Acute myeloid leukaemia blast cells bind to human endothelium in vitro utilizing E-selectin and vascular cell adhesion molecule-1 (VCAM-1)

Understanding the interaction between leukaemia stem cells and their microenvironment to improve therapeutic approaches

Although chemotherapeutic regimens can eliminate blasts in leukaemia patients, such therapies are associated with toxicity and often fail to eliminate all malignant cells resulting in disease relapse. Disease relapse has been attributed to the persistence of leukaemia cells in the bone marrow (BM) with the capacity to recapitulate disease; these cells are often referred to as leukaemia stem cells (LSCs). Although LSCs have distinct characteristics in terms of pathobiology and immunophenotype, they are still regulated by their interactions with the surrounding microenvironment. Thus, understanding the interaction between LSCs and their microenvironment is critical to identify effective therapies. To this end, there are numerous efforts to develop models to study such interactions. In this review, we will focus on the reciprocal interactions between LSCs and their milieu in the BM. Furthermore, we will highlight relevant therapies targeting these interactions and discuss some of the promising in vitro models designed to mimic such relationship. LINKED ARTICLES: This article is part of a themed issue on Cancer Microenvironment and Pharmacological Interventions. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.2/issuetoc.

Targeting integrins in drug-resistant acute myeloid leukaemia

Acute myeloid leukaemia (AML) continues to have a poor prognosis, warranting new therapeutic strategies. The bone marrow (BM) microenvironment consists of niches that interact with not only normal haematopoietic stem cells (HSC) but also leukaemia cells like AML. There are many adhesion molecules in the BM microenvironment; therein, integrins have been of central interest. AML cells express integrins that bind to ligands in the microenvironment, enabling adhesion of leukaemia cells in the microenvironment, thereby initiating intracellular signalling pathways that are associated with cell migration, cell proliferation, survival, and drug resistance that has been described to mediate cell adhesion-mediated drug resistance (CAM-DR). Identifying and targeting integrins in AML to interrupt interactions with the microenvironment have been pursued as a strategy to overcome CAM-DR. Here, we focus on the BM microenvironment and review the role of integrins in CAM-DR of AML and discuss integrin-targeting strategies. LINKED ARTICLES: This article is part of a themed issue on Cancer Microenvironment and Pharmacological Interventions. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.2/issuetoc.

Abnormal adipogenic signaling in the bone marrow mesenchymal stem cells contributes to supportive microenvironment for leukemia development

BACKGROUND

Acute myeloid leukemia (AML) is an aggressive hematological malignancy, associated with unfavorable patient outcome, primarily due to disease relapse. Mesenchymal stem cells (MSCs) residing in the bone marrow (BM) niche are the source of mesenchyma-derived subpopulations, including adipocytes, and osteocytes, that are critical for normal hematopoiesis. This study aimed to characterize BM-derived adipocyte/osteocyte fractions and their crosstalk with AML cells as a potential mechanism underlying leukemogenesis.

METHODS

BM cell subpopulations derived from primary AML patients were evaluated using humanized ex-vivo and in-vivo models, established for this study. The models comprised AML blasts, normal hematopoietic stem and progenitor cells and mesenchymal stromal subpopulations. ELISA, FACS analysis, colony forming unit assay, whole exome sequencing and real-time qPCR were employed to assess the differentiation capacity, genetic status, gene expression and function of these cell fractions. To explore communication pathways between AML cells and BM subpopulations, levels of signaling mediators, including cytokines and chemokines, were measured using the ProcartaPlex multiplex immunoassay.

RESULTS

The study revealed deficiencies in adipogenic/osteogenic differentiation of BM-MSCs derived from AML patients, with adipocytes directly promoting survival and clonogenicity of AML cells in-vitro. In whole exome sequencing of BM-MSC/stromal cells, the AHNAK2 gene, associated with the stimulation of adipocyte differentiation, was found to be mutated and significantly under-expressed, implying its abnormal function in AML. The evaluation of communication pathways between AML cells and BM subpopulations demonstrated pronounced alterations in the crosstalk between these cell fractions. This was reflected by significantly elevated levels of signaling mediators cytokines/chemokines, in AML-induced adipocytes/osteocytes compared to non-induced MSCs, indicating abnormal hematopoiesis. Furthermore, in-vivo experiments using a fully humanized 3D scaffold model, showed that AML-induced adipocytes were the dominant component of the tumor microenvironment, providing preferential support to leukemia cell survival and proliferation.

CONCLUSIONS

This study has disclosed direct contribution of impaired functional, genetic and molecular properties of AML patient-derived adipocytes to effective protection of AML blasts from apoptosis and to stimulation of their growth in vitro and in vivo, which overall leads to disease propagation and relapse. The detected AHNAK2 gene mutations in AML-MSCs point to their involvement in the mechanism underlying abnormal adipogenesis. Video Abstract.

The biology of E-selectin ligands in leukemogenesis

Both the cascade whereby a blood-borne cell enters a tissue and the anchoring of hematopoietic stem/progenitor cells (HSPCs) within bone marrow critically pivots on cell-cell interactions mediated by E-selectin binding to its canonical carbohydrate ligand, the tetrasaccharide termed "sialylated Lewis X" (sLeX). E-selectin, a member of the selectin class of adhesion molecules that is exclusively expressed by vascular endothelium, engages sLeX-bearing glycoconjugates that adorn mature leukocytes and HSPCs, as well as malignant cells, thereby permitting these cells to extravasate into various tissues. E-selectin expression is induced on microvascular endothelial cells within inflammatory loci at all tissues. However, conspicuously, E-selectin is constitutively expressed within microvessels in skin and marrow and, additionally, is inducibly expressed at these sites. Within the marrow, E-selectin receptor/ligand interactions promote lodgment of HSPCs and their malignant counterparts within hematopoietic growth-promoting microenvironments, collectively known as "vascular niches". Indeed, E-selectin receptor/ligand interactions have been reported to regulate both hematopoietic stem, and leukemic, cell proliferative dynamics. As such, signaling induced via engagement of E-selectin ligands is gaining interest as a critical mediator of homeostatic and malignant hematopoiesis, and this review will present current perspectives on the glycoconjugates mediating E-selectin receptor/ligand interactions and their currently defined role(s) in leukemogenesis.

Present and Future Role of Immune Targets in Acute Myeloid Leukemia

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

Raised SPINK1 levels play a role in angiogenesis and the transendothelial migration of ALL cells

The present study was designed to assess whether raised Serine protease inhibitor Kazal type 1 (SPINK1) expressions modulates angiogenesis. Human umbilical vein endothelial cells (HUVECs) exposed to SPINK1 were noted to exhibit raised expressions of interleukin-8 (IL-8) as well as VCAM-1 and ICAM-1 cell adhesion molecules in a dose-dependent manner. In co-culture system of HUVECs and Acute lymphoblastic leukemia (ALL) cells, SPINK1 exposure also resulted in enhanced endothelial cell motility and ALL cells trans-endothelial migration. High concentrations of SPINK1 caused in vitro cellular reorganization into tubes in Matrigel-cultured HUVECs and induced in vivo vascularization and brain infiltration of NOD/SCID ALL model mice. The further transcriptomic analysis indicated that SPINK1 treatment altered several biological processes of endothelial cells and led to activation of the MAPK pathway. This study is the first to determine the neovascularization effects of raised SPINK1.

