Hematopoietic stem cell and progenitor cell mechanisms in myelodysplastic syndromes

Targeting PD-1/PD-L1 pathway in myelodysplastic syndromes and acute myeloid leukemia

Myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) are clonal hematopoietic stem cell diseases arising from the bone marrow (BM), and approximately 30% of MDS eventually progress to AML, associated with increasingly aggressive neoplastic hematopoietic clones and poor survival. Dysregulated immune microenvironment has been recognized as a key pathogenic driver of MDS and AML, causing high rate of intramedullary apoptosis in lower-risk MDS to immunosuppression in higher-risk MDS and AML. Immune checkpoint molecules, including programmed cell death-1 (PD-1) and programmed cell death ligand-1 (PD-L1), play important roles in oncogenesis by maintaining an immunosuppressive tumor microenvironment. Recently, both molecules have been examined in MDS and AML. Abnormal inflammatory signaling, genetic and/or epigenetic alterations, interactions between cells, and treatment of patients all have been involved in dysregulating PD-1/PD-L1 signaling in these two diseases. Furthermore, with the PD-1/PD-L1 pathway activated in immune microenvironment, the milieu of BM shift to immunosuppressive, contributing to a clonal evolution of blasts. Nevertheless, numerous preclinical studies have suggested a potential response of patients to PD-1/PD-L1 blocker. Current clinical trials employing these drugs in MDS and AML have reported mixed clinical responses. In this paper, we focus on the recent preclinical advances of the PD-1/PD-L1 signaling in MDS and AML, and available and ongoing outcomes of PD-1/PD-L1 inhibitor in patients. We also discuss the novel PD-1/PD-L1 blocker-based immunotherapeutic strategies and challenges, including identifying reliable biomarkers, determining settings, and exploring optimal combination therapies.

NPM1 ablation induces HSC aging and inflammation to develop myelodysplastic syndrome exacerbated by p53 loss

Myelodysplastic syndrome (MDS) is characterized by ineffective hematopoiesis with morphologic dysplasia and a propensity to transform into overt acute myeloid leukemia (AML). Our analysis of two cohorts of 20 MDS and 49 AML with multi-lineage dysplasia patients shows a reduction in Nucleophosmin 1 (NPM1) expression in 70% and 90% of cases, respectively. A mouse model of Npm1 conditional knockout (cKO) in hematopoietic cells reveals that Npm1 loss causes premature aging of hematopoietic stem cells (HSCs). Mitochondrial activation in Npm1-deficient HSCs leads to aberrant activation of the NLRP3 inflammasome, which correlates with a developing MDS-like phenotype. Npm1 cKO mice exhibit shortened survival times, and expansion of both the intra- and extra-medullary myeloid populations, while evoking a p53-dependent response. After transfer into a p53 mutant background, the resulting Npm1/p53 double KO mice develop fatal leukemia within 6 months. Our findings identify NPM1 as a regulator of HSC aging and inflammation and highlight the role of p53 in MDS progression to leukemia.

Clonal Expansion of Stem/Progenitor Cells in Cancer, Fibrotic Diseases, and Atherosclerosis, and CD47 Protection of Pathogenic Cells

We proposed and demonstrated that myelogenous leukemia has a preleukemic phase. In the premalignant phase, normal hematopoietic stem cells (HSCs) gradually accumulate mutations leading to HSC clonal expansion, resulting in the emergence of leukemic stem cells (LSCs). Here, we show that preleukemic HSCs are the basis of clonal hematopoiesis, as well as late-onset blood diseases (chronic-phase chronic myeloid leukemia, myeloproliferative neoplasms, and myelodysplastic disease). The clones at some point each trigger surface expression of "eat me" signals for macrophages, and in the clones and their LSC progeny, this is countered by upregulation of "don't eat me" signals for macrophages such as CD47,opening the possibility of CD47-based therapies. We include evidence that similar processes result in fibroblast expansion in a variety of fibrotic diseases, and arterial smooth muscle clonal expansion is a basis of atherosclerosis, including upregulation of both "eat me" and "don't eat me" molecules on the pathogenic cells.

Emilin-2 is a component of bone marrow extracellular matrix regulating mesenchymal stem cell differentiation and hematopoietic progenitors

Background

Dissection of mechanisms involved in the regulation of bone marrow microenvironment through cell–cell and cell–matrix contacts is essential for the detailed understanding of processes underlying bone marrow activities both under physiological conditions and in hematologic malignancies. Here we describe Emilin-2 as an abundant extracellular matrix component of bone marrow stroma.

Methods

Immunodetection of Emilin-2 was performed in bone marrow sections of mice from 30 days to 6 months of age. Emilin-2 expression was monitored in vitro in primary and mesenchymal stem cell lines under undifferentiated and adipogenic conditions. Hematopoietic stem cells and progenitors in bone marrow of 3- to 10-month-old wild-type and Emilin-2 null mice were analyzed by flow cytometry.

Results

Emilin-2 is deposited in bone marrow extracellular matrix in an age-dependent manner, forming a meshwork that extends from compact bone boundaries to the central trabecular regions. Emilin-2 is expressed and secreted by both primary and immortalized bone marrow mesenchymal stem cells, exerting an inhibitory action in adipogenic differentiation. In vivo Emilin-2 deficiency impairs the frequency of hematopoietic stem/progenitor cells in bone marrow during aging.

Conclusion

Our data provide new insights in the contribution of bone marrow extracellular matrix microenvironment in the regulation of stem cell niches and hematopoietic progenitor differentiation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02674-2.

LC3-associated phagocytosis in bone marrow macrophages suppresses acute myeloid leukemia progression through STING activation

The bone marrow (BM) microenvironment regulates acute myeloid leukemia (AML) initiation, proliferation, and chemotherapy resistance. Following cancer cell death, a growing body of evidence suggests an important role for remaining apoptotic debris in regulating the immunologic response to and growth of solid tumors. Here, we investigated the role of macrophage LC3–associated phagocytosis (LAP) within the BM microenvironment of AML. Depletion of BM macrophages (BMMs) increased AML growth in vivo. We show that LAP is the predominate method of BMM phagocytosis of dead and dying cells in the AML microenvironment. Targeted inhibition of LAP led to the accumulation of apoptotic cells (ACs) and apoptotic bodies (ABs), resulting in accelerated leukemia growth. Mechanistically, LAP of AML-derived ABs by BMMs resulted in stimulator of IFN genes (STING) pathway activation. We found that AML-derived mitochondrial damage–associated molecular patterns were processed by BMMs via LAP. Moreover, depletion of mitochondrial DNA (mtDNA) in AML-derived ABs showed that it was this mtDNA that was responsible for the induction of STING signaling in BMMs. Phenotypically, we found that STING activation suppressed AML growth through a mechanism related to increased phagocytosis. In summary, we report that macrophage LAP of apoptotic debris in the AML BM microenvironment suppressed tumor growth.

Targeting the cluster of differentiation 47/signal-regulatory protein alpha axis in myeloid malignancies

PURPOSE OF REVIEW

The antitumor activity of macrophages is regulated by a balance of prophagocytic and antiphagocytic signals. Cluster of differentiation 47 (CD47), the dominant macrophage immune checkpoint ('do not eat me' signal), interacts with its receptor signal-regulatory protein alpha (SIRPα) to suppress phagocytic activities. This axis plays a pivotal role in immune evasion in myeloid malignancies as well as multiple cancers providing strong rationale for therapeutic exploitation.

