Evaluation and clinical correlations of bone marrow angiogenesis in myelofibrosis with myeloid metaplasia

Revisiting Circulating Extracellular Matrix Fragments as Disease Markers in Myelofibrosis and Related Neoplasms

Philadelphia chromosome-negative chronic myeloproliferative neoplasms (MPNs) arise due to acquired somatic driver mutations in stem cells and develop over 10-30 years from the earliest cancer stages (essential thrombocythemia, polycythemia vera) towards the advanced myelofibrosis stage with bone marrow failure. The JAK2V617F mutation is the most prevalent driver mutation. Chronic inflammation is considered to be a major pathogenetic player, both as a trigger of MPN development and as a driver of disease progression. Chronic inflammation in MPNs is characterized by persistent connective tissue remodeling, which leads to organ dysfunction and ultimately, organ failure, due to excessive accumulation of extracellular matrix (ECM). Considering that MPNs are acquired clonal stem cell diseases developing in an inflammatory microenvironment in which the hematopoietic cell populations are progressively replaced by stromal proliferation-"a wound that never heals"-we herein aim to provide a comprehensive review of previous promising research in the field of circulating ECM fragments in the diagnosis, treatment and monitoring of MPNs. We address the rationales and highlight new perspectives for the use of circulating ECM protein fragments as biologically plausible, noninvasive disease markers in the management of MPNs.

Systematic dissection of coordinated stromal remodeling identifies Sox10+ glial cells as a therapeutic target in myelofibrosis

Remodeling of the tissue niche is often evident in diseases, yet, the stromal alterations and their contribution to pathogenesis are poorly characterized. Bone marrow fibrosis is a maladaptive feature of primary myelofibrosis (PMF). We performed lineage tracing and found that most collagen-expressing myofibroblasts were derived from leptin-receptor-positive (LepR+) mesenchymal cells, whereas a minority were from Gli1-lineage cells. Deletion of Gli1 did not impact PMF. Unbiased single-cell RNA sequencing (scRNA-seq) confirmed that virtually all myofibroblasts originated from LepR-lineage cells, with reduced expression of hematopoietic niche factors and increased expression of fibrogenic factors. Concurrently, endothelial cells upregulated arteriolar-signature genes. Pericytes and Sox10+ glial cells expanded drastically with heightened cell-cell signaling, suggesting important functional roles in PMF. Chemical or genetic ablation of bone marrow glial cells ameliorated fibrosis and improved other pathology in PMF. Thus, PMF involves complex remodeling of the bone marrow microenvironment, and glial cells represent a promising therapeutic target.

Overexpression of VEGF in the MOPC 315 Plasmacytoma Induces Tumor Immunity in Mice

Vascular endothelial growth factor (VEGF) has important effects on hematopoietic and immune cells. A link between VEGF expression, tumor progression, and metastasis has been established in various solid tumors; however, the impact of VEGF expression by hematopoietic neoplasias remains unclear. Here, we investigated the role of VEGF in plasma cell neoplasia. Overexpression of VEGF in MOPC 315 tumor cells (MOPCSVm) had no effect on their growth in vitro. However, constitutive ectopic expression of VEGF dramatically reduced tumorigenicity of MOPC 315 when implanted subcutaneously into BALB/c mice. Mice implanted with MOPCSVm effectively rejected tumor grafts and showed strong cytotoxic T lymphocyte (CTL) activity against parental MOPC 315 cells. MOPCSVm implants were not rejected in nude mice, suggesting the process is T-cell-dependent. Adoptive transfer of splenocytes from recipients inoculated with MOPCSVm cells conferred immunity to naïve BALB/c mice, and mice surviving inoculation with MOPCSVm rejected the parental MOPC 315 tumor cells following a second inoculation. Immunohistochemical analysis showed that MOPCSVm induced a massive infiltration of CD3+ cells and MHC class II+ cells in vivo. In addition, exogenous VEGF induced the expression of CCR3 in T cells in vitro. Together, these data are the first to demonstrate that overexpression of VEGF in plasmacytoma inhibits tumor growth and enhances T-cell-mediated antitumor immune response.

Myelofibrosis: Genetic Characteristics and the Emerging Therapeutic Landscape

Primary myelofibrosis (PMF) is one of three myeloproliferative neoplasms (MPN) that are morphologically and molecularly inter-related, the other two being polycythemia vera (PV) and essential thrombocythemia (ET). MPNs are characterized by JAK-STAT-activating JAK2, CALR, or MPL mutations that give rise to stem cell-derived clonal myeloproliferation, which is prone to leukemic and, in case of PV and ET, fibrotic transformation. Abnormal megakaryocyte proliferation is accompanied by bone marrow fibrosis and characterizes PMF, while the clinical phenotype is pathogenetically linked to ineffective hematopoiesis and aberrant cytokine expression. Among MPN-associated driver mutations, type 1-like CALR mutation has been associated with favorable prognosis in PMF, while ASXL1, SRSF2, U2AF1-Q157, EZH2, CBL, and K/NRAS mutations have been shown to be prognostically detrimental. Such information has enabled development of exclusively genetic (GIPSS) and clinically integrated (MIPSSv2) prognostic models that facilitate individualized treatment decisions. Allogeneic stem cell transplantation remains the only treatment modality in MF with the potential to prolong survival, whereas drug therapy, including JAK2 inhibitors, is directed mostly at the inflammatory component of the disease and is therefore palliative in nature. Similarly, disease-modifying activity remains elusive for currently available investigational drugs, while their additional value in symptom management awaits controlled confirmation. There is a need for genetic characterization of clinical observations followed by in vitro and in vivo preclinical studies that will hopefully identify therapies that target the malignant clone in MF to improve patient outcomes.

Inflammation-related genes S100s, RNASE3, and CYBB and risk of leukemic transformation in patients with myelodysplastic syndrome with myelofibrosis

Myelodysplastic syndrome with myelofibrosis (MDS-MF) has been associated with an inferior prognosis compared with MDS without MF. However, MDS-MF is not listed independently as a subtype of MDS, and its clinical and genetic characteristics remain poorly understood. We retrospectively compared 53 patients with MDS-MF (44 MF grade 1/MF₁; 9 MF grade 2-3/MF_2 - 3) and 31 with de novo MDS without MF (MDS). The leukemic transformation risks of both MDS-MF_2 - 3 and MDS-MF₁ were increased compared with the MDS group. To identify the potential mechanisms responsible for the leukemic transformation of MDS-MF, we performed single-cell sequencing for one MDS-MF_2 - 3 patient before and after leukemic transformation to explore the variations in gene expression levels. In addition to upgraded expression levels of acute myeloid leukemia-related genes during leukemic transformation, expression levels of some inflammation-related genes (such as S100s, RNASE3, and CYBB) were also increased, and inflammation-related pathways were up-regulated. These results suggest that inflammation-related genes and pathways may play an important role in the leukemic transformation of MDS-MF.

The value of bone marrow, liver, and spleen imaging in diagnosis, prognostication, and follow-up monitoring of myeloproliferative neoplasms: a systematic review

Background

Diagnostic and treatment response criteria for the JAK2/CALR/MPL mutation-related myeloproliferative neoplasms (MPNs) are largely based on bone marrow (BM) biopsy results. However, these biopsies have several limitations, such as the risk of sampling error. Also, the prognostic impact of BM abnormalities is largely unclear. Although not currently used in clinical practice, imaging techniques might offer additional information. In this review, we investigated the value of BM, liver, and spleen imaging for diagnosis, prognostication, and response monitoring of the JAK2/CALR/MPL mutation-related MPNs (i.e. essential thrombocythemia (ET), polycythemia vera (PV), and myelofibrosis (MF)).