The Bone Marrow Microenvironment Mechanisms in Acute Myeloid Leukemia

Bone marrow (BM) is a highly complex tissue that provides important regulatory signals to orchestrate hematopoiesis. Resident and transient cells occupy and interact with some well characterized niches to produce molecular and cellular mechanisms that interfere with differentiation, migration, survival, and proliferation in this microenvironment. The acute myeloid leukemia (AML), the most common and severe hematological neoplasm in adults, arises and develop in the BM. The osteoblastic, vascular, and reticular niches provide surface co-receptors, soluble factors, cytokines, and chemokines that mediate important functions on hematopoietic cells and leukemic blasts. There are some evidences of how AML modify the architecture and function of these three BM niches, but it has been still unclear how essential those modifications are to maintain AML development. Basic studies and clinical trials have been suggesting that disturbing specific cells and molecules into the BM niches might be able to impair leukemia competencies. Either through niche-specific molecule inhibition alone or in combination with more traditional drugs, the bone marrow microenvironment is currently considered the potential target for new strategies to treat AML patients. This review describes the cellular and molecular constitution of the BM niches under healthy and AML conditions, presenting this anatomical compartment by a new perspective: as a prospective target for current and next generation therapies.

Leukapheresis Does Not Improve Early Survival Outcome of Acute Myeloid Leukemia with Leukostasis Patients - A Dual-Center Retrospective Cohort Study

Introduction

Leukostasis is a medical emergency with high mortality which often occurs in acute myeloid leukemia patients with hyperleukocytosis. One of the therapies that can be used for leukostasis in acute myeloid leukemia is leukapheresis. However, whether leukapheresis can provide better survival benefit when compared with patients not receiving leukapheresis is still unclear. Hence, we aimed to evaluate the effect of chemotherapy plus leukapheresis combination versus chemotherapy only on 28-day survival of acute myeloid leukemia patients with leukostasis.

Methods

This study was a dual-center retrospective cohort using secondary data from medical records collected from November 2018 to March 2019. Inclusion criteria were adult patients aged 18 years old or above, diagnosed with acute leukemia with hyperleukocytosis status defined by WBC count greater than 100,000/uL, and with symptoms of leukostasis. One-month survival analysis was conducted using Kaplan–Meier curve method. Univariate and multivariate analyses were then conducted using Cox proportional hazards model to obtain value of hazard ratio (HR) with a 95% confidence interval (CI).

Results

A total of 38 patients were obtained for analysis. The median overall survival was 25 days (95% CI: 17.001–32.999 days) in the chemotherapy only group and 20 days (95% CI: 1.497–38.503) in the chemotherapy with leukapheresis group. The use of leukapheresis did not affect 28-day survival (HR: 1.140; 95% CI: 0.396–3.283; p value: 0.809) and 7-day survival (HR: 1.073; 95% CI: 0.277–4.152; p value: 0.919). In the multivariate analysis, age ≥60 years, blast percentage ≥90%, creatinine ≥1.4 mg/dL, and presence of disseminated intravascular coagulation were associated with worse 28-day survival.

Conclusion

AML patients with leukostasis who received both chemotherapy and leukapheresis did not have better 28-day survival and 7-day survival when compared with patients receiving chemotherapy only. Old age, high blast percentage, high creatinine, and presence of disseminated intravascular coagulation were prognostic factors for worse 28-day survival.

Characterization of somatic mutation-associated microenvironment signatures in acute myeloid leukemia patients based on TCGA analysis

Recurrent genetic mutations occur in acute myeloid leukemia (AML) and have been incorporated into risk stratification to predict the prognoses of AML patients. The bone marrow microenvironment plays a critical role in the development and progression of AML. However, the characteristics of the genetic mutation-associated microenvironment have not been comprehensively identified to date. In this study, we obtained the gene expression profiles of 173 AML patients from The Cancer Genome Atlas (TCGA) database and calculated their immune and stromal scores by applying the ESTIMATE algorithm. Immune scores were significantly associated with OS and cytogenetic risk. Next, we categorized the intermediate and poor cytogenetic risk patients into individual-mutation and wild-type groups according to RUNX1, ASXL1, TP53, FLT3-ITD, NPM1 and biallelic CEBPA mutation status. The relationships between the immune microenvironment and each genetic mutation were investigated by identifying differentially expressed genes (DEGs) and conducting functional enrichment analyses of them. Significant immune- and stromal-relevant DEGs associated with each mutation were identified, and most of the DEGs (from the FLT3-ITD, NPM1 and biallelic CEBPA mutation groups) were validated in the GSE14468 cohort downloaded from the Gene Expression Omnibus (GEO) database. In summary, we identified key immune- and stromal-relevant gene signatures associated with genetic mutations in AML, which may provide new biomarkers for risk stratification and personalized immunotherapy.

Hyperleukocytosis and Leukostasis in Acute Myeloid Leukemia: Can a Better Understanding of the Underlying Molecular Pathophysiology Lead to Novel Treatments?

Up to 18% of patients with acute myeloid leukemia (AML) present with a white blood cell (WBC) count of greater than 100,000/µL, a condition that is frequently referred to as hyperleukocytosis. Hyperleukocytosis has been associated with an adverse prognosis and a higher incidence of life-threatening complications such as leukostasis, disseminated intravascular coagulation (DIC), and tumor lysis syndrome (TLS). The molecular processes underlying hyperleukocytosis have not been fully elucidated yet. However, the interactions between leukemic blasts and endothelial cells leading to leukostasis and DIC as well as the processes in the bone marrow microenvironment leading to the massive entry of leukemic blasts into the peripheral blood are becoming increasingly understood. Leukemic blasts interact with endothelial cells via cell adhesion molecules such as various members of the selectin family which are upregulated via inflammatory cytokines released by leukemic blasts. Besides their role in the development of leukostasis, cell adhesion molecules have also been implicated in leukemic stem cell survival and chemotherapy resistance and can be therapeutically targeted with specific inhibitors such as plerixafor or GMI-1271 (uproleselan). However, in the absence of approved targeted therapies supportive treatment with the uric acid lowering agents allopurinol and rasburicase as well as aggressive intravenous fluid hydration for the treatment and prophylaxis of TLS, transfusion of blood products for the management of DIC, and cytoreduction with intensive chemotherapy, leukapheresis, or hydroxyurea remain the mainstay of therapy for AML patients with hyperleukocytosis.

Communication between stromal and hematopoietic stem cell by exosomes in normal and malignant bone marrow niche

Extracellular vesicles (EVs) have been regarded as important tools for cell-cell communication. They act as carriers for the transfer of various molecules such as genes, proteins and miRNA. EVs shift and transfer their ingredients to target cells in an active form. These particles have prominent roles in modulation of bone marrow (BM) niche; therefore they can regulate proliferation, differentiation, and other properties of hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs). This review discusses the different roles of EVs on BM niche; HPCs fate regulation and downstream effects of them on HSCs. Moreover, cellular and molecular mechanisms of BM microenvironment cross-talking are explained in healthy and malignant settings.

