Print Page   |   Sign In   |   Become a Member
Site Search
Experimental Hematology
Blog Home All Blogs
Search all posts for:   


Inside the May and June 2013 Issues

Posted By Connections Editor, Sunday, June 30, 2013
Updated: Friday, June 28, 2013

Take a quick tour of the May and June issues and get a feel for the publication's cutting-edge scientific content. Read the full issues online.

In this Issue – May 2013

#Migration of hematopoietic precursors during development and its clinical implications
Ciriza et al.

Fetal hematopoietic stem cells (HSCs) need to migrate through different niches located in diverse anatomic microenvironments to gain the necessary molecule repertoire to engraft and home into the bone marrow. This review by Ciriza etal. comprehensively summarizes early and recent work related to multipotential cells in the yolk sac, placenta, intraembryonic sites including the AGM and the fetal liver, as well as factors that affect interaction of these cells with the local microenvironment. These factors include a host of adhesion molecules, chemokines, cytokines, and ECM molecules, which are discussed in much detail and without significant bias in a presentation of opposing models. The authors also devote a significant amount of discussion to the important issue of embryonic stem cell differentiation into transplantable, long-term self-renewing HSCs, and they propose intriguing ideas for why this process might not be efficient. This timely review is highly relevant to readers looking to further their understanding of fetal HSC migration and of the potential application of that knowledge to stem cell and transplantation biology.

#A step further toward the generation of a viable in-vitro stem cell niche
Deneault et al.

The importance of extrinsic regulation of hematopoietic stem cell (HSC) activity is increasingly acknowledged. Invivo, the stem cell niche integrates a complex mixture of different cells and signaling molecules. This microenvironment is not easily imitable invitro, making it difficult to maintain HSC activity in culture for extended periods of time. In this study, Deneault etal. engineered niche cells to overexpress several nuclear factors agonists of HSC activity, which they identified in a previous report. They find that most of the tested intrinsic factors have actually a non–cell autonomous effect on HSC activity. In addition, they explore the transcriptional regulatory networks that have been rewired within engineered niche cells. Interestingly, the identification of the involvement of FOS, SPI1, KLF10, TFEC, and PRDM16, which consistently interact epistatically, reveal a novel non–cell autonomous network in engineered niche cells that support HSC activity. Moreover, these five factors are normally involved in osteoclastogenesis invivo, supporting the hypothesis that osteoclasts might also be part of the functional HSC niche. Finally, the authors uncover an important contrast between mouse and human HSC biology, because the engineered niches failed to enhance activity of human HSCs, as opposed to mouse HSCs. This finding suggests that HSC self-renewal determinants are poorly conserved between the two species. These findings contribute to characterize the functional niche that supports HSC activity and pave the way for the identification of new secreted growth factors that expand HSC numbers in culture to improve transplantation-based therapies.

#The hematopoietic role of the sodium-dependent phosphate import protein Sodium-Dependent Phosphate Import Protein, PiT1, is not associated with phosphate transport
Liu et al.

Emerging data suggest that the sodium-dependent phosphate import protein, PiT1 (SLC20A1), modulates cellular proliferation. In this article, Liu L. etal. characterize the hematopoietic phenotype of mice with conditional deletion of Pit1 and show that the animals develop a severe macrocytic anemia with a block in terminal erythroid differentiation around the proerythroblast stage. The mice also have a profound B cell deficiency, which primarily reflects a block at the pro-B stage in development, mild neutropenia, and thrombocytopenia. Importantly, the mice have a general hematopoietic cell defect in cell cycle progression in the absence of a change in cellular phosphate uptake, consistent with a phosphate import–independent role for PiT1 in governing cellular proliferation. This work contributes to the currently limited published data on the role of metabolite transporters in hematopoiesis and raises the intriguing possibility that PiT1 could have separable phosphate transport and cellular proliferation signaling functions. Moreover, as the hematopoietic phenotype of Pit1-deleted mice shares several features with low-grade myelodysplastic syndrome (MDS), and MDS is associated with Gibbon Ape leukemia virus and feline leukemia virus B infections (both utilize PiT1 for cell entry) in nonhuman primates and cats, respectively, future studies of these Pit1-deleted mice and PiT1-associated pathways could also provide insight into the pathobiology of these disorders.

#KI haplotype A: A novel predictive factor of complete molecular response in chronic myeloid leukemia patients treated with tyrosine kinase inhibitors
La Nasa et al.

