Identification of TIM-3 as a Leukemic Stem Cell Surface Molecule in Primary Acute Myeloid Leukemia

Optimization of anti-TIM3 chimeric antigen receptor with CD8α spacer and TNFR-based costimulation for enhanced efficacy in AML therapy

CAR T cell therapy for AML remains limited due to the lack of a proper target without on-target off-tumor toxicity. TIM3 is a promising target due to its high expression on AML cells and absence in most normal hematopoietic cells. Previous reports have shown that each CAR component impacts CAR functionality. Here, we optimized TIM-3 targeting CAR T cells for AML therapy. We generated CARs targeting TIM3 with two different non-signaling domains: an IgG2-CH3 spacer with CD28 transmembrane domain (CH3/CD28) and a CD8α spacer with CD8α transmembrane domain (CD8/CD8), and evaluated their characteristics and function. Incorporating the non-signaling CH3/CD28 domain resulted in unstable CAR expression in anti-TIM3 CAR T cells, leading to lower surface CAR expression over time and reduced cytotoxic function compared to anti-TIM3 CARs with the CD8/CD8 domain. Both types of anti-TIM3 CAR T cells transiently exhibited fratricide, which subsided overtime, and both CAR T cells achieved substantial T cell expansion. To further optimize the design, we explored the effects of different costimulatory domains. Compared with CD28 costimulation, 4-1BB and CD27 combined with a CD8/CD8 non-signaling domain showed higher cytokine secretion, superior antitumor activity, and enhanced T-cell persistence after repeated antigen exposure. These findings emphasize the impact of the optimal design of CAR constructs that provide efficient function. In the context of anti-TIM3 CAR T cells, using a CD8α spacer and transmembrane domain with TNFR-based costimulation is a promising CAR design to improve anti-TIM3 CAR T cell function for AML therapy.

Therapeutic targeting of PARP with immunotherapy in acute myeloid leukemia

Targeting the poly (ADP-ribose) polymerase (PARP) protein has shown therapeutic efficacy in cancers with homologous recombination (HR) deficiency due to BRCA mutations. Only small fraction of acute myeloid leukemia (AML) cells carry BRCA mutations, hence the antitumor efficacy of PARP inhibitors (PARPi) against this malignancy is predicted to be limited; however, recent preclinical studies have demonstrated that PARPi monotherapy has modest efficacy in AML, while in combination with cytotoxic chemotherapy it has remarkable synergistic antitumor effects. Immunotherapy has revolutionized therapeutics in cancer treatment, and PARPi creates an ideal microenvironment for combination therapy with immunomodulatory agents by promoting tumor mutation burden. In this review, we summarize the role of PARP proteins in DNA damage response (DDR) pathways, and discuss recent preclinical studies using synthetic lethal modalities to treat AML. We also review the immunomodulatory effects of PARPi in AML preclinical models and propose future directions for therapy in AML, including combined targeting of the DDR and tumor immune microenvironment; such combination regimens will likely benefit patients with AML undergoing PARPi-mediated cancer therapy.

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.

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.

TP53-mutated acute myeloid leukemia and myelodysplastic syndrome: biology, treatment challenges, and upcoming approaches

Improved understanding of TP53 biology and the clinicopathological features of TP53-mutated myeloid neoplasms has led to the recognition of TP53-mutated acute myeloid leukemia/myelodysplastic syndrome (TP53m AML/MDS) as a unique entity, characterized by dismal outcomes following conventional therapies. Several clinical trials have investigated combinations of emerging therapies for these patients with the poorest molecular prognosis among myeloid neoplasms. Although some emerging therapies have shown improvement in overall response rates, this has not translated into better overall survival, hence the notion that p53 remains an elusive target. New therapeutic strategies, including novel targeted therapies, immune checkpoint inhibitors, and monoclonal antibodies, represent a shift away from cytotoxic and hypomethylating-based therapies, towards approaches combining non-immune and novel immune therapeutic strategies. The triple combination of azacitidine and venetoclax with either magrolimab or eprenetapopt have demonstrated safety in early trials, with phase III trials currently underway, and promising interim clinical results. This review compiles background on TP53 biology, available and emerging therapies along with their mechanisms of action for the TP53m disease entity, current treatment challenges, and recently published data and status of ongoing clinical trials for TP53m AML/MDS.

