Expansion of human umbilical cord blood SCID-repopulating cells using chromatin-modifying agents

Ex vivo expansion of human hematopoietic stem cells and clinical applications

Hematopoietic stem cells (HSCs) are a rare population of cells found in the bone marrow that play a critical role in lifelong hematopoiesis and the reconstitution of the hematopoietic system after hematopoietic stem cell transplantation. Hematopoietic stem cell transplantation remains the only curative treatment for patients with refractory hematologic disorders, and umbilical cord blood (CB) serves as an alternative stem cell source due to its several advantageous characteristics, including human leukocyte antigen flexibility and reduced donor burden. However, CB also has the disadvantage of containing a small number of cells, resulting in limited donor selection and a longer time for engraftment. Therefore, the development of techniques to expand HSCs ex vivo, particularly umbilical CB, is a goal in hematology. While various combinations of cytokines were once the mainstream approach, these protocols had limited expansion rates and did not lead to clinical application. However, in recent years, the development of a technique in which small molecules are added to cytokines has enabled the stable, long-term ex vivo expansion of human HSCs. Clinical trials of expanded umbilical CB using these techniques have been undertaken and have confirmed their efficacy and safety. In addition, we have successfully developed a recombinant-cytokine-free and albumin-free culture system for the long-term expansion of human HSCs. This approach could offer the potential for more selective expansion of human HSCs compared to previous protocols. This review discusses ex vivo culture protocols for expanding human HSCs and presents the results of clinical trials using these techniques, along with future perspectives.

AA2P-mediated DNA demethylation synergizes with stem cell agonists to promote expansion of hematopoietic stem cells

Small molecules have enabled expansion of hematopoietic stem and progenitor cells (HSPCs), but limited knowledge is available on whether these agonists can act synergistically. In this work, we identify a stem cell agonist in AA2P and optimize a series of stem cell agonist cocktails (SCACs) to help promote robust expansion of human HSPCs. We find that SCACs provide strong growth-promoting activities while promoting retention and function of immature HSPC. We show that AA2P-mediated HSPC expansion is driven through DNA demethylation leading to enhanced expression of AXL and GAS6. Further, we demonstrate that GAS6 enhances the serial engraftment activity of HSPCs and show that the GAS6/AXL pathway is critical for robust HSPC expansion.

In Vitro Human Haematopoietic Stem Cell Expansion and Differentiation

The haematopoietic system plays an essential role in our health and survival. It is comprised of a range of mature blood and immune cell types, including oxygen-carrying erythrocytes, platelet-producing megakaryocytes and infection-fighting myeloid and lymphoid cells. Self-renewing multipotent haematopoietic stem cells (HSCs) and a range of intermediate haematopoietic progenitor cell types differentiate into these mature cell types to continuously support haematopoietic system homeostasis throughout life. This process of haematopoiesis is tightly regulated in vivo and primarily takes place in the bone marrow. Over the years, a range of in vitro culture systems have been developed, either to expand haematopoietic stem and progenitor cells or to differentiate them into the various haematopoietic lineages, based on the use of recombinant cytokines, co-culture systems and/or small molecules. These approaches provide important tractable models to study human haematopoiesis in vitro. Additionally, haematopoietic cell culture systems are being developed and clinical tested as a source of cell products for transplantation and transfusion medicine. This review discusses the in vitro culture protocols for human HSC expansion and differentiation, and summarises the key factors involved in these biological processes.

Development and clinical advancement of small molecules for ex vivo expansion of hematopoietic stem cell

Hematopoietic stem cell (HSC) transplantation is the only curative therapy for many diseases. HSCs from umbilical cord blood (UCB) source have many advantages over from bone marrow. However, limited HSC dose in a single CB unit restrict its widespread use. Over the past two decades, ex vivo HSC expansion with small molecules has been an effective approach for obtaining adequate HSCs. Till now, several small-molecule compounds have entered the phase I/II trials, showing safe and favorable pharmacological profiles. As HSC expansion has become a hot topic over recent years, many newly identified small molecules along with novel biological mechanisms for HSC expansion would help solve this challenging issue. Here, we will give an overview of HSC biology, discovery and medicinal chemistry development of small molecules, natural products targeting for HSC expansion, and their recent clinical progresses, as well as potential protein targets for HSC expansion.