RECENT FINDINGS

Preclinical studies have revealed overexpression of CD47 on leukemic stem cells and myeloblasts from patients with myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML), which contributes to immune surveillance evasion and is associated with poor outcomes. Blockade of CD47 with different approaches has demonstrated proof-of-concept antitumor activities mainly through phagocytic clearance. Early phase clinical trials combining the anti-CD47 mAb magrolimab with the hypomethylating agent azacitidine have showed synergistic activities, deep and durable responses, as well as a tolerable safety profile in these patients, including those with TP53 mutations.

SUMMARY

Targeting CD47/SIRPα axis, in combination with other therapeutic agents, represents a promising treatment approach for patients with myeloid malignancies, particularly the challenging TP53-mutated subgroup.

Bone marrow endothelial dysfunction promotes myeloid cell expansion in cardiovascular disease

Abnormal hematopoiesis advances cardiovascular disease by generating excess inflammatory leukocytes that attack the arteries and the heart. The bone marrow niche regulates hematopoietic stem cell proliferation and hence the systemic leukocyte pool, but whether cardiovascular disease affects the hematopoietic organ's microvasculature is unknown. Here we show that hypertension, atherosclerosis and myocardial infarction (MI) instigate endothelial dysfunction, leakage, vascular fibrosis and angiogenesis in the bone marrow, altogether leading to overproduction of inflammatory myeloid cells and systemic leukocytosis. Limiting angiogenesis with endothelial deletion of Vegfr2 (encoding vascular endothelial growth factor (VEGF) receptor 2) curbed emergency hematopoiesis after MI. We noted that bone marrow endothelial cells assumed inflammatory transcriptional phenotypes in all examined stages of cardiovascular disease. Endothelial deletion of Il6 or Vcan (encoding versican), genes shown to be highly expressed in mice with atherosclerosis or MI, reduced hematopoiesis and systemic myeloid cell numbers in these conditions. Our findings establish that cardiovascular disease remodels the vascular bone marrow niche, stimulating hematopoiesis and production of inflammatory leukocytes.

Immune-Based Therapeutic Strategies for Acute Myeloid Leukemia

Simple Summary

This review summarizes various therapeutic immune approaches representing their targets, the efficacy and toxicity in the treatment of acute myeloid leukemia. In particular, immune checkpoint inhibitors, bispecific T-cell engager antibodies and chimeric antigen receptor-T-cell approaches are highlighted.

Abstract

The development and design of immune-based strategies have become an increasingly important topic during the last few years in acute myeloid leukemia (AML), based on successful immunotherapies in solid cancer. The spectrum ranges from antibody drug conjugates, immune checkpoint inhibitors blocking programmed cell death protein 1 (PD1), cytotoxic T lymphocyte antigen 4 (CTLA4) or T cell immunoglobulin and mucin domain containing-3 (TIM3), to T-cell based monoclonal and bispecific T-cell engager antibodies, chimeric antigen receptor-T-cell (CAR-T) approaches and leukemia vaccines. Currently, there are many substances in development and multiple phase I/II studies are ongoing. These trials will help us to deepen our understanding of the pathogenesis of AML and facilitate the best immunotherapeutic strategy in AML. We discuss here the mode of action of immune-based therapies and provide an overview of the available data.

Why Single-Cell Sequencing Has Promise in MDS

Myelodysplastic syndromes (MDS) are a heterogeneous group of diseases characterized by ineffective hematopoiesis. The risk of MDS is associated with aging and the accumulation of somatic mutations in hematopoietic stem cells and progenitors (HSPC). While advances in DNA sequencing in the past decade unveiled clonal selection driven by mutations in MDS, it is unclear at which stage the HSPCs are trapped or what prevents mature cells output. Single-cell-sequencing techniques in recent years have revolutionized our understanding of normal hematopoiesis by identifying the transitional cell states between classical hematopoietic hierarchy stages, and most importantly the biological activities behind cell differentiation and lineage commitment. Emerging studies have adapted these powerful tools to investigate normal hematopoiesis as well as the clonal heterogeneity in myeloid malignancies and provide a progressive description of disease pathogenesis. This review summarizes the potential of growing single-cell-sequencing techniques, the evolving efforts to elucidate hematopoiesis in physiological conditions and MDS at single-cell resolution, and discuss how they may fill the gaps in our current understanding of MDS biology.

Cancer stem cells: advances in biology and clinical translation-a Keystone Symposia report

The test for the cancer stem cell (CSC) hypothesis is to find a target expressed on all, and only CSCs in a patient tumor, then eliminate all cells with that target that eliminates the cancer. That test has not yet been achieved, but CSC diagnostics and targets found on CSCs and some other cells have resulted in a few clinically relevant therapies. However, it has become apparent that eliminating the subset of tumor cells characterized by self-renewal properties is essential for long-term tumor control. CSCs are able to regenerate and initiate tumor growth, recapitulating the heterogeneity present in the tumor before treatment. As great progress has been made in identifying and elucidating the biology of CSCs as well as their interactions with the tumor microenvironment, the time seems ripe for novel therapeutic strategies that target CSCs to find clinical applicability. On May 19-21, 2021, researchers in cancer stem cells met virtually for the Keystone eSymposium "Cancer Stem Cells: Advances in Biology and Clinical Translation" to discuss recent advances in the understanding of CSCs as well as clinical efforts to target these populations.

Intralesional TTI-621, a novel biologic targeting the innate immune checkpoint CD47, in patients with relapsed or refractory mycosis fungoides or Sézary syndrome: a multicentre, phase 1 study

BACKGROUND

Intravenous TTI-621 (SIRPα-IgG1 Fc) was previously shown to have activity in relapsed or refractory haematological malignancies. This phase 1 study evaluated the safety and activity of TTI-621 in patients with percutaneously accessible relapsed or refractory mycosis fungoides, Sézary syndrome, or solid tumours. Here we report the clinical and translational results among patients with mycosis fungoides or Sézary syndrome.

METHODS

This multicentre, open-label, phase 1 study was conducted at five academic health-care and research centres in the USA. Eligible patients were aged 18 years or older; had injectable, histologically or cytologically confirmed relapsed or refractory cutaneous T-cell lymphoma (CTCL) or solid tumours; Eastern Cooperative Oncology Group performance status of 2 or less; and adequate haematological, renal, hepatic, and cardiac function. TTI-621 was injected intralesionally in a sequential dose escalation (cohorts 1-5; single 1 mg, 3 mg, or 10 mg injection or three 10 mg injections weekly for 1 or 2 weeks) and in expansion cohorts (cohorts 6-9; 2 week induction at the maximum tolerated dose; weekly continuation was allowed). In cohort 6, patients were injected with TTI-621 in a single lesion and in cohort 7, they were injected in multiple lesions. In cohort 8, TTI-621 was combined with pembrolizumab 200 mg injections per product labels. In cohort 9, TTI-621 was combined with the standard labelled dose of subcutaneous pegylated interferon alpha-2a 90 μg. The primary endpoint was the incidence and severity of adverse events. The study is registered with ClinicalTrials.gov, NCT02890368, and was closed by the sponsor to focus on intravenous studies with TTI-621.

FINDINGS

Between Jan 30, 2017, and March 31, 2020, 66 patients with mycosis fungoides, Sézary syndrome, other CTCL, or solid tumours were screened, 35 of whom with mycosis fungoides or Sézary syndrome were enrolled and received intralesional TTI-621 (escalation, n=13; expansion, n=22). No dose-limiting toxicities occurred; the maximum tolerated dose was not established. In the dose expansion cohorts, the maximally assessed regimen (10 mg thrice weekly for 2 weeks) was used. 25 (71%) patients had treatment-related adverse events; the most common (occurring in ≥10% of patients) were chills (in ten [29%] patients), injection site pain (nine [26%]), and fatigue (eight [23%]). No treatment-related adverse events were grade 3 or more or serious. There were no treatment-related deaths. Rapid responses (median 45 days, IQR 17-66) occurred independently of disease stage or injection frequency. 26 (90%) of 29 evaluable patients had decreased Composite Assessment of Index Lesion Severity (CAILS) scores; ten (34%) had a decrease in CAILS score of 50% or more (CAILS response). CAILS score reductions occurred in adjacent non-injected lesions in eight (80%) of ten patients with paired assessments and in distal non-injected lesions in one additional patient.