Methods

A systematic literature search was performed via PubMed, Embase and the Cochrane Library up to 2020 March 26th. Of 5505 identified records, 55 publications met the eligibility criteria (i.e. containing original data on the imaging appearance of BM, spleen, or liver in adult ET, PV, or MF patients, published in a peer-reviewed journal, written in English).

Results

Many explorative studies described imaging features, sometimes with comparisons to clinical characteristics. Studies reporting measures of diagnostic accuracy included 1) splenic transient elastography to predict BM fibrosis grade in MF, 2) dynamic contrast-enhanced MRI to discern MF patients from ET patients and healthy controls, and 3) 18-fluorodeoxyglucose PET to detect residual disease after stem cell transplantation in MF. The diagnostic accuracies of radiography and ^99mTc-colloid scintigraphy were derived from several other articles. Except for the study on 18-fluorodeoxyglucose PET, we established substantial concerns regarding risk of bias and applicability across these studies, using the QUADAS-2 tool. Three publications described a correlation between imaging results and prognosis, of which one quantified the effect.

Conclusions

Based on current data, MRI (T1-weighted/STIR, Dixon) seems especially promising for the evaluation of BM fat content - and indirectly cellularity/fibrosis - in MF, and possibly for estimating BM cellularity in ET/PV. 18-fluorodeoxyglucose and 18-fluorothymidine PET/CT might be useful for evaluating BM fibrosis, with good reported accuracy of the former for the diagnosis of residual disease. Further research on these and other techniques is warranted to determine their exact value. Future researchers should improve methodology and focus on evaluation of diagnostic accuracy and prognostic implications of results.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40644-021-00405-7.

Tumor-associated antigen CAPERα and microvessel density in hepatocellular carcinoma

PURPOSE

CAPERα, a tumor-associated antigen, was identified from a cDNA clone with autoantibody from a patient with hepatocellular carcinoma (HCC). It has been implicated, by way of alternative splicing of VEGF pre-mRNA, in the regulation of microvessel formation in Ewing's sarcoma. In this study, we looked for possible association of alterations in CAPERα with microvessel density in HCC.

METHODS

Enzyme-linked immunosorbent assay using recombinant CAPERα as antigen were used to detect antibody against CAPERα. Immunohistochemistry (IHC) on liver sections was performed to analyze expression profiles of CAPERα, VEGF and CD34 in HCC and control tissues and was further used to assess the correlation of expression among CAPERα, VEGF and CD34 in HCC development.

RESULTS

Autoantibody to CAPERα was highest in HCC (22/76, 28.9%), not detected in prostate cancer (0/79) and at 3.4% (3/88) in breast cancer. In immunohistochemical analysis of grades II and III HCC tissues, significantly decreased immunostaining for CAPERα was observed and this correlated directly with decreased immunostaining for VEGF (R=0.534, P=0.0003). Using CD34 immunostaining for detecting newly formed microvessels, strong staining was observed in grades II and III HCC. Normal liver sections, all of which have high expression of CAPERα were totally negative for CD34 immunostaining. A significant inverse correlation was seen between CAPERα and CD34 immunostaining (R=-0.481, P=0.0012).

CONCLUSIONS

Decreased expression of CAPERα appears to be correlated with appearance of microvessels. It would be of interest to elucidate the cause of altered CAPERα since new formation of microvessels is important in progression of HCC.

The microenvironment in myelodysplastic syndromes: Niche-mediated disease initiation and progression

Myelodysplastic syndromes (MDSs) are clonal disorders of hematopoietic stem and progenitor cells and represent the most common cause of acquired marrow failure. Hallmarked by ineffective hematopoiesis, dysplastic marrow, and risk of transformation to acute leukemia, MDS remains a poorly treated disease. Although identification of hematopoietic aberrations in human MDS has contributed significantly to our understanding of MDS pathogenesis, evidence now identify the bone marrow microenvironment (BMME) as another key contributor to disease initiation and progression. With improved understanding of the BMME, we are beginning to refine the role of the hematopoietic niche in MDS. Despite genetic diversity in MDS, interaction between MDS and the BMME appears to be a common disease feature and therefore represents an appealing therapeutic target. Further understanding of the interdependent relationship between MDS and its niche is needed to delineate the mechanisms underlying hematopoietic failure and how the microenvironment can be targeted clinically. This review provides an overview of data from human MDS and murine models supporting a role for BMME dysfunction at several steps of disease pathogenesis. Although no models or human studies so far have combined all of these findings, we review current data identifying BMME involvement in each step of MDS pathogenesis organized to reflect the chronology of BMME contribution as the normal hematopoietic system becomes myelodysplastic and MDS progresses to marrow failure and transformation. Although microenvironmental heterogeneity and dysfunction certainly add complexity to this syndrome, data are already demonstrating that targeting microenvironmental signals may represent novel therapeutic strategies for MDS treatment.

Prognostic significance of a comprehensive histological evaluation of reticulin fibrosis, collagen deposition and osteosclerosis in primary myelofibrosis patients

AIMS

To evaluate whether a comprehensive histological evaluation of reticulin fibrosis, collagen deposition and osteosclerosis in bone marrow trephine biopsies (BMBs) of primary myelofibrosis (PMF) patients may have prognostic implications.

METHODS AND RESULTS

Reticulin fibrosis, collagen deposition and osteosclerosis were graded from 0 to 3 in a series of 122 baseline BMBs. Then, we assigned to each case a comprehensive score [reticulin, collagen, osteosclerosis (RCO) score, ranging from 0 to 9] that allowed us to distinguish two groups of patients, with low-grade (RCO score 0-4) and high-grade (RCO score 5-9) stromal changes. Of 122 patients, 88 displayed a low-grade and 34 a high-grade RCO score. The latter was associated more frequently with anaemia, thrombocytopenia, peripheral blood blasts and increased lactate dehydrogenase levels. The RCO score was correlated strictly with overall mortality (P = 0.013) and International Prognostic Scoring System (IPSS) risk categories, and was able to discriminate the overall survival of both low- and high-grade patients (log-rank test: P < 0.001). Moreover, it proved to be more accurate than the European Consensus on Grading of Bone Marrow Fibrosis (ECGMF grade) in identifying high-risk patients with poor prognosis. Finally, a combined analysis of RCO scores and IPSS risk categories in an integrated clinical-pathological evaluation was able to increase the positive predictive value (PPV) for mortality in high-risk patients.

CONCLUSION

The comprehensive RCO score, obtained by histological evaluation of reticulin fibrosis, collagen deposition and osteosclerosis was prognostically significant and more accurate than ECGMF grade in identifying high-risk patients and improved PPV when applied in addition to IPSS.