Beyond T cell exhaustion: TIM-3 regulation of myeloid cells

T cell immunoglobulin and mucin domain-containing protein 3 (TIM-3) is an important immune checkpoint molecule initially identified as a marker of IFN-γ-producing CD4+ and CD8+ T cells. Since then, our understanding of its role in immune responses has significantly expanded. Here, we review emerging evidence demonstrating unexpected roles for TIM-3 as a key regulator of myeloid cell function, in addition to recent work establishing TIM-3 as a delineator of terminal T cell exhaustion, thereby positioning TIM-3 at the interface between fatigued immune responses and reinvigoration. We share our perspective on the antagonism between TIM-3 and T cell stemness, discussing both cell-intrinsic and cell-extrinsic mechanisms underlying this relationship. Looking forward, we discuss approaches to decipher the underlying mechanisms by which TIM-3 regulates stemness, which has remarkable potential for the treatment of cancer, autoimmunity, and autoinflammation.

Relapse of acute myeloid leukemia after allogeneic stem cell transplantation: immune escape mechanisms and current implications for therapy

Acute myeloid leukemia (AML) is a heterogeneous disease characterized by the expansion of immature myeloid cells in the bone marrow (BM) and peripheral blood (PB) resulting in failure of normal hematopoiesis and life-threating cytopenia. Allogeneic hematopoietic stem cell transplantation (allo-HCT) is an established therapy with curative potential. Nevertheless, post-transplant relapse is common and associated with poor prognosis, representing the major cause of death after allo-HCT. The occurrence of relapse after initially successful allo-HCT indicates that the donor immune system is first able to control the leukemia, which at a later stage develops evasion strategies to escape from immune surveillance. In this review we first provide a comprehensive overview of current knowledge regarding immune escape in AML after allo-HCT, including dysregulated HLA, alterations in immune checkpoints and changes leading to an immunosuppressive tumor microenvironment. In the second part, we draw the line from bench to bedside and elucidate to what extend immune escape mechanisms of relapsed AML are yet exploited in treatment strategies. Finally, we give an outlook how new emerging technologies could help to improve the therapy for these patients, and elucidate potential new treatment options.

The role of bone marrow microenvironment (BMM) cells in acute myeloid leukemia (AML) progression: immune checkpoints, metabolic checkpoints, and signaling pathways

Acute myeloid leukemia (AML) comprises a multifarious and heterogeneous array of illnesses characterized by the anomalous proliferation of myeloid cells in the bone marrow microenvironment (BMM). The BMM plays a pivotal role in promoting AML progression, angiogenesis, and metastasis. The immune checkpoints (ICs) and metabolic processes are the key players in this process. In this review, we delineate the metabolic and immune checkpoint characteristics of the AML BMM, with a focus on the roles of BMM cells e.g. tumor-associated macrophages, natural killer cells, dendritic cells, metabolic profiles and related signaling pathways. We also discuss the signaling pathways stimulated in AML cells by BMM factors that lead to AML progression. We then delve into the roles of immune checkpoints in AML angiogenesis, metastasis, and cell proliferation, including co-stimulatory and inhibitory ICs. Lastly, we discuss the potential therapeutic approaches and future directions for AML treatment, emphasizing the potential of targeting metabolic and immune checkpoints in AML BMM as prognostic and therapeutic targets. In conclusion, the modulation of these processes through the use of directed drugs opens up new promising avenues in combating AML. Thereby, a comprehensive elucidation of the significance of these AML BMM cells' metabolic and immune checkpoints and signaling pathways on leukemic cells can be undertaken in the future investigations. Additionally, these checkpoints and cells should be considered plausible multi-targeted therapies for AML in combination with other conventional treatments in AML. Video Abstract.

Immunotherapy in leukaemia

Leukaemia is the common name for a group of malignant diseases of the haematopoietic system with complex classifications and characteristics. Remarkable progress has been made in basic research and preclinical studies for acute leukaemia compared to that of the many other types/subtypes of leukaemia, especially the exploration of the biological basis and application of immunotherapy in acute myeloid leukaemia (AML) and B-cell acute lymphoblastic leukaemia (B-ALL). In this review, we summarize the basic approaches to immunotherapy for leukaemia and focus on the research progress made in immunotherapy development for AML and ALL. Importantly, despite the advances made to date, big challenges still exist in the effectiveness of leukaemia immunotherapy, especially in AML. Therefore, we use AML as an example and summarize the mechanisms of tumour cell immune evasion, describe recently reported data and known therapeutic targets, and discuss the obstacles in finding suitable treatment targets and the results obtained in recent clinical trials for several types of single and combination immunotherapies, such as bispecific antibodies, cell therapies (CAR-T-cell treatment), and checkpoint blockade. Finally, we summarize novel immunotherapy strategies for treating lymphocytic leukaemia and clinical trial results.