INTERPRETATION

Intralesional TTI-621 was well tolerated and had activity in adjacent or distal non-injected lesions in patients with relapsed or refractory mycosis fungoides or Sézary syndrome, suggesting it has systemic and locoregional abscopal effects and potential as an immunotherapy for these conditions.

FUNDING

Trillium Therapeutics.

Philadelphia-Negative MPN: A Molecular Journey, from Hematopoietic Stem Cell to Clinical Features

Philadelphia negative Myeloproliferative Neoplasms (MPN) are a heterogeneous group of hematopoietic stem cell diseases. MPNs show different risk grades of thrombotic complications and acute myeloid leukemia evolution. In the last couple of decades, from JAK2 mutation detection in 2005 to the newer molecular trademarks studied through next generation sequencing, we are learning to approach MPNs from a deeper perspective. Here, we intend to elucidate the important factors affecting MPN clonal advantage and the reasons why some patients progress to more aggressive disease. Understanding these mechanisms is the key to developing new treatment approaches and targeted therapies for MPN patients.

The promise and perils of immunotherapy

Advances in understanding the ways in which the immune system fails to control tumor growth or prevent autoimmunity have led to the development of powerful therapeutic strategies to treat these diseases. In contrast to conventional therapies that have a broadly suppressive effect, immunotherapies are more akin to targeted therapies because they are mechanistically driven and are typically developed with the goal of "drugging" a specific underlying pathway or phenotype. This means that their effects and toxicities are, at least in theory, more straightforward to anticipate. The development of functionalized antibodies, genetically engineered T cells, and immune checkpoint inhibitors continues to accelerate, illuminating new biology and bringing new treatment to patients. In the following sections, we provide an overview of immunotherapeutic concepts, highlight recent advances in the field of immunotherapies, and discuss controversies and future directions, particularly as these pertain to hematologic oncology or blood-related diseases. We conclude by illustrating how original research published in this journal fits into and contributes to the overall framework of advances in immunotherapy.

Personalized Medicine for TP53 Mutated Myelodysplastic Syndromes and Acute Myeloid Leukemia

Targeting TP53 mutated myelodysplastic syndromes and acute myeloid leukemia remains a significant unmet need. Recently, new drugs have attempted to improve the outcomes of this poor molecular subgroup. The aim of this article is to review all the current knowledge using active agents including hypomethylating agents with venetoclax, eprenetapopt or magrolimab. We include comprehensive analysis of clinical trials to date evaluating these drugs in TP53 myeloid neoplasms as well as discuss future novel combinations for consideration. Additionally, further understanding of the unique clinicopathologic components of TP53 mutant myeloid neoplasms versus wild-type is critical to guide future study. Importantly, the clinical trajectory of patients is uniquely tied with the clonal burden of TP53, which enables serial TP53 variant allele frequency analysis to be a critical early biomarker in investigational studies. Together, significant optimism is now possible for improving outcomes in this patient population.

Stem Cells in Myelodysplastic Syndromes and Acute Myeloid Leukemia: First Cousins or Unrelated Entities?

Myelodysplastic syndromes (MDSs) are associated with a significant risk of transformation to acute myeloid leukemia (AML), supported by alterations affecting malignant stem cells. This review focuses on the metabolic, phenotypic and genetic characteristics underlying this dynamic evolution, from myelodysplastic stem cells (MDS-SCs) to leukemic stem cells (LSCs). MDS-SCs are more likely to be derived from healthy hematopoietic stem cells (HSCs), whereas LSCs may originate from healthy progenitors, mostly LMPP (lymphoid-primed multipotential progenitors). Moreover, overexpression of CD123 and CLL1 markers by LSCs and MDS-SCs in high risk-MDS [HR-MDS] has led to exciting therapeutic applications. Single-cell sequencing has suggested that clonal evolution in the stem cell compartment was non-linear during MDS initiation and progression to AML, with pre-MDS-SC acquiring distinct additional mutations in parallel, that drive either MDS blast production or AML transformation. In AML and HR-MDS, common metabolic alterations have been identified in malignant stem cells, including activation of the protein machinery and dependence on oxidative phosphorylation. Targeting these metabolic abnormalities could prevent HR-MDS from progressing to AML. Strikingly, in low risk-MDS-SC, the expression of ribosomal proteins is decreased, which may be accompanied by a reduction in protein synthesis.

Sequential Use of Romiplostim after Eltrombopag for Refractory Thrombocytopenia in Hydrocarbon-Induced Myelodysplasia

We describe the clinical course of a 65-year-old male patient who suffered from hydrocarbon-induced myelodysplasia and was successfully treated with the thrombopoietin receptor agonist (TPO-RA), romiplostim. Myelodysplastic syndromes (MDS) are characterized by ineffective hematopoiesis, cytopenias, and increased risk of leukemic transformation. Here, we present a clinical vignette of MDS-associated thrombocytopenia refractory to first-line drugs as well as the TPO-RA, eltrombopag. To date, romiplostim is an U.S. Food and Drug Administration (FDA)-approved drug for idiopathic thrombocytopenic purpura and thrombocytopenia secondary to liver disease. Of note, currently the FDA advises against its use in MDS based on previous long-term safety concerns. Since the therapeutic options for thrombocytopenia in MDS patients are sparse, repurposing and reassessing romiplostim in this setting have been the focus of recent studies. At the time of writing, no published double-blind randomized clinical trials have conducted a head-to-head comparison between romiplostim and eltrombopag in thrombocytopenic MDS patients. To the best of our knowledge, for a thrombocytopenic patient in the setting of MDS, this is the first documented report of refractory clinical response after a 2-year use of eltrombopag in which replacement of treatment with romiplostim resulted in sustained physiological counts of thrombocytes within four weeks.

Nature or Nurture? Role of the Bone Marrow Microenvironment in the Genesis and Maintenance of Myelodysplastic Syndromes

Myelodysplastic syndrome (MDS) are clonal haematopoietic stem cell (HSC) disorders driven by a complex combination(s) of changes within the genome that result in heterogeneity in both clinical phenotype and disease outcomes. MDS is among the most common of the haematological cancers and its incidence markedly increases with age. Currently available treatments have limited success, with <5% of patients undergoing allogeneic HSC transplantation, a procedure that offers the only possible cure. Critical contributions of the bone marrow microenvironment to the MDS have recently been investigated. Although the better understanding of the underlying biology, particularly genetics of haematopoietic stem cells, has led to better disease and risk classification; however, the role that the bone marrow microenvironment plays in the development of MDS remains largely unclear. This review provides a comprehensive overview of the latest developments in understanding the aetiology of MDS, particularly focussing on understanding how HSCs and the surrounding immune/non-immune bone marrow niche interacts together.

Myelodysplastic syndrome and immunotherapy novel to next in-line treatments

Patients with Myelodysplastic syndromes (MDS) have few therapy options for sustainable responses in the frontline setting, and even less after hypomethylating agent (HMA) failure in relapsed and refractory setting. The only potential cure is an allogeneic hematopoietic stem cell transplant which is an unrealistic option for the majority of MDS patients. Immunotherapy with checkpoint inhibition, CAR-T cells, and vaccine therapy few have shown promise in a variety cancer and have now been tested in patients with MDS. Most trials have focused on AML patients and included small numbers of MDS patients. Until now, a dedicated review of immunotherapy outcomes in MDS patients has been lacking. Thus, herein we review outcomes of MDS patients after immunotherapies on a variety of clinical trials reported to date.

