High expression of costimulatory molecules correlates with low relapse-free survival probability in acute myeloid leukemia (AML)

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.

CD33 BiTE® molecule-mediated immune synapse formation and subsequent T-cell activation is determined by the expression profile of activating and inhibitory checkpoint molecules on AML cells

Bispecific T-cell engager (BiTE^®) molecules recruit T cells to cancer cells through CD3ε binding, independently of T-cell receptor (TCR) specificity. Whereas physiological T-cell activation is dependent on signal 1 (TCR engagement) and signal 2 (co-stimulation), BiTE molecule-mediated T-cell activation occurs without additional co-stimulation. As co-stimulatory and inhibitory molecules modulate the strength and nature of T-cell responses, we studied the impact of the expression profile of those molecules on target cells for BiTE molecule-mediated T-cell activation in the context of acute myeloid leukemia (AML). Accordingly, we created a novel in vitro model system using murine Ba/F3 cells transduced with human CD33 ± CD86 ± PD-L1. T-cell fitness was assessed by T-cell function assays in co-cultures and immune synapse formation by applying a CD33 BiTE molecule (AMG 330). Using our cell-based model platform, we found that the expression of positive co-stimulatory molecules on target cells markedly enhanced BiTE molecule-mediated T-cell activation. The initiation and stability of the immune synapse between T cells and target cells were significantly increased through the expression of CD86 on target cells. By contrast, the co-inhibitory molecule PD-L1 impaired the stability of BiTE molecule-induced immune synapses and subsequent T-cell responses. We validated our findings in primary T-cell-AML co-cultures, demonstrating a PD-L1-mediated reduction in redirected T-cell activation. The addition of the immunomodulatory drug (IMiD) lenalidomide to co-cultures led to stabilization of immune synapses and improved subsequent T-cell responses. We conclude that target cells modulate CD33 BiTE molecule-dependent T-cell activation and hence, combinatorial strategies might contribute to enhanced efficacy.

The prevention of disease relapse after allogeneic hematopoietic cell transplantation in acute myeloid leukemia

Disease relapse represents by far the most frequent cause of hematopoietic cell transplantation (HCT) failure. Patients with acute leukemia suffering relapse after HCT have limited conventional treatment options with little possibility of cure and represent, de facto, suitable candidates for the evaluation of novel cellular and biological-based therapies. Donor lymphocyte infusions (DLI) has been one of the first cellular therapies adopted to treat post HCT relapse of acute leukemia patients and still now, it is widely adopted in preemptive and prophylactic settings, with renewed interest for manipulated cellular products such as NK-DLI. The acquisition of novel biological insights into pathobiology of leukemia relapse are translating into the clinic, with novel combinations of target therapies and novel agents, helping delineate new therapeutical landscapes. Hypomethylating agents alone or in combination with novel drugs demonstrated their efficacy in pre-clinical models and controlled trials. FLT3 inhibitors represent an essential therapeutical instrument incorporated in post-transplant maintenance strategies. The Holy grail of allogeneic transplantation lies in the separation of graft-vs.-host disease from graft vs. tumor effects and after more than five decades, is still the most ambitious goal to reach and many ways to accomplish are on their way.

Immune Checkpoint Inhibition in Acute Myeloid Leukemia and Myelodysplastic Syndromes

Immune checkpoint inhibitors (ICIs) have revolutionized the treatment of many solid tumors, with limited progress made in the area of myeloid malignancies. The low mutational burden of acute myeloid leukemia (AML) is one potential reason behind the lack of activity of T-cell harnessing ICIs, particularly CTLA-4 and PD-1 inhibitors. Innate immune checkpoints play a critical role in the immune escape of AML and myelodysplastic syndromes (MDS). The CD47 targeting agent, magrolimab, has shown promising activity when combined with azacitidine in early phase trials conducted in AML and higher-risk MDS, especially among patients harboring a TP53 mutation. Similarly, sabatolimab (an anti-TIM-3 monoclonal antibody) plus hypomethylating agents have shown durable responses in higher-risk MDS and AML in early clinical trials. Randomized trials are currently ongoing to confirm the efficacy of these agents. In this review, we will present the current progress and future directions of immune checkpoint inhibition in AML and MDS.

A multi-arm phase Ib/II study designed for rapid, parallel evaluation of novel immunotherapy combinations in relapsed/refractory acute myeloid leukemia

We conducted a phase Ib/II multi-arm, parallel cohort study to simultaneously evaluate various immunotherapeutic agents and combinations in relapsed/refractory acute myeloid leukemia (AML). Overall, 50 patients were enrolled into one of 6 arms: (A) single agent PF-04518600 (OX40 agonist monoclonal antibody), (B) azacitidine + venetoclax + gemtuzumab ozogamicin (GO), (C) azacitidine + avelumab (anti-PD-L1 monoclonal antibody) + GO, (D) azacitidine + venetoclax + avelumab, (E) azacitidine + avelumab + PF-04518600, and (F) glasdegib + GO. Among all regimens evaluated, azacitidine + venetoclax + GO appeared most promising. In this arm, the CR/CRi rates among venetoclax-naïve and prior venetoclax-exposed patients were 50% and 22%, respectively, and the 1-year OS rate was 31%. This study shows the feasibility of a conducting a multi-arm trial to efficiently and simultaneously evaluate novel therapies in AML, a needed strategy in light of the plethora of emerging therapies. This trial was registered at www.clinicaltrials.gov as NCT03390296.

Endocan in Acute Leukemia: Current Knowledge and Future Perspectives

Endocan is a soluble dermatan sulfate proteoglycan expressed by endothelial cells and detected in serum/plasma. Its expression is increased in tumors/tumor vessels in several human malignancies, and high expression (high serum/plasma levels or tumor levels) has an adverse prognostic impact in several malignancies. The p14 endocan degradation product can also be detected in serum/plasma, but previous clinical studies as well as previously unpublished results presented in this review suggest that endocan and p14 endocan fragment levels reflect different biological characteristics, and the endocan levels seem to reflect the disease heterogeneity in acute leukemia better than the p14 fragment levels. Furthermore, decreased systemic endocan levels in previously immunocompetent sepsis patients are associated with later severe respiratory complications, but it is not known whether this is true also for immunocompromised acute leukemia patients. Finally, endocan is associated with increased early nonrelapse mortality in (acute leukemia) patients receiving allogeneic stem cell transplantation, and this adverse prognostic impact seems to be independent of the adverse impact of excessive fluid overload. Systemic endocan levels may also become important to predict cytokine release syndrome after immunotherapy/haploidentical transplantation, and in the long-term follow-up of acute leukemia survivors with regard to cardiovascular risk. Therapeutic targeting of endocan is now possible, and the possible role of endocan in acute leukemia should be further investigated to clarify whether the therapeutic strategy should also be considered.