Growing evidence suggests that the occurrence of chronic myeloid leukemia (CML), the disease course, and the response of patients to therapy with tyrosine kinase inhibitors can be influenced by inhibitory and activating receptors regulating the function of natural killer (NK) cells. NK cells are important mediators of both innate and adaptive immune responses. NK cell recognition and lysis of tumor cells is regulated by the interaction of killer cell immunoglobulin-like receptors (KIRs) expressed on the NK cell surface and human leukocyte antigen (HLA) class I alleles expressed on target cells. It is speculated that changes in the balance of inhibitory and activating KIR signals could lead to NK cell deficiency, contributing to the occurrence of CML and hampering patients’ response to treatment. In this study by La Nasa etal., the authors present a retrospective study of KIR profiles and response to therapy in an ethnically and genetically homogeneous cohort of CML patients and control subjects. They show that patients homozygous for the KIR haplotype A have a significantly higher probability of achieving early and sustained complete molecular response (CMR) than do patients with AB or BB genotypes. Achievement of CMR is also associated with a reduced frequency of KIR2DL2 and a low number of inhibitory KIR genes. Considering that group A haplotypes have only six inhibitory genes and that KIR2DL2 is exclusively carried by group B haplotypes, it is possible that the KIR haplotype AA could represent a valuable marker of durable CMR. The identification of such markers, combined with the currently known prognostic factors for CMR, should help clinicians make informed decisions regarding the modulation and possible withdrawal of tyrosine kinase inhibitor treatment in patients with CML.

In this Issue – June 2013

#A mouse model of Hoxa9-mediated pre-T Lymphoblastic Leukemia
Beachy et al.

Despite the strong association of Hoxa9 expression with T cell and myeloid leukemia, enforced expression of Hoxa9 in murine bone marrow or thymus has only modest malignant transforming abilities. To gain a better understanding of the relationship between Hoxa9 overexpression and hematopoietic malignancies, Beachy etal. generated transgenic mice that ectopically expressed Hoxa9, by targeting transgene expression to hematopoietic tissues with Vav regulatory elements. When studying four lines of Hoxa9 transgenic mice from different potential founders, two major findings were observed. First, overexpression of the Hoxa9 transgene was associated with embryonic lethality, as two of the four potential founders did not transmit the transgene to surviving offspring, but analysis of embryos from timed pregnancies indicated that the embryos were viable until at least E9.5. Second and somewhat unexpected, a fraction of viable Hoxa9 mice developed pre-T lymphoblastic leukemia (LBL) or lymphoma, all with Notch1 mutations, but none of the mice developed acute myeloid leukemia (AML). Notably, Hoxa9 mice with pre-T LBL lacked global upregulation of other Hoxa cluster genes or mir-196b, which expression has been shown to be increased in other genetically engineered mice that express leukemic fusion genes (e.g., MLL-AF9, CALM-AF10, NUP98-HOXD13). Interestingly, Hoxa9 bone marrow could be immortalized invitro with the addition of Meis1, suggesting that lack of Meis1 overexpression in the Hoxa9 mice might partially explain why AML was not observed in this study. The authors propose that this Hoxa9 transgenic mouse might be a useful tool for studying collaborative events needed for the development of pre-T LBL or AML.

#Increased sensitivity of acute myeloid leukemia CD34+ cells to bortezomib by targeting NF-κB and MCL-1
Bosman et al.

Despite treatment with intensive chemotherapy, many patients with acute myeloid leukemia (AML) still have unfavorable outcomes. Various innovative therapeutic options have been explored to target the small population of leukemic stem cells that is responsible for the development of leukemia and relapse after treatment. Constitutive activation of NF-κB has been observed in AML blasts, and proteasome inhibition, which results in degradation of NF-κB, has been suggested to specifically induce apoptosis in AML CD34+/CD38 cells. Clinical studies evaluating the effect of the proteasome inhibitor bortezomib in patients with AML have been initiated. However, the efficacy of bortezomib in targeting AML stem cells has not been investigated thoroughly. This article by Bosman etal. provides evidence that the leukemic stem cell–enriched CD34+ fraction is resistant to bortezomib, using invitro stem cells assays on CD34+ samples from patients with AML. Interestingly, bortezomib resistance in CD34+ AML cells was largely dependent on inadequate inhibition of NF-κB, which might be related to differences in NF-κB activation in AML CD34+ versus CD34 cells. Intriguingly, proteasome inhibition resulted in the upregulation of the important antiapoptotic protein MCL-1. Inhibition of MCL-1 strongly increased the sensitivity of AML CD34+ cells to bortezomib. Future research should therefore be focused on combining bortezomib with MCL-1 inhibitors for the treatment of patients with AML. Furthermore, it will be important to evaluate whether the second-generation proteasome inhibitors that bind the proteasome in an irreversible manner, such as carfilzomib and oprozomib, can, in contrast to bortezomib, reduce the frequency of AML stem cells as single agents.

#Cytokine-induced killer cells as therapy against multiple myeloma
Liu et al.

Multiple myeloma (MM) remains an incurable plasma cell malignancy, and innovative therapeutic approaches are urgently needed. In addition to small molecules, immunotherapy using adoptively transferred immune cells, cancer vaccines, and virotherapy using tumor-selective oncolytic viruses are being pursued in clinical trials. This study by Liu etal. explores the potential of cytokine-induced killer (CIK) cells as therapy against MM. CIK cells are a heterogeneous subset of ex-vivo expanded T lymphocytes that present phenotypic and functional properties of both natural killer and T cells, and have major histocompatibility complex–unrestricted antitumor activity against both solid tumors and hematologic malignancies. The authors show that allogeneic CIK cells have antitumor activity against subcutaneous and disseminated animal models of human myeloma (KAS-6/1). The antimyeloma activity of CIK cells can be further enhanced by pretreating the myeloma cells with ionizing radiation or by loading CIK cells with a virotherapy agent—an oncolytic measles virus (MV) that is currently in phase I clinical testing in patients with relapsed or refractory myeloma. Irradiation of the myeloma cells enhanced the delivery of CIK to the irradiated tumors and induced mRNA and protein expression of natural killer group 2 D (NKG2D) ligands, which mediate the antitumor activity of CIK cells. CIK cells can also serve as carriers to protect and deliver the oncolytic virus to tumors to initiate viral induced oncolysis, resulting in superior antitumor activity. This study demonstrates the potential of CIK against MM, and that combination of virotherapy with radiation could be used to enhance therapeutic outcome using CIK cells. CIK therapy is already a clinical reality; therefore, the clinical translation of this promising delivery platform is highly feasible and worth pursuing in future studies.