Preferential expansion of human CD34+CD133+CD90+ hematopoietic stem cells enhances gene-modified cell frequency for gene therapy

CD34+CD133+CD90+ hematopoietic stem cells (HSCs) are responsible for long-term multi-lineage hematopoiesis and the high frequency of gene-modified HSCs is crucial for the success of hematopoietic stem and progenitor cell (HSPC) gene therapy. However, the ex vivo culture and gene manipulation steps of HSPC graft preparation significantly reduce the frequency of HSCs, thus necessitating large doses of HSPCs and reagents for the manipulation. Here, we identified a combination of small molecules, Resveratrol, UM729, and SR1 that preferentially expands CD34+CD133+CD90+ HSCs over other subpopulations of adult HSPCs in ex vivo culture. The preferential expansion enriches the HSCs in ex vivo culture, enhances the adhesion and results in a 6-fold increase in the long-term engraftment in NSG mice. Further, the culture enriched HSCs are more responsive to gene modification by lentiviral transduction and gene editing, increasing the frequency of gene-modified HSCs up to 10-fold in vivo. The yield of gene-modified HSCs obtained by the culture enrichment is similar to the sort-purification of HSCs and superior to Cyclosporin-H treatment. Our study addresses a critical challenge of low frequency of gene-modified HSCs in HSPC graft by developing and demonstrating a facile HSPC culture condition that increases the frequency of gene-modified cells in vivo. This strategy will improve the outcome of HSPC gene therapy and also simplify the gene manipulation process.

Mechanistic Basis of ex Vivo Umbilical Cord Blood Stem Progenitor Cell Expansion

Umbilical cord blood (CB) transplantation has been used successfully in humans for three decades due to its rapid availability for patients lacking a suitable allogeneic donor, less stringent HLA matching requirements, and low rates of relapse and chronic graft-versus-host disease (GVHD). However, CB transplantation is associated with complications, such as delayed hematopoietic engraftment, graft failure, which increases infection and bleeding and causes longer hospital stays, and transplant-related mortality. The majority of these biological limitations are due to the unforeseeable functional potency of multipotent hematopoietic stem cells (HSCs), which reduce the predictability of successful transplantation; however, several strategies have been developed to increase the number of hematopoietic stem progenitor cells (HSPCs) infused during CB transplantation. This review primarily addresses the methods that promote ex vivo CB expansion within the context of symmetrical and asymmetrical HSC division and those that rely on epigenetic mechanisms, along with the reportedly most successful cytokine combinations. We also review recent clinical research on small molecules (StemRegenin-1, UM171, and nicotinamide) in ex vivo expanded CB and discuss yet unvalidated preclinical strategies. Expanding and transplanting CB graft enriched in HSPCs in a single CB unit is a particularly exciting prospect with the potential to improve the use and availability of CB grafts. Greater knowledge of optimal ex vivo expansion strategies, cell longevity, and graft potency will expand the scope of cellular therapies. Also the development of adequate ex vivo HSPC expansion strategies could bring expanded cord blood grafts to the forefront of transplant therapy and regenerative medicine.

Effect of Small Molecule on ex vivo Expansion of Cord Blood Hematopoietic Stem Cells: A Concise Review

Hematopoietic stem cells (HSCs) are a group of cells being produced during embryogenesis to preserve the blood system. They might also be differentiated to non-hematopoietic cells, including neural, cardiac and myogenic cells. Therefore, they have vast applications in the treatment of human disorders. Considering the restricted quantities of HSCs in the umbilical cord blood, inadequate mobilization of bone marrow stem cells, and absence of ethnic dissimilarity, ex vivo expansion of these HSCs is an applicable method for obtaining adequate amounts of HSCs. Several molecules such as NR-101, zVADfmk, zLLYfmk, Nicotinamide, Resveratrol, the Copper chelator TEPA, dmPGE2, Garcinol, and serotonin have been used in combination of cytokines to expand HSCs ex vivo. The most promising results have been obtained from cocktails that influence multipotency and self-renewal features from different pathways. In the current manuscript, we provide a concise summary of the effects of diverse small molecules on expansion of cord blood HSCs.