Immune Therapies for Myelodysplastic Syndromes and Acute Myeloid Leukemia

Myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) are hematologic malignancies arising from the bone marrow. Despite recent advances in treating these diseases, patients with higher-risk MDS and AML continue to have a poor prognosis with limited survival. It has long been recognized that there is an immune component to the pathogenesis of MDS and AML, but until recently, immune therapies have played a limited role in treating these diseases. Immune suppressive therapy exhibits durable clinical responses in selected patients with MDS, but the question of which patients are most suitable for this treatment remains unclear. Over the past decade, there has been remarkable progress in identifying genomic features of MDS and AML, which has led to an improved discernment of the molecular pathogenesis of these diseases. An improved understanding of immune and inflammatory molecular mechanisms of MDS and AML have also recently revealed novel therapeutic targets. Emerging treatments for MDS and AML include monoclonal antibodies such as immune checkpoint inhibitors, bispecific T-cell-engaging antibodies, antibody drug conjugates, vaccine therapies, and cellular therapeutics including chimeric antigen receptor T-cells and NK cells. In this review, we provide an overview of the current understanding of immune dysregulation in MDS and AML and an update on novel immune therapies for these bone marrow malignancies.

Eradication of Measurable Residual Disease in AML: A Challenging Clinical Goal

In non-promyelocytic (non-M3) AML measurable residual disease (MRD) detected by multi-parameter flow cytometry and molecular technologies, which are guided by Consensus-based guidelines and discover very low leukemic cell numbers far below the 5% threshold of morphological assessment, has emerged as the most relevant predictor of clinical outcome. Currently, it is well-established that MRD positivity after standard induction and consolidation chemotherapy, as well as during the period preceding an allogeneic hematopoietic stem cell transplant (allo-HSCT), portends to a significantly inferior relapse-free survival (RFS) and overall survival (OS). In addition, it has become absolutely clear that conversion from an MRD-positive to an MRD-negative state provides a favorable clinical outcome similar to that associated with early MRD negativity. Thus, the complete eradication of MRD, i.e., the clearance of the few leukemic stem cells-which, due to their chemo-radiotherapy resistance, might eventually be responsible of disease recurrence-has become an un-met clinical need in AML. Nowadays, this goal might potentially be achieved thanks to the development of novel innovative treatment strategies, including those targeting driver mutations, apoptosis, methylation patterns and leukemic proteins. The aim of this review is to analyze these strategies and to suggest any potential combination able to induce MRD negativity in the pre- and post-HSCT period.

High mutation burden in the checkpoint and micro-RNA processing genes in myelodysplastic syndrome

A number of sequencing studies identified the prognostic impact of somatic mutations in myelodysplastic syndrome (MDS). However the majority of them focused on methylation regulation, apoptosis and proliferation genes. Despite the number of experimental studies published on the role of micro-RNA processing and checkpoint genes in the development of MDS, the clinical data about mutational landscape in these genes is limited. We performed a pilot study which evaluated mutational burden in these genes and their association with common MDS mutations. High prevalence of mutations was observed in the genes studied: 54% had mutations in DICER1, 46% had mutations in LAG3, 20% in CTLA4, 23% in B7-H3, 17% in DROSHA, 14% in PD-1 and 3% in PD-1L. Cluster analysis that included these mutations along with mutations in ASXL1, DNMT3A, EZH2, IDH1, RUNX1, SF3B1, SRSF2, TET2 and TP53 effectively predicted overall survival in the study group (HR 4.2, 95%CI 1.3-13.6, p = 0.016). The study results create the rational for incorporating micro-RNA processing and checkpoint genes in the sequencing panels for MDS and evaluate their role in the multicenter studies.

Potential of immunotherapies in the mediation of antileukemic responses for patients with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) - With a focus on Dendritic cells of leukemic origin (DCleu)

New (non-immunotherapeutic) treatment-strategies for AML/MDS-patients are under development. Dendritic cells (DCs) and 'leukemia-derived DC' (DC_leu) connect the innate and the adaptive immunesystem and (re-)activate it, in their capacity as professional antigen-presenting cells (APCs). They can be generated ex vivo from peripheral blood mononuclear cells (PBMNCs) or whole blood (WB), containing the -physiological-cellular/soluble microenvironment of individual patients using various DC/DC_leu-generating methods or (for WB) minimalized 'Kits', containing granulocyte-macrophage-colony-stimulating-factor (GM-CSF) and a second response-modifier. Proof for DC/DC_leu-mediated activation of the immune-system after T-cell-enriched mixed lymphocyte culture (MLC) is done by flowcytometry, demonstrating increased fractions of certain activated, leukemia-specific or antileukemic cell-subsets of the innate and the adaptive immune-system. Generation of DC/DC_leu is possible independent of patients' age, MHC-, mutation- or transplantation-status. In vivo-treatment of AML-/MDS-patients with blast-modulating, DC/DC_leu- inducing 'Kits' could contribute to create migratory DCs, as well as antileukemically reactivated and memory-mediating immune-cells, which patrol tissue and blood and could contribute to stabilizing disease or remissions.

Immune Escape after Hematopoietic Stem Cell Transplantation (HSCT): From Mechanisms to Novel Therapies

Acute myeloid leukemia (AML) is the most common type of acute leukemia in adults. Recent advances in understanding its molecular basis have opened the way to new therapeutic strategies, including targeted therapies. However, despite an improvement in prognosis it has been documented in recent years (especially in younger patients) that allogenic hematopoietic stem cell transplantation (allo-HSCT) remains the only curative treatment in AML and the first therapeutic option for high-risk patients. After allo-HSCT, relapse is still a major complication, and is observed in about 50% of patients. Current evidence suggests that relapse is not due to clonal evolution, but instead to the ability of the AML cell population to escape immune control by a variety of mechanisms including the altered expression of HLA-molecules, production of anti-inflammatory cytokines, relevant metabolic changes and expression of immune checkpoint (ICP) inhibitors capable of “switching-off” the immune response against leukemic cells. Here, we review the main mechanisms of immune escape and identify potential strategies to overcome these mechanisms.

A Review of Efficacy and Safety of Checkpoint Inhibitor for the Treatment of Acute Myeloid Leukemia

Immune checkpoint inhibitors (ICIs) as positive modulators of immune response have revolutionized the treatment of cancer and have achieved impressive efficacy in melanoma and numerous solid tumor malignancies. These agents are being investigated in acute myeloid leukemia (AML) to further enhance response rate as induction therapy and to improve relapse-free survival (RFS) post chemotherapy and bone marrow transplantation. PD-1 and CTLA-4 are the two most actively investigated checkpoint receptors, which play a role in different stages of anti-tumor immune response. This study reviews data from ongoing phase I, II clinical trials evaluating PD-1 and CTLA-4 inhibitors on AML patients and discusses especially efficacy and adverse events as well as prospects of these drugs in treating AML. Single anti-PD-1 monoclonal antibody infusion shows rather modest clinical efficacy. While combinations of PD-1 inhibitor with hypomethylating agents (HMAs) represent encouraging outcome for relapsed/refractory (R/R) AML patients as well as for elderly patients as first-line therapy option. Adding PD-1 inhibitor to traditional induction therapy regimen is also safe and feasible. CTLA-4 inhibitor ipilimumab exhibits specific potency in treating relapsed AML patients with extramedullary disease in later post-transplantation stage. In terms of side effects, irAEs found in these trials can mostly be appropriately managed with steroids but are occasionally fatal. More rationally designed combinational therapies are under investigation in ongoing clinical trials and will further advance our understanding of checkpoint inhibitors as well as lead us to the most appropriate application of these agents.