#Narrowing down the origin of endogenic mesoderm
Kataoka et al.

Hematopoietic precursor cells (HPCs) develop from hemogenic endothelial cells (EC), a specialized type of ECs undergoing hematopoietic transition. Despite their importance, the origin of hemogenic ECs has not been defined clearly. Ets variant 2 (Etv2)/ER71 is a master regulator generating ECs/HPCs from mesoderm. Etv2 deficiency causes complete EC or HPC loss in mouse embryos and differentiated ES cells. In this study by Kataoka etal., the authors tested regional deletion of Etv2 to narrow the critical mesoderm subset that gives rise to hemogenic ECs. They report that among region-specific Cre deleters, Etv2 ablations by Hoxb6 Cre and CreER revealed that caudal-lateral mesoderm including allantois is a critical mesoderm source of intraembryonic hematopoiesis. Explant cultures before hematopoietic cells circulate showed that Etv2 deletion in Hoxb6+ E7.5–8.5 mesoderm causes severe intraembryonic hematopoietic defect with intact yolk sac hematopoiesis. Etv2 deletion in that area also resulted in significant reduction in intraaortic c-Kit+ clusters and umbilical cord Runx1+ cells. Labeling of the relevant population in differentiated ES cells (Flk-1+/Hoxb6+ cells) showed that those cells have hemogenic characteristics over Hoxb6 negative population, including T lymphocyte generation. These findings suggest that Hoxb6+ mesoderm will be a promising source for inducing definitive hematopoietic cells in developing embryos and invitro–differentiated embryonic stem cells. Currently, conventional hematopoietic differentiation methods are failing to efficiently generate Hoxb6+/Flk-1+ cells. Future efforts are necessary to optimize the culture condition for efficiently inducing Hoxb6+ mesoderm

This post has not been tagged.

Share |
PermalinkComments (0)

Inside the March and April 2013 Issues

Posted By Connections Editor, Wednesday, April 24, 2013
Updated: Wednesday, April 24, 2013

Take a quick tour of the January and February issues and get a feel for the publication's cutting-edge scientific content. Read the full issues online.

In this Issue – March 2013

#The mitochondrial redox environment during erythroid development affects mitochondria-less mature red blood cells
Mohanty et al.

Manganese superoxide dismutase (SOD2) maintains a low oxidative environment in mitochondria by converting toxic superoxide free radicals to hydrogen peroxide. Mature red blood cells (RBCs) do not contained SOD2 protein as they do not possess mitochondria, however; its deficiency or malfunction during erythroid development results in lasting changes to the mature RBC. In this manuscript, Mohanty et al. used an established hematopoietic specific SOD2 knockout mice chimera model to study the effect of SOD2 deficiency on two characteristics of RBCs: deformability and oxidative stress levels. They report that SOD2-/- RBCs have reduced deformability, higher amounts of heme degradation products, and a higher rate of hemoglobin oxidation compared to controls. These changes may explain the reduced RBC lifetime in circulation leading to increased RBC loss, which is associated with the anemia phenotype previously reported in these mice. These results support and expand the findings published by Case et al. in December 2012 in Free Radic Biol Med, which show that the disruption of the superoxide balance within the mitochondria leads to improper heme formation, gene regulation, and erythrocyte development. . Oxidative stress has been linked to sideroblastic, hemolytic and sickle cell anemia, and thalassemia. Studies such as these ones that further the understanding of how the mitochondrial redox environment affects RBC physiology may lead to novel therapies for those diseases.

#Acute lymphoblastic leukemia cells come out of the bone marrow protective niche for increased sensitivity to chemotherapy
Welschinger et al.