Endothelial-to-Mesenchymal Transition in Bone Marrow and Spleen of Primary Myelofibrosis

Primary myelofibrosis is characterized by the development of fibrosis in the bone marrow that contributes to ineffective hematopoiesis. Bone marrow fibrosis is the result of a complex and not yet fully understood interaction among megakaryocytes, myeloid cells, fibroblasts, and endothelial cells. Here, we report that >30% of the endothelial cells in the small vessels of the bone marrow and spleen of patients with primary myelofibrosis have a mesenchymal phenotype, which is suggestive of the process known as endothelial-to-mesenchymal transition (EndMT). EndMT can be reproduced in vitro by incubation of cultured endothelial progenitor cells or spleen-derived endothelial cells with inflammatory cytokines. Megakaryocytes appear to be implicated in this process, because EndMT mainly occurs in the microvessels close to these cells, and because megakaryocyte-derived supernatant fluid can reproduce the EndMT switch in vitro. Furthermore, EndMT is an early event in a JAK2-V617F knock-in mouse model of primary myelofibrosis. Overall, these data show for the first time that microvascular endothelial cells in the bone marrow and spleen of patients with primary myelofibrosis show functional and morphologic changes that are associated to the mesenchymal phenotype.

CD106 is a novel mediator of bone marrow mesenchymal stem cells via NF-κB in the bone marrow failure of acquired aplastic anemia

BACKGROUND

Acquired aplastic anemia (AA) is characterized by deficiency or dysfunction of the bone marrow (BM) microenvironment. However, little is known about the impairment of BM-derived mesenchymal stem cells (MSCs) in AA patients.

METHODS

We used Illumina HiSeqTM 2000 sequencing, quantitative real-time polymerase chain reaction (qRT-PCR), flow cytometry (FCM), and Western blotting to test the expression of CD106 gene (vascular cell adhesion molecule 1 (VCAM1)) and CD106 protein of BM-MSCs. Furthermore, we used hematoxylin and eosin (H&E) and histochemical staining analysis, immunofluorescence, and the formation of capillary-like structures to analyze capillary tube-like formation in vitro; we also used the Matrigel plug assay to test in vivo vasculogenesis, and an assay of colony forming units (CFUs) and colony-forming unit-megakaryocyte (CFU-MK) to detect the support function of MSCs in vitro. The in vivo engraftment of CD34⁺ cells and MSCs in NOD/SCID mice was tested by FACS and survival assay; the expression of NF-κB was tested by NanoPro analysis and immunofluorescence. NF-κB-regulated CD106 gene (VCAM1) was confirmed by tumor necrosis factor alpha (TNF-α)-stimulated and lipopolysaccharide (LPS)-stimulated MSCs, blockade assay, and immunofluorescence.

RESULTS

Here, we report that BM-MSCs from AA patients exhibited downregulation of the CD06 gene (VCAM1) and low expression of CD106 in vitro. Further analysis revealed that CD106⁺ MSCs from both AA patients and healthy controls had increased potential for in vitro capillary tube-like formation and in vivo vasculogenesis compared with CD106^- MSCs, and the results were similar when healthy MSCs were compared with AA MSCs. CD106⁺ MSCs from both AA patients and healthy controls more strongly supported in vitro growth and in vivo engraftment of CD34⁺ cells in NOD/SCID mice than CD106^- MSCs, and similar results were obtained when healthy MSCs and AA MSCs were compared. The expression of NF-κB was decreased in AA MSCs, and NF-κB regulated the CD106 gene (VCAM1) which supported hematopoiesis.

CONCLUSIONS

These results revealed the effect of CD106 and NF-κB in BM failure of AA.

Imetelstat, a telomerase inhibitor, differentially affects normal and malignant megakaryopoiesis

Imetelstat (GRN163L) is a specific telomerase inhibitor that has demonstrated clinical activity in patients with myeloproliferative neoplasms (MPN) and in patients with solid tumors. The antitumor effects were associated with the development of thrombocytopenia, one of the common side effects observed in patients treated with imetelstat. The events underlying these adverse effects are not apparent. In this report, we investigated the potential mechanisms that account for imetelstat's beneficial effects in MPN patients and the manner by which imetelstat treatment leads to a reduction in platelet numbers. Using a well-established system of ex vivo megakaryopoiesis, we demonstrated that imetelestat treatment affects normal megakaryocyte (MK) development by exclusively delaying maturation of MK precursor cells. By contrast, additional stages along MPN MK development were affected by imetelstat resulting in reduced numbers of assayable colony-forming unit MK and impaired MK maturation. In addition, treatment with imetelstat inhibited the secretion of fibrogenic growth factors by malignant but not by normal MK. Our results indicate that the delay observed in normal MK maturation may account for imetelstat-induced thrombocytopenia, while the more global effects of imetelstat on several stages along the hierarchy of MPN megakaryopoiesis may be responsible for the favorable clinical outcomes reported in MPN patients.

The role of the extracellular matrix in primary myelofibrosis

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm that arises from clonal proliferation of hematopoietic stem cells and leads to progressive bone marrow (BM) fibrosis. While cellular mutations involved in the development of PMF have been heavily investigated, noteworthy is the important role the extracellular matrix (ECM) plays in the progression of BM fibrosis. This review surveys ECM proteins contributors of PMF, and highlights how better understanding of the control of the ECM within the BM niche may lead to combined therapeutic options in PMF.

Bone marrow microvessel density and plasma angiogenic factors in myeloproliferative neoplasms: clinicopathological and molecular correlations

Increased angiogenesis in BCR-ABL1 negative myeloproliferative neoplasms (MPNs) has been recognized, but its connection with clinical and molecular markers needs to be defined. The aims of study were to (1) assess bone marrow (BM) angiogenesis measured by microvessel density (MVD) using CD34 and CD105 antibodies; (2) analyze correlation of MVD with plasma angiogenic factors including vascular endothelial growth factor, basic fibroblast growth factor, and interleukin-8; (3) examine the association of MVD with clinicopathological and molecular markers. We examined 90 de novo MPN patients (30 polycythemia vera (PV), primary myelofibrosis (PMF), essential thrombocythemia (ET)) and 10 age-matched controls. MVD was analyzed by immunohistochemistry "hot spot" method, angiogenic factors by immunoassay and JAK2V617F, and CALR mutations by DNA sequencing and allelic PCR. MVD was significantly increased in MPNs compared to controls (PMF > PV > ET). Correlation between MVD and plasma angiogenic factors was found in MPNs. MVD was significantly increased in patients with JAK2V617F mutation and correlated with JAK2 mutant allele burden (CD34-MVD: ρ = 0.491, p < 0.001; CD105-MVD: ρ = 0.276, p = 0.02) but not with CALR mutation. MVD correlated with leukocyte count, serum lactate dehydrogenase, hepatomegaly, and splenomegaly. BM fibrosis was significantly associated with CD34-MVD, CD105-MVD, interleukin-8, and JAK2 mutant allele burden. JAK2 homozygote status had positive predictive value (100%) for BM fibrosis. Patients with prefibrotic PMF had significantly higher MVD than patients with ET, and we could recommend MVD to be additional histopathological marker to distinguish these two entities. This study also highlights the strong correlation of MVD with plasma angiogenic factors, JAK2 mutant allele burden, and BM fibrosis in MPNs.