Cancer stem cells: an insight into the development of metastatic tumors and therapy resistance

The term "cancer stem cells" (CSCs) refers to cancer cells that exhibit traits parallel to normal stem cells, namely the potential to give rise to every type of cell identified in a tumor microenvironment. It has been found that CSCs usually develops from other neoplastic cells or non-cancerous somatic cells by acquiring stemness and malignant characteristics through particular genetic modifications. A trivial number of CSCs, identified in solid and liquid cancer, can give rise to an entire tumor population with aggressive anticancer drug resistance, metastasis, and invasiveness. Besides, cancer stem cells manipulate their intrinsic and extrinsic features, regulate the metabolic pattern of the cell, adjust efflux-influx efficiency, modulate different signaling pathways, block apoptotic signals, and cause genetic and epigenetic alterations to retain their pluripotency and ability of self-renewal. Notably, to keep the cancer stem cells' ability to become malignant cells, mesenchymal stem cells, tumor-associated fibroblasts, immune cells, etc., interact with one another. Furthermore, CSCs are characterized by the expression of particular molecular markers that carry significant diagnostic and prognostic significance. Because of this, scientific research on CSCs is becoming increasingly imperative, intending to understand the traits and behavior of cancer stem cells and create more potent anticancer therapeutics to fight cancer at the CSC level. In this review, we aimed to elucidate the critical role of CSCs in the onset and spread of cancer and the characteristics of CSCs that promote severe resistance to targeted therapy.

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.

Characterization of sabatolimab, a novel immunotherapy with immuno-myeloid activity directed against TIM-3 receptor

Objectives

Sabatolimab is a humanized monoclonal antibody (hIgG4, S228P) directed against human T-cell immunoglobulin domain and mucin domain-3 (TIM-3). Herein, we describe the development and characterization of sabatolimab.

Methods

Sabatolimab was tested for binding to its target TIM-3 and blocking properties. The functional effects of sabatolimab were tested in T-cell killing and myeloid cell cytokine assays. Antibody-mediated cell phagocytosis (ADCP) by sabatolimab was also assessed.

Results

Sabatolimab was shown to (i) enhance T-cell killing and inflammatory cytokine production by dendritic cells (DCs); (ii) facilitate the phagocytic uptake of TIM-3-expressing target cells; and (iii) block the interaction between TIM-3 and its ligands PtdSer/galectin-9.

Conclusion

Taken together, our results support both direct anti-leukemic effects and immune-mediated modulation by sabatolimab, reinforcing the notion that sabatolimab represents a novel immunotherapy with immuno-myeloid activity, holding promise for the treatment of myeloid cell neoplasms.

Catch me if you can: how AML and its niche escape immunotherapy

In spite of the remarkable progress in basic and preclinical studies of acute myeloid leukemia (AML), the five-year survival rate of AML patients remains poor, highlighting the urgent need for novel and synergistic therapies. Over the past decade, increased attention has been focused on identifying suitable immunotherapeutic strategies for AML, and in particular on targeting leukemic cells and their progenitors. However, recent studies have also underlined the important contribution of the leukemic microenvironment in facilitating tumor escape mechanisms leading to disease recurrence. Here, we describe the immunological features of the AML niche, with particular attention to the crosstalk between the AML blasts and the cellular components of the altered tumor microenvironment (TME) and the mechanisms of immune escape that hamper the therapeutic effects of the most advanced treatments. Considering the AML complexity, immunotherapy approaches may benefit from a rational combination of complementary strategies aimed at preventing escape mechanisms without increasing toxicity.

Modulation of the Gal-9/TIM-3 Immune Checkpoint with α-Lactose. Does Anomery of Lactose Matter?

Simple Summary

The disaccharide lactose is a common excipient in pharmaceutical products. In addition, the two anomers α- and β-lactose can exert immuno-modulatory effects. α-Lactose functions as a major regulator of the T-cell immunoglobulin mucin-3 (Tim-3)/Galectin-9 (Gal-9) immune checkpoint, through direct binding to the β-galactoside-binding lectin galectin-9. The blockade of TIM-3 with monoclonal antibodies or small molecules represents a promising approach to combat onco-hematological diseases, in particular myelodysplastic syndromes, and acute myeloid leukemia. Alternatively, the activity of the checkpoint can be modulated via targeting of Gal-9 with both α- and β-lactose. In fact, lactose is a quasi-pan-galectin ligand, capable of modulating the functions of most of the 16 galectin molecules. This review discusses the capacity of lactose and Gal-9 to modulate the TIM-3/Gal-9 and PD-1/PD-L1 immune checkpoints in oncology. The immuno-regulatory roles of lactose and Gal-9 are highlighted.