Immune checkpoint-based therapy in myeloid malignancies: a promise yet to be fulfilled

INTRODUCTION

Immune system evasion is essential for tumor cell survival and is mediated by the immunosuppressive tumor microenvironment and the activation of inhibitory immune checkpoints. While immune checkpoint-based therapy yielded impressive results in several advanced solid malignancies such as melanoma and non-small cell lung cancer, its role in acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) is still evolving. Areas covered: Here we review the immunology in the tumor microenvironment in the bone marrow and discuss the current preclinical and clinical data for immune checkpoint-based therapy in myeloid neoplasms. Expert commentary: Clinical trials of immune checkpoint inhibitors (ICI) in AML and MDS are still in early stages and reported results so far have been modest especially for monotherapy use in the refractory settings. However, there are preliminary data for synergistic effects for combination of multiple ICI with hypomethylating agents and conventional chemotherapy. ICI might also be effective in eradicating minimal residual disease and to prevent relapse following induction chemotherapy or hematopoietic stem cell transplant. Additional trials to provide insight into the efficacy and safety profile of immune checkpoint-based therapy, its optimal timing and potential combination with other types of therapy as well as identification of predictive biomarkers are needed.

Checkpoint inhibitors and acute myelogenous leukemia: promises and challenges

INTRODUCTION

Immunity, for treatment of acute myelogenous leukemia (AML), has been leveraged historically in the form of allogeneic stem cell transplantation. Checkpoint inhibitors (CPI) as positive modulators of immune response have been recent major breakthroughs in solid tumors. Areas covered: Emerging concepts and clinical data with CPIs in acute Myeloid Leukemia - the focus of this review- will be discussed. CPIs can potentially be effective in absence of 'actionable' mutations and are expected to be effective against poor-risk AML. Immune inhibitory checkpoint molecules are upregulated in both de novo and relapsed AML. Similar data also suggest role of checkpoint molecules in mediating resistance particularly to hypomethylating agent (HMA) therapy, which can potentially be reversed by using checkpoint inhibitors. Expert commentary: Ongoing clinical trials in combination with HMAs are showing early promise, with doubling of response than that seen in historic controls. The optimal combinations of CPIs and the optimal space that they will fit in the continuum of AML therapies need lot of in depth work.

Targeting Immune Signaling Checkpoints in Acute Myeloid Leukemia

The modest successes of targeted therapies along with the curative effects of allogeneic hematopoietic stem cell transplantation (alloHSCT) in acute myeloid leukemia (AML) stimulate the development of new immunotherapies. One of the promising methods of immunotherapy is the activation of immune response by the targeting of negative control checkpoints. The two best-known inhibitory immune checkpoints are cytotoxic T-lymphocyte antigen-4 (CTLA-4) and the programmed cell death protein 1 receptor (PD-1). In AML, PD-1 expression is observed in T-cell subpopulations, including T regulatory lymphocytes. Increased PD-1 expression on CD8+ T lymphocytes may be one of the factors leading to dysfunction of cytotoxic T cells and inhibition of the immune response during the progressive course of AML. Upregulation of checkpoint molecules was observed after alloHSCT and therapy with hypomethylating agents, pointing to a potential clinical application in these settings. Encouraging results from recent clinical trials (a response rate above 50% in a relapsed setting) justify further clinical use. The most common clinical trials employ two PD-1 inhibitors (nivolumab and pembrolizumab) and two anti-PD-L1 (programmed death-ligand 1) monoclonal antibodies (atezolizumab and durvalumab). Several other inhibitors are under development or in early phases of clinical trials. The results of these clinical trials are awaited with great interest in, as they may allow for the established use of checkpoint inhibitors in the treatment of AML.

Immunotherapy in acute myeloid leukemia and myelodysplastic syndromes: The dawn of a new era?

Immunotherapy has revolutionized therapy in both solid and liquid malignancies. The ability to cure acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) with an allogeneic hematopoietic stem cell transplant (HSCT) is proof of concept for the application of immunotherapy in AML and MDS. However, outside of HSCT, only the anti-CD33 antibody drug conjugate gemtuzumab ozogamicin is currently approved as an antibody-targeted therapy for AML. Several avenues of immunotherapeutic drugs are currently in different stages of clinical development. Here, we review recent advances in antibody-based therapy, immune checkpoint inhibitors, vaccines and adoptive cell-based therapy for patients with AML and MDS. First, we discuss different antibody constructs. Immune checkpoint inhibitors targeting cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein-1 (PD-1) and CD47 as well as peptide, dendritic cell and dendritic/AML cell-based vaccines are reviewed next. Lastly, adoptive cell-based therapy including chimeric antigen receptor (CAR)-T cell and NK cell therapy is discussed.

A Jurkat 76 based triple parameter reporter system to evaluate TCR functions and adoptive T cell strategies

Adoptive T cell therapy using TCR transgenic autologous T cells has shown great potential for the treatment of tumor patients. Thorough characterization of genetically reprogrammed T cells is necessary to optimize treatment success. Here, we describe the generation of triple parameter reporter T cells based on the Jurkat 76 T cell line for the evaluation of TCR and chimeric antigen receptor functions as well as adoptive T cell strategies. This Jurkat subline is devoid of endogenous TCR alpha and TCR beta chains, thereby circumventing the problem of TCR miss-pairing and unexpected specificities. The resultant reporter cells allow simultaneous determination of the activity of the transcription factors NF-κB, NFAT and AP-1 that play key roles in T cell activation. Human TCRs directed against tumor and virus antigens were introduced and reporter responses were determined using tumor cell lines endogenously expressing the antigens of interest or via addition of antigenic peptides. Finally, we demonstrate that coexpression of adhesion molecules like CD2 and CD226 as well as CD28 chimeric receptors represents an effective strategy to augment the response of TCR-transgenic reporters to cells presenting cognate antigens.