Combination of SB431542, Chir9901, and Bpv as a novel supplement in the culture of umbilical cord blood hematopoietic stem cells

Background

Small molecule compounds have been well recognized for their promising power in the generation, expansion, and maintenance of embryonic or adult stem cells. The aim of this study was to identify a novel combination of small molecules in order to optimize the ex vivo expansion of umbilical cord blood-derived CD34⁺ cells.

Methods

Considering the most important signaling pathways involved in the self-renewal of hematopoietic stem cells, CB-CD34⁺ cells were expanded with cytokines in the presence of seven small molecules including SB, PD, Chir, Bpv, Pur, Pμ, and NAM. The eliminativism approach was used to find the best combination of selected small molecules for effective ex vivo expansion of CD34⁺ cell. In each step, proliferation, self-renewal, and clonogenic potential of the expanded cells as well as expression of some hematopoietic stem cell-related genes were studied. Finally, the engraftment potential of expanded cells was also examined by the mouse intra-uterine transplantation model.

Results

Our data shows that the simultaneous use of SB431542 (TGF-β inhibitor), Chir9901 (GSK3 inhibitor), and Bpv (PTEN inhibitor) resulted in a 50-fold increase in the number of CD34⁺CD38⁻ cells. This was further reflected in approximately 3 times the increase in the clonogenic potential of the small molecule cocktail-expanded cells. These cells, also, showed a 1.5-fold higher engraftment potential in the peripheral blood of the NMRI model of in utero transplantation. These results are in total conformity with the upregulation of HOXB4, GATA2, and CD34 marker gene as well as the CXCR4 homing gene.

Conclusion

Taken together, our findings introduce a novel combination of small molecules to improve the yield of existing protocols used in the expansion of hematopoietic stem cells.

Strategies for elevating hematopoietic stem cells expansion and engraftment capacity

Hematopoietic stem cells (HSCs) are a rare cell population in adult bone marrow, mobilized peripheral blood, and umbilical cord blood possessing self-renewal and differentiation capability into a full spectrum of blood cells. Bone marrow HSC transplantation has been considered as an ideal option for certain disorders treatment including hematologic diseases, leukemia, immunodeficiency, bone marrow failure syndrome, genetic defects such as thalassemia, sickle cell anemia, autoimmune disease, and certain solid cancers. Ex vivo proliferation of these cells prior to transplantation has been proposed as a potential solution against limited number of stem cells. In such culture process, MSCs have also been shown to exhibit high capacity for secretion of soluble mediators contributing to the principle biological and therapeutic activities of HSCs. In addition, endothelial cells have been introduced to bridge the blood and sub tissues in the bone marrow, as well as, HSCs regeneration induction and survival. Cell culture in the laboratory environment requires cell growth strict control to protect against contamination, symmetrical cell division and optimal conditions for maximum yield. In this regard, microfluidic systems provide culture and analysis capabilities in micro volume scales. Moreover, two-dimensional cultures cannot fully demonstrate extracellular matrix found in different tissues and organs as an abstract representation of three dimensional cell structure. Microfluidic systems can also strongly describe the effects of physical factors such as temperature and pressure on cell behavior.

Safety and efficacy of ex vivo expanded CD34+ stem cells in murine and primate models

Background

Hematopoietic stem cell (HSC) transplantation has been widely applied to the treatment of malignant blood diseases. However, limited number of functional HSCs hinders successful transplantation. The purpose of our current study is to develop a new and cost-efficient medium formulation that could greatly enhance the expansion of HSCs while retaining their long-term repopulation and hematopoietic properties for effective clinical transplantation.

Methods

Enriched human CD34⁺ cells and mobilized nonhuman primate peripheral blood CD34⁺ cells were expanded with a new, cost-efficient expansion medium formulation, named hematopoietic expansion medium (HEM), consisting of various cytokines and nutritional supplements. The long-term repopulation potential and hematologic-lineage differentiation ability of expanded human cells were studied in the non-obese diabetic/severe combined immunodeficiency mouse model. Furthermore, the efficacy and safety studies were performed by autologous transplantation of expanded primate cells in the nonhuman primate model.