Leukocytapheresis for patients with acute myeloid leukemia presenting with hyperleukocytosis and leukostasis: a contemporary appraisal of outcomes and benefits

Introduction: Hyperleukocytosis, defined as a total white blood cell count (WBC) >50 or more commonly >100 × 10⁹ cells/L, is a presenting feature of acute myeloid leukemia (AML) in about 6-20% of cases and is associated with a higher risk of tumor lysis syndrome (TLS), disseminated intravascular coagulation (DIC), clinical leukostasis with end organ damage, and mortality.Areas covered: In this review, authors discuss the implications of hyperleukocytosis in AML and the current understanding of cytoreductive strategies with a focus on the use of leukocytapheresis.Expert commentary: Efforts to rapidly reduce peripheral myeloblasts have included the use of leukocytapheresis. Early studies demonstrated feasibility in reducing peripheral WBC and blast counts as well as clinically relevant patient outcomes which prompted its common use for many years. However, more recent data have directly challenged the previously touted reports of reduced TLS and DIC incidence as well as survival benefit, even in patients with clinical leukostasis. The use of leukocytapheresis remains highly controversial with wide practice variations among physicians, institutions, and countries given the lack of high-quality data, risks associated with leukocytapheresis itself, associated high costs, resource utilization, and lack of evidence-based clinical guidelines.

Dissecting the role of the CXCL12/CXCR4 axis in acute myeloid leukaemia

Acute myeloid leukaemia (AML) is the most common adult acute leukaemia with the lowest survival rate. It is characterised by a build-up of immature myeloid cells anchored in the protective niche of the bone marrow (BM) microenvironment. The CXCL12/CXCR4 axis is central to the pathogenesis of AML as it has fundamental control over AML cell adhesion into the protective BM niche, adaptation to the hypoxic environment, cellular migration and survival. High levels of CXCR4 expression are associated with poor relapse-free and overall survival. The CXCR4 ligand, CXCL12 (SDF-1), is expressed by multiple cells types in the BM, facilitating the adhesion and survival of the malignant clone. Blocking the CXCL12/CXCR4 axis is an attractive therapeutic strategy providing a 'multi-hit' therapy that both prevents essential survival signals and releases the AML cells from the BM into the circulation. Once out of the protective niche of the BM they would be more susceptible to destruction by conventional chemotherapeutic drugs. In this review, we disentangle the diverse roles of the CXCL12/CXCR4 axis in AML. We then describe multiple CXCR4 inhibitors, including small molecules, peptides, or monoclonal antibodies, which have been developed to date and their progress in pre-clinical and clinical trials. Finally, the review leads us to the conclusion that there is a need for further investigation into the development of a 'multi-hit' therapy that targets several signalling pathways related to AML cell adhesion and maintenance in the BM.

Acute Myeloid Leukaemia in Its Niche: the Bone Marrow Microenvironment in Acute Myeloid Leukaemia

Purpose of Review

Acute myeloid leukaemia (AML) is a heterogeneous malignancy for which treatment options remain suboptimal. It is clear that a greater understanding of the biology of the AML niche will enable new therapeutic strategies to be developed in order to improve treatment outcomes for patients.

Recent Findings

Recent evidence has highlighted the importance of the bone marrow microenvironment in protecting leukaemia cells, and in particular leukaemic stem cells from chemotherapy-induced cell death. This includes mesenchymal stem cells supporting growth and preventing apoptosis, and altered action and secretion profiles of other niche components including adipocytes, endothelial cells and T cells.

Summary

Here, we provide a detailed overview of the current understanding of the AML bone marrow microenvironment. Clinical trials of agents that mobilise leukaemic stem cells from the bone marrow are currently ongoing and show early promise. Future challenges will involve combining these novel therapies targeted at the AML niche with conventional chemotherapy treatment.

Redistribution, homing and organ-invasion of neoplastic stem cells in myeloid neoplasms

The development of a myeloid neoplasm is a step-wise process that originates from leukemic stem cells (LSC) and includes pre-leukemic stages, overt leukemia and a drug-resistant terminal phase. Organ-invasion may occur in any stage, but is usually associated with advanced disease and a poor prognosis. Sometimes, extra-medullary organ invasion shows a metastasis-like or even sarcoma-like destructive growth of neoplastic cells in local tissue sites. Examples are myeloid sarcoma, mast cell sarcoma and localized blast phase of chronic myeloid leukemia. So far, little is known about mechanisms underlying re-distribution and extramedullary dissemination of LSC in myeloid neoplasms. In this article, we discuss mechanisms through which LSC can mobilize out of the bone marrow niche, can transmigrate from the blood stream into extramedullary organs, can invade local tissue sites and can potentially create or support the formation of local stem cell niches. In addition, we discuss strategies to interfere with LSC expansion and organ invasion by targeted drug therapies.

Extracellular vesicles in leukemia

Extracellular vesicles (EV) are nano-sized membrane enclosed vehicles that are involved in cell-to-cell communication and carry cargo that is representative of the parent cell. Recent studies have highlighted the significant roles leukemia EVs play in tumor progression, and ways in which they can lead to treatment evasion, thus meriting further investigation. Leukemia EVs are involved in crosstalk between the leukemia cell and its surroundings, transforming it into a cancer favorable microenvironment. Due to the diverse biological content found in leukemia EVs, they have an assortment of effects on the cells they interact with and can be harnessed as candidates for diagnostic and therapeutic treatments. This review focuses on EVs in the context of leukemia and the means by which they modulate their microenvironment, hematopoiesis, and the immune system to facilitate malignancy. We will also address current and prospective EV-based therapeutics.

Leukostasis in adult acute hyperleukocytic leukemia: a clinician's digest

Leukostasis is a poorly understood and life-threatening complication of acute hyperleukocytic leukemia. The incidence of hyperleukocytosis and leukostasis differs among various subtypes of leukemias. While the pathophysiology of leukostasis is not fully understood, recent research has elucidated many novel pathways that may have therapeutic implications in the future. Respiratory and neurological compromise represents the classical clinical manifestations of leukostasis. If it is not diagnosed and treated rapidly, the one-week mortality rate is approximately 40%. Targeted induction chemotherapy is an important component of the successful treatment of leukostasis, although other modalities of cytoreduction are being used and investigated. Copyright © 2016 John Wiley & Sons, Ltd.

How I treat hyperleukocytosis in acute myeloid leukemia

Hyperleukocytosis (HL) per se is a laboratory abnormality, commonly defined by a white blood cell count >100 000/µL, caused by leukemic cell proliferation. Not the high blood count itself, but complications such as leukostasis, tumor lysis syndrome, and disseminated intravascular coagulation put the patient at risk and require therapeutic intervention. The risk of complications is higher in acute than in chronic leukemias, and particularly leukostasis occurs more often in acute myeloid leukemia (AML) for several reasons. Only a small proportion of AML patients present with HL, but these patients have a particularly dismal prognosis because of (1) a higher risk of early death resulting from HL complications; and (2) a higher probability of relapse and death in the long run. Whereas initial high blood counts and high lactate dehydrogenase as an indicator for high proliferation are part of prognostic scores guiding risk-adapted consolidation strategies, HL at initial diagnosis must be considered a hematologic emergency and requires rapid action of the admitting physician in order to prevent early death.