Significance of Frequencies, Compositions, and/or Antileukemic Activity of (DC-stimulated) Invariant NKT, NK and CIK Cells on the Outcome of Patients With AML, ALL and CLL

Invariant natural killer T (iNKT)/natural killer (NK)/cytokine-induced killer (CIK) cells are important for immune surveillance. (I) Novel combinations of antibody 6B11 (targeting the Vα24-Jα18-invariant T-cell receptor) with CD4/CD8/CD1d/Vα24 for iNKT subset detection and "T/NK cell-like"-iNKT subsets were defined. Compared with healthy peripheral blood mononuclear cells (MNC) (significantly) lower proportions of iNKT cells (6B11/6B11CD3/6B11CD161), NK cells (CD3CD56/CD3CD161), and CIK cells (CD3CD56/CD3CD161) were found in peripheral blood MNC from acute myeloid (AML)/acute myeloid, lymphoid (ALL)/chronic lymphoid leukemia (CLL) patients in acute disease stages. Subtyping of iNKT cells revealed (significantly) higher proportions of CD3 T cells and CD161 NK cells in AML/ALL/CLL expressing 6B11 compared with healthy MNC. Prognostic evaluations showed higher proportions of iNKT/NK/CIK cells in favorable AML subgroups (younger age, primary, no extramedullary disease, achievement/maintenance of complete remission) or adult ALL and CLL patients. (II) iNKT/NK/CIK cell frequencies increased after (vs. before) mixed lymphocyte cultures of T-cell-enriched immune reactive cells stimulated with MNC/whole blood with or without pretreatment with "cocktails" (dendritic cells generating methods/kits inducing blasts' conversion to leukemia-derived dendritic cells from AML patients). Individual "cocktails" leading to "highest" iNKT cell frequencies could be defined. Antileukemic blast lytic activity correlated significantly with frequencies of iNKT/NK/CIK cells. In summary healthy MNC show significantly more iNKT/NK/CIK cells compared with AML/ALL/CLL MNC, a shift in the iNKT cell composition is seen in healthy versus leukemic samples and iNKT/NK/CIK cell-proportions in AML/ALL/CLL MNC samples correlate with prognosis. "Cocktail"-treated AML blasts lead to higher iNKT/NK/CIK cell frequencies and samples with antileukemic activity show significantly higher frequencies of iNKT/NK/CIK cells. Proportions of iNKT/NK/CIK cells should regularly be evaluated in AML/ALL/CLL diagnosis panels for quantitative/prognostic estimation of individual patients' antileukemic potential and their role in dendritic cells/leukemia-derived dendritic cells triggered immune surveillance.

Immune therapies in acute myeloid leukemia: a focus on monoclonal antibodies and immune checkpoint inhibitors

PURPOSE OF REVIEW

This review discusses the rationale, efficacy, and toxicity of a variety of immune approaches being evaluated in the therapy of acute myeloid leukemia (AML) including naked and conjugated monoclonal antibodies, bispecific T-cell engager antibodies, and immune checkpoint blockade via antibodies targeting cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed-death 1 (PD-1).

RECENT FINDINGS

The stellar success of immune therapies that harness the power of T cells in solid tumors and an improved understanding of the immune system in patients with hematologic malignancies have resulted in major efforts to develop immune therapies for the treatment of patients with AML. Monoclonal antibodies in AML therapy include naked antibodies against AML surface antigens such as CD33 (e.g. lintuzumab) or CD38 (e.g. daratumumab), antibodies conjugated to toxins in various anti-CD33 (gemtuzumab ozogamicin, SGN33A, IMGN779) and anti-CD123 (SL-401, SGN-CD123A) formulations, and antibodies conjugated to radioactive particles such as I or Ac-labeled anti-CD33 or anti-CD45 antibodies. Additional antigenic targets of interest in AML include CLL1, CD38, CD25, TIM3, FLT3, and others. Approaches to harness the body's own T cells against AML include antibodies that recruit and induce cytotoxicity of tumor cells by T cells (bispecific T-cell engager [BiTE] such as CD33 x CD3 (e.g. AMG 330) or CD123 x CD3 (e.g. flotetuzumab, JNJ-63709178) or antibodies that block immune checkpoint receptors CTLA4 (e.g. ipilimumab) or PD1/PD-L1 (e.g. nivolumab, pembrolizumab, avelumab) on T cells, unleashing the patients' T cells against leukemic cells.

SUMMARY

The ongoing trials and well designed correlative interrogation of the immune system in patients treated on such trials will further enhance our understanding and clinical application of immune therapies as single-agent and combination approaches for the treatment of AML.

Immunomodulatory Drugs: Immune Checkpoint Agents in Acute Leukemia

Intrinsic immune responses to acute leukemia are inhibited by a variety of mechanisms, such as aberrant antigen expression by leukemia cells, secretion of immunosuppressive cytokines and expression of inhibitory enzymes in the tumor microenvironment, expansion of immunoregulatory cells, and activation of immune checkpoint pathways, all leading to T cell dysfunction and/or exhaustion. Leukemic cells, similar to other tumor cells, hijack these inhibitory pathways to evade immune recognition and destruction by cytotoxic T lymphocytes. Thus, blockade of immune checkpoints has emerged as a highly promising approach to augment innate anti-tumor immunity in order to treat malignancies. Most evidence for the clinical efficacy of this immunotherapeutic strategy has been seen in patients with metastatic melanoma, where anti-CTLA-4 and anti-PD-1 antibodies have recently revolutionized treatment of this lethal disease with otherwise limited treatment options. To meet the high demand for new treatment strategies in acute leukemia, clinical testing of these promising therapies is commencing. Herein, we review the biology of multiple inhibitory checkpoints (including CTLA-4, PD-1, TIM-3, LAG-3, BTLA, and CD200R) and their contribution to immune evasion by acute leukemias. In addition, we discuss the current state of preclinical and clinical studies of immune checkpoint inhibition in acute leukemia, which seek to harness the body's own immune system to fight leukemic cells.

The emerging role of immune checkpoint based approaches in AML and MDS

The development of immune checkpoint inhibitors represents a major breakthrough in the field of cancer therapeutics. Pursuant to their success in melanoma and numerous solid tumor malignancies, these agents are being investigated in hematological malignancies including acute myelogenous leukemia (AML) and myelodysplastic syndromes (MDS). Although AML/MDS have traditionally been considered to be less immunogenic than solid tumor malignancies, recent pre-clinical models suggest a therapeutic role for immune checkpoint inhibition in these diseases. CTLA-4 inhibition may be especially effective in treating late post-allogeneic stem cell transplant relapse of AML in patients with limited or no graft versus host disease. Immune checkpoint inhibition, specifically PD-1 inhibition, demonstrated limited single agent efficacy in patients with relapsed AML and with MDS post-hypomethylating therapy. Rationally designed combinations of PD-1 inhibitors with standard anti-leukemic therapy are needed. Hypomethylating agents such as azacitidine, up-regulate PD-1, PD-L1, and PD-L2 in patients with AML/MDS and up-regulation of these genes was associated with the emergence of resistance. The combination of azacitidine and PD-1/PD-L1 inhibition may be a potential mechanism to prevent or overcome resistance to 5-azacitidine. A number of such combinations are being evaluated in clinical trials with early encouraging results. Immune checkpoint inhibition is also an attractive option to improve relapse-free survival or eliminate minimal residual disease post induction and consolidation by enhancing T-cell surveillance in patients with high-risk AML. The ongoing clinical trials with checkpoint inhibitors in AML/MDS will improve our understanding of the immunobiology of these diseases and guide us to the most appropriate application of these agents in the therapy of AML/MDS.