Acute lymphoblastic leukemia (ALL) is the most common cancer in children, and represents 20% of adult acute leukemias. Despite good initial responses to combination chemotherapy, remission remains a significant problem. This lack of efficacy of therapy can be partly attributed to the protection provided to the leukemia cells by the bone marrow (BM) microenvironment, and thus, there is a lot of interest in finding therapies to get the cells out of this protective niche. However, the BM microenvironment also enhances the survival of normal hematopoietic stem and progenitor cells (HSPCs), making it important to determine whether mobilizing therapy by itself or in combination with chemotherapy increases toxicity towards these cells. The interaction of the cytokine SDF-1 with the CXCR4 receptor on the surface of HPSCs and leukemic cells has been implicated in the retention of normal and leukemic cells in the BM, and in this study by Welschinger et al., the authors show that inhibition of the interaction by the CXCR4 antagonist plerixafor (AMD3100) results in the mobilization of ALL cells from the BM and spleen for a longer period of time than normal HSPCs. Unlike what has been reported with acute myeloid leukemia cells, mobilization of ALL cells is associated with increased cell cycle activity, which may be capitalized upon by combination with chemotherapy, as demonstrated by increased survival of ALL xenografts treated with a combination of vincristine and AMD3100. This clinically important information can be leverage to design clinical trials to test the combined use of chemotherapy with AMD3100 for maximal effect on leukemic as opposed to normal hematopoietic cells. Such clinical trials will bring new hope to patients with relapsed or high-risk ALL.

#Mechanistic insights provide scientific justification for the use of Histone Deacetylase Inhibitors in Myeloproliferative Neoplasms
Gao et al., and Caldaza et al.

Philadelphia-negative myeloproliferative neoplasms (MPNs) are a collection of clonal hematological malignant diseases in which more than 50% of patients carry a single mutation (V617F) in the autoinhibitory region of the JAK2 tyrosine. This has lead to the presumption that aberrant gene expression controlled by the deregulated JAK2/STAT pathway is the main cause underlying the disease pathobiology. However, clinical trials with different JAK2 kinase inhibitors have not yet shown eradication of the malignant clone, warranting the search for alternative targets for therapy. Recently, studies have revealed a number of epigenetic alterations that also likely contribute to the pathogenesis of MPNs and determine clinical outcome. Indeed, abnormal histone deacetylase activity has been noted in MPNs and provides a rationale for treatment with Histone deacetylase inhibitors (HDACi). However, the extent and specific role of histone deacetylase-mediated epigenetic aberrations in MPN are still poorly understood. Two articles published in this issue of ExpHem provide mechanistic rationales for the use of HDACi in the treatment of MPN, either alone or in combination with existing therapies.

The article by Gao et al. sheds light on the mechanism of action of the HDACi sodium butyrate (SB) on the JAK/STAT signaling pathway in MPNs. SB is a short-chain fatty acid that induces the accumulation of acetylated histone leading to cell cycle arrest, differentiation and apoptosis in various cancer cells. In this study, the authors found that SB downregulates the JAK/STAT signaling through upregulation of the suppressors of cytokine signaling (SOCS)1 and 3, both of which are potent feedback inhibitors of JAK2/STAT signaling. Their Chip analysis links the downregulation of SOCS1 and 3 to the accumulation of acetylated histones on the genes’ promoter, which is potentially mediated by HDAC8, as demonstrated in a selective siRNA knockdown experiment. Confirmation of these findings is important; if HDAC8 inhibition alone is enough to cause cell death or colony formation inhibition of MPN cells, this concept can be utilized to address the off-target toxicities associated with the utilization of pan-HDAC inhibitors in MPN patients.

The manuscript by Caldaza et al. provides a scientific rationale for combination therapy of the pan-HDACi Givinostat (ITF2357, GVS) and hydroxyurea (HU) for the treatment of MPN patients. GVS has been shown to specifically inhibit proliferation of cells bearing the JAK2V617F mutation and has demonstrated significant activity with good tolerability in clinical studies in MPN. Moreover, a randomized Phase II clinical trial of GVS and HU has recently been completed and has indicated a favourable clinical activity of the combination of these two compounds in the treatment of Policytemia Vera patients. In this study, the authors used MPN cell lines and patients’ cells to demonstrate that a low dose of the two drugs induces synergistic apoptosis, what they link to the inhibition by HU of GVS-mediated induction of p21 and to increased caspase-3 activity. This timely manuscript clarifies the mechanism of the drugs' synergy at the cell cycle and molecular level and provides a scientific justification to their use as combination therapy for the treatment of MPNs.

In this Issue – April 2013

#Gene Set Control Analysis, a new bioinformatic tool to enhance our understanding of blood cell differentiation
Joshi et al.

Transcription factors (TFs) have the unique property that they recognise specific DNA sequence motifs, and therefore have the ability to decipher gene regulatory information encoded in our genome sequence. Recent technological breakthroughs in sequencing technology have made the generation of genome-wide transcription factor binding maps almost routine. However, it is still largely unclear how transcription factor proteins "read” regulatory information when they interact with our genomes. Progress in this area will be vital to enhance our understanding of blood cell differentiation, and, given the complexity and scale of genome-scale binding maps, is likely to depend on new bioinformatic data integration and analysis tools. The paper by Joshi et al reports the generation of a TF binding map compendium, where 142 publicly available datasets for both normal and leukemic murine blood cell types have been re-analysed, integrated and analysis results made available for use by the wider research community ( In addition, the group also report the development of a new bioinformatic web-tool, called Gene Set Control Analysis (GSCA). Experimental biologists commonly generate gene lists, such as differentially expressed genes, from a treatment/control microarray experiment. Such lists are then scrutinized for functional or pathway enrichment by, for example, gene ontology analysis. The new GSCA tool utilises the integrated 142 transcription factor binding maps to predict likely transcriptional regulators for any gene set of interest. Using GSCA, the authors predicted the reactivation of blood stem cell control mechanisms as a likely contributor to LMO2 driven leukemia, and also clarified the recent debate on the role of Myc in leukemia stem cell transcriptional programs. The GSCA tool is freely available, and a web interface for use by the wider community can be found at GSCA accepts both mouse and human gene lists for the prediction of likely upstream regulators. It is anticipated that the underlying compendium will grow further as the community generates ever-increasing numbers of transcription factor binding maps. Nevertheless, even in its current incarnation it is hoped that GSCA will be recognised by the community as a valuable new tool in the bioinformatic toolbox available to us all; hopefully it will increase our ability of extracting biological knowledge from genome-scale datasets.