Leukemia Mediated Endothelial Cell Activation Modulates Leukemia Cell Susceptibility to Chemotherapy through a Positive Feedback Loop Mechanism

In acute myeloid leukemia (AML), the chances of achieving disease-free survival are low. Studies have demonstrated a supportive role of endothelial cells (ECs) in normal hematopoiesis. Here we show that similar intercellular relationships exist in leukemia. We demonstrate that leukemia cells themselves initiate these interactions by directly modulating the behavior of resting ECs through the induction of EC activation. In this inflammatory state, activated ECs induce the adhesion of a sub-set of leukemia cells through the cell adhesion molecule E-selectin. These adherent leukemia cells are sequestered in a quiescent state and are unaffected by chemotherapy. The ability of adherent cells to later detach and again become proliferative following exposure to chemotherapy suggests a role of this process in relapse. Interestingly, differing leukemia subtypes modulate this process to varying degrees, which may explain the varied response of AML patients to chemotherapy and relapse rates. Finally, because leukemia cells themselves induce EC activation, we postulate a positive-feedback loop in leukemia that exists to support the growth and relapse of the disease. Together, the data defines a new mechanism describing how ECs and leukemia cells interact during leukemogenesis, which could be used to develop novel treatments for those with AML.

Role of exosomes released by chronic myelogenous leukemia cells in angiogenesis

Our study is designed to assess if exosomes released from chronic myelogenous leukemia (CML) cells may modulate angiogenesis. We have isolated and characterized the exosomes generated from LAMA84 CML cells and demonstrated that addition of exosomes to human vascular endothelial cells (HUVEC) induces an increase of both ICAM-1 and VCAM-1 cell adhesion molecules and interleukin-8 expression. The stimulation of cell-cell adhesion molecules was paralleled by a dose-dependent increase of adhesion of CML cells to a HUVEC monolayer. We further showed that the treatment with exosomes from CML cells caused an increase in endothelial cell motility accompanied by a loss of VE-cadherin and β-catenin from the endothelial cell surface. Functional characterization of exosomes isolated from CML patients confirmed the data obtained with exosomes derived from CML cell line. CML exosomes caused reorganization into tubes of HUVEC cells cultured on Matrigel. When added to Matrigel plugs in vivo, exosomes induced ingrowth of murine endothelial cells and vascularization of the Matrigel plugs. Our results suggest for the first time that exosomes released from CML cells directly affect endothelial cells modulating the process of neovascularization.

Shear stress-mediated adhesion of acute myeloid leukemia and KG-1 cells to endothelial cells involves functional P-selectin

Acute myeloid leukemia (AML) shows malignant behavior through the ability of immature cells to circulate in blood and to invade peripheral tissues. Whereas binding of human AML cells to endothelial cells (ECs) through E-selectin has been shown to occur using classical adhesion assays, little is known about the ability of endothelial P-selectin to support this process. We therefore characterized the ability of AML blasts and KG-1 cells to bind to endothelial selectin type ligands. Flow cytometry revealed that, in addition to various integrin adhesion receptors, AML cells regularly express the P-selectin glycoprotein ligand (PSGL)-1, a ligand for P- and E-selectin on ECs. In parallel flow chambers, AML cells both rolled and adhered to TNF-alpha pretreated human umbilical vein endothelial cells (HUVECs). Pretreatment of HUVECs with anti-P- or anti-E-selectin function blocking antibodies significantly reduced both, rolling and subsequent arrest of primary AML cells. Intravital microscopy of i.v. injected fluorescence-labeled KG-1 cells into P-selectin deficient or wild type mice confirmed a significant role of endothelial P-selectin in the binding of human primary AML cells to ECs also in vivo. Thus, the currently available data suggest a role of P- and E-selectin in coordinated circulation of AML cells. Thus, P- or E-selectin mediated adhesion of AML cells may provide a target for the development anti-leukemic therapies.

Leukapheresis and cranial irradiation in patients with hyperleukocytic acute myeloid leukemia: no impact on early mortality and intracranial hemorrhage

To assess the role of leukapheresis and cranial irradiation in reducing the incidence of intracranial hemorrhage (ICH) and early death in patients with hyperleukocytic acute myeloid leukemia (AML) and the impact of such treatment on survival. This study retrospectively analyzed the records of 75 patients with hyperleukocytic AML who had a white cell count over 100,000/microL. All patients had de novo AML except for two with therapy-related AML. Various factors were assessed for their impact on morbidity and mortality, particularly the role of pre-induction leukapharesis and cranial irradiation. The most significant risk factors for ICH were the presence of two or more symptoms of leukostasis (odds ratios [OR] 10.6, 95% CI: 2.67-42.02; P = 0.001) and respiratory distress (OR 5.41, 95% CI: 1.44-20.32, P = 0.012). The most significant risk factors for early death were age >or= 65 (OR 4.21, 95% CI: 1.45-12.21, P = 0.008), respiratory failure (OR 3.34, 95% CI: 1.24-9.50, P = 0.018), and two or more symptoms (OR 3.50 95% CI: 1.16-10.52, P = 0.026). Neither leukapheresis nor cranial irradiation were significantly associated with a decreased incidence of ICH (P = 0.349 and 0.378, respectively). Leukapheresis had no significant influence on early death (P = 0.367). The median survival patients receiving no pretreatment was 10.50 months (range 2.58-18.42) and for those receiving pretreatment 1.50 months (range 0.10-3.16; log-rank test, P = 0.062). Leukapheresis and cranial irradiation do not improve survival or decrease the incidence of ICH in adults with hyperleukocytic AML.

beta2 Integrins are characteristically absent in acute promyelocytic leukemia and rapidly upregulated in vivo upon differentiation with all-trans retinoic acid

Although little is known about migration of hematopoietic stem cells and their neoplastic counterparts into tissues and peripheral blood, adhesion proteins likely play an important role. We studied 339 patients with acute myelogenous leukemia (AML) to discern the relationship between adhesion protein expression, circulating blasts, and white blood cell (WBC) count. Expression levels of CD11b and CD11c strongly correlated with increased WBC count, independent of FAB subtype (p<0.0001). However, 93% (25/27) of cases of AML-M3 completely lacked beta2 integrin expression, compared to 11% (35/312) of the non-M3 cases (p<0.0001). Seven of the 27 patients with AML-M3 were followed during standard induction therapy with ATRA. Within 3 days, weak CD11c became detectable, followed by CD11b and CD11a. Our data suggest an important link between beta2 integrin expression and the level of circulating leukemic cells in AML. We demonstrate the clinical usefulness of a panel of beta2 integrins (CD11a, CD11b and CD11c) in accurate prediction of AML-M3, and recommend inclusion of this immunophenotypic analysis to identify patients who require ATRA therapy. Finally, we illustrate the rapidity at which AML-M3 blasts up-regulate beta2 integrins, and suggest a possible association between this finding and the tissue infiltration that characterizes the "ATRA syndrome".

Effect of ICAM-1 and LFA-1 in hyperleukocytic acute myeloid leukaemia

Acute hyperleukocytic leukemia [AHL; WBC count >100 x 10(9)/l] is associated with a life-threatening complication. The mechanisms of hyperleukocytosis in acute myeloid leukaemia (AML) remain unclear. However, the interaction of intercellular adhesion molecule-1 (ICAM-1) and lymphocyte function-associated antigen-1 (LFA-1) plays an important role in the adhesion and migration of normal leukocytes and AML cells. Therefore, effects of ICAM-1 and LFA-1 were studied in hyperleukocytic AML. The adhesion of hyperleukocytic AML blasts and human umbilical vein endothelial cells (HUVECs) was significantly increased compared with that of blasts from non-hyperleukocytic AML (WBC < 100 x 10(9)/l). The adhesion of normal neutrophils and HUVECs treated with hyperleukocytic AML blast supernatant was increased significantly. Finally, we determined the ICAM-1 on the surface of HUVECs treated with the supernatant of hyperleukocytic AML blasts and LFA-1 on hyperleukocytic AML blasts by flow cytometry. It showed that the ICAM-1 expression on the surface of the HUVECs treated with hyperleukocytic AML blast supernatant for 24 h could be increased, and the expression of LFA-1 on hyperleukocytic AML was also increased significantly. Our data show that hyperleukocytic AML blasts stimulate the endothelium to secrete more ICAM-1 and promote their own adhesion to vascular endothelium, suggesting that ICAM-1 and LFA-1 may have a role in hyperleukocytic AML.