Myelodysplastic Syndromes: A New Decade

Myelodysplastic syndromes (MDS) are a group of heterogeneous clonal hematopoietic stem cell disorders. The 2020 Surveillance, Epidemiology, and End Results data demonstrates the incidence rate of MDS increases with age especially in those greater than 70 years of age. Risk stratification that impact prognosis, survival, and rate of acute myeloid leukemia (AML) transformation in MDS is largely dependent on revised International Prognostic Scoring System along with molecular genetic testing as a supplement. Low risk MDS typically have a more indolent disease course in which treatment is only initiated to ameliorate symptoms of cytopenias. In many, anemia is the most common cytopenia requiring treatment and erythroid stimulating agents, are considered first line. In contrast, high risk MDS tend to behave more aggressively for which treatment should be initiated rapidly with Hypomethylating Agents (HMA) being in the frontline. In those with high risk MDS and eligible, evaluation for allogeneic stem cell transplant should be considered as this is the only potential curative option for MDS. With the use of molecular genetic testing, a personalized approach to therapy in MDS has ensued. As the treatment landscape in MDS continues to flourish with novel targeted agents, we ambitiously seek to improve survival rates especially among the relapsed/refractory and transplant ineligible.

Stem Cells in the Myelodysplastic Syndromes

The myelodysplastic syndromes (MDS) represent a group of clonal disorders characterized by ineffective hematopoiesis, resulting in peripheral cytopenias and frequent transformation to acute myeloid leukemia (AML). We and others have demonstrated that MDS arises in, and is propagated by malignant stem cells (MDS-SCs), that arise due to the sequential acquisition of genetic and epigenetic alterations in normal hematopoietic stem cells (HSCs). This review focuses on recent advancements in the cellular and molecular characterization of MDS-SCs, as well as their role in mediating MDS clinical outcomes. In addition to discussing the cell surface proteins aberrantly upregulated on MDS-SCs that have allowed the identification and prospective isolation of MDS-SCs, we will discuss the recurrent cytogenetic abnormalities and genetic mutations present in MDS-SCs and their roles in initiating disease, including recent studies demonstrating patterns of clonal evolution and disease progression from pre-malignant HSCs to MDS-SCs. We also will discuss the pathways that have been described as drivers or promoters of disease, including hyperactivated innate immune signaling, and how the identification of these alterations in MDS-SC have led to investigations of novel therapeutic strategies to treat MDS. It is important to note that despite our increasing understanding of the pathogenesis of MDS, the molecular mechanisms that drive responses to therapy remain poorly understood, especially the mechanisms that underlie and distinguish hematologic improvement from reductions in blast burden. Ultimately, such distinctions will be required in order to determine the shared and/or unique molecular mechanisms that drive ineffective hematopoiesis, MDS-SC maintenance, and leukemic transformation.

Targeting low-risk myelodysplastic syndrome with novel therapeutic strategies

Myelodysplastic syndrome (MDS) is a group of hematopoietic disorders with limited treatment options. Anemia is a common symptom in MDS, and although erythropoiesis-stimulating agents such as erythropoietin, lenalidomide, and luspatercept are available to treat anemia, many MDS patients do not respond to these first-line therapies. Therefore, alternative drug development strategies are needed to improve therapeutic efficacy. Splicing modulators to correct splicing-related defects have shown promising results in clinical trials. Targeting differentiation of early erythroid progenitors to increase the erythroid output in MDS is another novel approach, which has shown encouraging results at the pre-clinical stage. Together, these therapeutic strategies provide new avenues to target MDS symptoms untreatable previously.

Myeloid-Derived Suppressor Cells and Mesenchymal Stem/Stromal Cells in Myeloid Malignancies

Myeloid malignancies arise from an altered hematopoietic stem cell and mainly comprise acute myeloid leukemia, myelodysplastic syndromes, myeloproliferative malignancies, and chronic myelomonocytic leukemia. Myeloid neoplastic leukemic cells may influence the growth and differentiation of other hematopoietic cell lineages in peripheral blood and bone marrow. Myeloid-derived suppressor cells (MDSCs) and mesenchymal stromal cells (MSCs) display immunoregulatory properties by controlling the innate and adaptive immune systems that may induce a tolerant and supportive microenvironment for neoplasm development. This review analyzes the main features of MDSCs and MSCs in myeloid malignancies. The number of MDSCs is elevated in myeloid malignancies exhibiting high immunosuppressive capacities, whereas MSCs, in addition to their immunosuppression contribution, regulate myeloid leukemia cell proliferation, apoptosis, and chemotherapy resistance. Moreover, MSCs may promote MDSC expansion, which may mutually contribute to the creation of an immuno-tolerant neoplasm microenvironment. Understanding the implication of MDSCs and MSCs in myeloid malignancies may favor their potential use in immunotherapeutic strategies.

Myeloid-Derived Suppressor Cells and Mesenchymal Stem/Stromal Cells in Myeloid Malignancies

Myeloid malignancies arise from an altered hematopoietic stem cell and mainly comprise acute myeloid leukemia, myelodysplastic syndromes, myeloproliferative malignancies, and chronic myelomonocytic leukemia. Myeloid neoplastic leukemic cells may influence the growth and differentiation of other hematopoietic cell lineages in peripheral blood and bone marrow. Myeloid-derived suppressor cells (MDSCs) and mesenchymal stromal cells (MSCs) display immunoregulatory properties by controlling the innate and adaptive immune systems that may induce a tolerant and supportive microenvironment for neoplasm development. This review analyzes the main features of MDSCs and MSCs in myeloid malignancies. The number of MDSCs is elevated in myeloid malignancies exhibiting high immunosuppressive capacities, whereas MSCs, in addition to their immunosuppression contribution, regulate myeloid leukemia cell proliferation, apoptosis, and chemotherapy resistance. Moreover, MSCs may promote MDSC expansion, which may mutually contribute to the creation of an immuno-tolerant neoplasm microenvironment. Understanding the implication of MDSCs and MSCs in myeloid malignancies may favor their potential use in immunotherapeutic strategies.

Phagocytosis checkpoints on hematopoietic stem cells in patients with myelodysplastic syndromes

BACKGROUND

The myelodysplastic syndrome (MDS) is a high-risk hemocytopenia easily converted to acute myeloid leukemia. CD47 plays an important role in regulating phagocytosis, and its role in the pathogenesis of MDS is unclear.

METHODS

CD47 and PI3K/AKT/mTOR on CD34⁺ CD38^- cells were detected by flow cytometry. NF-κB, PI3K, AKT, PTEN, and mTOR mRNA overexpressed in CD34⁺ CD38^- CD47⁺ cells were performed by real-time quantitative transcriptase-polymerase chain reaction. Phagocytic capacity of macrophages was measured with carboxyfluorescein succinimidyl ester and fluorescent microspheres. Sorted CD34⁺ CD38^- CD47⁺ cells were injected into NOD-Prkdc^scid Il2rg^null mice.

RESULTS

The expression of CD47 on CD34⁺ CD38^- cells of the patients in high-risk MDS based on IPSS-R/WPSS score was higher than that in low-risk MDS and controls. The signaling pathway of PI3K/AKT/mTOR is active in CD34⁺ CD38^- CD47⁺ cells of MDS patients. CD47 overexpressing CD34⁺ CD38^- cells has antiphagocytosis. CD47 overexpressing leukemia stem cell (LSC) -transplanted mice has a short survival time. The macrophages originated from MDS might elicit a pro-tumor response in MDS by inhibiting phagocytosis.