Harnessing the Immune System Against Leukemia: Monoclonal Antibodies and Checkpoint Strategies for AML

Acute myeloid leukemia (AML) is the most common leukemia among adults and is associated with a poor prognosis, especially in patients with adverse prognostic factors, older age, or relapsed disease. The last decade has seen a surge in successful immune-based therapies in various solid tumors; however, the role of immune therapies in AML remains poorly defined. This chapter describes the rationale, clinical data, and toxicity profiles of immune-based therapeutic modalities in AML including naked and conjugated monoclonal antibodies, bispecific T-cell engager antibodies, chimeric antigen receptor (CAR)-T cells, and checkpoint blockade via blockade of PD1/PDL1 or CTLA4. Monoclonal antibodies commonly used in AML therapy target highly expressed "leukemia" surface antigens and include (1) naked antibodies against common myeloid markers such as anti-CD33 (e.g., lintuzumab), (2) antibody-drug conjugates linked to either, (a) a highly potent toxin such as calicheamicin, pyrrolobenzodiazepine, maytansine, or others in various anti-CD33 (gemtuzumab ozogamicin, SGN 33A), anti-123 (SL-401), and anti-CD56 (lorvotuzumab mertansine) formulations, or (b) radioactive particles, such as 131I, 213Bi, or 225Ac-labeled anti-CD33 or CD45 antibodies. Novel monoclonal antibodies that recruit and promote proximity-induced cytotoxicity of tumor cells by T cells (bispecific T-cell engager [BiTE] such as anti CD33/CD3, e.g., AMG 330) or block immune checkpoint pathways such as CTLA4 (e.g., ipilimumab) or PD1/PD-L1 (e.g., nivolumab) unleashing the patients T cells to fight leukemic cells are being evaluated in clinical trials in patients with AML. The numerous ongoing clinical trials with immunotherapies in AML will improve our understanding of the biology of AML and allow us to determine the best approaches to immunotherapy in AML.

Targeting Immune Checkpoints in Hematologic Malignancies

The use of antibodies that target immune checkpoint molecules on the surface of T-lymphocytes and/or tumor cells has revolutionized our approach to cancer therapy. Cytotoxic-T-lymphocyte antigen (CTLA-4) and programmed cell death protein 1 (PD-1) are the two most commonly targeted immune checkpoint molecules. Although the role of antibodies that target CTLA-4 and PD-1 has been established in solid tumor malignancies and Food and Drug Administration approved for melanoma and non-small cell lung cancer, there remains a desperate need to incorporate immune checkpoint inhibition in hematologic malignancies. Unlike solid tumors, a number of considerations must be addressed to appropriately employ immune checkpoint inhibition in hematologic malignancies. For example, hematologic malignancies frequently obliterate the bone marrow and lymph nodes, which are critical immune organs that must be restored for appropriate response to immune checkpoint inhibition. On the other hand, hematologic malignancies are the quintessential immune responsive tumor type, as proven by the success of allogeneic stem cell transplantation (allo-SCT) in hematologic malignancies. Also, sharing an immune cell lineage, malignant hematologic cells often express immune checkpoint molecules that are absent in solid tumor cells, thereby offering direct targets for immune checkpoint inhibition. A number of clinical trials have demonstrated the potential for immune checkpoint inhibition in hematologic malignancies before and after allo-SCT. The ongoing clinical studies and complimentary immune correlatives are providing a growing body of knowledge regarding the role of immune checkpoint inhibition in hematologic malignancies, which will likely become part of the standard of care for hematologic malignancies.

Functional exhaustion of CD4+ T cells induced by co-stimulatory signals from myeloid leukaemia cells

To cope with immune responses, tumour cells implement elaborate strategies such as adaptive resistance and induction of T-cell exhaustion. T-cell exhaustion has been identified as a state of hyporesponsiveness that arises under continuous antigenic stimulus. Nevertheless, contribution of co-stimulatory molecules to T-cell exhaustion in cancer remains to be better defined. This study explores the role of myeloid leukaemia-derived co-stimulatory signals on CD4⁺ T helper (Th) cell exhaustion, which may limit anti-tumour immunity. Here, CD86 and inducible T-cell co-stimulator ligand (ICOS-LG) co-stimulatory molecules that are found on myeloid leukaemia cells supported Th cell activation and proliferation. However, under continuous stimulation, T cells co-cultured with leukaemia cells, but not with peripheral blood monocytes, became functionally exhausted. These in vitro-generated exhausted Th cells were defined by up-regulation of programmed cell death 1 (PD-1), cytotoxic T-lymphocyte antigen 4 (CTLA-4), lymphocyte activation gene 3 (LAG3) and T-cell immunoglobulin and mucin domain-containing protein 3 (TIM-3) inhibitory receptors. They were reluctant to proliferate upon re-stimulation and produced reduced amounts of interleukin-2 (IL-2), tumour necrosis factor-α (TNF-α) and interferon-γ (IFN-γ). Nonetheless, IL-2 supplementation restored the proliferation capacity of the exhausted Th cells. When the co-stimulation supplied by the myeloid leukaemia cells were blocked, the amount of exhausted Th cells was significantly decreased. Moreover, in the bone marrow aspirates from patients with acute myeloid leukaemia (AML) or myelodysplastic syndrome (MDS), a subpopulation of Th cells expressing PD-1, TIM-3 and/or LAG3 was identified together with CD86⁺ and/or ICOS-LG⁺ myeloid blasts. Collectively, co-stimulatory signals derived from myeloid leukaemia cells possess the capacity to facilitate functional exhaustion in Th cells.

Expression of 4-1BB and its ligand on blasts correlates with prognosis of patients with AML

Costimulatory ligands (COLs) and their receptors (COR) regulate immune reactions and cellular survival and might be relevant in acute myeloid leukemia (AML). This study evaluated the clinical relevance of 4-1BBL, glucocorticoid-induced TNFR-related protein (GITR) and ligand (GITRL), CD80, and CD86 in case of expression on AML blasts. 98 patients were evaluated at initial diagnosis. Immunophenotypically evaluated specific fluorescence index (SFI) levels of COR and COL on blasts were correlated with morphological, cytogenetic, and several prognostic parameters. Significantly higher COR expression was seen in monocytic versus non-monocytic AML subtypes; GITR, p=0.05; GITRL, p=0.005; CD86, p=0.001). Cut-off values for two COR and their ligands were evaluated: cases presenting with 4-1BB values above cut-off 1.2 SFI levels correlated (tendentially) significantly with a higher probability for disease-free survival (DFS, p=0.06) and a favorable HR of 0.2; p=0.04 for relapse. HR for death was also significantly lower in this group (0.12; p=0.04). In contrast, a lower probability for DFS and overall survival was seen in cases with 4-1BBL expression above 2.2 SFI levels (p=0.08 and p=0.09). In addition, multivariate analysis showed a significantly higher probability of death in this group (HR 10.3, p=0.04). Expression of CD80 and CD86 did not show significant prognostic relevance. On initial diagnosis, 4-1BB and 4-1BBL qualify as markers for prediction of patients' course and represent a valuable screening target for patients with AML at initial diagnosis.