#Novel strategy to generate engineered T cell precursors for immunotherapy
Liu et al.

Adoptive T-cell immunotherapy appears promising to treat T cell immunodeficiency or to improve immune reconstitution after hematopoietic stem cell transplantation. In addition, adoptive transfer of peripheral T cells engineered to express a tumor antigen-specific T cell receptor (TCR) presents a new approach to selectively target malignant cells. Despite recent advances in both stem cell and lymphocyte manipulations, these experimental approaches still have several limitations, particularly in optimal and safe generation, as well as expansion of specific T cell from TCR-transduced stem cells. In this study, Liu et al present a novel strategy for the manipulation of early stage T lymphopoiesis using a two step co-culture system. They show that TCR-transduced hematopoietic progenitors co-cultured on telomerized stromal cells in the presence of SCF, Flt3L and TPO, followed by co-culture on Delta-1- and -4-expressing stromal cells, produce pre-T cell precursors that have the potential to proliferate and differentiate. This study highlights the potential value of engineered human stromal cells to manipulate early T cell development for clinical application, and provides a culture system that could help accelerate the translation of the next generation of adoptive T-cell therapies to the clinical setting.

#Cord blood-derived MSC: a potential tool to accelerate bone marrow recovery after ionizing radiation
Shim et al.

Mesenchymal stem cells (MSCs) have a great capacity for self-renewal while maintaining their multilineage differentiation potential, making them a promising tool for tissue repair. Compared with bone marrow MSCs, human umbilical cord blood-derived MSCs (hUCB-MSCs) are easy to obtain without harm to the donor and have a faster proliferation rate. In this study by Shim et al, the authors investigate the potential of hUCB-MSCs to improve the recovery of hematopoiesis after total body irradiation in comparison with the well-studied agent granulocyte colony stimulating factor (G-CSF). Using sub-lethally irradiated mice, they show that hUCB-MSCs treatment significantly increased the number of peripheral leukocyte counts following a radiation dose for which G-CSF treatment was unsuccessful. Moreover, at some post-irradiation intervals, hUCB-MSCs treatment was more effective than G-CSF in supporting proliferation of various cells in the BM and, in contrast with G-CSF, modulated the plasma level of hematopoietic cytokines. Together, these observations show that hUCB-MSCs treatment is superior to G-CSF, providing support for their use in the treatment of ionizing radiation-induced bone marrow injury. In addition, this study has important implications in the clinical setting, in which hCB-MCSs could be used to accelerate bone marrow recovery after chemotherapy and especially after hematopoietic stem cell transplantation.

#A modified high dose cyclophosphamide regime that could lower the cost of treatment of patients with several aplastic anemia
Zhang et al.

Aplastic anemia (AA) is a potentially fatal disease characterized by depletion of hematopoietic precursors in bone marrow (BM). The standard therapy for patients with this disease who are not candidates for an allogeneic BM transplantation is immunosuppression with a combination of horse-antithymocyte globulin (ATG) and cyclosporine A (CsA). This treatment results in good overall survival rates. However, relapses and event-free survival are still not satisfying. Furthermore, horse-ATG is not routinely available in developing countries and the costs for ATG-preparations in general are substantial. Therefore, alternative treatments are urgently needed. In this context, this manuscript by Zhang et al reports a retrospective study of patients with severe or very severe AA that received either a modified high dose cyclophosphamide (HD-CTX) regime with CsA or a therapy with rabbit-ATG in combination with CsA. Both treatment groups showed comparable response rates, survival rates and toxicities. In previous clinical trials, HD-CTX showed promising remission rates but unacceptable toxic effects. In this regard, this is a notable study that shows that a lower dose of CTX might overcome the immense toxic effects of the conventional high dose regime. Importantly, the modified HD-CTX plus CsA therapy is significantly cheaper than the ATG plus CsA therapy, thus providing an affordable treatment alternative for severe AA patients that cannot afford ATG therapy. This preliminary study merits further investigation in well-designed, prospective, and randomized clinical trials.

This post has not been tagged.

Share |
PermalinkComments (0)

January and February 2013

Posted By Connections Editor, Wednesday, March 6, 2013
Updated: Wednesday, February 27, 2013

Take a quick tour of the January and February issues and get a feel for the publication's cutting-edge scientific content. Read the full issues online.