CONCLUSIONS

Phagocytosis checkpoints are impaired in MDS. High expression of CD47 on CD34+CD38^- cells indicates poor clinical prognosis in MDS.

Innate immune pathways and inflammation in hematopoietic aging, clonal hematopoiesis, and MDS

With a growing aged population, there is an imminent need to develop new therapeutic strategies to ameliorate disorders of hematopoietic aging, including clonal hematopoiesis and myelodysplastic syndrome (MDS). Cell-intrinsic dysregulation of innate immune- and inflammatory-related pathways as well as systemic inflammation have been implicated in hematopoietic defects associated with aging, clonal hematopoiesis, and MDS. Here, we review and discuss the role of dysregulated innate immune and inflammatory signaling that contribute to the competitive advantage and clonal dominance of preleukemic and MDS-derived hematopoietic cells. We also propose how emerging concepts will further reveal critical biology and novel therapeutic opportunities.

Stem cell concepts in myelodysplastic syndromes: lessons and challenges

According to the cancer stem cell (CSC) hypothesis, CSCs are the only cancer cells that can give rise to and sustain all cells that constitute a cancer as they possess inherent or acquired self-renewal potential, and their elimination is required and potentially sufficient to achieve a cure. Whilst establishing CSC identity remains challenging in most cancers, studies of low-intermediate risk myelodysplastic syndromes (MDS), other chronic myeloid malignancies and clonal haematopoiesis of indeterminant potential (CHIP) strongly support that the primary target cell usually resides in the rare haematopoietic stem cell (HSC) compartment. This probably reflects the unique self-renewal potential of HSCs in normal human haematopoiesis, combined with the somatic initiating genomic driver lesion not conferring extensive self-renewal potential to downstream progenitor cells. Mutational 'fate mapping' further supports that HSCs are the only disease-propagating cells in low-intermediate risk MDS, but that MDS-propagating potential might be extended to progenitors upon disease progression. The clinical importance of MDS stem cells has been highlighted through the demonstration of selective persistence of MDS stem cells in patients at complete remission in response to therapy. This implies that MDS stem cells might possess unique resistance mechanisms responsible for relapses following otherwise efficient treatments. Specific surveillance of MDS stem cells should be considered to assess the efficiency of therapies and as an early indicator of emerging relapses in patients in clinical remission. Moreover, further molecular characterization of purified MDS stem cells should facilitate identification and validation of improved and more stem cell-specific therapies for MDS.

Overexpression of CD47 is associated with brain overgrowth and 16p11.2 deletion syndrome

Copy number variation (CNV) at the 16p11.2 locus is associated with neuropsychiatric disorders, such as autism spectrum disorder and schizophrenia. CNVs of the 16p gene can manifest in opposing head sizes. Carriers of 16p11.2 deletion tend to have macrocephaly (or brain enlargement), while those with 16p11.2 duplication frequently have microcephaly. Increases in both gray and white matter volume have been observed in brain imaging studies in 16p11.2 deletion carriers with macrocephaly. Here, we use human induced pluripotent stem cells (hiPSCs) derived from controls and subjects with 16p11.2 deletion and 16p11.2 duplication to understand the underlying mechanisms regulating brain overgrowth. To model both gray and white matter, we differentiated patient-derived iPSCs into neural progenitor cells (NPCs) and oligodendrocyte progenitor cells (OPCs). In both NPCs and OPCs, we show that CD47 (a "don't eat me" signal) is overexpressed in the 16p11.2 deletion carriers contributing to reduced phagocytosis both in vitro and in vivo. Furthermore, 16p11.2 deletion NPCs and OPCs up-regulate cell surface expression of calreticulin (a prophagocytic "eat me" signal) and its binding sites, indicating that these cells should be phagocytosed but fail to be eliminated due to elevations in CD47. Treatment of 16p11.2 deletion NPCs and OPCs with an anti-CD47 antibody to block CD47 restores phagocytosis to control levels. While the CD47 pathway is commonly implicated in cancer progression, we document a role for CD47 in psychiatric disorders associated with brain overgrowth.

Ectopic humanized mesenchymal niche in mice enables robust engraftment of myelodysplastic stem cells

Myelodysplastic syndrome (MDS) are clonal stem cell diseases characterized mainly by ineffective hematopoiesis. Here, we present an approach that enables robust long-term engraftment of primary MDS stem cells (MDS-SCs) in mice by implantation of human mesenchymal cell-seeded scaffolds. Critically for modelling MDS, where patient sample material is limiting, mononuclear bone marrow cells containing as few as 104 CD34+ cells can be engrafted and expanded by this approach with the maintenance of the genetic make-up seen in the patients. Non-invasive high-resolution ultrasound imaging shows that these scaffolds are fully perfused. Our data shows that human microenvironment but not mouse is essential to MDS-SCs homing and engraftment. Notably, the alternative niche provided by healthy donor MSCs enhanced engraftment of MDS-SCs. This study characterizes a new tool to model MDS human disease with the level of engraftment previously unattainable in mice, and offers insights into human-specific determinants of MDS-SC microenvironment.

Altered microRNA expression links IL6 and TNF-induced inflammaging with myeloid malignancy in humans and mice

Aging is associated with significant changes in the hematopoietic system, including increased inflammation, impaired hematopoietic stem cell (HSC) function, and increased incidence of myeloid malignancy. Inflammation of aging ("inflammaging") has been proposed as a driver of age-related changes in HSC function and myeloid malignancy, but mechanisms linking these phenomena remain poorly defined. We identified loss of miR-146a as driving aging-associated inflammation in AML patients. miR-146a expression declined in old wild-type mice, and loss of miR-146a promoted premature HSC aging and inflammation in young miR-146a-null mice, preceding development of aging-associated myeloid malignancy. Using single-cell assays of HSC quiescence, stemness, differentiation potential, and epigenetic state to probe HSC function and population structure, we found that loss of miR-146a depleted a subpopulation of primitive, quiescent HSCs. DNA methylation and transcriptome profiling implicated NF-κB, IL6, and TNF as potential drivers of HSC dysfunction, activating an inflammatory signaling relay promoting IL6 and TNF secretion from mature miR-146a-/- myeloid and lymphoid cells. Reducing inflammation by targeting Il6 or Tnf was sufficient to restore single-cell measures of miR-146a-/- HSC function and subpopulation structure and reduced the incidence of hematological malignancy in miR-146a-/- mice. miR-146a-/- HSCs exhibited enhanced sensitivity to IL6 stimulation, indicating that loss of miR-146a affects HSC function via both cell-extrinsic inflammatory signals and increased cell-intrinsic sensitivity to inflammation. Thus, loss of miR-146a regulates cell-extrinsic and -intrinsic mechanisms linking HSC inflammaging to the development of myeloid malignancy.

The relationship between red cell distribution width and prognostic scores in myelodysplastic syndrome

Introduction

The myelodysplastic syndrome (MDS) represents a group of hematopoietic neoplasms that is characterized by clonal hematopoiesis, cytopenia and abnormal cellular maturation. Red cell distribution width (RDW) refers to the variation degree of erythrocyte size and it is a reflection of anisocytosis. Higher values have been linked to adverse outcomes, such as increased mortality, vascular events, kidney and liver disease and demonstrated to harbor poor prognosis in solid and hematological malignancies. The RDW value can be used as a contributing parameter for MDS diagnosis, as well as its prognosis. In this study, we essentially aimed to demonstrate the correlation between the RDW and MDS prognostic indexes.

