CD105 (endoglin) is highly overexpressed in a subset of cases of acute myeloid leukemias

Immunotherapeutic targeting of surfaceome heterogeneity in AML

Immunotherapy remains underexploited in acute myeloid leukemia (AML) compared to other hematological malignancies. Currently, gemtuzumab ozogamicin is the only therapeutic antibody approved for this disease. Here, to identify potential targets for immunotherapeutic intervention, we analyze the surface proteome of 100 genetically diverse primary human AML specimens for the identification of cell surface proteins and conduct single-cell transcriptome analyses on a subset of these specimens to assess antigen expression at the sub-population level. Through this comprehensive effort, we successfully identify numerous antigens and markers preferentially expressed by primitive AML cells. Many identified antigens are targeted by therapeutic antibodies currently under clinical evaluation for various cancer types, highlighting the potential therapeutic value of the approach. Importantly, this initiative uncovers AML heterogeneity at the surfaceome level, identifies several antigens and potential primitive cell markers characterizing AML subgroups, and positions immunotherapy as a promising approach to target AML subgroup specificities.

Endoglin and squamous cell carcinomas

Despite the fact that the role of endoglin on endothelial cells has been extensively described, its expression and biological role on (epithelial) cancer cells is still debatable. Especially its function on squamous cell carcinoma (SCC) cells is largely unknown. Therefore, we investigated SCC endoglin expression and function in three types of SCCs; head and neck (HNSCC), esophageal (ESCC) and vulvar (VSCC) cancers. Endoglin expression was evaluated in tumor specimens and 14 patient-derived cell lines. Next to being expressed on angiogenic endothelial cells, endoglin is selectively expressed by individual SCC cells in tumor nests. Patient derived HNSCC, ESCC and VSCC cell lines express varying levels of endoglin with high interpatient variation. To assess the function of endoglin in signaling of TGF-β ligands, endoglin was overexpressed or knocked out or the signaling was blocked using TRC105, an endoglin neutralizing antibody. The endoglin ligand BMP-9 induced strong phosphorylation of SMAD1 independent of expression of the type-I receptor ALK1. Interestingly, we observed that endoglin overexpression leads to strongly increased soluble endoglin levels, which in turn decreases BMP-9 signaling. On the functional level, endoglin, both in a ligand dependent and independent manner, did not influence proliferation or migration of the SCC cells. In conclusion, these data show endoglin expression on individual cells in the tumor nests in SCCs and a role for (soluble) endoglin in paracrine signaling, without directly affecting proliferation or migration in an autocrine manner.

Quantification and Phenotypic Characterization of Extracellular Vesicles from Patients with Acute Myeloid and B-Cell Lymphoblastic Leukemia

Extracellular vesicles (EVs) act in cell-to-cell communication, delivering cargo from donor to recipient cells and modulating their physiological condition. EVs secreted by leukemic blasts in patients with leukemia have been shown to influence the fate of recipient cells in the bone marrow microenvironment. Methods to quantify and to characterize them phenotypically are therefore urgently needed to study their functional role in leukemia development and to evaluate their potential as targets for therapy. We have used cryo-electron microscopy to study morphology and size of leukemic EVs, and nanoparticle tracking analysis and fluorescence triggering flow cytometry to quantify EVs in platelet-free plasma from a small cohort of leukemia patients and healthy blood donors. Additional studies with a capture bead-based assay allowed us to establish phenotypic signatures of leukemic EVs from 17 AML and 3 B-ALL patients by evaluating the expression of 37 surface antigens. In addition to tetraspanins and lineage-specific markers we found several adhesion molecules (CD29, and CD146) to be highly expressed by EVs from B-ALL and several leukemic stem cell antigens (CD44, CD105, CD133, and SSEA-4) to be expressed by EVs from AML patients. Further improvements in analytical methods to study EVs are needed before potentially using them as biomarkers for leukemia prognosis and follow-up.

Combined utility of CD177, P53, CD105 and c-kit immunohistochemical stains improves the detection of myelodysplastic syndrome

The diagnosis of myelodysplastic syndrome (MDS) relies primarily on identifying peripheral blood cytopenia and morphologic dysplasia as well as detecting cytogenetic aberrations in a subset of patients. Accumulating data points to the importance of examining certain immunophenotypic changes characteristic of MDS, most of which are tested by flow cytometry. The role of immunohistochemistry in the diagnostic workup of MDS is less known. In this study, we used immunohistochemistry to survey the expression patterns of CD177, P53, CD105 and c- kit in a cohort of MDS bone marrow specimens (n = 57) and compared the results with a control group of patients who had cytopenia for other benign conditions (n = 49). MDS cases showed significant higher rates of: CD177-loss (13/57, 23% vs 1/49, 2%; P = .0016), P53 overexpression (8/57, 14% vs none; P = .005) and the presence of clusters of CD105-positive cells (6/57, 11% vs none; P = .021). Increased c-kit-positive cells was more common in MDS patients, but not statistically significant (17/57, 30% vs 8/49, 16%; P = .102). On multivariate analysis, only loss of CD177 expression was significantly higher in MDS group (P = .014). These findings suggest that a panel of immunohistochemical stains could serve as an adjunct tool in investigating unexplained cytopenias and warrant further comparative studies with flow cytometry.