In this Issue – January 2013

Role of Wnt antagonists in the regulation of hematopoietic stem cells fate decisions
Cain and Manilay

The Wingless (Wnt) are secreted lipid-modified signaling proteins of 350–400 amino acids in length. The Frizzled (FZD) proteins are seven-pass transmembrane receptors to which Wnts bind. The Wnt signaling is involved in cell fate decisions during hematopoietic differentiation in the bone marrow, in the maintenance of bone homeostasis, and in hematopoietic differentiation in a non-cell autonomous manner. There are 19 different Wnt ligands and 10 FZD receptors identified in humans and mice. In addition, Wnts utilize distinct co-receptor proteins that initiate "canonical” and "noncanonical” Wnt signaling pathways. Additional levels of complexity are added by secreted Wnt antagonists expressed in bone and bone marrow stromal cells that either bind to Wnt ligands directly or block Wnt receptors and co-receptors to halt Wnt-mediated signal transduction in both osteolineage and hematopoietic cell types. In this timely review, Cain et al. compared and contrasted the roles of these Wnt antagonists and their effects on hematopoietic development in mice and also discussed the clinical significance of targeting Wnt antagonists within the context of hematopoietic disease. This manuscript provides an interesting and comprehensive reading for anybody looking to update their knowledge of the field.

An improved method to track kinetics of hematopoietic stem cell reconstitution
Cornils et al.

Integrating viral vectors provide a unique and heritable genomic mark for the identification of single stem cell–derived clones. Linear amplification–mediated (LAM) PCR is an integration-site directed PCR method to sequence the unknown DNA flanking sequences down to the single cell. It has enabled qualitative and quantitative measurements of the clonal kinetics of hematopoietic regeneration in gene transfer studies and uncovered the clonal derivation of non-leukemogenic and leukemogenic insertional side effects in preclinical and clinical gene therapy studies. In this report, Cornils et al. presented a time-course clonal analysis of hematopoietic reconstitution following transplantation of retrovirus and lentivirus transduced cells using a multiarm, 2 restriction enzymes LAM-PCR analysis coupled to next generation sequencing (NGS). They found that the number of clones contributing to hematopoiesis over time were relatively stable for both vectors; however, the change of size of individual clones marked with the lentiviral vector followed wave-like kinetics, whereas retrovirally tag clones showed a tendency for continuous expansion. They also detected that long-term reconstituting clones marked with the retroviral vector had a tendency toward overrepresentation of insertions in the vicinity of proto-oncogenes, which supports the notion that clonal dominance due to insertional mutagenesis is more likely to develop after transduction with retroviral than with lentiviral vector. Finally they performed ligation-mediated (LM)-PCR, a method of sequencing directly from genomic DNA using a specific primer for the region of interest, and found that quantification of LAM-products did not always correlate with results from qPCR. As shown in this and other studies, even the use of two different restriction enzymes for LAM-PCR may not strictly ensure a complete figure of gene-marked clones. Thus, improved technologies are needed to benefit many areas of hematopoietic stem cell research, including in vitro cell expansion, gene therapy, and cancer progression and treatment.

Gpr171: a possibly new regulator of HSC differentiation
Rossi et al.

The G protein-coupled receptor (GPR) 171 is structurally and evolutionally related to a subfamily of the GPR family of purinergic receptors (P2YRs) for extracellular nucleotides, a group of mediators that regulate hematopoietic progenitor cells. GPR171 is an orphan receptor, and its signaling pathway and biological role remain unknown. In this study, Rossi et al. investigated the role of Gpr171 in the murine hematopoietic system. Their phylogenetic analysis confirmed that Gpr171 is evolutionally related to members of a P2Y gene-cluster that is localized on mouse chromosome 3. Interestingly, examination of its expression profile showed that, as opposed to other P2YRs, Gpr171 is downregulated in monocytes and granulocytes. Moreover, its enforced over-expression resulted in decreased expression of myeloid markers and increased the generation of colonies in vitro. Conversely, Gpr171 silencing diminished the expression of myeloid markers and the clonogenic potential of cells. In addition, mice transplanted with HPCs over-expressing Gpr171 displayed a significant reduction in the percentage of myeloid cells. Together, these elegant experiments demonstrated that Gpr171 plays a role in myeloid-monocytic lineage development and suggested that Gpr171 may have followed a separate evolutionary pathway as compared to other P2YRs belonging to the same gene-cluster. This work provides the framework for the identification of Gpr171 agonists and antagonists, which will not only help achieve a deeper understanding of the role of this orphan receptor, but also of the molecular mechanisms underlying the multi-step process that leads from committed progenitors to terminally differentiated cells.

Sca-1 as a possible early-response marker to identify hematopoietic stem/progenitor cells with increased self-renewal capacity in response to HDIs in vitro
Walasek et al.