Abstract

The disaccharide lactose is an excipient commonly used in pharmaceutical products. The two anomers, α- and β-lactose (α-L/β-L), differ by the orientation of the C-1 hydroxyl group on the glucose unit. In aqueous solution, a mutarotation process leads to an equilibrium of about 40% α-L and 60% β-L at room temperature. Beyond a pharmaceutical excipient in solid products, α-L has immuno-modulatory effects and functions as a major regulator of TIM-3/Gal-9 immune checkpoint, through direct binding to the β-galactoside-binding lectin galectin-9. The blockade of the co-inhibitory checkpoint TIM-3 expressed on T cells with anti-TIM-3 antibodies represents a promising approach to combat different onco-hematological diseases, in particular myelodysplastic syndromes and acute myeloid leukemia. In parallel, the discovery and development of anti-TIM-3 small molecule ligands is emerging, including peptides, RNA aptamers and a few specifically designed heterocyclic molecules. An alternative option consists of targeting the different ligands of TIM-3, notably Gal-9 recognized by α-lactose. Modulation of the TIM-3/Gal-9 checkpoint can be achieved with both α- and β-lactose. Moreover, lactose is a quasi-pan-galectin ligand, capable of modulating the functions of most of the 16 galectin molecules. The present review provides a complete analysis of the pharmaceutical and galectin-related biological functions of (α/β)-lactose. A focus is made on the capacity of lactose and Gal-9 to modulate both the TIM-3/Gal-9 and PD-1/PD-L1 immune checkpoints in oncology. Modulation of the TIM-3/Gal-9 checkpoint is a promising approach for the treatment of cancers and the role of lactose in this context is discussed. The review highlights the immuno-regulatory functions of lactose, and the benefit of the molecule well beyond its use as a pharmaceutical excipient.

Prognostic significance of TIM-3 expression pattern at diagnosis in patients with t(8;21) acute myeloid leukemia

Acute myeloid leukemia (AML) with t(8;21) is a heterogeneous disease and needs to be stratified. Both, cancer cells and immune cells participate in tumor initiation, growth and progression and might affect clinical outcomes. TIM-3 (T cell immunoglobulin and mucin domain-containing protein 3), an immune checkpoint molecule, is expressed not only on immune cells but also on leukemic stem cells (LSCs) in AML. This prompted us to investigate the prognostic significance of TIM-3 in t(8;21) AML. A total of 47 t(8;21) AML patients were tested for TIM-3 expression by multi-parameter flow cytometry at diagnosis. 35 of these, who received chemotherapy alone or along with allogeneic hematopoietic stem cell transplantation were followed up. The expression pattern of TIM-3 on T-cells and NK (natural killer) cells as a whole (T + NK) and LSCs were evaluated independently. High percentage of T + NK - TIM-3⁺ and CD34⁺CD38^-TIM-3⁺ cells were significantly associated with a high 2-year cumulative incidence of relapse (CIR) (p = 0.028, 0.016). Further, concurrent high frequencies of T + NK-TIM-3⁺ and CD34⁺CD38^-TIM-3⁺ cells at diagnosis were significantly associated with a high 2-year CIR (p < 0.0001) and this together with c-KIT D816 mutation were the independent adverse prognostic factors for relapse (hazard ratio (HR)=2.5, [95% confidence interval (CI), 1.1-6.0], p = 0.04; HR = 46.5, [95% CI, 2.7-811.5], p = 0.009). In conclusion, the expression pattern of TIM-3 on both T and NK cells and LSCs at diagnosis had prognostic significance in t (8;21) AML.

One Stone, Two Birds: The Roles of Tim-3 in Acute Myeloid Leukemia

T cell immunoglobulin and mucin protein 3 (Tim-3) is an immune checkpoint and plays a vital role in immune responses during acute myeloid leukemia (AML). Targeting Tim-3 kills two birds with one stone by balancing the immune system and eliminating leukemia stem cells (LSCs) in AML. These functions make Tim-3 a potential target for curing AML. This review mainly discusses the roles of Tim-3 in the immune system in AML and as an AML LSC marker, which sheds new light on the role of Tim-3 in AML immunotherapy.

Mitochondrial and Metabolic Pathways Regulate Nuclear Gene Expression to Control Differentiation, Stem Cell Function, and Immune Response in Leukemia

Mitochondria are involved in many biological processes including cellular homeostasis, energy generation, and apoptosis. Moreover, mitochondrial and metabolic pathways are interconnected with gene expression to regulate cellular functions such as cell growth, survival, differentiation, and immune recognition. Metabolites and mitochondrial enzymes regulate chromatin-modifying enzymes, chromatin remodeling, and transcription regulators. Deregulation of mitochondrial pathways and metabolism leads to alterations in gene expression that promote cancer development, progression, and evasion of the immune system. This review highlights how mitochondrial and metabolic pathways function as a central mediator to control gene expression, specifically on stem cell functions, differentiation, and immune response in leukemia. SIGNIFICANCE: Emerging evidence demonstrates that mitochondrial and metabolic pathways influence gene expression to promote tumor development, progression, and immune evasion. These data highlight new areas of cancer biology and potential new therapeutic strategies.