Clinical Courses of Two Pediatric Patients with Acute Megakaryoblastic Leukemia Harboring the CBFA2T3-GLIS2 Fusion Gene

Acute megakaryoblastic leukemia (AMKL) in children without Down syndrome (DS) has an extremely poor outcome with 3-year survival of less than 40%, whereas AMKL in children with DS has an excellent survival rate. Recently, a novel recurrent translocation involving CBFA2T3 and GLIS2 was identified in about 30% of children with non-DS AMKL, and the fusion gene was reported as a strong poor prognostic factor in pediatric AMKL. We report the difficult clinical courses of pediatric patients with AMKL harboring the CBFA2T3-GLIS2 fusion gene.

Novel immunotherapeutic approaches for the treatment of acute leukemia (myeloid and lymphoblastic)

There have been major advances in our understanding of the multiple interactions between malignant cells and the innate and adaptive immune system. While the attention of immunologists has hitherto focused on solid tumors, the specific immunobiology of acute leukemias is now becoming defined. These discoveries have pointed the way to immune interventions building on the established graft-versus-leukemia (GVL) effect from hematopoietic stem-cell transplant (HSCT) and extending immunotherapy beyond HSCT to individuals with acute leukemia with a diversity of immune manipulations early in the course of the leukemia. At present, clinical results are in their infancy. In the coming years larger studies will better define the place of immunotherapy in the management of acute leukemias and lead to treatment approaches that combine conventional chemotherapy, immunotherapy and HSCT to achieve durable cures.

T-cell ligands modulate the cytolytic activity of the CD33/CD3 BiTE antibody construct, AMG 330

Preclinical and emerging clinical studies demonstrate that bispecific T-cell engaging (BiTE) antibody constructs can potently lyse targeted tumor cells, but the determinants for their activity remain incompletely understood. Using human acute myeloid leukemia (AML) cell lines engineered to overexpress individual T-cell ligands, we found that expression of the inhibitory ligands, PD-L1 and PD-L2, reduced the cytolytic activity of the BiTE antibody construct targeting CD33, AMG 330; conversely, expression of the activating ligands, CD80 and CD86, augmented the cytotoxic activity of AMG 330. Consistent with these findings, treatment with an activating antibody directed at the co-stimulatory T-cell receptor, CD28, significantly increased AMG 330-induced cytotoxicity in human AML cell lines. Using specimens from 12 patients with newly diagnosed or relapsed/refractory AML, we found that activation of CD28 also increased the activity of AMG 330 in primary human AML cells (P=0.023). Together, our findings indicate that T-cell ligands and co-receptors modulate the anti-tumor activity of the CD33/CD3 BiTE antibody construct, AMG 330. These findings suggest that such ligands/co-receptors could serve as biomarkers of response and that co-treatment strategies with pharmacological modulators of T-cell receptor signaling could be utilized to further enhance the activity of this targeted therapeutic.

Adaptive resistance: a tumor strategy to evade immune attack

A dilemma in cancer immunology is that, although patients often develop active antitumor immune responses, the tumor still outgrows. It has become clear that under the pressure of the host's immune system, cancer cells have adapted elaborate tactics to reduce their immunogenicity (also known as immunoselection) and/or to actively suppress immune cells and promote immune tolerance (also known as immunosubversion). In this issue of the European Journal of Immunology, Dolen and Esendagli [Eur. J. Immunol. 2013. 43: 747-757] show that acute myeloid leukemia (AML) cells develop an adaptive immune phenotype switching mechanism: In response to attack by activated T cells, the leukemia cells quickly downregulate the T-cell costimulatory ligand B7-H2 and reciprocally upregulate the coinhibitory ligands B7-H1 and B7-DC in order to shut down T-cell activation via the PD-1 pathway. These novel findings and their relevance for cancer immunotherapy, especially potential applications in PD-1 check-point blockade therapy are discussed in this Commentary.

Combined immunophenotyping and fluorescence in situ hybridization with chromosome-specific DNA probes allows quantification and differentiation of ex vivo generated dendritic cells, leukemia-derived dendritic cells and clonal leukemic cells in patients with acute myeloid leukemia

Antileukemic T-cell responses induced by leukemia-derived dendritic cells (DC(leu)) are variable, due to varying DC/DC(leu) composition/quality. We studied DC/DC(leu) composition/quality after blast culture in four DC media by flow cytometry (FC) and combined fluorescence in situ hybridization/immunophenotyping analysis (FISH-IPA). Both methods showed that DC methods produce variable proportions of DC subtypes. FISH-IPA is an elaborate method to study clonal aberrations in blast/DC cells on slides, however without preselection of distinct cell populations for FISH analysis. FISH-IPA data proved previous FC data: not every clonal/blast cell is converted to DC(leu) (resulting in various proportions of DC(leu)) and not every detectable DC is of clonal/leukemic origin. Preselection of the best of four DC methods for "best" DC/DC(leu) generation is necessary. DC(leu) proportions correlate with the antileukemic functionality of DC/DC(leu)-stimulated T-cells, thereby proving the necessity of studying the quality of DC/DC(leu) after culture. FC is the superior method to quantify DC/DC(leu), since a blast phenotype is available in every given patient, even with low/no proportions of clonal aberrations, and can easily be used to study cellular compositions after DC culture.

Various ‘dendritic cell antigens’ are already expressed on uncultured blasts in acute myeloid leukemia and myelodysplastic syndromes

Aim and methods: Leukemia-derived dendritic cells (DCleu) potentially present the whole leukemic antigen repertoire. We studied antigen-expression profiles of blasts/dendritic cells (DCs) generated from 137 acute myeloid leukemia (AML)/49 myelodysplastic syndromes (MDS) patients with six different DC-generating media by flow-cytometry combining expression of blast/maturation and DC antigens (DCA:CD1a,b,c, CD25, CD40, CD80, CD83, CD86, CD137-L and CD206). Results: First, DCA are regularly and variably expressed on uncultured blasts/mononuclear cells (MNCs). Individual patients’ DCA profiles must be evaluated before DC-culture to find suitable DCA to estimate quality/quantity of DC after culture. Second, after culture in every patient, at least one marker fulfilled these criteria. Third, different DC-generating methods showed varying efficiency to generate DC: not every method was always successful. Fourth, individual FACS-DCA profiles showed a successful DC/DCleu generation with at least one of three previously tested methods in every given AML/MDS case. Fifth, pooling results of all selected best methods in every given case, 28/30% DC were generated from AML/MDS samples: >60% viable DC, on average 49/56% mature DC and on average 36% of blasts were convertible to DCleu resulting in on average 49% DCleu of AML-DC. Conclusions: Individual DCA-expression profiles should be evaluated before culture to evaluate DC counts/subtypes (mature/viableDC, DCleu) in individual patients.