Materials and methods

Ninety-four MDS patients at the Aydın Adnan Menderes University Hematology Division were included in the study. The correlations between the RDW and laboratory values (either lactate dehydrogenase, albumin, globulin or ferritin) and the RDW prognostic scoring indexes (IPSS, WPSS, IPSS-R and LR-PSS) were investigated. The PASW for Windows, version 21.0 (SPSS Inc., Chicago, IL, USA), was used for statistical assessment. A p-value below 0.05 was the cut-off for the statistical significance.

Results

The mean age of all the patients was 73 ± 10 years. Patients were observed for 41.88 ± 25 months. The mean RDW value for all cases was 15.5 ± 2.39. We found a statistically significant difference of survival between RDW values below and above 15.5% (p = 0.016). A significant difference was also observed according to the prognostic scoring indexes (see below).

Conclusion

An increase in RDW is probably related to dysplasia in the MDS and this constitutes a possible explanation for the poor outcome. Prognostic indexes might incorporate the RDW as a parameter in the future.

Phase I Study of the CD47 Blocker TTI-621 in Patients with Relapsed or Refractory Hematologic Malignancies

PURPOSE

TTI-621 (SIRPα-IgG1 Fc) is a novel checkpoint inhibitor that activates antitumor activity by blocking the CD47 "don't eat me" signal. This first-in-human phase I study (NCT02663518) evaluated the safety and activity of TTI-621 in relapsed/refractory (R/R) hematologic malignancies.

PATIENTS AND METHODS

Patients with R/R lymphoma received escalating weekly intravenous TTI-621 to determine the maximum tolerated dose (MTD). During expansion, patients with various malignancies received weekly single-agent TTI-621 at the MTD; TTI-621 was combined with rituximab in patients with B-cell non-Hodgkin lymphoma (B-NHL) or with nivolumab in patients with Hodgkin lymphoma. The primary endpoint was the incidence/severity of adverse events (AEs). Secondary endpoint included overall response rate (ORR).

RESULTS

Overall, 164 patients received TTI-621: 18 in escalation and 146 in expansion (rituximab combination, n = 35 and nivolumab combination, n = 4). On the basis of transient grade 4 thrombocytopenia, the MTD was determined as 0.2 mg/kg; 0.1 mg/kg was evaluated in combination cohorts. AEs included infusion-related reactions, thrombocytopenia, chills, and fatigue. Thrombocytopenia (20%, grade ≥3) was reversible between doses and not associated with bleeding. Transient thrombocytopenia that determined the initial MTD may not have been dose limiting. The ORR for all patients was 13%. The ORR was 29% (2/7) for diffuse large B-cell lymphoma (DLBCL) and 25% (8/32) for T-cell NHL (T-NHL) with TTI-621 monotherapy and was 21% (5/24) for DLBCL with TTI-621 plus rituximab. Further dose optimization is ongoing.

CONCLUSIONS

TTI-621 was well-tolerated and demonstrated activity as monotherapy in patients with R/R B-NHL and T-NHL and combined with rituximab in patients with R/R B-NHL.

Immune-Checkpoint Inhibitors in B-Cell Lymphoma

Simple Summary

Immune-based treatment strategies, which include immune checkpoint inhibition, have recently become a new frontier for the treatment of B-cell-derived lymphoma. Whereas checkpoint inhibition has given oncologists and patients hope in specific lymphoma subtypes like Hodgkin lymphoma, other entities do not benefit from such promising agents. Understanding the factors that determine the efficacy and safety of checkpoint inhibition in different lymphoma subtypes can lead to improved therapeutic strategies, including combinations with various chemotherapies, biologics and/or different immunologic agents with manageable safety profiles.

Abstract

For years, immunotherapy has been considered a viable and attractive treatment option for patients with cancer. Among the immunotherapy arsenal, the targeting of intratumoral immune cells by immune-checkpoint inhibitory agents has recently revolutionised the treatment of several subtypes of tumours. These approaches, aimed at restoring an effective antitumour immunity, rapidly reached the market thanks to the simultaneous identification of inhibitory signals that dampen an effective antitumor response in a large variety of neoplastic cells and the clinical development of monoclonal antibodies targeting checkpoint receptors. Leading therapies in solid tumours are mainly focused on the cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) and programmed death 1 (PD-1) pathways. These approaches have found a promising testing ground in both Hodgkin lymphoma and non-Hodgkin lymphoma, mainly because, in these diseases, the malignant cells interact with the immune system and commonly provide signals that regulate immune function. Although several trials have already demonstrated evidence of therapeutic activity with some checkpoint inhibitors in lymphoma, many of the immunologic lessons learned from solid tumours may not directly translate to lymphoid malignancies. In this sense, the mechanisms of effective antitumor responses are different between the different lymphoma subtypes, while the reasons for this substantial difference remain partially unknown. This review will discuss the current advances of immune-checkpoint blockade therapies in B-cell lymphoma and build a projection of how the field may evolve in the near future. In particular, we will analyse the current strategies being evaluated both preclinically and clinically, with the aim of fostering the use of immune-checkpoint inhibitors in lymphoma, including combination approaches with chemotherapeutics, biological agents and/or different immunologic therapies.

Human hematopoiesis: aging and leukemogenic risk

PURPOSE OF REVIEW

Our understanding of the effects of aging on human hematopoiesis has advanced significantly in recent years, yet the full ramifications of these findings are not fully understood. This review summarizes these findings and discusses their implication as they relate to malignant hematopoiesis.

RECENT FINDINGS

With human aging there is an impaired immune response, loss of hematopoietic stem cell (HSC) function, increase in clonal hematopoiesis, and higher frequency of myeloid malignancies. Although murine models have implicated abnormalities in DNA damage repair, autophagy, metabolism, and epigenetics, studies in primary human specimens are more limited. The development of age-related clonal hematopoiesis and the risk associated with this is one of the major findings in the field of recent years. This is accompanied by changes in bone marrow stem and progenitor composition, changes in the epigenetic program of stem cells and an inflammatory milieu in the bone marrow. The precise consequences of these changes for the development of age-related malignancies are still unclear.

SUMMARY

Advances in the field have begun to reveal the mechanisms driving human HSC loss of function with age. It will be critical to delineate between normal and malignant aging in order to better prevent age-associated myeloid malignancies.

Identification of Novel Insertions and Deletions in Haematopoietic Stem/Progenitor Cells in de novo Myelodysplastic Syndromes

Myelodysplastic Syndromes (MDS) are clonal haematological stem cell disorders. The molecular basis of MDS is heterogeneous and the molecular mechanisms underlying biology of this complex disorder are not fully understood. Genetic variations (GVs) occur in about 90% of patients with MDS. It has been shown that in addition to the single nucleotide variations, insertions and deletions (indels) in the key genes that are known to drive MDS, could also play a role in pathogenesis of MDS. However, only a few genetic studies have analyzed indels in MDS. The present study reports indels of bone marrow (BM) derived CD34⁺ haematopoietic stem/progenitor cells of 20 newly diagnosed de novo MDS patients using next generation sequencing.A total of 88 indels (9 insertions and 79 deletions) across 28 genes were observed. The genes that showed more than five indels are BCOR (N=6), RAD21 (N=6), TP53 (N=8), ASXL1 (N=9), TET2 (N=9) and BCORL1 (N=10). Deletion in the BCORL1 gene (c.3957_3959delGGA, TGAG>TGAG/T) was the most recurrent deletion and was observed in 4/20 patients. The other recurrent deletions reported were EZH2 (W15X, N=2) and RAD21 (G274X, N=3). The recurrent insertions were detected in the FLT3 (E598DYVDFREYE, N=3) and in the NPM1 (L287LCX, N=3) genes. The findings of this study may have a diagnostic, prognostic and a therapeutic value for MDS after validation using a larger cohort.