Tie2 Expressing Monocytes in the Spleen of Patients with Primary Myelofibrosis

Primary myelofibrosis (PMF) is a Philadelphia-negative (Ph−) myeloproliferative disorder, showing abnormal CD34⁺ progenitor cell trafficking, splenomegaly, marrow fibrosis leading to extensive extramedullary haematopoiesis, and abnormal neoangiogenesis in either the bone marrow or the spleen. Monocytes expressing the angiopoietin-2 receptor (Tie2) have been shown to support abnormal angiogenic processes in solid tumors through a paracrine action that takes place in proximity to the vessels. In this study we investigated the frequency of Tie2 expressing monocytes in the spleen tissue samples of patients with PMF, and healthy subjects (CTRLs), and evaluated their possible role in favouring spleen angiogenesis. We show by confocal microscopy that in the spleen tissue of patients with PMF, but not of CTRLs, the most of the CD14⁺ cells are Tie2⁺ and are close to vessels; by flow cytometry, we found that Tie2 expressing monocytes were Tie2⁺CD14^lowCD16^brightCDL62⁻CCR2⁻ (TEMs) and their frequency was higher (p = 0.008) in spleen tissue-derived mononuclear cells (MNCs) of patients with PMF than in spleen tissue-derived MNCs from CTRLs undergoing splenectomy for abdominal trauma. By in vitro angiogenesis assay we evidenced that conditioned medium of immunomagnetically selected spleen tissue derived CD14⁺ cells of patients with PMF induced a denser tube like net than that of CTRLs; in addition, CD14⁺Tie2⁺ cells sorted from spleen tissue derived single cell suspension of patients with PMF show a higher expression of genes involved in angiogenesis than that found in CTRLs. Our results document the enrichment of Tie2⁺ monocytes expressing angiogenic genes in the spleen of patients with PMF, suggesting a role for these cells in starting/maintaining the pathological angiogenesis in this organ.

Functional and Biological Role of Endothelial Precursor Cells in Tumour Progression: A New Potential Therapeutic Target in Haematological Malignancies

It was believed that vasculogenesis occurred only during embryo life and that postnatal formation of vessels arose from angiogenesis. Recent findings demonstrate the existence of Endothelial Precursor Cells (EPCs), which take partin postnatal vasculogenesis. EPCs are recruited from the bone marrow under the stimulation of growth factors and cytokines and reach the sites of neovascularization in both physiological and pathological conditions such as malignancies where they contribute to the “angiogenic switch” and tumor progression. An implementation of circulating EPCs in the bloodstream of patients with haematological malignancies has been demonstrated. This increase is strictly related to the bone marrow microvessel density and correlated with a poor prognosis. The EPCs characterization is a very complex process and still under investigation. This literature review aims to provide an overview of the functional and biological role of EPCs in haematological malignancies and to investigate their potential as a new cancer therapeutic target.

Nuclear factor-erythroid 2, nerve growth factor receptor, and CD34-microvessel density are differentially expressed in primary myelofibrosis, polycythemia vera, and essential thrombocythemia

Because of the presence of various overlapping findings, the discrimination of polycythemia vera (PV) from prefibrotic/fibrotic primary myelofibrosis (PF/F-PMF) and essential thrombocythemia (ET) may be challenging, particularly in suboptimal bone marrow biopsy specimens. In this study, we assessed whether differences in the expression of nuclear factor-erythroid 2 (NF-E2), nerve growth factor receptor (NGFR; CD271), CD34, CD68, p53, CD3, CD20, and CD138 by immunohistochemistry could be useful in separating among them. Higher frequencies of nuclear positive erythroblasts with NF-E2 were observed in ET and PV cases (50% ± 13.3% and 41.5% ± 9.4%, respectively) when compared with both PF-PMF (21% ± 11.7%) and F-PMF (28.5% ± 10.8%). We found that with a cutoff level of at least 30% nuclear staining for NF-E2 in erythroblasts, we could reliably exclude the possibility of PMF. Conversely, NGFR+ stromal cells per high-power field (HPF) was significantly increased in F-PMF (53.5 ± 19.1/HPF) and PF-PMF (13.5 ± 3.8/HPF) compared with ET (4.4 ± 2.2/HPF) and PV (6.6 ± 3.3/HPF). Similarly, differences in CD34-microvessel density was remarkable in F-PMF and PF-PMF cases in comparison with PV and ET (49.9 ± 12.1/HPF, 29.3 ± 12.4/HPF, 13.7 ± 4.6/HPF, and 11.9 ± 5.1/HPF, respectively). Thus, the assessment of NF-E2 and NGFR expression and the evaluation of CD34-microvessel density may provide additional support in reaching a correct diagnosis in these cases of myeloproliferative neoplasms.

Study of prognostic significance of marrow angiogenesis assessment in patients with de novo acute leukemia

BACKGROUND

Angiogenesis is the highly ordered formation of new blood vessels from pre-existing vessels. It is seen throughout growth, in wound healing, menses, and is important in cancer, where pro- and antiangiogenic signals can be released by cancer cells, endothelial cells, stromal cells, blood, and the extracellular matrix. Aim of the study is to use standardized method for counting blood vessels to verify the significance and prognostic value of assessing marrow angiogenesis at diagnosis of de novo acute leukemia.

SUBJECTS AND METHODS

The study included 70 newly diagnosed acute leukemia cases and a control group composed of 35 bone marrow biopsy sections obtained from breast cancer patients. Examination of CD34 immunohistochemically stained sections for the assessment of marrow angiogenesis by quantification of its microvessel density (MVD).

RESULTS

MVD was significantly increased in acute leukemia patients in comparison to control group (P-value <0.001). Increased MVD was associated with unfavorable outcome.

CONCLUSION

The study demonstrated an evidence of increased angiogenesis in acute leukemia detected by high bone marrow MVD which may play a significant role in leukemic process. Understanding its role may help in designing new therapeutic strategies for acute leukemia.

Vascular endothelial growth factor A (VEGFA) expression in mycosis fungoides

AIMS

High levels of vascular endothelial growth factor A (VEGFA) seem to herald a worse prognosis in mycosis fungoides (MF). In this study, we aimed to characterize more clearly VEGFA gene and protein expression in MF.

METHODS AND RESULTS

First, we compared VEGFA mRNA levels in MF and in normal T lymphocyte samples; significantly higher VEGFA levels were found in MF. We then studied VEGFA expression in different normal T cell subsets, focusing on CD4(+) , CD8(+) , resting and activated T lymphocytes. We applied the gene signatures of the normal T cell subsets to MF samples and found that activated T lymphocytes represented the closest normal counterpart of the tumour. However, VEGFA mRNA levels were significantly higher in MF than in activated normal T cells, suggesting that VEGFA overexpression in MF represents an attribute acquired during neoplastic transformation: no significant VEGFA expression differences were recorded between early and advanced stages. Gene expression profile results were supported by immunohistochemistry in routine sections from 27 MF cases.

CONCLUSIONS

For the first time, we demonstrate VEGFA expression in MF cells, suggesting that the VEGF pathway may be implicated in MF pathogenesis and can represent a novel therapeutic target.

Increased angiogenesis in primary myelofibrosis: latent transforming growth factor-β as a possible angiogenic factor

Objective

The aim of this work was to demonstrate a possible relationship between anti-latency-associated peptide human latent transforming growth factor beta 1 (latent TGF-β1) expression in megakaryocytes and microvascular density in bone marrow biopsies from patients with essential thrombocythemia and primary myelofibrosis.

Methods

Microvascular density was evaluated by immunohistochemical analysis and the expression of latent TGF-β1 in samples (100 megakaryocytes per bone marrow sample) from 18 essential thrombocythemia and 38 primary myelofibrosis (19 prefibrotic and 19 fibrotic) patients. Six bone marrow donor biopsies were used as controls. Fibrosis in the bone marrow biopsies was evaluated according to the European Consensus.