Levels of soluble forms of ICAM and VCAM in patients with myelodysplastic syndromes and their prognostic significance

The aim of this study was to assess circulating soluble intercellular adhesion molecule-1 (sICAM-1), soluble vascular cell adhesion molecule-1 (sVCAM-1), and interleukin-1beta (IL-1beta) in myelodysplastic syndromes (MDS) in order to evaluate their clinical significance. Seventy patients with untreated MDS [21 refractory anemia (RA), nine RA with ringed sideroblasts (RARS), 17 RA with excess of blasts (RAEB), 11 RAEB in transformation (RAEBt), and 12 chronic myelomonocytic leukemia (CMML)] were included in this study. Serum levels of sICAM, sVCAM, and IL-1beta were determined at diagnosis using commercially available immunoassays. In addition, 15 healthy volunteers were studied as a control group. sICAM, sVCAM, and IL-1beta serum levels were significantly higher in MDS patients in comparison with the control group (P <0.001). Patients with CMML showed the highest sICAM, sVCAM, and IL-1beta levels in comparison with other MDS-related subtypes. Furthermore significantly elevated levels of the studied parameters were detected in high-risk MDS patients (RAEB, RAEB-t, and CMML) in comparison with low-risk MDS (RA and RARS). IL-1beta was strongly correlated both to sICAM and sVCAM. In conclusion we have provided evidence that increased sICAM and sVCAM serum levels are related to MDS severity.

Platelet factor 4 enhances the adhesion of normal and leukemic hematopoietic stem/progenitor cells to endothelial cells

Platelet factor 4 (PF4) is a growth regulator of hematopoietic stem/progenitor cells (HSPCs), but its role in modulating the adhesive property of normal and leukemic cells remains unclear. We used CD34(+) cord blood cells, KG1a cell line, human umbilical vein endothelial cells (HUVECs) and a transformed HUVECs ECV-304 cells to study the effect of PF4 on cell adhesion. When CD34(+) cord blood cells were cultured either in fibronectin-coated (FN) culture plate or over the layer of HUVECs for 2h, a concentration-dependent increase of the number of adhered cells was observed in the culture containing PF4. FACS analysis revealed that the treatment of PF4 resulted in an increased expression of CD49d and CXCR-4 on CD34(+) cells. Moreover, when CD34(+) cells were expanded in the presence of PF4, the adhesive ability to culture plate of CD34(+) cells was significantly increased. To elucidate the mechanism of action of PF4, KG1a cells were incubated with or without PF4 for 2h on pre-established layer of ECV-304 cells. The percentage of CD49d(+) KG1a cells increased about 1.56 +/- 0.4 fold, and that of CD54(+) ECV-304 increased about 1.7 +/- 0.6 fold. Furthermore, the mRNA expression of CD49d and CD54 was upregulated when KG1a or ECV-304 cells were incubated with PF4. The adhesion capacity of KG1a cells was reduced after incubation with the blocking monoclonal antibodies against CD49d and CD54, respectively. Our data demonstrate that PF4 is able to enhance the adhesive ability of normal and leukemia HSPCs.

Acute myeloid leukemia

In this chapter, Drs. Keating and Willman review recent advances in our understanding of the pathophysiology of acute myeloid leukemia (AML) and allied conditions, including the advanced myelodysplastic syndromes (MDS), while Drs. Goldstone, Avivi, Giles, and Kantarjian focus on therapeutic data with an emphasis on current patient care and future research studies. In Section I, Dr. Armand Keating reviews the role of the hematopoietic microenvironment in the initiation and progression of leukemia. He also discusses recent data on the stromal, or nonhematopoietic, marrow mesenchymal cell population and its possible role in AML. In Section II, Drs. Anthony Goldstone and Irit Avivi review the current role of stem cell transplantation as therapy for AML and MDS. They focus on data generated on recent Medical Research Council studies and promising investigation approaches. In Section III, Dr. Cheryl Willman reviews the current role of molecular genetics and gene expression analysis as tools to assist in AML disease classification systems, modeling of gene expression profiles associated with response or resistance to various interventions, and identifying novel therapeutic targets. In Section IV, Drs. Hagop Kantarjian and Francis Giles review some promising agents and strategies under investigation in the therapy of AML and MDS with an emphasis on novel delivery systems for cytotoxic therapy and on targeted biologic agents.

L and E selectins in acute myeloid leukemia: expression, clinical relevance and relation to patient outcome

The aim of this study was to assess circulating soluble L (sL) and soluble E (sE) selectins adhesion molecules in acute myeloid leukemia (AML) blasts in order to evaluate their clinical significance. Fifty patients with AML (4 M0, 8 M1, 16 M2, 5 M3, 7 M4, 6 M5, 4 M6) were included in this study. sL and sE selectins were evaluated at diagnosis, remission and in relapsed patients; whole membrane expression of L and E selectins by AML blast was investigated only at diagnosis. In addition, 15 normal persons were studied as a control group. sL and sE selectins were significantly higher in AML patients at diagnosis when compared to controls (P<0.01), but less at remission (P<0.01). Furthermore, elevated sL and sE selectin levels were detected in patients with AML at relapse. sE and sL selectins were significantly higher in AML patients with extramedullary infiltration as compared to patients without extramedullary disease (P<0.001). Membrane expression of L selectin was positive in 20% of AML patients. However, none of the patients showed significant E selectin expression. Patients with higher sE and sL selectins at diagnosis have high probability of relapse compared to those with normal levels (P<0.01 and <0.001, respectively). The overall relapse predictability of sE and sL selectins was 84%. Moreover, patients with higher sE and sL selectins levels had shorter event free survival than patients with lower levels (P<0.001 for both). The overall mortality prediction using sE, sL, and cellular L selectin was 96%.

IN CONCLUSION

(1) AML blast cell express and release sL selectins but not sE selectin, (2) sE and sL selectins and cellular L selectin may be useful prognostic markers in evaluating AML patients at diagnosis.