Histone deacetylase inhibitors (HDIs) are epigenetic modifiers that control gene expression by altering the acetylation status of chromatin and other non-histone proteins. These small molecules can enhance the ex vivo self-renewal and propagation of hematopoietic stem/progenitor cells (HSPCs) as well as modify the process of differentiation. In a paper published in Blood in March 2012, this group reported the molecular and functional changes induced on HSPCs by a 7-day treatment with valproic acid (VPA), a widely used HDI. In the current study, Walasek et al. performed microarrays after short-term, 24h VPA stimulation, to identify early response VPA-targets in HSPCs. Their genome-wide gene expression studies identified the well-known and widely used HSPC marker Sca-1 as an early VPA-responsive gene. Early up-regulation of Sca-1 was also seen with two additional HDIs, Apicidin and MS-275, which differ from VPA in their chemical structure and their specificity. Strikingly, VPA not only strongly preserved Sca-1 expression and the LSK (Lin-Sca1+cKit+) phenotype of isolated HSPCs after 24h culture, but it also re-induced Sca-1 on committed common myeloid and granulocyte macrophage progenitor cells that had lost its expression in the process of differentiation, reverting those cells to a more immature LSK phenotype. Moreover, Sca-1 re-induction coincided with induced self-renewal capacity as measured by in vitro re-plating assays, while Sca-1 itself was dispensable for the functional effects of VPA. Together, the authors provided the first analysis of direct VPA targets in primitive hematopoietic cells and showed that Sca-1 is a faithful marker to identify cells with increased self-renewal capacity in response to HDIs in vitro. Studies like this one, aimed at understanding the spectrum of both biological and molecular effects of VPA, are crucial to determine the potential of this HDI to improve hematopoietic reconstitution and engraftment of ex vivo expanded HSPCs, a vital goal for transplantation, gene, and cellular therapies

In this Issue – February 2013

Improved therapeutic outcome of patients with Multiple Myeloma requires novel treatments and a better understanding of the mechanistic underlying drug resistance
See Salem et al. and Wolschke et al.

Multiple myeloma (MM) is a rare but devastating plasma cell malignancy that affects mainly older adults. In the last ten years, induction regimens that combine the glucocorticoid-analog dexametasone (Dex) with novel chemotherapeutic agents, such as the proteasome-inhibitor bortezomib (BTZ) or the antiangiogenetic and immunomodulator drugs thalidomide and its derivative lenalidomide, have significantly increased the complete response (CR) rate before and after Allogenic Stem Cell Transplantation (ASCT) with a positive impact on progression-free survival. Maintenance therapy with thalidomide and lenalidomide may further prolong remission duration. However, in spite of these advances, MM remains incurable, as the disease ultimately acquires resistance to therapies. Thus, novel treatment approaches and a better understanding of the mechanism(s) underlying resistance are essential to improve the therapeutic outcome of patients with relapsed MM.

The manuscript by Salem et al. provides a mechanistic rationale for combining Dex and BTZ, which is one of the most effective and widely used treatments for MM. Both drugs are inhibitors of the nuclear factor (NF)-κB pathway, which is chronically active in myeloma cells and can induce stromal cells to produce myeloma growth factors such as interleukin (IL)-6. Concomitantly, aberrant NF-kB activation has been associated with the emergence of resistance to anti-cancer drugs and radiation in MM, and elevated IL-6 serum levels correlate with poor prognosis. Dex and BTZ inhibit NF-κB by different pathways, and the authors found that the combination potentiated direct cell death of both the drug-sensitive, and, importantly, drug-resistant MM cells. Furthermore, combination therapy down-regulated the NF-κB targeted gene expression of IL-6 and manganese superoxide dismutase, which can induce chemo- and radio-resistance in MM, supporting potential combinations of these drugs with radiotherapy and additional chemotherapeutic drugs for the clinical benefit of MM patients.

The manuscript by Wolschke et al. reports a prospective phase I/II study to define the dose-limiting toxicity and the immunological effects of lenalidomide given to MM patients early post-ASCT. Lenalidomide is a more potent analog of thalidomide, developed to enhance immunomodulatory properties with improved safety. Its antitumor activity seems to be mediated through the modulation of cytokines and activation of T- and natural killer (NK) cell-mediated antitumor response. Increasing evidence of NK cell allo-reactivity in MM patients after ASCT provides a rationale for an early application of lenalidomide after transplantation. In this context, two recent clinical trials published by McCarthy et al. and Attal et al. in May 2012 in the New England Journal of Medicine showed that lenalidomide maintenance therapy significantly lengthens disease-free progression and improves overall survival among patients with MM. However, as described in the first study, this was associated with more toxicity and second cancers. Undesired side effects were also found in the HOVON 76 Trial published in Blood in September 2011, which excluded the feasibility of using lenalidomide as maintenance after ASCT due to Graft versus Host Disease (GvHD). Although encouraging, these clinical trials underscore the need to determine lenalidomides maximum tolerated dose as well as the mechanism underlying its unwanted side effects. In this study, the authors found that 5 mg of lenalidomide given daily for 21 days was the maximal tolerable dosage early after ASCT, with the major limiting factor being the occurrence of acute liver and gut toxicity due to GvHD, supporting the results of the HOVON trial. In agreement with the two New England Journal of Medicine papers, they also reported that lenalidomide treatment strongly increased complete remission rate, which they linked to its immunomodulatory effect.

The current five-year survival rate for patients with MM is 40% and thus, studies such as these that search for mechanistic insights of current therapies, drug resistance and side effects, offer great hope for MM patients who are in desperate need of treatments with a better response and survival rate. Such studies might also provide better target therapies and new immunomodulator regimes to supply physicians with a wider variety of treatment options to tailor the most appropriate and efficacious treatment to their patients' disease.