Impact of CD105 Flow-Cytometric Expression on Childhood B-Acute Lymphoblastic Leukemia

Background

CD105 (Endoglin) is a receptor of the transforming growth factor-Beta (TGF- β) superfamily. It is expressed in angiogenic endothelial cells and is considered a powerful marker of angiogenesis and a potential main player in the pathogenesis of vascular diseases as well as tumor progression. CD105 expression was correlated with poor prognosis in many types of solid malignancies, however, its influence on hematological neoplasms is still an area of interest.

Purpose

To assess the flow-cytometric expression of CD105 in childhood B-acute lymphoblastic leukemia (B-ALL) and its relation to disease response after the induction chemotherapy.

Subjects and Methods

Eighty children newly diagnosed with B-ALL were screened for flow-cytometric expression of CD105 at time of diagnosis, then they were followed up to detect their response to induction therapy.

Results

CD105 was expressed in 41.2% of B-ALL patients. Higher expression of CD105 was observed in high and very high-risk groups. The multivariate analysis considered CD105 positivity as an independent prognostic marker for response to induction therapy. Values higher than 2.5 Specific fluorescence indices (SFIs) and 35% expression were sensitive predictors to induction failure.

Conclusion

CD105 can be considered as a potential prognostic marker for the detection of response to induction therapy in childhood B-ALL, and it can serve to optimize treatment decisions.

Endoglin is Highly Expressed in Human Mast Cells

Endoglin, known to be expressed in proliferating vessels, is of worth when evaluating microvessel density as a prognostic factor in many types of malignancies, including some subtypes of leukemia cells. In childhood acute lymphoblastic leukemia, endoglin is associated with adverse outcome. In bone marrow, endoglin identifies the repopulating hematopoietic stem cells. Mast cells are a component of normal tissue and play an important role in the regulation of several processes, including inflammation and neoplasia. The aim of this study was to evaluate the use of endoglin as a biological marker of mast cells compared with the gold standard stains. We studied 15 specimens of neurofibroma, 9 of mastocytosis, and 6 of fibrous scar tissue through immunohistochemistry (for endoglin and mast cell tryptase) and histochemical staining using toluidine blue. Quantitative analysis of the cells was performed by counting 5 hotspots. The validity of endoglin as a mast cell marker was assessed by intraclass correlation coefficient. The Kruskal-Wallis test was used to compare mast cell count for each marker. A strong endoglin expression was found in the cytoplasmic granules of mast cells within the 3 groups. Similar results were observed with mast cell tryptase as well as toluidine blue. The intraclass correlation coefficient revealed that endoglin is a highly reliable biomarker of mast cells when compared with mast cell tryptase and toluidine blue. In conclusion, endoglin may assist in the diagnosis and pathogenesis study of various processes associated with mast cells. An endoglin-neutralizing treatment for solid cancers and leukemia could also affect mastocytes and the immunologic system.

Endoglin: Beyond the Endothelium

Keywords: endoglin; CD105 TGF-β; BMP9; ALK-1; TRC105; tumor microenvironment.

CD105 (Endoglin) as negative prognostic factor in AML

While several genetic and morphological markers are established and serve to guide therapy of acute myeloid leukaemia (AML), there is still profound need to identify additional markers to better stratify patients. CD105 (Endoglin) is a type I transmembrane protein reported to induce activation and proliferation of endothelial cells. In addition, CD105 is expressed in haematological malignancies and the vessels of solid tumours. Here, CD105 associates with unfavourable disease course, but so far no data are available on the prognostic relevance of CD105 in haematological malignancies. We here generated a novel CD105 antibody for analysis of expression and prognostic relevance of CD105 in a cohort of 62 AML patients. Flow cytometric analysis revealed substantial expression in the various AML FAB types, with FAB M3 type displaying significantly lower surface levels. Next we established a cut-off specific fluorescence level of 5.22 using receiver-operating characteristics, which allowed to group patients in cases with CD105^lo and CD105^hi surface expression and revealed that high CD105 expression correlated significantly with poor overall and progression free survival. In conclusion, we here identify CD105 expression as a novel prognostic marker in AML, which may serve to optimize follow up and treatment decisions for AML patients.