Leukocytoreduction for acute leukemia

Both in children and adults, acute leukemia may present with extremely high blast counts; a phenomenon known as hyperleukocytosis. Respiratory failure, intracranial bleeding, and severe metabolic abnormalities frequently occur in acute hyperleukocytic leukemias (AHLs) and are the primary determinants of the high early mortality (20% to 40%) observed. The process leading to these complications has long been known as leukostasis, but the biological mechanisms underlying its development and progression have remained unclear. Traditionally, leukostasis has been attributed to overcrowding of leukemic blasts in the microcirculation, and its treatment has focused on prompt leukocytoreduction. However, it is becoming increasingly evident that leukostasis results from the adhesive interactions between leukemic blasts and the endothelium; a mechanism that none of the current therapies directly addresses. The endothelial damage associated with leukostasis is likely to be mediated by cytokines released in situ and by subsequent migration of leukemic blasts in the perivascular space. The adhesion molecules displayed by the leukemic blasts and their chemotactic response to the cytokines in the vascular microenvironment are probably more important in causing leukostasis than the cell number. This may explain why leukostasis may develop in some patients with AHL and not in others, and why some patients with acute leukemia without hyperleukocytosis (<50,000 blasts/mm(3)) develop leukostasis and respond to leukocytoreduction. Leukapheresis effectively reduces the blast count in many patients with AHL and is routinely used for immediate leukocytoreduction. However, the most appropriate use of leukapheresis in acute leukemia remains unclear, and the procedure may not prevent early death more efficiently than fluid therapy, hydroxyurea, and prompt induction chemotherapy. The use of cranial irradiation remains very controversial and is not generally recommended. The identification of the adhesion molecules, soluble cytokines, and chemotactic ligand-receptor pairs mediating endothelial cell damage in AHL should become a priority if better outcomes are desired.

A minor E-selectin ligand, CD65, is critical for extravascular infiltration of acute myeloid leukemia cells

Adhesive ligands on acute myeloid leukemic (AML) blasts may mediate transmigration and extravascular infiltration. In this study, 30 AML samples were examined for expression and density of adhesion antigens. By univariate analysis, four patients with extravascular infiltration showed significantly higher expression of CD2, CD11a, CD11b, CD11c, CD15, CD65, CD86, and HLA-DR as compared with patients without infiltration. These four patients also showed significantly higher density of CD11a, CD11b, CD11c, CD15 and CD65 expression. By multivariate analysis, CD65 expression was the only significant independent risk factor for infiltration, suggesting that this is a critical adhesion molecule for extravascular AML infiltration.

AC133 antigen as a prognostic factor in acute leukemia

AC133 is a novel 5-transmembrane antigen present on a CD34((bright)) subset of human hematopoietic stem cells (HSCs) and it is also expressed on the subset of CD34 positive (CD34(+)) leukemias. But the clinical significance of AC133 expression on leukemic blasts is not yet known. We investigated the expression of AC133 antigen on blast cells of acute leukemia. Forty-one cases of acute leukemia were examined for expression of AC133, CD34, and other antigens using multicolor flow-cytometry. Samples were considered positive if at least 20% of the cells specifically stained with monoclonal antibodies (MoAbs) revealed a higher fluorescence intensity compared to cells of corresponding negative control samples (=20% cut-off level). 14/36 (38.9%) acute myelogenous leukemia (AML) samples and 6/20 (30%) acute lymphoblastic leukemia (ALL) samples were positive for AC133, the difference was not significant. All AC133 positive (AC133(+)) leukemias expressed CD34, whereas 13 of 33 CD34(+) leukemias were negative for AC133, and AC133(+)/CD34(-) leukemia was not found. Expression rates of CD31, CD62L, CD62E, CD105 and CD144 were significantly higher in AC133(+) leukemia compared to those of AC133(-) leukemia (P=0.045, P<0.001, P<0.001, P<0.001, P=0.003, respectively), but bcl-2, CXCR-1, CXCR4, VLA-4, CD106 expression rates were not significantly different between AC133(+) and AC133(-) leukemias. None of the clinical prognostic markers such as age, hemogram, lactate dehydrogenase, and chromosomal aberration were significantly different between AC133(+) and AC133(-) leukemias. CR rates of AC133(+) AML and AC133(-) AML were not significantly different, although there was a trend toward higher CR rates in AC133(-) AML (18/22[81.8%] AC133(-) AML versus 9/14[64.3%] AC133(+) AML), but the 1-year relapse rate of AC133(+) AML was significantly higher than that of AC133(-) AML (8/9 (88.9%) versus 7/19 (36.8%), P=0.016). Median disease-free survival (DFS) times of AC133(+) and AC133(-) AML were significantly different (11 and 18 months, respectively, P=0.006), although overall survival (OS) times were not significantly different (AC133(+) 15 months versus AC133(-) 20 months, respectively, P=0.06). Similar results regarding clinical outcomes were found when AC133(+)/CD34(+) and AC133(-)/CD34(+) were analyzed separately, but the difference did not attain statistical significance. In ALL, 9/11 (81.8%) AC133(-) and 2/4 (50%) AC133(+) cases achieved CR, but the difference was not significant. Four of 11 AC133(-) ALL (36.4%) and 2 of 3 AC133(+) ALL (66.7%) relapsed within 1 year. In survival analysis, median DFS time and OS time of the AC133(+) group were 7 and 18 months, respectively, and these were not significantly different from those of the AC133(-) group (median DFS 15, OS 22 months, respectively). Our results demonstrate that AC133 expression in AML blasts is associated with poor clinical outcomes in terms of higher early relapse and shorter disease-free survival, suggesting that the AC133 antigen might provide the prognostic stratification of acute leukemia. However, to verify the effect of AC133 expression on the therapeutic outcomes of adult acute leukemia, further study including more cases is needed.

Intercellular adhesion molecule-1 in extravasation of normal mononuclear and leukaemia cells

Interaction of intercellular adhesion molecules (ICAMs) with their receptors has a key role in normal leucocyte adhesion and migration, whereas in leukaemia this has not been well established. In this study, we have evaluated the roles of different adhesion molecules in normal and leukaemia cell extravasation in a novel organotypic model for vessel wall and measured plasma ICAM-1 and -2 levels in acute leukaemia patients at diagnosis and during chemotherapy. We found that both normal mononuclear cells and blast cells from acute leukaemia patients, as well as retinoic acid-treated promyelocytic leukaemia cells, rapidly extravasated through endothelial cell layers into the underlying collagen matrix. ICAM-1 antibody prevented the extravasation, while antibodies to other adhesion molecules showed little (CD18, ICAM-2) or no inhibition (CD11a and ICAM-3). Soluble ICAM-1 (sICAM-1) protein had no effect. We also observed increased plasma sICAM-1 and -2 levels in leukaemia patients and found that they correlated only weakly with the white blood cell count. No correlation was found between sICAM-1 or -2 levels and the response to therapy. Although elevated sICAM-2 levels decreased rapidly during chemotherapy, sICAM-1 levels did not. Because sICAM-1 protein had no effect on leukaemia cell extravasation in vitro, it is probable that the increased plasma sICAM-1 levels in leukaemia patients may not play a role in leukaemia cell infiltration. However, as we showed that ICAM-1 mediated leukaemia cell extravasation on the cell surface, it is possible that cellular ICAM-1 has an important role in disease progression.