The evolution of epigenetic therapy in myelodysplastic syndromes and acute myeloid leukemia

Mutations in the group of epigenetic modifiers are the largest group of mutated genes in Myelodysplastic Syndromes (MDS) and are very frequently found in Acute Myeloid Leukemia (AML). Our advancements in the understanding of epigenetics in these diseases have helped develop groundbreaking therapeutics that have changed the treatment landscape of MDS and AML, significantly improving outcomes. In this review we describe the most common epigenetic aberrations in MDS and AML, and current treatments that target mutations in epigenetic modifiers, as well as novel treatment combinations, from standard therapies to investigational treatments.

Current and emerging strategies for management of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are characterized by ineffective hematopoiesis with varying degrees of dysplasia and peripheral cytopenias. MDS are driven by structural chromosomal alterations and somatic mutations in neoplastic myeloid cells, which are supported by a tumorigenic and a proinflammatory marrow microenvironment. Current treatment strategies for lower-risk MDS focus on improving quality of life and cytopenias, while prolonging survival and delaying disease progression is the focus for higher-risk MDS. Several promising drugs are in the horizon, including the hypoxia-inducible factor stabilizer roxadustat, telomerase inhibitor imetelstat, oral hypomethylating agents (CC-486), TP53 modulators (APR-246 and ALRN-6924), and the anti-CD47 antibody magrolimab. Targeted therapies approved for acute myeloid leukemia treatment, such as isocitrate dehdyrogenase inhibitors and venetoclax, are also being studied for use in MDS. In this review, we provide a brief overview of pathogenesis and current treatment strategies in MDS followed by a discussion of newer agents that are under clinical investigation.

Proteomic analysis of young and old mouse hematopoietic stem cells and their progenitors reveals post-transcriptional regulation in stem cells

The balance of hematopoietic stem cell (HSC) self-renewal and differentiation is critical for a healthy blood supply; imbalances underlie hematological diseases. The importance of HSCs and their progenitors have led to their extensive characterization at genomic and transcriptomic levels. However, the proteomics of hematopoiesis remains incompletely understood. Here we report a proteomics resource from mass spectrometry of mouse young adult and old adult mouse HSCs, multipotent progenitors and oligopotent progenitors; 12 cell types in total. We validated differential protein levels, including confirmation that Dnmt3a protein levels are undetected in young adult mouse HSCs until forced into cycle. Additionally, through integrating proteomics and RNA-sequencing datasets, we identified a subset of genes with apparent post-transcriptional repression in young adult mouse HSCs. In summary, we report proteomic coverage of young and old mouse HSCs and progenitors, with broader implications for understanding mechanisms for stem cell maintenance, niche interactions and fate determination.

Insulin Modulates Inflammatory Cytokine Release in Acute Stages and Augments Expression of Adhesion Molecules and Leukocytes in Lungs on Chronic Stages of Paracoccidioidomycosis

Type 1 diabetesmellitus (T1D) is caused by partial destruction of the insulin-producing beta cells in the pancreas and is a major issue for public health care worldwide. Reduced or impaired immunological responses, which render patients more susceptible to infections, have been observed in T1D, and this dysfunction is often related to a lack of insulin in the blood. Paracoccidioidomycosis is an important systemic mycosis endemic in Latin America. To evaluate the effects of T1D on this fungal infection and the modulatory effects of insulin, we induced diabetes in C57Bl/6 male mice (alloxan, 60 mg/kg), infected the mice (Pb18, 1 x 106 cells), and treated the mice with neutral protamine Hagedorn (NPH) insulin (2 IU/600 mg/dL blood glucose). Twenty-four hours after infection, infected diabetic mice showed reduced secretion of interferon (IFN)-γ and interleukine (IL)-12 p70 compared to infected nondiabetic controls. On the 45th day of infection, infected diabetic mice presented higher IFN-γ levels, a higher tumor necrosis factor (TNF)-α:IL-10 ratio, and lower adhesion molecule expression levels than nondiabetic mice. In the in vitro experiments, alveolar macrophages from diabetic animals showed reduced phagocytic activity compared to those from control animals at 4, 12, and 24 h. In infected diabetic mice, treatment with insulin restored IL-12 p70 levels at 24 h of infection, reduced IFN-γ levels and the TNF-α:IL-10 ratio at 45 days, and restored vascular cell adhesion molecule (VCAM)-1 expression in pulmonary blood vessels, and this treatment reduced the diminished phosphorylation of extracellular signal-regulated kinases (ERK) and increased nuclear factor-kappa-B(iκb)-α and jun amino-terminal kinases (JNK) p46 levels in infected nondiabetic mice. In addition, insulin promoted increased phagocytic activity in the alveolar macrophages of diabetic mice. These data suggest that T1D mice are more susceptible to Pb18 infection and that insulin modulates this inflammation in diabetic mice by augmenting the expression of adhesion molecules and leukocytes in the lungs and by reducing chronic inflammation.

The promise of macrophage directed checkpoint inhibitors in myeloid malignancies

To date, many of the most successful checkpoint inhibitor-based therapies in cancer have targeted T-cells and adaptive immunity. However, there is an ongoing search for novel checkpoints with targeting innate immunity via activation of macrophage phagocytosis representing an exciting therapeutic strategy. CD47 is the dominant negative macrophage immune checkpoint expressed on cancer cells which acts as a "don't eat me signal", preventing phagocytosis via its interaction with SIRP-α on macrophages. CD47 has been shown to be upregulated in many cancer types including myeloid malignancies with increased expression associated with inferior OS. Magrolimab, an anti-CD47 antibody, has shown proof-of-principle of efficacy in this therapeutic class with promising early results in both higher risk myelodysplastic syndromes (MDS) and TP53 mutant acute myeloid leukemia (AML). The toxicity profile to date has been shown safe and manageable with on-target anemia related to CD47 being present on aged red blood cells and without evidence of immune related toxicities. Investigation of novel agents targeting this pathway and novel combinations are ongoing. New strategies targeting macrophage checkpoints are encouraging and likely will lead a paradigm shift in the current treatment of myeloid malignancies.

Chronic myelomonocytic leukaemia stem cell transcriptomes anticipate disease morphology and outcome

BACKGROUND

Chronic myelomonocytic leukaemia (CMML) is a clinically heterogeneous stem cell malignancy with overlapping features of myelodysplasia and myeloproliferation. Over 90% of patients carry mutations in epigenetic and/or splicing genes, typically detectable in the Lin-CD34+CD38- immunophenotypic stem cell compartment in which the leukaemia-initiating cells reside. Transcriptional dysregulation at the stem cell level is likely fundamental to disease onset and progression.

METHODS

We performed single-cell RNA sequencing on 6826 Lin-CD34+CD38-stem cells from CMML patients and healthy controls using the droplet-based, ultra-high-throughput 10x platform.

FINDINGS

We found substantial inter- and intra-patient heterogeneity, with CMML stem cells displaying distinctive transcriptional programs. Compared with normal controls, CMML stem cells exhibited transcriptomes characterized by increased expression of myeloid-lineage and cell cycle genes, and lower expression of genes selectively expressed by normal haematopoietic stem cells. Neutrophil-primed progenitor genes and a MYC transcription factor regulome were prominent in stem cells from CMML-1 patients, whereas CMML-2 stem cells exhibited strong expression of interferon-regulatory factor regulomes, including those associated with IRF1, IRF7 and IRF8. CMML-1 and CMML-2 stem cells (stages distinguished by proportion of downstream blasts and promonocytes) differed substantially in both transcriptome and pseudotime, indicating fundamentally different biology underpinning these disease states. Gene expression and pathway analyses highlighted potentially tractable therapeutic vulnerabilities for downstream investigation. Importantly, CMML patients harboured variably-sized subpopulations of transcriptionally normal stem cells, indicating a potential reservoir to restore functional haematopoiesis.