Results

The average fibrosis grade differed between essential thrombocythemia and primary myelofibrosis groups when compared to the control group. Latent TGF-β1 expression differed significantly between the fibrotic primary myelofibrosis (PMF) group and the control group (p-value < 0.01). A high degree of neo-angiogenesis (demonstrated by analysis of CD34 expression) was detected in patients with myelofibrosis. There were correlations between latent TGF-β1 expression and microvascular density (r = 0.45; p-value < 0.0009) and between degree of microvascular density and fibrosis grade (r = 0.80; p-value < 0.0001). Remarkable differences for neo-angiogenesis were not observed between patients with essential thrombocythemia and controls.

Conclusion

Angiogenesis participates in the pathogenesis of primary myelofibrosis, in both the prefibrotic and fibrotic stages, while latent TGF-β is differentially expressed only in the prefibrotic stage.

Enhanced expression of Stim, Orai, and TRPC transcripts and proteins in endothelial progenitor cells isolated from patients with primary myelofibrosis

Background

An increase in the frequency of circulating endothelial colony forming cells (ECFCs), the only subset of endothelial progenitor cells (EPCs) truly belonging to the endothelial phenotype, occurs in patients affected by primary myelofibrosis (PMF). Herein, they might contribute to the enhanced neovascularisation of fibrotic bone marrow and spleen. Store-operated Ca²⁺ entry (SOCE) activated by the depletion of the inositol-1,4,5-trisphosphate (InsP₃)-sensitive Ca²⁺ store drives proliferation in ECFCs isolated from both healthy donors (N-ECFCs) and subjects suffering from renal cellular carcinoma (RCC-ECFCs). SOCE is up-regulated in RCC-ECFCs due to the over-expression of its underlying molecular components, namely Stim1, Orai1, and TRPC1.

Methodology/Principal Findings

We utilized Ca²⁺ imaging, real-time polymerase chain reaction, western blot analysis and functional assays to evaluate molecular structure and the functional role of SOCE in ECFCs derived from PMF patients (PMF-ECFCs). SOCE, induced by either pharmacological (i.e. cyclopiazonic acid or CPA) or physiological (i.e. ATP) stimulation, was significantly higher in PMF-ECFCs. ATP-induced SOCE was inhibited upon blockade of the phospholipase C/InsP₃ signalling pathway with U73111 and 2-APB. The higher amplitude of SOCE was associated to the over-expression of the transcripts encoding for Stim2, Orai2–3, and TRPC1. Conversely, immunoblotting revealed that Stim2 levels remained constant as compared to N-ECFCs, while Stim1, Orai1, Orai3, TRPC1 and TRPC4 proteins were over-expressed in PMF-ECFCs. ATP-induced SOCE was inhibited by BTP-2 and low micromolar La³⁺ and Gd³⁺, while CPA-elicited SOCE was insensitive to Gd³⁺. Finally, BTP-2 and La³⁺ weakly blocked PMF-ECFC proliferation, while Gd³⁺ was ineffective.

Conclusions

Two distinct signalling pathways mediate SOCE in PMF-ECFCs; one is activated by passive store depletion and is Gd³⁺-resistant, while the other one is regulated by the InsP₃-sensitive Ca²⁺ pool and is inhibited by Gd³⁺. Unlike N- and RCC-ECFCs, the InsP₃-dependent SOCE does not drive PMF-ECFC proliferation.

Thalidomide treatment in a myelofibrosis patient with leukemia transformation

Primary myelofibrosis is a clonal disease of chronic myeloproliferative neoplasm, and is a progressive clinical course with short median survival of less than 5 years after diagnosis. Leukemic transformation occurs in 8-23 % of myelofibrosis patients, and survival is about 3 months after transformation to leukemia. Thalidomide, an oral immunomodulatory drug, has been used effectively in the treatment of primary myelofibrosis, in which some patients could become transfusion independent, and showed improvement in thrombocytopenia and reduction in spleen size. Here, we report a patient with primary myelofibrosis with leukemic transformation who survived for more than 6 years with thalidomide monotherapy. Thalidomide may be beneficial for some myelofibrosis patients with leukemic transformation for whom intensive chemotherapy is not indicated.

Rescue of a primary myelofibrosis model by retinoid-antagonist therapy

Molecular targeting of the two receptor interaction domains of the epigenetic repressor silencing mediator of retinoid and thyroid hormone receptors (SMRT(mRID)) produced a transplantable skeletal syndrome that reduced radial bone growth, increased numbers of bone-resorbing periosteal osteoclasts, and increased bone fracture risk. Furthermore, SMRT(mRID) mice develop spontaneous primary myelofibrosis, a chronic, usually idiopathic disorder characterized by progressive bone marrow fibrosis. Frequently linked to polycythemia vera and chronic myeloid leukemia, myelofibrosis displays high patient morbidity and mortality, and current treatment is mostly palliative. To decipher the etiology of this disease, we identified the thrombopoietin (Tpo) gene as a target of the SMRT-retinoic acid receptor signaling pathway in bone marrow stromal cells. Chronic induction of Tpo in SMRT(mRID) mice results in up-regulation of TGF-β and PDGF in megakaryocytes, uncontrolled proliferation of bone marrow reticular cells, and fibrosis of the marrow compartment. Of therapeutic relevance, we show that this syndrome can be rescued by retinoid antagonists, demonstrating that the physical interface between SMRT and retinoic acid receptor can be a potential therapeutic target to block primary myelofibrosis disease progression.

Differential regulation of CXCL5 by FGF2 in osteoblastic and endothelial niche cells supports hematopoietic stem cell migration

Stem cell maintenance requires a specific microenvironment. Hematopoietic stem cells (HSCs) are mainly maintained by the endosteal osteoblast (OB) niche, which provides a quiescent HSC microenvironment, and the vascular niche, which regulates the proliferation, differentiation, and mobilization of HSCs. The systemic administration of FGF2 failed to induce normal hematopoiesis in bone marrow (BM) by reducing SDF-1, an important factor for hematopoiesis. Interestingly, SDF-1 levels were decreased in the OBs, but increased in vascular endothelial C166 cells when FGF2 was administered. We hypothesized that FGF2 induces changes in HSC migration from BM; therefore, we investigated FGF2-induced factors of HSC migration by a microarray chip. We searched the genes that were decreased in primary OBs, but increased in C166 cells upon FGF2 treatment. We confirmed selected genes that function in the extracellular region and identified the CXCR2-related chemokine candidate LIX/Cxcl5. A chemotaxis assay showed that CXCL5 induced the migration of HSCs (CD34(-/low)LSK). Our data suggest that the differential regulation of the chemokine CXCL5 between OBs and endothelial cells upon FGF2 treatment is involved in HSC mobilization from the OB niche or BM to peripheral blood.

Megakaryocytes, malignancy and bone marrow vascular niches

Dynamic interactions between hematopoietic cells and their specialized bone marrow microenvironments, namely the vascular and osteoblastic 'niches', regulate hematopoiesis. The vascular niche is conducive for thrombopoiesis and megakaryocytes may, in turn, regulate the vascular niche, especially in supporting vascular and hematopoietic regeneration following irradiation or chemotherapy. A role for platelets in tumor growth and metastasis is well established and, more recently, the vascular niche has also been implicated as an area for preferential homing and engraftment of malignant cells. This article aims to provide an overview of the dynamic interactions between cellular and molecular components of the bone marrow vascular niche and the potential role of megakaryocytes in bone marrow malignancy.