Morphological and Immunophenotypic Clues to the WHO Categories of Acute Myeloid Leukaemia

Diagnosis and classification of acute myeloid leukaemia (AML) require cytogenetic and molecular genetic investigation. However, while these evaluations are pending, morphology supplemented by immunophenotyping can provide clues to the diagnosis of specific cytogenetic/genetic categories of AML. Most importantly, acute promyelocytic leukaemia can be diagnosed with a high degree of certainty. However, provisional identification of cases associated with t(8; 21), inv(16), t(1; 22), and NPM1 mutation may also be possible. In addition, transient abnormal myelopoiesis of Down's syndrome can generally be diagnosed morphologically.

Endoglin: a novel target for therapeutic intervention in acute leukemias revealed in xenograft mouse models

Endoglin (CD105), a receptor of the transforming growth factor-β superfamily, has been reported to identify functional long-term repopulating hematopoietic stem cells, and has been detected in certain subtypes of acute leukemias. Whether this receptor plays a functional role in leukemogenesis remains unknown. We identified endoglin expression on the majority of blasts from patients with acute myeloid leukemia (AML) and acute B-lymphoblastic leukemia (B-ALL). Using a xenograft model, we find that CD105⁺ blasts are endowed with superior leukemogenic activity compared with the CD105^- population. We test the effect of targeting this receptor using the monoclonal antibody TRC105, and find that in AML, TRC105 prevented the engraftment of primary AML blasts and inhibited leukemia progression following disease establishment, but in B-ALL, TRC105 alone was ineffective due to the shedding of soluble CD105. However, in both B-ALL and AML, TRC105 synergized with reduced intensity myeloablation to inhibit leukemogenesis, indicating that TRC105 may represent a novel therapeutic option for B-ALL and AML.

The role of endoglin in post-ischemic revascularization

Following arterial occlusion, blood vessels respond by forming a new network of functional capillaries (angiogenesis), by reorganizing preexisting capillaries through the recruitment of smooth muscle cells to generate new arteries (arteriogenesis) and by growing and remodeling preexisting collateral arterioles into physiologically relevant arteries (collateral development). All these processes result in the recovery of organ perfusion. The importance of endoglin in post-occlusion reperfusion is sustained by several observations: (1) endoglin expression is increased in vessels showing active angiogenesis/remodeling; (2) genetic endoglin haploinsufficiency in humans causes deficient angiogenesis; and (3) the reduction of endoglin expression by gene disruption or the administration of endoglin-neutralizing antibodies reduces angiogenesis and revascularization. However, the precise role of endoglin in the several processes associated with revascularization has not been completely elucidated and, in some cases, the function ascribed to endoglin by different authors is controversial. The purpose of this review is to organize in a critical way the information available for the role of endoglin in several phenomena (angiogenesis, arteriogenesis and collateral development) associated with post-ischemic revascularization.

CD105 Over-expression Is Associated with Higher WHO Grades for Gliomas

CD105 is an ancillary receptor of transforming growth factor beta (TGF-β), which has been suggested as a suitable biomarker for cancer-related angiogenesis and neovascularization (Nassiri et al. in Anticancer Res 31:2283-2290, 2011). However, the clinical significance of CD105 in WHO grade was rarely reported and the effects of CD105 signal transduction pathway on gliomas remain controversial and unclear. To get a convincing conclusion, performing a meta-analysis is essential. Relevant literature studies were included via careful evaluation, and standard mean difference (SMD) and hazard ratio (HR) with 95 % confidence intervals (95 % CIs) was calculated. We also made funnel plots to test the heterogeneity. In the present meta-analysis, a total of 11 eligible literatures involving 796 patients were incorporated. They were all conducted in China, revealing that CD105 overexpression in glioma tissues was strongly linked to high WHO grading (III+IV) (SMD -1.785, 95 % CI -2.133, -1.437; p = 0.000). No significant associations between CD105 and age (SMD -0.505, 95 % CI -1.054, 0.043; p = 0. 071), CD105 and gender (SMD 0.101, 95 % CI -0.103, 0.305; p = 0.333), and CD105 and tumor size (SMD -0.433, 95 % CI -1.326, 0.459; p = 0. 341) were detected. Besides, CD105 expression was closely associated with glioma patients' 3-year overall survival (OS; n = 2; HR = 4.357, 95 % CI 1.412, 7.303; p = 0.004). On the basis of Begg's and Egger's test or funnel plot, no publication bias was detected. In a nutshell, this meta-analysis demonstrated that CD105 overexpression correlates to higher WHO grade and poor survival and could be indicated as a helpful prognostic and diagnostic marker, or a useful therapy target.