The binding of acute myeloid leukemia blast cells to human endothelium

Effectiveness and safety of leukapheresis in hyperleukocytic leukemias: a retrospective multicenter study

Leukapheresis is an effective adjuvant therapy for leukemia patients with hyperleukocytosis, but few studies have reported recent data with modern modalities and comparisons among different leukemia types. We conducted a retrospective study on leukapheresis among 420 patients with AML, ALL and CML in four local centers. WBC counts decreased significantly (p < 0.001) postleukapheresis in all three cohorts. Clearance efficiency was higher in acute leukemia patients than CML patients (p < 0.01). Concomitant leukocytoreduction drugs improved WBC reduction only in AML patients (p < 0.05). Leukocyte, hemoglobin and platelet levels preleukapheresis might affect the clearance efficiency in AML and/or ALL patients. Hematological toxicities were the major concerns, but most of them were mild, and only 11 patients died of all causes within one week postleukapheresis. In conclusion, leukapheresis can safely reduce the leukemic burden, especially for patients with acute leukemias.

Leukaemia cell of origin identified by chromatin landscape of bulk tumour cells

The precise identity of a tumour's cell of origin can influence disease prognosis and outcome. Methods to reliably define tumour cell of origin from primary, bulk tumour cell samples has been a challenge. Here we use a well-defined model of MLL-rearranged acute myeloid leukaemia (AML) to demonstrate that transforming haematopoietic stem cells (HSCs) and multipotent progenitors results in more aggressive AML than transforming committed progenitor cells. Transcriptome profiling reveals a gene expression signature broadly distinguishing stem cell-derived versus progenitor cell-derived AML, including genes involved in immune escape, extravasation and small GTPase signal transduction. However, whole-genome profiling of open chromatin reveals precise and robust biomarkers reflecting each cell of origin tested, from bulk AML tumour cell sampling. We find that bulk AML tumour cells exhibit distinct open chromatin loci that reflect the transformed cell of origin and suggest that open chromatin patterns may be leveraged as prognostic signatures in human AML.

A tumour's cell of origin may influence tumour progression and response to therapy. Here, the authors demonstrate that the cell of origin determines the aggressiveness of AML in a mouse model and identify unique biomarkers of the specific leukaemia cell of origin by profiling open chromatin regions of AML samples.

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.

Outcome of acute myeloid leukemia patients with hyperleukocytosis in Brazil

Acute myeloid leukemia (AML) with a high white blood cell (WBC) count at presentation has been associated with an increased early mortality rate, usually secondary to leukostasis. However, the value of the WBC count at which there is a high risk of early death (ED) and the efficiency of supportive treatments remain unclear. In this report, a series of 187 consecutive adult patients with AML in our institution was reviewed. The outcome of 40 patients with WBC above 50×10(9) L(-1) (hyperleukocytosis) was compared to 147 patients with a leukocyte count lower than 50×10(9) L(-1). The group with hyperleukocytosis showed a significantly shorter OS (P<0.0001) and a higher rate of ED (P=0.0008). Even when the data from ED patients were removed from analysis, we still detected a shorter OS in patients with hyperleukocytosis (P=0.0049), which suggests that high WBC number influences long-term survival, and not only ED. We also observed higher lactic dehydrogenase (LDH) and serum creatinine levels in the group of patients with hyperleukocytosis (P=0.0003 and 0.0406, respectively). Besides considering all the patients with ED, we could observe higher levels of lactic dehydrogenase, a serum creatinine and nitrogen urea (P=0.0056, P=0.0008 and P<0.0001, respectively). Pulmonary involvement was more frequent in patients with ED (P=0.0277). In conclusion, hyperleukocytosis confers a poorer prognosis in patients with AML.

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.

The role of osteoblasts in the hematopoietic microenvironment

Hematopoietic stem cell differentiation occurs in direct proximity to osteoblasts within the bone marrow cavity. Despite this striking affiliation, surprisingly little is known about the precise cellular and molecular impact of osteoblasts on the bone marrow microenvironment. Recently, it has been proposed that human osteoblasts support the growth of primitive human hematopoietic cells in vitro and possibly in vivo. Evidence to support this hypothesis is reviewed as follows: the influence of osteoblasts on osteoclast development; the participation of osteoblasts in long-term bone marrow cultures; the production of positive hematopoietic regulatory molecules by osteoblasts; the production of cell-cycle inhibitory factors by osteoblasts, and cell-cell interactions between early hematopoietic cells and osteoblasts.