TIM-3 pathway dysregulation and targeting in cancer

INTRODUCTION

Dysfunction of the immune system is a hallmark of cancer. Through increased understanding of the complex interactions between immunity and cancer, immunotherapy has emerged as a treatment modality for different types of cancer. Promising activity with immunotherapy has been reported in numerous malignancies, but challenges such as limited response rates and treatment resistance remain. Furthermore, outcomes with this therapeutic approach in hematologic malignancies are even more limited than in solid tumors. T-cell immunoglobulin domain and mucin domain 3 (TIM-3) has emerged as a potential immune checkpoint target in both solid tumors and hematologic malignancies. TIM-3 has been shown to promote immune tolerance, and overexpression of TIM-3 is associated with more aggressive or advanced disease and poor prognosis.

AREAS COVERED

This review examines what is currently known regarding the biology of TIM-3 and clinical implications of targeting TIM-3 in cancer. Particular focus is given to myeloid malignancies.

EXPERT OPINION

The targeting of TIM-3 is a promising therapeutic approach in cancers, including hematologic cancers such as myeloid malignancies which have not benefited much from current immunotherapeutic treatment approaches. We anticipate that with further clinical evaluation, TIM-3 blockade will emerge as an important treatment strategy in myeloid malignancies.

Targeting novel inhibitory receptors in cancer immunotherapy

T cells play a critical role in promoting tumor regression in both experimental models and humans. Yet, T cells that are chronically exposed to tumor antigen during cancer progression can become dysfunctional/exhausted and fail to induce tumor destruction. Such tumor-induced T cell dysfunction may occur via multiple mechanisms. In particular, immune checkpoint inhibitory receptors that are upregulated by tumor-infiltrating lymphocytes in many cancers limit T cell survival and function. Overcoming this inhibitory receptor-mediated T cell dysfunction has been a central focus of recent developments in cancer immunotherapy. Immunotherapies targeting inhibitory receptor pathways such as programmed cell death 1 (PD-1)/programmed death ligand 1 and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), alone or in combination, confer significant clinical benefits in multiple tumor types. However, many patients with cancer do not respond to immune checkpoint blockade, and dual PD-1/CTLA-4 blockade may cause serious adverse events, which limits its indications. Targeting novel non-redundant inhibitory receptor pathways contributing to tumor-induced T cell dysfunction in the tumor microenvironment may prove efficacious and non-toxic. This review presents preclinical and clinical findings supporting the roles of two key pathways-T-cell immunoglobulin and mucin-domain containing-3 (TIM-3) and T cell immunoreceptor with Ig and ITIM domain (TIGIT)/CD226/CD96/CD112R-in cancer immunotherapy.

Cancer Stem Cells-Origins and Biomarkers: Perspectives for Targeted Personalized Therapies

The use of biomarkers in diagnosis, therapy and prognosis has gained increasing interest over the last decades. In particular, the analysis of biomarkers in cancer patients within the pre- and post-therapeutic period is required to identify several types of cells, which carry a risk for a disease progression and subsequent post-therapeutic relapse. Cancer stem cells (CSCs) are a subpopulation of tumor cells that can drive tumor initiation and can cause relapses. At the time point of tumor initiation, CSCs originate from either differentiated cells or adult tissue resident stem cells. Due to their importance, several biomarkers that characterize CSCs have been identified and correlated to diagnosis, therapy and prognosis. However, CSCs have been shown to display a high plasticity, which changes their phenotypic and functional appearance. Such changes are induced by chemo- and radiotherapeutics as well as senescent tumor cells, which cause alterations in the tumor microenvironment. Induction of senescence causes tumor shrinkage by modulating an anti-tumorigenic environment in which tumor cells undergo growth arrest and immune cells are attracted. Besides these positive effects after therapy, senescence can also have negative effects displayed post-therapeutically. These unfavorable effects can directly promote cancer stemness by increasing CSC plasticity phenotypes, by activating stemness pathways in non-CSCs, as well as by promoting senescence escape and subsequent activation of stemness pathways. At the end, all these effects can lead to tumor relapse and metastasis. This review provides an overview of the most frequently used CSC markers and their implementation as biomarkers by focussing on deadliest solid (lung, stomach, liver, breast and colorectal cancers) and hematological (acute myeloid leukemia, chronic myeloid leukemia) cancers. Furthermore, it gives examples on how the CSC markers might be influenced by therapeutics, such as chemo- and radiotherapy, and the tumor microenvironment. It points out, that it is crucial to identify and monitor residual CSCs, senescent tumor cells, and the pro-tumorigenic senescence-associated secretory phenotype in a therapy follow-up using specific biomarkers. As a future perspective, a targeted immune-mediated strategy using chimeric antigen receptor based approaches for the removal of remaining chemotherapy-resistant cells as well as CSCs in a personalized therapeutic approach are discussed.