Perfusion parameters analysis of the vertebral bone marrow in patients with Ph¹⁻ chronic myeloproliferative neoplasms (Ph(neg) MPN): a dynamic contrast-enhanced MRI (DCE-MRI) study

PURPOSE

To evaluate perfusion parameters of the vertebral bone marrow in patients with Philadelphia negative chronic myeloproliferative neoplasms (Ph(neg) MPN) using dynamic contrast-enhanced MRI (DCE-MRI).

MATERIALS AND METHODS

The study enrolled 24 patients with Ph(neg) MPN: 12 patients with myelofibrosis (Group A), 6 with essential thrombocythemia (ET), and 6 with polycythemia vera (PV) (Group B) who underwent DCE-MRI of the lumbosacral spine. Twelve normal individuals served as control group (Group C). Wash-in (WIN), wash-out (WOUT), maximum contrast-enhancement (CE  max), time-to-peak (TTPK), time-to-maximum slope (TMSP), and the WIN/TMSP ratio (WTSP) were calculated.

RESULTS

WIN, CE(max) , and WTSP parameters were higher in Group A than in Group C (P < 0.05). These parameters were significant (P < 0.0001) in discriminating patients with myelofibrosis from normal individuals with sensitivities 74.14%, 87.93%, 74.14%, and specificities 91.07%, 83.93%, 91.07%, respectively. WIN, WOUT, CE(max) , and WTSP parameters were higher in Group A than in Group B (P < 0.05). Group B exhibited no differences in perfusion parameters as compared with Group C with the exception of WOUT.

CONCLUSION

Patients with myelofibrosis exhibited increased perfusion parameters in vertebral bone marrow, which could be consisted with increased vascularity, probably related to neoangiogenesis as opposed to ET or PV patients showing no increased perfusion. DCE-MRI may be of value in discriminating subgroups of Ph(neg) MPN patients and in indicating those progressing to myelofibrosis.

The bone marrow stroma in hematological neoplasms--a guilty bystander

In the setting of hematological neoplasms, changes in the bone marrow (BM) stroma might arise from pressure exerted by the neoplastic clone in shaping a supportive microenvironment, or from chronic perturbation of the BM homeostasis. Under such conditions, alterations in the composition of the BM stroma can be profound, and could emerge as relevant prognostic factors. In this Review, we delineate the multifaceted contribution of the BM stroma to the pathobiology of several hematological neoplasms, and discuss the impact of stromal modifications on the natural course of these diseases. Specifically, we highlight the involvement of BM stromal components in lymphoid and myeloid malignancies, and present the most relevant processes responsible for remodeling the BM stroma. The role of bystander BM stromal elements in the setting of hematological neoplasms is discussed, strengthening the rationale for treatment strategies that target the BM stroma.

Pomalidomide therapy for multiple myeloma and myelofibrosis: an update

Thalidomide possesses potent anti-inflammatory, immunomodulatory, and antiangiogenic properties. Thalidomide combined with corticosteroids is therapeutically active in multiple myeloma and myelofibrosis (MF). Lenalidomide and pomalidomide are second-generation immunomodulatory drugs (IMiDs) that were created by chemical modification of thalidomide with the intent to reduce toxicity and enhance therapeutic activity. Both drugs have also been shown to be active in the treatment of myeloma and MF. Thalidomide is US Food and Drug Administration (FDA)-approved for use in acute erythema nodosum leprosum and, in combination with dexamethasone, in newly diagnosed myeloma. Lenalidomide is approved for use in low/intermediate-1 risk myelodysplastic syndromes associated with transfusion-dependent anemia and a deletion 5q cytogenetic abnormality and, in combination with dexamethasone, in relapsed myeloma. Pomalidomide is currently not FDA-approved. Herein, we summarize what is currently known about the biologic and therapeutic effects of pomalidomide.

Increased expression of vascular endothelial growth factor receptor 1 correlates with VEGF and microvessel density in Philadelphia chromosome-negative myeloproliferative neoplasms

Aims

The authors investigated vascular endothelial growth factor receptor 1 (VEGFR-1) protein expression in a series of Philadelphia chromosome-negative myeloproliferative neoplasms (Ph- MPNs) and its correlations with microvessel density (MVD) and vascular endothelial growth factor (VEGF).

Methods

83 bone marrow biopsies of Ph- MPNs patients, including 27 essential thrombocythaemia (ET), 21 polycythaemia vera (PV) and 35 primary myelofibrosis (PMF), and 10 normal controls (NCs) were investigated by immunohistochemistry.

Results

Patients with PV and PMF showed an increased MVD (PV: 20.1±10.6; PMF: 25.8±6.5) compared with those with ET or NCs (ET: 10.4±4.6; NCs: 7±3.4). VEGFR-1 expression was increased in Ph- MPNs, particularly in PV and PMF (NCs: 0.07±0.03; ET: 0.15±0.09; PV: 0.31±0.2; PMF: 0.31±0.04). VEGF expression parallelled VEGFR-1 and resulted increased in Ph- MPNs (NCs: 0.08±0.04; ET: 0.13±0.06; PV: 0.29±0.2; PMF: 0.31±0.15) and higher in post-polycythaemic myelofibrosis and in the fibrotic stage of PMF than in the non-fibrotic phases of both diseases. VEGFR-1 protein expression correlated with MVD and VEGF expression in Ph- MPNs. VEGFR-1 and VEGF were expressed by the same bone marrow populations: megakaryocytes, macrophages and immature myeloid precursors showed a moderate to strong immunostaining intensity in both Ph- MPNs and NCs. The erythroid precursors were not immunoreactive.

Conclusions

VEGFR-1 and VEGF were increased and co-localised in megakaryocytes, macrophages and myeloid precursors of Ph- MPNs. This finding supports the hypothesis of a VEGF/VEGFR-1 autocrine loop in the neoplastic cells of Ph- MPNs.

High frequency of endothelial colony forming cells marks a non-active myeloproliferative neoplasm with high risk of splanchnic vein thrombosis

Increased mobilization of circulating endothelial progenitor cells may represent a new biological hallmark of myeloproliferative neoplasms. We measured circulating endothelial colony forming cells (ECFCs) in 106 patients with primary myelofibrosis, fibrotic stage, 49 with prefibrotic myelofibrosis, 59 with essential thrombocythemia or polycythemia vera, and 43 normal controls. Levels of ECFC frequency for patient's characteristics were estimated by using logistic regression in univariate and multivariate setting. The sensitivity, specificity, likelihood ratios, and positive predictive value of increased ECFC frequency were calculated for the significantly associated characteristics. Increased frequency of ECFCs resulted independently associated with history of splanchnic vein thrombosis (adjusted odds ratio = 6.61, 95% CI = 2.54–17.16), and a summary measure of non-active disease, i.e. hemoglobin of 13.8 g/dL or lower, white blood cells count of 7.8×10⁹/L or lower, and platelet count of 400×10⁹/L or lower (adjusted odds ratio = 4.43, 95% CI = 1.45–13.49) Thirteen patients with splanchnic vein thrombosis non associated with myeloproliferative neoplasms were recruited as controls. We excluded a causal role of splanchnic vein thrombosis in ECFCs increase, since no control had elevated ECFCs. We concluded that increased frequency of ECFCs represents the biological hallmark of a non-active myeloproliferative neoplasm with high risk of splanchnic vein thrombosis. The recognition of this disease category copes with the phenotypic mimicry of myeloproliferative neoplasms. Due to inherent performance limitations of ECFCs assay, there is an urgent need to arrive to an acceptable standardization of ECFC assessment.