Endothelial cell activation by myeloblasts: molecular mechanisms of leukostasis and leukemic cell dissemination

Leukostasis and tissue infiltration by leukemic cells are poorly understood life-threatening complications of acute leukemia. This study has tested the hypothesis that adhesion receptors and cytokines secreted by blast cells play central roles in these reactions. Immunophenotypic studies showed that acute myeloid leukemia (AML) cells (n = 78) of the M0 to M5 subtypes of the French-American-British Cooperative Group expressed various amounts of adhesion receptors, including CD11a, b, c/CD18, CD49d, e, f/CD29, CD54, sCD15, and L-selectin. The presence of functional adhesion receptors was evaluated using a nonstatic adhesion assay. The number of blast cells attached to unactivated endothelium increased by 7 to 31 times after a 6-hour exposure of endothelium to tumor necrosis factor (TNF)-alpha. Inhibition studies showed that multiple adhesion receptors--including L-selectin, E-selectin, VCAM-1, and CD11/CD18--were involved in blast cell adhesion to TNF-alpha-activated endothelium. Leukemic cells were then cocultured at 37 degrees C on unactivated endothelial cell monolayers for time periods up to 24 hours. A time-dependent increase in the number of blasts attached to the endothelium and a concomitant induction of ICAM-1, VCAM-1, and E-selectin were observed. Additional experiments revealed that endothelial cell activation by leukemic myeloblasts was caused by cytokine secretion by blast cells, in particular TNF-alpha and IL-1 beta, and direct contacts between adhesion receptors expressed by blast cells and endothelial cells. Thus, leukemic cells have the ability to generate conditions that promote their own adhesion to vascular endothelium, a property that may have important implications for the pathophysiology of leukostasis and tissue infiltration by leukemic blast cells. (Blood. 2001;97:2121-2129)

Hyperleukocytic leukemias and leukostasis: a review of pathophysiology, clinical presentation and management

Acute hyperleukocytic leukemias (AHL) are associated with a very high early mortality rate mostly due to respiratory failure or intracranial bleeding. The pathophysiological process leading to these complications is called leukostasis but the biological mechanisms underlying its development and progression remain unclear. Although traditionally related to "over-crowding" of leukemic blasts in the capillaries of the microcirculation, leukostasis is likely to result from direct endothelial cell damage. This damage is probably mediated by soluble cytokines released during the interaction between leukemic cells and vascular endothelium and by the subsequent migration of leukemic blasts in the perivascular space. Leukemic cell's ability to respond to chemotactic cytokines and their expression of specific adhesion molecules are probably more important in determining whether leukostasis will develop than the number of circulating blasts. This could explain why leukostasis does not develop in all patients with AHL. The identification of the adhesion molecules, cytokines and receptors mediating endothelial cell damage in AHL should become a priority if therapeutic improvements are desired. Leukapheresis is widely used but it is unclear whether it provides additional benefit to a simpler and less invasive intervention with allopurinol, hydroxyurea and intravenous fluids. Cranial irradiation is not generally recommended. Induction chemotherapy should be started without delay. It is hoped that specific pharmacological inhibitors of the interaction between leukemic cells and vascular endothelium will result in an improved outcome for this very high-risk population.

Different expression of adhesion molecules on CD34+ cells in AML and B-lineage ALL and their normal bone marrow counterparts

The expression of adhesion molecules on CD34+ cells in acute myeloid leukemia (AML) and B-lineage acute lymphoblastic leukemia (B-lineage ALL) was compared with that on the myeloid and B-lymphoid CD34+ cells in normal bone marrow. Bone marrow aspirates of 10 patients with AML, 8 patients with B-lineage ALL and of 6 healthy volunteers were examined. The phenotype of the CD34+ cells was determined with a double immunofluorescence method and flow cytometry. CD34+ cells in AML and B-lineage ALL showed a lower expression of VLA-2 and VLA-3 and a higher expression of ICAM-1 and LFA-3 than their normal bone marrow counterparts. AML CD34+ cells had less L-selectin but more VLA-5 on their surface membrane than normal myeloid CD34+ cells. B-lineage ALL CD34+ cells showed an overexpression of LFA-3. In individual patients deficiencies or over-expression of the beta1 integrin chain, VLA-4, PECAM-1 or HCAM also occurred. An abnormal adhesive capacity of the leukemic cells may influence their proliferation, their localisation and apoptosis. An aberrant expression of adhesion molecules may be used for the detection of minimal residual leukemia in these patients.

A comparative study of the cell cycle status and primitive cell adhesion molecule profile of human CD34+ cells cultured in stroma-free versus porcine microvascular endothelial cell cultures

Porcine microvascular endothelial cells (PMVECs) plus cytokines support a rapid proliferation and expansion of human CD34+CD38- cells that are capable of multilineage engraftment within the bone marrow of a secondary host. CD34+CD38- cells contain the self-renewing, long-term culture-initiating cells (LTC-IC) that are ideal targets for retroviral gene transfer experiments. Previous experiments attempting retroviral infection of CD34+CD38- cells have failed partly because these cells do not enter cell cycle in response to cytokine combinations. In this study, we determined the cell cycle status and the cell adhesion molecule profile on purified CD34+ cells and the CD34+CD38- subset before and after ex vivo expansion on PMVECs. Purified human CD34+ cells were cocultured with PMVECs for 7 days in the presence of optimal concentrations of granulocyte/macrophage-colony-stimulating factor (GM-CSF) + interleukin (IL)-3 + IL-6 + stem cell factor (SCF) + Flt-3 ligand. The total CD34+ population and the CD34+CD38- subset increased 8.4- and 67-fold, respectively, with absolute increases in the number of colony-forming unit-granulocyte macrophage (CFU-GM) (28.2-fold), CFU-Mix (8.7 fold), and burst-forming unit-erythroid (BFU-E) (4.0-fold) progenitor cells. After 7 days of coculture with PMVECs, 44% of the CD34+CD38+ subset were found to be in G1, and 51% were in G2/S/M phase of the cell cycle. More remarkably, 53% of the CD34+CD38- subset were in G1, and 17% were in G2/S/M phase after 7 days of PMVEC coculture. In contrast, only 22% of the CD34+CD38- subset remaining after 7 days of stroma-free culture were in G1, and 6% were in G2/S/M phase. Despite the high level of cellular activation and proliferation induced by PMVEC coculture, the surface expression of adhesion molecules CD11a (LFA-1), CD11b, CD15s (sialyl-Lewis x), CD43, and CD44 (HCAM) on the total CD34+ population was maintained, and the surface expression of CD49d (VLA-4), CD54 (ICAM), CD58, and CD62L (L selectin) increased after ex vivo expansion. In contrast, CD34+ cells expanded on stroma-free cultures showed lower and more variable expression of CD62L and CD15s. These findings demonstrate that the primitive CD34+CD38- subset of marrow progenitor cells can be induced to enter cell cycle and can be significantly expanded ex vivo on a hematopoietic supportive microenvironment (PMVECs) while preserving the expression of cell adhesion molecules that may be important in stem cell homing and engraftment.

Expression and release of adhesion molecules by human acute myelogenous leukemia blasts

The expression and release of adhesion molecules by acute myelogenous leukemia (AML) blasts was investigated in vitro. For most patients AML blasts expressed relatively low levels of membrane-bound L-selectin and Intercellular adhesion molecule 1 (ICAM-1), but their soluble forms were detected in the supernatants for the majority of patients when AML blasts were cultured in vitro. These in vitro levels of SL-selectin and sICAM-1 were considerably lower than the normal serum levels. Divergent and relatively small alterations in SL-selectin and sICAM-1 levels were usually observed when exogenous growth factors were present during AML blast culture, whereas increased SL-selectin levels were observed after coculture of AML blasts and normal leucocytes. E- and P-selectin were neither expressed nor released by AML blasts. We conclude that AML blasts are a source of soluble adhesion molecules.