Finding new lanes: Chimeric antigen receptor (CAR) T-cells for myeloid leukemia

BACKGROUND

Myeloid leukemia represents a heterogeneous group of cancers of blood and bone marrow which arise from clonal expansion of hematopoietic myeloid lineage cells. Acute myeloid leukemia (AML) has traditionally been treated with multi-agent chemotherapy, but conventional therapies have not improved the long-term survival for decades. Chronic myeloid leukemia (CML) is an indolent disease which requires lifelong treatment, is associated with significant side effects, and carries a risk of progression to potentially lethal blast crises.

RECENT FINDINGS

Recent advances in molecular biology, virology, and immunology have enabled researchers to grow and modify T lymphocytes ex-vivo. Chimeric antigen receptor (CAR) T-cell therapy has been shown to specifically target cells of lymphoid lineage and induce remission in acute lymphoblastic leukemia (ALL) patients. While the success of CAR T-cells against ALL is considered a defining moment in modern oncology, similar efficacy against myeloid leukemia cells remains elusive. Over the past 10 years, numerous CAR T-cells have been developed that can target novel myeloid antigens, and many clinical trials are finally starting to yield encouraging results. In this review, we present the recent advances in this field and discuss strategies for future development of myeloid targeting CAR T-cell therapy.

CONCLUSIONS

The field of CAR T-cell therapy has rapidly evolved over the past few years. It represents a radically new approach towards cancers, and with continued refinement it may become a viable therapeutic option for patients of acute and chronic myeloid leukemia.

Pre-transplant sTIM-3 levels may have a predictive impact on transplant outcome in acute leukemia patients

Objectives: T-cell immunoglobulin and mucin domain-containing protein-3 (TIM-3) is considered as a negative regulator of T-cell driven immune response. This study is planned to investigate the prognostic role of pre-transplant soluble TIM-3 (sTIM-3) levels in allogeneic hematopoietic stem cell transplantation (allo-HSCT) recipients. Methods: Pre-transplant serum sTIM-3 levels were measured in 177 allo-HSCT recipients [median age: 36(16-66) years; male/female: 111/66]. Results: Pre-transplant sTIM-3 levels were significantly higher in acute myeloid leukemia (AML) patients compared to acute lymphoblastic leukemia (ALL) patients (p = 0.01). Pre-transplant sTIM-3 levels were significantly lower in patients with abnormal cytogenetics (p = 0.017). Pre-transplant sTIM-3 levels were significantly higher in patients who developed viral hemorrhagic cystitis (p = 0.034). A positive correlation was demonstrated between sTIM-3 levels and acute graft versus host disease (GvHD) grade (p = 0.013; r = 0.299). Overall survival (OS) was not statistically different between low- and high-TIM-3 groups (%35.2 vs %20.4; p > 0.05). Primary diagnosis (p = 0.042), sinusoidal obstruction syndrome (p < 0.001), acute GvHD (p = 0.001), chronic GvHD (p = 0.009) and post-transplant relapse (p = 0.003) represented significant impact on OS. Discussion: Increased sTIM-3 levels in AML patients seem to be compatible with the previous reports. The inhibitor role of TIM-3 in cellular immune response may be a possible explanation for the association of sTIM-3 with viral infections and GvHD. However, the main challenge remains to be the ambiguous association of pre-transplant sTIM-3 levels and post-transplant complications, as allo-HSCT recipients are expected to represent donor genetic features in the post-transplant setting. Conclusion: Further studies are warranted to clarify the particular role of sTIM-3 in the allo-HSCT setting.

TIM3 comes of age as an inhibitory receptor

T cell immunoglobulin and mucin domain-containing protein 3 (TIM3), a member of the TIM family, was originally identified as a receptor expressed on interferon-γ-producing CD4⁺ and CD8⁺ T cells. Initial data indicated that TIM3 functioned as a 'co-inhibitory' or 'checkpoint' receptor, but due to the lack of a definable inhibitory signalling motif, it was also suggested that TIM3 might act as a co-stimulatory receptor. Recent studies have shown that TIM3 is part of a module that contains multiple co-inhibitory receptors (checkpoint receptors), which are co-expressed and co-regulated on dysfunctional or 'exhausted' T cells in chronic viral infections and cancer. Furthermore, co-blockade of TIM3 and programmed cell death 1 (PD1) can result in tumour regression in preclinical models and can improve anticancer T cell responses in patients with advanced cancers. Here, we highlight the developments in understanding TIM3 biology, including novel ligand identification and the discovery of loss-of-function mutations associated with human disease. In addition, we summarize emerging data from human clinical trials showing that TIM3 indeed acts as a 'checkpoint' receptor and that inhibition of TIM3 enhances the antitumour effect of PD1 blockade.

