion and IL-2R (CD25) content

Interleukin-2 (IL-2) and its receptor play a pivotal role in the regulation of immune response and possess both immune-regulatory and immune-stimulatory functions. As a cytokine of lymphoid cells, the role of IL-2 has been revealed in hematopoietic stem cell (HSC) maintenance and proper hematopoiesis. Here, we investigated that small molecule Ro 26-4550 trifluoroacetate (Ro) mediated competitive inhibition of IL-2 and its receptor alpha subunit (IL-2Rα) throughout ex vivo culture. Ro treatment induced murine and human ex vivo expansion of hematopoietic stem and progenitor cells (HSPCs). Ro treated HSPCs sustained self-renewal ability and low apoptotic activity. As a competitive inhibitor of IL-2/IL-2Rα interaction, Ro small molecule induced human HSPCs to entry into cell cycle. The proliferation of bone marrow mesenchymal stem cells (MSC) and fibroblasts were also highly increased post treatment. Besides, Ro treatment enhanced IL-2Rα (CD25) expression independent of IL-2 administration in human mPB-derived HSPCs and BM-derived HSPCs. Increased IL-2Rα (CD25) expression in BM-HSPCs was associated with the increase in the CD4⁺CD25⁺ T cell population. Xenotransplantation of immunodeficient mice with ex vivo expanded human CD34⁺ cells after Ro treatment revealed an efficient multi-lineage reconstitution in the recipient. These findings shed light on the role of IL-2/IL-2Rα interaction in HSC expansion, in vivo and in vitro HSC self-renewal ability and repopulation capacity as well as a possible mean for the induction of CD25 expressing cells in hematopoietic compartments.

Drug Resistance Mechanisms of Acute Myeloid Leukemia Stem Cells

Acute myeloid leukemia (AML) is a polyclonal and heterogeneous hematological malignancy. Relapse and refractory after induction chemotherapy are still challenges for curing AML. Leukemia stem cells (LSCs), accepted to originate from hematopoietic stem/precursor cells, are the main root of leukemogenesis and drug resistance. LSCs are dynamic derivations and possess various elusive resistance mechanisms. In this review, we summarized different primary resistance and remolding mechanisms of LSCs after chemotherapy, as well as the indispensable role of the bone marrow microenvironment on LSCs resistance. Through a detailed and comprehensive review of the spectacle of LSCs resistance, it can provide better strategies for future researches on eradicating LSCs and clinical treatment of AML.

Prioritizing risk genes as novel stratification biomarkers for acute monocytic leukemia by integrative analysis

Acute myeloid leukemia (AML) is a blood cancer with high heterogeneity and stratified as M0-M7 subtypes in the French-American-British (FAB) diagnosis system. Improved diagnosis with leverage of key molecular inputs will assist precisive medicine. Through deep-analyzing the transcriptomic data and mutations of AML, we report that a modern clustering algorithm, t-distributed Stochastic Neighbor Embedding (t-SNE), successfully demarcates M2, M3 and M5 territories while M4 bias to M5 and M0 & M1 bias to M2, consistent with the traditional FAB classification. Combining with mutation profiles, the results show that top recurrent AML mutations were unbiasedly allocated into M2 and M5 territories, indicating the t-SNE instructed transcriptomic stratification profoundly outperforms mutation profiling in the FAB system. Further functional data mining prioritizes several myeloid-specific genes as potential regulators of AML progression and treatment by Venetoclax, a BCL2 inhibitor. Among them two encode membrane proteins, LILRB4 and LRRC25, which could be utilized as cell surface biomarkers for monocytic AML or for innovative immuno-therapy candidates in future. In summary, our deep functional data-mining analysis warrants several unappreciated immune signaling-encoding genes as novel diagnostic biomarkers and potential therapeutic targets.

A multiparametric niche-like drug screening platform in acute myeloid leukemia

Functional precision medicine in AML often relies on short-term in vitro drug sensitivity screening (DSS) of primary patient cells in standard culture conditions. We designed a niche-like DSS assay combining physiologic hypoxia (O₂ 3%) and mesenchymal stromal cell (MSC) co-culture with multiparameter flow cytometry to enumerate lymphocytes and differentiating (CD11/CD14/CD15+) or leukemic stem cell (LSC)-enriched (GPR56+) cells within the leukemic bulk. After functional validation of GPR56 expression as a surrogate for LSC enrichment, the assay identified three patterns of response, including cytotoxicity on blasts sparing LSCs, induction of differentiation, and selective impairment of LSCs. We refined our niche-like culture by including plasma-like amino-acid and cytokine concentrations identified by targeted metabolomics and proteomics of primary AML bone marrow plasma samples. Systematic interrogation revealed distinct contributions of each niche-like component to leukemic outgrowth and drug response. Short-term niche-like culture preserved clonal architecture and transcriptional states of primary leukemic cells. In a cohort of 45 AML samples enriched for NPM1c AML, the niche-like multiparametric assay could predict morphologically (p = 0.02) and molecular (NPM1c MRD, p = 0.04) response to anthracycline-cytarabine induction chemotherapy. In this cohort, a 23-drug screen nominated ruxolitinib as a sensitizer to anthracycline-cytarabine. This finding was validated in an NPM1c PDX model.