INTERPRETATION

Our findings provide novel insights into the CMML stem cell compartment, revealing an unexpected degree of heterogeneity and demonstrating that CMML stem cell transcriptomes anticipate disease morphology, and therefore outcome.

FUNDING

Project funding was supported by Oglesby Charitable Trust, Cancer Research UK, Blood Cancer UK, and UK Medical Research Council.

Genetics of progression from MDS to secondary leukemia

Our understanding of the genetics of acute myeloid leukemia (AML) development from myelodysplastic syndrome (MDS) has advanced significantly as a result of next-generation sequencing technology. Although differences in cell biology and maturation exist between MDS and AML secondary to MDS, these 2 diseases are genetically related. MDS and secondary AML cells harbor mutations in many of the same genes and functional categories, including chromatin modification, DNA methylation, RNA splicing, cohesin complex, transcription factors, cell signaling, and DNA damage, confirming that they are a disease continuum. Differences in the frequency of mutated genes in MDS and secondary AML indicate that the order of mutation acquisition is not random during progression. In almost every case, disease progression is associated with clonal evolution, typically defined by the expansion or emergence of a subclone with a unique set of mutations. Monitoring tumor burden and clonal evolution using sequencing provides advantages over using the blast count, which underestimates tumor burden, and could allow for early detection of disease progression prior to clinical deterioration. In this review, we outline advances in the study of MDS to secondary AML progression, with a focus on the genetics of progression, and discuss the advantages of incorporating molecular genetic data in the diagnosis, classification, and monitoring of MDS to secondary AML progression. Because sequencing is becoming routine in the clinic, ongoing research is needed to define the optimal assay to use in different clinical situations and how the data can be used to improve outcomes for patients with MDS and secondary AML.

The Ban on US Government Funding Research Using Human Fetal Tissues: How Does This Fit with the NIH Mission to Advance Medical Science for the Benefit of the Citizenry?

Some have argued that human fetal tissue research is unnecessary and/or immoral. Recently, the Trump administration has taken the drastic––and we believe misguided––step to effectively ban government-funded research on fetal tissue altogether. In this article, we show that entire lines of research and their clinical outcomes would not have progressed had fetal tissue been unavailable. We argue that this research has been carried out in a manner that is ethical and legal, and that it has provided knowledge that has saved lives, particularly those of pregnant women, their unborn fetuses, and newborns. We believe that those who support a ban on the use of fetal tissue are halting medical progress and therefore endangering the health and lives of many, and for this they should accept responsibility. At the very least, we challenge them to be true to their beliefs: if they wish to short-circuit a scientific process that has led to medical advances, they should pledge to not accept for themselves the health benefits that such advances provide.

Immune checkpoint inhibition in myeloid malignancies: Moving beyond the PD-1/PD-L1 and CTLA-4 pathways

Immune checkpoint inhibitors (ICI) have yielded mixed but largely underwhelming results in clinical trials in patients with acute myeloid leukemia and myelodysplastic syndromes to date. However, increasing understanding of the immunologic landscape, potential biomarkers for benefits, and mechanisms of resistance, as well as the use of rational combinations, and identification of novel targets leaves plenty of room for optimism. Herein, we review recent advances in the preclinical and clinical development of ICI therapy in patients with myeloid malignancies and explore some of the important challenges facing the field such as the absence of validated biomarkers, the development of synergistic and safe combination therapies, and efforts to determine the best setting of ICI along the disease course. We finally foresee the future of the field and propose solutions to some of the major beforementioned obstacles.

A 4-gene leukemic stem cell score can independently predict the prognosis of myelodysplastic syndrome patients

Myelodysplastic syndrome (MDS) comprised a heterogeneous group of diseases. The prognosis of patients varies even in the same risk groups. Searching for novel prognostic markers is warranted. Leukemic stem cells (LSCs) are responsible for chemoresistance and relapse in leukemia. Recently, expressions of 17 genes related to stemness of LSCs were found to be associated with prognosis in acute myeloid leukemia patients. However, the clinical impact of LSC genes expressions in MDS, a disorder arising from hematopoietic stem cells, remains unclear. We analyzed expression profile of the 17 stemness-related genes in primary MDS patients and identified expression of 4 genes (LAPTM4B, NGFRAP1, EMP1, and CPXM1) were significantly correlated with overall survival (OS). We constructed an LSC4 scoring system based on the weighted sums of the expression of 4 genes and explored its clinical implications in MDS patients. Higher LSC4 scores were associated with higher revised International Prognostic Scoring System (IPSS-R) scores, complex cytogenetics, and mutations in RUNX1, ASXL1, and TP53. High-score patients had significantly shorter OS and leukemia-free survival (LFS), which was also confirmed in 2 independent validation cohorts. Subgroup analysis revealed the prognostic significance of LSC4 scores for OS remained valid across IPSS-R lower- and higher-risk groups. Furthermore, higher LSC4 score was an independent adverse risk factor for OS and LFS in multivariate analysis. In summary, LSC4 score can independently predict prognosis in MDS patients irrespective of IPSS-R risks and may be used to guide the treatment of MDS patients, especially lower-risk group in whom usually only supportive treatment is given.

Therapeutic Targeting of the Macrophage Immune Checkpoint CD47 in Myeloid Malignancies

In recent years, immunotherapies have been clinically investigated in AML and other myeloid malignancies. While most of these are focused on stimulating the adaptive immune system (including T cell checkpoint inhibitors), several key approaches targeting the innate immune system have been identified. Macrophages are a key cell type in the innate immune response with CD47 being identified as a dominant macrophage checkpoint. CD47 is a "do not eat me" signal, overexpressed in myeloid malignancies that leads to tumor evasion of phagocytosis by macrophages. Blockade of CD47 leads to engulfment of leukemic cells and therapeutic elimination. Pre-clinical data has demonstrated robust anti-cancer activity in multiple hematologic malignancies including AML and myelodysplastic syndrome (MDS). In addition, clinical studies have been underway with CD47 targeting agents in both AML and MDS as monotherapy and in combination. This review will describe the role of CD47 in myeloid malignancies and pre-clinical data supporting CD47 targeting. In addition, initial clinical data of CD47 targeting in AML/MDS will be reviewed, and including the first-in-class anti-CD47 antibody magrolimab.

Age-Associated TET2 Mutations: Common Drivers of Myeloid Dysfunction, Cancer and Cardiovascular Disease

Acquired, inactivating mutations in Tet methylcytosine dioxygenase 2 (TET2) are detected in peripheral blood cells of a remarkable 5%–10% of adults greater than 65 years of age. They impart a hematopoietic stem cell advantage and resultant clonal hematopoiesis of indeterminate potential (CHIP) with skewed myelomonocytic differentiation. CHIP is associated with an overall increased risk of transformation to a hematological malignancy, especially myeloproliferative and myelodysplastic neoplasms (MPN, MDS) and acute myeloid leukemia (AML), of approximately 0.5% to 1% per year. However, it is becoming increasingly possible to identify individuals at greatest risk, based on CHIP mutational characteristics. CHIP, and particularly TET2-mutant CHIP, is also a novel, significant risk factor for cardiovascular diseases, related in part to hyper-inflammatory, progeny macrophages carrying TET2 mutations. Therefore, somatic TET2 mutations contribute to myeloid expansion and innate immune dysregulation with age and contribute to prevalent diseases in the developed world—cancer and cardiovascular disease. Herein, we describe the impact of detecting TET2 mutations in the clinical setting. We also present the rationale and promise for targeting TET2-mutant and other CHIP clones, and their inflammatory environment, as potential means of lessening risk of myeloid cancer development and dampening CHIP-comorbid inflammatory diseases.