Unraveling the journey of cancer stem cells from origin to metastasis

Cancer biology research over recent decades has given ample evidence for the existence of self-renewing and drug-resistant populations within heterogeneous tumors, widely recognized as cancer stem cells (CSCs). However, a lack of clear understanding about the origin, existence, maintenance, and metastatic roles of CSCs limit efforts towards the development of CSC-targeted therapy. In this review, we describe novel avenues of current CSC biology. In addition to cell fusion and horizontal gene transfer, CSCs are originated by mutations in somatic or differentiated cancer cells, resulting in de-differentiation and reprogramming. Recent studies also provided evidence for the existence of distinct or heterogeneous CSC populations within a single heterogeneous tumor. Our analysis of the literature also opens the doors for a novel hypothesis that CSC populations with specific phenotypes, metabolic profiles, and clonogenic potential metastasize to specific organs.

Evaluation of the effect of TIM-3 suppression by miR-498 and its effect on apoptosis and proliferation rate of HL-60 cell line

BACKGROUND

Acute Myeloid Leukemia (AML) is a Cancer of hematopoietic stem cells with a rapid progression. TIM-3 is expressed on leukemic stem cells (LSCs) in most types of AML and might have a positive effect on maintenance of malignant phenotype. MicroRNAs play important roles in either cancer progression or suppression. In this study were evaluated, the inhibitory effect of miR-498 on TIM-3 expression and its impact on proliferation and survival of HL-60 cell line.

METHODS

Firstly, the probable inhibitory effect of miR-498 on TIM-3 expression was predicted. HL-60 cells were cultured and expression of TIM-3 was induced on the cells using phorbol miristate acetate. The cells were transfected with miR-498 and expression level of TIM-3 were measured using with q-RT-PCR and flow cytometry methods. In addition, the effect of suppression of TIM-3 expression in HL-60 cell line was analyzed with apoptosis and cell proliferation assays.

RESULTS

Bioinformatics analyses predicted that miR-498 has high ability to silence TIM-3 gene expression. Our experiments confirmed that miR-498 was able to strongly silence TIM-3 expression (68% silencing) in HL-60 cell line (P < 0.002). Also, the cells with suppressed expression of TIM-3 had a lower proliferation and higher apoptosis rates.

CONCLUSION

Based on our results, the miR-498 can effectively suppress TIM-3 expression in the AML cell line. TIM-3 suppression, in turn, inhibits malignant cell proliferation and induces its apoptosis. Collectively, suppression of TIM-3 by miR-498 can be considered as a potential powerful way for treatment of AML.

Coexpression profile of leukemic stem cell markers for combinatorial targeted therapy in AML

Targeted immunotherapy in acute myeloid leukemia (AML) is challenged by the lack of AML-specific target antigens and clonal heterogeneity, leading to unwanted on-target off-leukemia toxicity and risk of relapse from minor clones. We hypothesize that combinatorial targeting of AML cells can enhance therapeutic efficacy without increasing toxicity. To identify target antigen combinations specific for AML and leukemic stem cells, we generated a detailed protein expression profile based on flow cytometry of primary AML (n = 356) and normal bone marrow samples (n = 34), and a recently reported integrated normal tissue proteomic data set. We analyzed antigen expression levels of CD33, CD123, CLL1, TIM3, CD244 and CD7 on AML bulk and leukemic stem cells at initial diagnosis (n = 302) and relapse (n = 54). CD33, CD123, CLL1, TIM3 and CD244 were ubiquitously expressed on AML bulk cells at initial diagnosis and relapse, irrespective of genetic characteristics. For each analyzed target, we found additional expression in different populations of normal hematopoiesis. Analyzing the coexpression of our six targets in all dual combinations (n = 15), we found CD33/TIM3 and CLL1/TIM3 to be highly positive in AML compared with normal hematopoiesis and non-hematopoietic tissues. Our findings indicate that combinatorial targeting of CD33/TIM3 or CLL1/TIM3 may enhance therapeutic efficacy without aggravating toxicity in immunotherapy of AML.