Phase II study of sunitinib in patients with primary or post-polycythemia vera/essential thrombocythemia myelofibrosis

BACKGROUND

Changes in the bone marrow microenvironment in myelofibrosis are triggered by a cytokine burst and consist of fibrosis, osteosclerosis, and angiogenesis. Sunitinib is a multitargeted small-molecule inhibitor of the receptor tyrosine kinases involved in cell proliferation and angiogenesis, including vascular endothelial growth factor receptors.

PATIENTS AND METHODS

Fourteen patients with myelofibrosis were treated with sunitinib at a daily continuous dose of 37.5 mg orally. The median duration of sunitinib treatment was 5.2 months (range, 1-18 months).

RESULTS

One patient (7%) showed a clinical improvement of anemia (increase in hemoglobin of 4 g/dL), with improvement in anemia-associated symptoms. The time to response was 6 months, and the benefit was sustained for 12 months. However, 8 patients (57%) experienced a total of 13 incidents of significant (grade 3-4) adverse events possibly related to sunitinib (fatigue, gastrointestinal disturbances, anemia, leukopenia, and thrombocytopenia were the most common). In 7 patients (50%), sunitinib was held, and subsequently the dose was reduced to 25 mg daily. Overall, 29% of patients withdrew from the study because of toxicity.

CONCLUSION

Sunitinib therapy, as applied here, was not well-tolerated by patients with myelofibrosis, and the benefits were minimal. Our experience with sunitinib combined with previous experience with other antiangiogenic medications suggest that this class of drugs may have limited usefulness in myelofibrosis when used as a single-agent therapy.

A dynamic prognostic model to predict survival in primary myelofibrosis: a study by the IWG-MRT (International Working Group for Myeloproliferative Neoplasms Research and Treatment)

Age older than 65 years, hemoglobin level lower than 100 g/L (10 g/dL), white blood cell count greater than 25 × 109/L, peripheral blood blasts 1% or higher, and constitutional symptoms have been shown to predict poor survival in primary myelofibrosis (PMF) at diagnosis. To investigate whether the acquisition of these factors during follow-up predicts survival, we studied 525 PMF patients regularly followed. All 5 variables had a significant impact on survival when analyzed as time-dependent covariates in a multivariate Cox proportional hazard model and were included in 2 separate models, 1 for all patients (Dynamic International Prognostic Scoring System [DIPSS]) and 1 for patients younger than 65 years (age-adjusted DIPSS). Risk factors were assigned score values based on hazard ratios (HRs). Risk categories were low, intermediate-1, intermediate-2, and high in both models. Survival was estimated by the HR. When shifting to the next risk category, the HR was 4.13 for low risk, 4.61 for intermediate-1, and 2.54 for intermediate-2 according to DIPSS; 3.97 for low risk, 2.84 for intermediate-1, and 1.81 for intermediate-2 according to the age-adjusted DIPSS. The novelty of these models is the prognostic assessment of patients with PMF anytime during their clinical course, which may be useful for treatment decision-making.

Abnormal immunity and stem/progenitor cells in acquired aplastic anemia

Acquired aplastic anemia (AA) is considered as an immune-mediated bone marrow failure syndrome, characterized by hypoplasia and pancytopenia with fatty bone marrow. Abnormal immunity is the major factor mediating the pathogenesis of acquired AA. Activated DCs might promote the polarization to Th1 cells, and activate CD8(+) T cells. A variety of immune molecules including IFN-gamma, TNF-alpha, MIP-1alpha and IL-2, 8, 12, 15, 17, 23, produced by them and stromal cells, compose a cytokine network to destruct stem/progenitor cells as well as hematopoietic stem/progenitor cells, mesenchymal stem cells (MSCs) and angioblasts/endothelial progenitor cells. Inversely, deficient MSCs, CD4(+)CD25(+) T cells, NK cells, NKT cells and early hematopoietic growth factors diminish the capacity of immune regulation and the support of hematopoiesis. As a result, stem/progenitor cells are significantly impaired to be disabled cells with markedly deficient proliferation, differentiation, induced apoptosis and dysfunctional response to growth factor stimuli, together with rare normal ones. Although some patients can be ameliorated by stem-cell transplantation or immunosuppressive therapy, more effective and convenient therapies such as patient-specific pluripotent iPS cells based on definite pathogenesis are expected.

Lenalidomide plus prednisone results in durable clinical, histopathologic, and molecular responses in patients with myelofibrosis

PURPOSE

To investigate the safety and efficacy of the combination of lenalidomide and prednisone in patients with myelofibrosis (MF).

PATIENTS AND METHODS

Forty patients with MF were treated. Therapy consisted of lenalidomide 10 mg/d (5 mg/d if baseline platelet count < 100 x 10(9)/L) on days 1 through 21 of a 28-day cycle for six cycles, in combination with prednisone 30 mg/d orally during cycle 1, 15 mg/d during cycle 2, and 15 mg/d every other day during cycle 3. Lenalidomide therapy was continued indefinitely in patients exhibiting clinical benefit.

RESULTS

The median follow-up was 22 months (range, 6 to 27). Responses were recorded in 12 patients (30%) and are ongoing in 10 (25%). The median time to response was 12 weeks (range, 2 to 32). According to the International Working Group for Myelofibrosis Research and Treatment consensus criteria, three patients (7.5%) had partial response and nine patients (22.5%) had clinical improvement durable for a median of 18 months (range, 3.5 to 24+). Overall response rates were 30% for anemia and 42% for splenomegaly. Moreover, 10 of 11 assessable responders who started therapy with reticulin fibrosis grade 4 experienced reductions to at least a score of 2. All eight JAK2(V617F)-positive responders experienced a reduction of the baseline mutant allele burden, which was greater than 50% in four, including one of whom the mutation became undetectable. Grade 3 to 4 hematologic adverse events included neutropenia (58%), anemia (42%), and thrombocytopenia (13%).

CONCLUSION

The combination of lenalidomide and prednisone induces durable clinical, molecular, and pathologic responses in MF.

JAK2 inhibitors: A reality? A hope?

Myelofibrosis (MF; primary or post-polycythemia vera/essential thrombocythemia) carries the worst prognosis among BCR-ABL-negative myeloproliferative neoplasms (MPNs). Stem cell transplantation is the only curative approach but is hampered by significant nonrelapse mortality. Thus, effective, targeted therapies are needed. A mutated Janus kinase 2 (JAK2) gene (JAK2(V617F)), found in a significant portion of patients with MPN, results in increased JAK2 tyrosine kinase activity, leading to clonal proliferation; several small molecules inhibit the growth of hematopoietic colonies harboring JAK2(V617). Several JAK2 inhibitors have reached the clinical trial stage and are reviewed here. The most developed among them is INCB018424, which has demonstrated noteworthy clinical activity, with a rapid and profound reduction in splenomegaly and associated improvement in constitutional symptoms in MF patients receiving 10-25 mg orally twice daily, continuously. Thrombocytopenia (reversible) was the most common adverse event, seen in 30% of patients treated with 25 mg twice daily but not with 10 mg twice daily. Interestingly, INCB018424 was equally active in patients with and without JAK2 mutation. Other JAK2 inhibitors are less developed but show a similar type of clinical benefit. Conclusively, JAK2 inhibitors, particularly INCB018424, are clinically active in MF and are well tolerated. Whether they have an effect on the natural course of MF in treated patients remains to be elucidated.