Azacitidine and decitabine are "coming of age” in treatment, but great challenges in understanding how they work remain
See Tsujioka et al.and Bernal et al.

Low dose regimes of the DNA demethylating agents Azacytidine (AZA) and its derivative decitabine (DAC) were approved in 2004 and 2006, respectively, by the US Food and Drug Administration for the treatment of myelodysplastic syndrome (MDS), a group of hematopoietic disorders characterized by ineffective hematopoiesis and increased risk of leukemic progression. In Europe, AZA is the only drug approved for the treatment of high-risk MDS not eligible for stem cell transplantation. These drugs are proposed to work by inducing functional re-expression of aberrantly hypermethylation-silenced tumor suppressor genes. However, whether epigenetic effects of the drugs account for all, or even some, of their clinical efficacy is still under debate. The mechanisms of resistance to AZA and DAC, which develops during treatment, are also still unclear, with some studies suggesting methylation-independent pathways. The importance of unravelling the mechanisms underlying AZA and DAC clinical efficacy and resistance is underscored by a recent clinical trial sponsored by Lung Cancer SPORE and Stand Up to Cancer. The results of the trial, published by Jurgens et al. in Cancer Discovery in December 2011, demonstrate the benefit of low doses of the drugs in patients with refractory lung cancer, and thus support the potential use of DAC and AZA for a wider management of cancer. Moreover, clinical trials in breast cancer have already begun in patients with advanced disease, and trials in colon cancer are planned. Searching for mechanistic insights, the paper by Tsujioka et al. show a positive relationship between growth suppression and demethylation by DAC or AZA in the MDS-derived cell line developed in their lab. Interestingly, DAC-induced cell death was preceded by DNA damage-induced G2 arrest via a p53-independent pathway, whereas AZA did not influence the pattern of the cell cycle. Their gene expression profiling suggest that at very low concentration, DAC significantly affect various gene biogroups, which include categories such as cellular movement, inflammatory response, hematological system development and function, hematopoiesis, and cell death. This work supports the finding of a recent important study by Tsai et al., published in Cancer Cell in March 2012, showing that transient low doses of AZA and DAC had antitumor effects on leukemic and epithelial tumor cells, which were accompanied by genome-wide changes in promoter DNA methylation and gene expression, which affected multiple key regulatory pathways.

Looking for mechanisms of drug resistance, the paper by Bernal et al. analyzes the effect of AZA on Matrix-Metalloproteinase (MMP)-9 expression. MMP-9 is a member of the MMP family of zinc-dependent proteolytic enzymes, which play a key role in angiogenesis and metastasis. MMP-9 regulates extramedullary disease in acute leukemia, and it is overexpressed in MDS cells, a phenomenon that in other cancers has been linked to its aberrant methylation. This article describes a dose-response increase of MMP-9 mRNA expression in two human cell lines established from patients with acute leukemia evolved from MDS and in six patients with MDS that relapsed after AZA treatment. This increment was associated with decreased DNA methylation levels in the MMP-9 promoter region and correlated with a higher invasiveness of the cells in vitro. Although the number of patient's samples analysed was small, the findings are interesting for their practical and speculative aspects, providing further evidence of the epigenetic regulation of MMP9, and suggesting that its aberrant methylation may play a role in the resistance to azacitidine in MDS patients. If these findings are confirmed in a larger cohort of patients, the role of MMP-9 in the therapeutic management of MDS or as a prognosis tool will warrant further investigation.

This post has not been tagged.

Share |
PermalinkComments (0)

Experimental Hematology offers fast publication time

Posted By Connections Editor, Wednesday, March 6, 2013
Updated: Wednesday, February 27, 2013

Experimental Hematology offers one of the fastest publication times in the field

*Articles published online 5 days after acceptance

*Initial review of manuscripts averages under 4 weeks

*Fast-Track Submission for research articles that have been previously considered by other top ranked journals and for which the previous reviewers' comments and the appropriate responses can be provided. Decisions are made within 7-10 days of submission.


This post has not been tagged.

Share |
PermalinkComments (0)

Regular and fast-track submissions are encouraged

Posted By Connections Editor, Wednesday, March 6, 2013
Updated: Monday, March 4, 2013
The publishing team seeks manuscripts, reviews, perspectives and letters to the editor describing basic in vitro and in vivo research centered on normal and malignant hematopoiesis, as well as non-malignant hematologic diseases. Submissions focused on non-hematopoietic stem cells (e.g. mesenchymal stem cells, embryonic stem cells and induced pluripotent stems) with potential relevance to hematopoiesis are also welcome, as are studies involving experimental or early phase clinical cell transplantation. Studies employing genomic and systems biology approaches to the study of normal and malignant hematopoiesis are strongly encouraged, as are those employing model organisms. Visit the Experimental Hematology website for more information.

This post has not been tagged.

Share |
PermalinkComments (0)
Page 4 of 4
1  |  2  |  3  |  4

Association Management Software Powered by YourMembership  ::  Legal