Dendritic cells (DCs) can be successfully generated from leukemic blasts in individual patients with AML or MDS: an evaluation of different methods

Myeloid-leukemic cells (AML, MDS, CML) can be differentiated to leukemia-derived dendritic cell [DC (DCleu)] potentially presenting the whole leukemic antigen repertoire without knowledge of distinct leukemia antigens and are regarded as promising candidates for a vaccination strategy. We studied the capability of 6 serum-free DC culture methods, chosen according to different mechanisms, to induce DC differentiation in 137 cases of AML and 52 cases of MDS. DC-stimulating substances were cytokines ("standard-medium", "MCM-Mimic", "cytokine-method"), bacterial lysates ("Picibanil"), double-stranded RNA ["Poly (I:C)"] or a cytokine bypass method ("Ca-ionophore"). The quality/quantity of DC generated was estimated by flow cytometry studying (co) expressions of "DC"antigens, costimulatory, maturation, and blast-antigens. Comparing these methods on average 15% to 32% DC, depending on methods used, could be obtained from blast-containing mononuclear cells (MNC) in AML/MDS cases with a DC viability of more than 60%. In all, 39% to 64% of these DC were mature; 31% to 52% of leukemic blasts could be converted to DCleu and DCleu-proportions in the suspension were 2% to 70% (13%). Average results of all culture methods tested were comparable, however not every given case of AML could be differentiated to DC with 1 selected method. However performing a pre-analysis with 3 DC-generating methods (MCM-Mimic, Picibanil, Ca-ionophore) we could generate DC in any given case. Functional analyses provided proof, that DC primed T cells to antileukemia-directed cytotoxic cells, although an anti-leukemic reaction was not achieved in every case. In summary our data show that a successful, quantitative DC/DCleu generation is possible with the best of 3 previously tested methods in any given case. Reasons for different functional behaviors of DC-primed T cells must be evaluated to design a practicable DC-based vaccination strategy.

Evaluation of the prognostic relevance of L-selectin and ICAM1 expression in myelodysplastic syndromes

OBJECTIVES

An aberrant pattern of expression of L-selectin and intercellular adhesion molecule 1 (ICAM1) may characterise CD34+ blast cells in myelodysplastic syndromes (MDS) and secondary acute myeloid leukaemia (sAML).

METHODS

In a three-colour flow cytometric assay, we evaluated the expression of L-selectin and ICAM1 on CD34+ blast cells from the bone marrow (BM) of 66 MDS patients; for the purpose of comparison CD34+ blast cells of 18 sAML and CD34+ stem cells of 17 normal donors were also analysed.

RESULTS

The ratio of L-selectin/ICAM1 expression was identified as a parameter correlated with the percentage of BM blast infiltration and the time to leukaemic progression among MDS patients. In fact, the values of L-selectin/ICAM1 ratio were inversely correlated with the BM blast infiltration (r = -0.34, P = 0.004). Furthermore, MDS patients with a baseline ratio <1 had a higher leukaemic progression rate (41% vs. 19%, P = 0.008); the actuarial risk of disease progression for this subgroup of MDS patients was also higher (64% vs. 11% at 2 yr, P = 0.002). Furthermore, in two patients a decrease of the ratio was observed when overt leukaemic transformation occurred; conversely, restoration of a normal ratio was observed in two patients after a chemotherapy-induced remission.

CONCLUSION

(i) L-selectin is defective in the stem cell compartment of MDS and sAML, whereas ICAM1 is overexpressed; (ii) the ratio of their expression has a prognostic role; and (iii) a ratio <1 significantly predicts progression to overt leukaemia in MDS patients.

Specific inhibition of basal mitogen-activated protein kinases and phosphatidylinositol 3 kinase activities in leukemia cells: a possible therapeutic role for the kinase inhibitors

OBJECTIVE

The roles of phosphatidylinositol 3 (PI3K) and mitogen-activated protein kinases (MAPK) have been widely studied in terms of the differentiation process induced by several drugs (phorbol ester, vitamin D-3, retinoic acid, etc.), but their exact functions in leukemic cells' phenotype and their potential therapeutic role remain incompletely clarified.

MATERIALS AND METHODS

In order to investigate this query, leukemia cells were cultured in presence of kinase inhibitors (KIs). Proliferation, apoptosis, and differentiation were analyzed at the cellular and molecular levels, using flow cytometry and reverse transcriptase quantitative polymerase chain reaction.

RESULTS

SB203580, a P38 MAPK inhibitor, had no effect on cell proliferation, whereas LY294002, a PI3K inhibitor, and PD098059, a selective inhibitor of mitogen-activated extracellular regulated kinase (MEK) phosphorylation, arrested cells in G(0)/G(1). However, LY294002 and PD098059 acted using different mechanisms: LY294002 decreased the expression of phosphorylated S6RP, whereas PD098059 increased P21/waf1 antigen expression. SP600125, an inhibitor of N-terminal c-jun kinases, arrested cells in G(2) and induced an endoreplicative process. SP600125 increased p21 at both the mRNA and protein levels. G(2) blockage is dependent on the PI3K pathway and the endoreplicative process is dependent on the PI3K and extracellular regulated kinase (ERK) pathways and mRNA synthesis. On the other hand, PD098059 potentiated the apoptotic process induced by either SP600125 or LY294002. Modulation of the expression of CD11, CD15, CD18, and CD54 was cell-dependent.

CONCLUSION

Our results suggest that KIs modulate proliferation of leukemia cells and that the MEK/ERK inhibitor, PD098059, in combination with either SP600125 or LY294002, could have clinical value.

CTLA-4 expressed by chemoresistant, as well as untreated, myeloid leukaemia cells can be targeted with ligands to induce apoptosis

We have previously reported that about 80% of acute myeloid leukaemia (AML) samples tested at diagnosis constitutively expressed cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4). The present study compared CTLA-4 expression and function of leukaemic cells from AML patients at diagnosis with those from AML patients resistant to conventional chemotherapy. We also explored the possibility of targeting CTLA-4 for apoptosis induction in chemoresistant AML cells. AML cells either from untreated patients (n = 15) or in chemoresistant phase (n = 10) were analysed for CTLA-4 protein and transcript expression by flow cytometry and reverse transcription-polymerase chain reaction respectively. CTLA-4 expression was similar in untreated and in chemoresistant samples and was not associated with patients' clinical features. In chemoresistant AML cells, CTLA-4 transduced an apoptotic signal on engagement with its recombinant ligands r-CD80 and r-CD86, which induced an average of 71% and 62% apoptotic cells, respectively, at highest concentration. Apoptosis was equally induced in untreated leukaemic cells accompanied by cleavage of procaspase-8 and -3. Thus, this study provides the first evidence that killing of leukaemic cells from AML patients may be obtained by the engagement of CTLA-4 with its ligands, opening the way to a novel potential therapeutic approach based on triggering the CTLA-4 molecule to circumvent chemoresistance in AML.