Adhesion molecules in clinical medicine

Cellular adhesion molecules (CAMs) are critical components in the processes of embryogenesis, tissue repair and organization, lymphocyte function, lymphocyte homing and tumor metastasis, as well as being central to the interactions between hemopoietic progenitors and bone marrow microenvironment, and between leukocytes and platelets with vascular endothelium. Expression of CAMs regulates normal hemopoiesis and migration and function of mature hemopoietic cells. CAMs are an important part of the inflammatory response and may regulate cytokine synthesis. In addition, CAM expression may be critical for tumorigenesis. Monoclonal antibodies to CAMs have been developed for clinical use; initial results suggest that these agents have great potential in the prevention and treatment of inflammation, thrombosis, reperfusion injury, and graft rejection.

Serum levels of adhesion molecules and cytokines in patients with acute leukaemia

The cytokine network and the adhesion molecule system are intercellular signal pathways. The cytokine effects are modulated in vivo by soluble cytokine antagonists, whereas the cell to cell contact mediated by adhesion molecules and their ligands may be blocked by the soluble forms of the adhesion molecules. The cytokine network is important for proliferation and cytokine secretion by acute leukaemia blasts, and membrane-bound adhesion molecules are important for blast interactions with neighbouring cells of the in vivo microenvironment. Both these signal systems are operative during the period of cytopenia following intensive chemotherapy for acute leukaemia. In the present review, we discuss the influence of disease status, chemotherapy and complicating infections on serum levels of cytokines and soluble adhesion molecules in acute leukaemia patients. We have demonstrated increased serum levels of both cytokines and cytokine antagonists in acute leukaemia patients with complicating bacterial infections during chemotherapy-induced cytopenia. Serum levels of the selectin adhesion molecules were decreased during bacterial infections in leukopenic patients compared to healthy individuals. In contrast, the intercellular adhesion molecule-1 response and the cytokine/cytokine antagonist responses were qualitatively similar to responses seen in previously healthy individuals with serious bacterial infections.

Adhesion molecules in acute myeloid leukemia

That adhesion molecules play a major role in the regulation of normal hematopoiesis is suggested by the abundance of these molecules present on early bone marrow progenitor cells and their differential pattern of expression at discrete stages of differentiation along the various cell lineages. In particular, precursor cell matrix/endothelial interactions determine retainment or release of hematopoietic cells from the bone marrow microenvironment. Consequently, changes in the affinity or quantitative expression of adhesion molecules on either the bone marrow stroma or the blood cell precursor component-during normal development or due to activation or a malignant process-will affect cell attachment. Adhesion molecules, therefore, are modulator molecules which alter the biological behavior of normal or leukemic hematopoietic cells, primarily in terms of migration and localization properties, although they also participate in many other cell functions such as cytotoxicity, antigen presentation and binding of viruses or cancer cells. Several membrane-bound adhesion molecules and, in some instances, their soluble counterparts which may be biologically active, have been described in acute myeloid leukemia. The potential diagnostic or physiological significance of leukocyte antigens with adhesive properties will be addressed in this comment.

Selectin ligands on human melanoma cells

Twelve established human melanoma lines were screened for surface expression of the carbohydrate antigens Lewisa (Lea), sialyl Lewisa (SLea), dimeric sialyl Lewisa (diSLea), sialyl LewisX (SLex) and dimeric sialyl LewisX (diSLeX). None of the lines expressed SLex, but 11/12 were positive for diSLeX and 7/12 were positive for SLea. Although both diSLeX and SLea have been reported to bind to E-selectin, none of the melanoma lines exhibited E-selectin-dependent adhesion to activated human umbilical vein endothelial cells (HUVECs). Three melanoma lines infected with a retroviral vector carrying the cDNA for the human Lewis fucosyltransferase (FucT-III) subsequently expressed SLeX at their cell surface and exhibited E-selectin-dependent adhesion to activated HUVECs. Treatment of these transduced cells with inhibitors of O-linked or N-linked protein glycosylation significantly inhibited E-selectin-mediated adhesion, though fluorescence-activated cell sorter analysis indicated no decrease in cell surface expression of SLeX, Slea or diSLeX. This suggests that the majority of SLeX/SLea-type glycans endogenously produced by human melanoma cells are not protein-associated and do not mediate E-selectin-dependent adhesion. These results support the hypothesis that E-selectin-dependent adhesion requires presentation of SLeX-type moieties on appropriate glycoproteins.

Interaction of acute leukemia cells with the bone marrow microenvironment: implications for control of minimal residual disease

There is increasing evidence for an interaction between acute leukemia cells and the microenvironment of the bone marrow. Blast cells from cases of acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) bind to cellular and extracellular matrix components of the bone marrow stroma. In AML, adhesion to stroma is mediated by the combined action of beta 1 (principally VLA-4) and beta 2 integrins, while in precursor-B ALL VLA-4 and VLA-5 integrins play a major role. Adhesion molecules such as CD31, CD44, non-beta 1, beta 2 integrins, growth factor receptors such as c-kit, and other molecules are also likely to play a role. Binding of acute leukemia blasts to ligands on stroma has several pathophysiological consequences. Stromal contact is able to inhibit programmed cell death (apoptosis) in a proportion of cases of both AML and ALL. In ALL, diffusible molecules derived from stroma appear to contribute. Marrow stroma also plays a part in regulating leukemic cell proliferation. While this is partly due to stromal production of hemopoietic growth factors, in soluble or transmembrane form or bound to extracellular matrix, signalling mediated directly by binding of adhesion molecules on leukemic cells may also have a role. Contact of ALL blasts with marrow fibroblasts is followed by migration of leukemic cells, utilizing VLA-4 and VLA-5 integrins, potentially allowing homing of blasts to favourable microenvironmental sites, or controlling egress into the circulation. AML cells compete for stromal binding sites with natural killer cells and cytotoxic lymphocytes, which are known to inhibit their clonogenic growth. We speculate that these complex interactions between leukemic blasts, cellular and matrix components of stroma, and cytotoxic lymphocytes, play a critical role in determining the fate of small numbers of leukemic cells surviving after cytotoxic chemotherapy.

The binding of acute myeloid leukemia blast cells to human endothelium

AML blast cell adhesion to endothelium is in all likelihood a prerequisite for blast cell migration across the vascular wall in the periphery and the subsequent establishment of leukemic extravascular disease. A general feature of malignant cells is their acquisition of altered or aberrant adhesive capabilities which appear to be associated with their ability to metastasize. Aberrant expression of integrin adhesion molecules and of membrane oligosaccharide structures is found in AML and various solid tumors. With respect to AML, these alterations in adhesive phenotype may confer a proliferative advantage on the malignant cells in the marrow, may facilitate egress from the bone marrow into the peripheral vasculature and may enable AML blast cells to traverse the vessel wall and so establish extravascular disease. Oncogenes may be directly involved in the acquisition of such aberrant adhesive phenotypes. Neutrophil extravasation is described as a model for leukocyte migration across the vessel wall and brief summaries of experimental work involving aspects of AML blast cell and normal CD34+ bone marrow cell adhesion to endothelium in vitro are described.

SLe(x) expression of normal CD34 positive bone marrow haemopoietic progenitor cells

We investigated sialylated Lewis x (sLe(x)) antigen expression on CD34 positive (CD34+) haemopoietic progenitors in the bone marrow of eight healthy volunteers using monoclonal antibodies. We found that in all the samples examined, CD34+ bone marrow progenitors strongly expressed the sLe(x) antigen. This contradicts previous publications which reported sLe(x) expression on malignant blast cells but not on normal CD34+ progenitor cells.