Flow Cytometry to Estimate Leukemia Stem Cells in Primary Acute Myeloid Leukemia and in Patient-derived-xenografts, at Diagnosis and Follow Up

Acute myeloid leukemia (AML) is a heterogeneous, and if not treated, fatal disease. It is the most common cause of leukemia-associated mortality in adults. Initially, AML is a disease of hematopoietic stem cells (HSC) characterized by arrest of differentiation, subsequent accumulation of leukemia blast cells, and reduced production of functional hematopoietic elements. Heterogeneity extends to the presence of leukemia stem cells (LSC), with this dynamic cell compartment evolving to overcome various selection pressures imposed upon during leukemia progression and treatment. To further define the LSC population, the addition of CD90 and CD45RA allows the discrimination of normal HSCs and multipotent progenitors within the CD34+CD38- cell compartment. Here, we outline a protocol to detect simultaneous expression of several putative LSC markers (CD34, CD38, CD45RA, CD90) on primary blast cells of human AML by multiparametric flow cytometry. Furthermore, we show how to quantify three progenitor populations and a putative LSC population with increasing degree of maturation. We confirmed the presence of these populations in corresponding patient-derived-xenografts. This method of detection and quantification of putative LSC may be used for clinical follow-up of chemotherapy response (i.e., minimal residual disease), as residual LSC may cause AML relapse.

Chimeric antigen receptors for adoptive T cell therapy in acute myeloid leukemia

Currently, conventional therapies for acute myeloid leukemia (AML) have high failure and relapse rates. Thus, developing new strategies is crucial for improving the treatment of AML. With the clinical success of anti-CD19 chimeric antigen receptor (CAR) T cell therapies against B-lineage malignancies, many studies have attempted to translate the success of CAR T cell therapy to other malignancies, including AML. This review summarizes the current advances in CAR T cell therapy against AML, including preclinical studies and clinical trials, and discusses the potential AML-associated surface markers that could be used for further CAR technology. Finally, we describe strategies that might address the current issues of employing CAR T cell therapy in AML.

Live kinase B1 maintains CD34+CD38- AML cell proliferation and self-renewal

Live kinase B1 (LKB1) has been recognized as a tumor suppressor in many human cancers; however, LKB1 maintains self-renewal of hematopoietic stem cells (HSCs). The existence of leukemia stem cells (LSCs) is responsible for drug resistance and leukemia relapse. In acute myeloid leukemia (AML), CD34⁺CD38^- fraction is the most enriched compartment for LSCs. We found that LKB1 was upregulated in CD34⁺CD38^- AML cells. LKB1 downregulation suppressed the long-term proliferation of CD34⁺CD38^- AML cells, induced CD34⁺CD38^- AML cells into G2/M phase, and enhanced the sensitivity of CD34⁺CD38^- AML cells to chemotherapy. Furthermore, LKB1 downregulation in CD34⁺CD38^- AML cells inhibited tumor formation in NOD-SCID mice. Downregulation of LKB1 gene makes LSCs partly loose the characters as stem cells. Gene expression microarray showed that MAPK/ERK pathway was implicated in the regulation of CD34⁺CD38^- AML cell proliferation by LKB1. Together, these findings demonstrate that LKB1 plays an important role in the maintenance of LSCs, which may be responsible for drug resistance and AML relapse.

Leukemic stem cells: identification and clinical application

Leukemic stem cells (LSCs) in acute myeloid leukemia (AML) represent a low-frequency subpopulation of leukemia cells that possess stem cell properties distinct from the bulk leukemia cells, including self-renewal capacity and drug resistance. Due to these properties, LSCs are supposed to facilitate the development of relapse. The existence of LSCs is demonstrated by the ability to engraft and initiate human AML in immune-compromised mouse models. Although several lines of evidence suggest the complex heterogeneity of phenotypes displayed by LSC, many studies consider the CD34+/CD38- compartment as the most relevant. To increase the understanding of the true LSC, techniques such as multicolor flow cytometry, side-population assay and ALDH assay are utilized in many laboratories and could aid in this. A better understanding of different LSC phenotypes is necessary to enhance risk group classification, guide clinical decision-making and to identify new therapeutic targets. These efforts to eliminate LSC should ultimately improve the dismal AML outcome by preventing relapse development.

The immune receptor Tim-3 acts as a trafficker in a Tim-3/galectin-9 autocrine loop in human myeloid leukemia cells

The immune receptor Tim-3 is often highly expressed in human acute myeloid leukemia (AML) cells where it acts as a growth factor and inflammatory receptor. Recently, it has been demonstrated that Tim-3 forms an autocrine loop with its natural ligand galectin-9 in human AML cells. However, the pathophysiological functions of Tim-3 in human AML cells remain unclear. Here, we report for the first time that Tim-3 is required for galectin-9 secretion in human AML cells. However, this effect is cell-type specific and was found so far to be applicable only to myeloid (and not, for example, lymphoid) leukemia cells. We concluded that AML cells might use Tim-3 as a trafficker for the secretion of galectin-9 which can then be possibly used to impair the anticancer activities of cytotoxic T cells and natural killer (NK) cells.