Predictable prognostic factor of CD56 expression in patients with acute myeloid leukemia with t(8:21) after high dose cytarabine or allogeneic hematopoietic stem cell transplantation

CD56 expression in acute myeloid leukemia (AML) has been associated with extramedullary leukemia and multidrug resistance, but its clinical and prognostic significance has not been clearly identified. This study examined CD56 expression in 37 adult de novo AML patients with t(8:21). CD56 was expressed in 25 cases (67.6%). Complete remission (CR) rates were similar in both groups (91.7% vs. 88.7%; P = 0.73), but the relapse rates differed considerably (60% vs. 25%; P = 0.02). The median duration of disease-free survival (DFS) was significantly shorter in the CD56+ (median, 12.2 +/- 6.4 months) than in the CD56- group (median, not reached) (P = 0.02). In addition, the median duration of survival differed significantly in the CD56+ group (median, 14.9 +/- 4.4 months) compared with the CD56- group (median, not reached) (P = 0.01). Of the fifteen transplanted patients who achieved CR, allogeneic HST was performed from their siblings. The median duration of DFS in the CD56+ patients was significantly shorter than the CD56- patients (median, 24.4 +/- 4.5 months vs. median, not reached; P = 0.02). We concluded that CD56 expression correlates to a reduced DFS and survival for AML patients with t(8:21), including those patients who underwent transplantation.

Molecular profiling reveals myeloid leukemia cell lines to be faithful model systems characterized by distinct genomic aberrations

To model and investigate different facets of leukemia pathogenesis, a widely accepted approach is to use immortalized leukemia cell lines. Although these provide powerful tools to our knowledge, few studies have addressed the question whether hematopoietic cell lines represent accurate and reliable model systems. To improve the molecular characterization of these model systems, we analyzed 17 myeloid leukemia cell lines using DNA microarray technology. By array-based comparative genomic hybridization, we identified recurrent genomic DNA gains and losses, as well as high-level amplifications. Parallel analysis of gene expression helped delineate potential candidate genes, and unsupervised analysis of gene expression data revealed cell lines to cluster in part based on underlying cytogenetic abnormalities. Comparison with clinical leukemia specimens showed that key signatures were retained, as myeloid cell lines with characteristic cytogenetic aberrations co-clustered with leukemia samples carrying the respective abnormality. Signatures were also quite robust, as expression data from cell lines correlated highly with published data. Thus, our analyses demonstrate myeloid cell lines to exhibit conserved and stable signatures reflecting the underlying primary cytogenetic aberrations. Our refined molecular characterization of myeloid cell lines supports the utility of cell lines as faithful and powerful model systems and provides additional insights into the molecular mechanisms of leukemogenesis.

Whole-blood leukoreduction filters are a source for cryopreserved cells for phenotypic and functional investigations on peripheral blood lymphocytes

BACKGROUND

Leukoreduction of blood is now widely performed by blood banks, and the possibility of recovering 10(8) to 10(9) white blood cells (WBCs) from leukoreduction filters, which are usually discarded, represents a promising source for normal human cells. Previous studies with these filters to prepare WBCs have performed their experimentation with fresh cells only. Whether these filter-derived cells could also be used to prepare frozen cell banks to facilitate work organization and open new avenues for their utilization as references in physiological studies and clinical investigations was investigated.

STUDY DESIGN AND METHODS

Blood samples or whole-blood leukoreduction filters were obtained, after informed consent, from volunteers or blood donors, respectively. The proportions of CD3+, CD14+, CD16+, CD19+, and CD45+ cells within peripheral blood mononuclear cells (PBMNCs) were determined by flow cytometry from all samples. B cells were isolated and their functional responses were evaluated in vitro.

RESULTS

The yield of PBMNCs recovered from whole-blood leukoreduction filters was lower (50%) than the one with fresh blood samples but still provided 2 x 10(8) to 4 x 10(8) PBMNCs per unit. After one cycle of freezing-thawing, the proportions of B- and T-cell populations were similar to normal blood values. Purified B cells issued from whole-blood leukoreduction filters displayed normal phenotypes and functions.

CONCLUSION

Leukoreduction filters represent a valuable source of PBMNCs. These cells could be easily recovered to prepare frozen cell banks useful in basic phenotypic and functional analyses involving the main subsets of B cells and the global T-cell population.

Expression of MAC-1 (CD11b) in acute myeloid leukemia (AML) is associated with an unfavorable prognosis

There is evidence to suggest, that cellular adhesion molecules and receptors could play a role in leukemia, e.g., through altered adhesive qualities of leukemic blasts. We have studied the expression of the beta2-integrin Mac-1 (CD11b) on mononuclear cells in 48 patients with AML at first diagnosis by flow cytometry using a direct fluorescein-conjugated antibody. A case was defined as positive if more than 20% of the cells expressed Mac-1. Within the FAB types, we observed a high expression rate in cases with M5 (100% MAC-1+ cases, 73% MAC-1+ cells), M4 (75% MAC-1+ cases, 48% MAC-1+ cells) and in cases with FAB-M1 with 71% MAC-1+ cases and 29% MAC-1+ cells. Separating our patients' cohort in cytogenetic risk groups, we could detect significant higher proportions of MAC-1+, cases (88% vs. 27%, P = 0.005) and cells (51% vs. 16%, P = 0.015) with poor cytogenetic risk compared to the favorable risk group. For clinical evaluations only patients treated according to the protocols of the German AML Cooperative Group (AML-CG) were included (n = 29, cases with AML-M3 were excluded). More MAC-1+ cases and cells were found in the "non-responders" group (n = 8) compared to the "responders" group (n = 24). We can conclude that AML cases with high MAC-1 expression are characterized by a worse prognosis. Evaluation of MAC-1 expression in AML might therefore contribute clinically important data with respect to develop new therapies that influence the interactions between integrins like MAC-1 on leukemic cells and endothelial or immunoreactive cells.

Correlation between expression of CD56/NCAM and severe leukostasis in hyperleukocytic acute myelomonocytic leukaemia

OBJECTIVE

The possible contribution of surface molecules to the development of leukostasis syndrome in hyperleukocytic acute myeloid leukaemia (AML) was assessed by routine immunophenotyping and grading of the probability of clinical leukostasis.

METHODS

Fifty-three patients (23 women, 30 men, median age 59 yr) with hyperleukocytic AML [white blood count (WBC) above 50 x 10(9)/L] were graded for the probability of clinical leukostasis according to the severity of neurologic, pulmonary and other symptoms possibly caused by leukostasis using a recently published scoring system. Age, WBC, absolute blast count, haemoglobin, cytogenetic risk group, infection, relative CD56 expression and absolute count of CD56 positive blasts were analyzed in multivariate stepwise backward logistic regression analysis.

RESULTS

In patients with acute monocytic leukaemia (AML M4/M5) the absolute count of leukaemic blasts expressing CD56/NCAM was highly associated with the development of symptoms graded as highly probable leukostasis and all three patients succumbing to early death were CD56 positive. Only the absolute count of CD56 positive blasts was a significant predictor of risk of severe leukostasis (P = 0.020). This was not found in AML without monocytic involvement (AML M1, M2, M3v).

CONCLUSIONS

The expression of CD56/NCAM, a surface marker used in routine immunophenotyping of AML, may help to predict severe and potentially fatal leukostasis in hyperleukocytic acute myelomonocytic leukaemia. These results emphasize the usefulness of this four-stage clinical grading scale for analysing the factors, which lead to severe leukostasis in hyperleukocytic patients. We extend previous findings that the mechanisms of leukostasis are different depending on the involvement of the monocytic lineage.