Bone marrow CD34+progenitor cells in Philadelphia chromosome-negative chronic myeloproliferative disorders – A clinicopathological study on 575 patients

Contrasting the circulating CD34+ hematopoietic progenitor cells (HPCs) in chronic myeloproliferative disorders (CMPDs), scant knowledge is available regarding their quantity in the bone marrow (BM). Therefore, a clinicopathological study was performed on trephine biopsies in 575 patients with CMPDs focused on chronic idiopathic myelofibrosis (CIMF). A comparison with 25 healthy subjects revealed no significant differences in the numbers of HPCs (6 +/- 3/mm2) in polycythemia vera, essential thrombocythemia and advanced fibro-osteosclerotic stages of CIMF. Pre-fibrotic and early-stage CIMF displayed 16 +/- 11 precursors per mm2 BM. Sequential biopsies in this disorder showed a decline in HPCs (10 +/- 6/mm2) with evolving myelofibrosis-myeloid metaplasia (MMM), while in terminal stages acceleration generated an increase (24 +/- 25/mm2). A significant association between the quantity of HPCs and the development of myelofibrosis, splenomegaly, and anemia as well as an increase in peripheral blasts was recognizable in CIMF. Moreover, in all subtypes of CMPDs, a favorable prognosis was significantly associated with a higher number of HPCs in the BM. In conclusion, enhanced inflow of precursors from the BM with subsequent trapping, self-renewal and mobilization by the spleen is assumed to indicate a progressive generalization and worsening of the outcome. This putative pathomechanism is significantly associated with the evolution of MMM.

The microenvironment in mature B-cell malignancies: a target for new treatment strategies

Despite major therapeutic advances, most mature B-cell malignancies remain incurable. Compelling evidence suggests that crosstalk with accessory stromal cells in specialized tissue microenvironments, such as the bone marrow and secondary lymphoid organs, favors disease progression by promoting malignant B-cell growth and drug resistance. Therefore, disrupting the crosstalk between malignant B cells and their milieu is an attractive novel strategy for treating selected mature B-cell malignancies. Here we summarize the current knowledge about the cellular and molecular interactions between neoplastic B lymphocytes and accessory cells that shape a supportive microenvironment, and the potential therapeutic targets that are emerging, together with the new problems they raise. We discuss clinically relevant aspects and provide an outlook into future biologically oriented therapeutic strategies. We anticipate a paradigm shift in the treatment of selected B-cell malignancies, moving from targeting primarily the malignant cells toward combining cytotoxic drugs with agents that interfere with the microenvironment's proactive role. Such approaches hopefully will help eliminating residual disease, thereby improving our current therapeutic efforts.

Vascular density in childhood acute lymphoblastic leukaemia correlates to biological factors and outcome

The issue of angiogenesis and its clinical relevance in childhood acute lymphoblastic leukaemia (ALL) is controversial. In the present study, microvessel density (MVD), analysed in 185 diagnostic bone marrow biopsies, was higher in T-cell ALL compared to B-cell precursor (BCP)-ALL (P = 0.013). In the BCP group, cases with t(12;21) were characterized by a low MVD while patients with high-hyperdiploid leukaemia (HeH, 51-61 chromosomes) showed a high MVD compared to other BCP patients (P = 0.001 and 0.002 respectively). There was a correlation between MVD and white blood cell (WBC) count in high-risk BCP patients (P = 0.021). In addition, BCP patients with a high marrow reticulin fibre density and high MVD had an unfavourable outcome compared to the other BCP patients (P = 0.002). The fraction of vessels in which lumina were filled with blasts (blast congested vessel fraction) correlated strongly with WBC count (P < 0.001). These findings indicate that the angiogenic process interacts with other stroma-factors, such as reticulin fibre density, in its effect on outcome, and is coupled to both the ALL genotype and phenotype. One possible implication is that different subtypes of childhood ALL may respond differently to anti-angiogenic drugs as a supplement in first-line treatment.

Elevated plasma levels of vascular endothelial growth factor is associated with marked splenomegaly in chronic myeloid leukemia

Recent investigations support the idea that angiogenesis is involved in the pathophysiology of hematologic malignancies, including chronic myeloid leukemia (CML). The aim of the present study was to evaluate plasma levels of VEGF and bFGF in a cohort of 51 chronic-phase CML patients at the time of diagnosis, as well as to investigate the effect of imatinib therapy on VEGF amounts in CML patients. Plasma VEGF levels were significantly higher in patients studied as compared with the 20 healthy subjects (p<0.001), the median plasma VEGF level detected in patients analysed and healthy controls was 433.4 pg mL(-1) (range 65.2-2,452.7 pg mL(-1)) and 81.6 pg mL(-1) (range 44.2-338.7 pg mL(-1)), respectively. On the other hand, no difference in bFGF plasma levels could be found between chronic-phase CML patients and the control group. There were significant associations between plasma VEGF levels and some characteristics of patients evaluated, with trends for higher VEGF values in patients with enlarged spleens (p = 0.02) and those with higher platelet count (p<0.001). Of the patients, 11 received imatinib treatment. The initial VEGF levels markedly decreased after 6 months of imatinib therapy in each patient (p<0.001). These data support the important pathophysiological role of VEGF in CML. Further studies aiming to explore the detailed angiogenic profile of CML may help in developing new therapeutic strategies for this myeloproliferative disorder.

Angiogenesis and vascular endothelial growth factor-/receptor expression in myeloproliferative neoplasms: correlation with clinical parameters and JAK2-V617F mutational status

Data on angiogenesis in the bone marrow of BCR-ABL1-negative myeloproliferative neoplasm (MPN) patients suggest an increase of the microvessel density (MVD) and vascular endothelial growth factor (VEGF) expression, but relations to the JAK2-V617F status remain controversial. We performed immunohistochemical studies of MVD and VEGF-expression in 100 MPN, including 24 essential thrombocythemia- (ET), 46 polycythemia vera- (PV), 26 primary myelofibrosis- (PMF), four myelodysplastic (MDS)/MPN- and 20 control reactive bone marrow cases, and correlated these findings with biological and clinical key data and the JAK2-V617F status. We found significantly increased MVD, particularly that assessed by CD105, and VEGF expression in MPN compared to controls (PMF > PV > MDS/MPN > ET). We observed stronger association between CD105-MVD and VEGF expression, fibrosis, and JAK2-V617F mutant allele burden, compared to CD34-MVD. MVD was strongly increased in MPN with high JAK2-V617F mutant allele burden. Our study highlights the importance of newly formed CD105+ vessels in the bone marrow of MPN patients, and indicates that assessment of CD105-MVD better reflects angiogenic activity in MPN. In addition, it provides evidence that despite the fact that angiogenesis is generally independent of the JAK2-V617F status in MPN, new vessel formation might be linked to Jak2 effects in some cases with high JAK2-V617F mutant allele burden.