Results

HEM could effectively expand human CD34⁺ cells by up to 129 fold within 9 days. Expanded HSCs retained long-term repopulation potential and hematologic-lineage differentiation ability, as indicated by (1) maintenance (over unexpanded HSCs) of immunophenotypes of CD38⁻CD90⁺CD45RA⁻CD49f⁺ in CD34⁺ cells after expansion; (2) significant presence of multiple human hematopoietic lineages in mouse peripheral blood and bone marrow following primary transplantation; (3) enrichment (over unexpanded HSCs) in SCID-repopulating cell frequency measured by limiting dilution analysis; and (4) preservation of both myeloid and lymphoid potential among human leukocytes from mouse bone marrow in week 24 after primary transplantation or secondary transplantation. Moreover, the results of autologous transplantation in nonhuman primates demonstrated that HEM-expanded CD34⁺ cells could enhance hematological recovery after myelo-suppression. All primates transplanted with the expanded autologous CD34⁺ cells survived for over 18 months without any noticeable abnormalities.

Conclusions

Together, these findings demonstrate promising potential for the utility of HEM to improve expansion of HSCs for clinical application.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1275-0) contains supplementary material, which is available to authorized users.

Synthesis and evaluation of pyrimidoindole analogs in umbilical cord blood ex vivo expansion

The scarcity of hematopoietic stem cells (HSCs) significantly hindered their clinical potentials. Umbilical cord blood (UCB) has become the leading source of HSCs for both research and clinical applications. But the low content of HSCs in a single UCB unit limited its use only to pediatric patients. Various cytokines and small molecules have demonstrated strong abilities in promoting HSC ex vivo expansion, of which UM171 is the newest and by far the most potent HSC ex vivo expansion agent. In this study, we synthesized 37 pyrimidoindole analogs and identified 6 compounds to be potent in promoting HSC ex vivo expansion. In particular, analog 11 was found to be the most effective in stimulating ex vivo expansion of UCB CD34⁺ cells and CD34⁺CD38^- cells. Initial data indicated that compound 11 promoted the absolute number of long term HSCs and inhibited their differentiation. UCB HSCs expanded with 11 retained adequate multi-lineage differentiation capacity. In addition, compound 11 is not cytotoxic at its test concentrations, suggesting that it merits further investigation for potential clinical applications.

Chromatin-Modifying Agent-Expanded Human Cord Blood Cells Display Reduced Allostimulatory Capacity

The limited number of hematopoietic stem cells (HSC) within a single unit of human cord blood currently limits its use as an alternate graft source. However, we have developed a strategy using 5-aza-2'-deoxycytidine (5azaD) and trichostatin A (TSA), which expands transplantable HSC 7- to 10-fold. In our current studies, we have assessed the allostimulatory capacity of the 5azaD/TSA-expanded grafts. The coexpression of immunophenotypic dendritic cell (DC) markers, such as HLA-DR/CD86 and HLA-DR/CD11c as determined by flow cytometry, and the allostimulatory capacity of 5azaD/TSA-expanded cells as determined by MLC were both significantly lower than control. It has been previously demonstrated that STAT3 is indispensable for the differentiation of DC from HSC. Real-time quantitative PCR analysis revealed that 5azaD/TSA-expanded cells expressed more STAT3 transcript than control while also expressing increased transcripts for STAT3 inhibitors including SHP1, p21, and GATA1. Western blot analysis indicates that chromatin-modifying agent-expanded grafts displayed a reduced ratio of p-STAT3 to total STAT3 than control cultures, which is likely indicative of STAT3 inactivity in 5azD/TSA-expanded grafts. Culturing 5azaD/TSA-expanded cord blood cells in extended cultures reveals that they are still capable of generating DC. Notably, STAT3 inactivity was transient because the transcript levels of STAT3 and its inhibitors, including SHP1, were comparable between 5azaD/TSA and control cultures following extended culture. Taken together, our studies indicate that the reduced allostimulatory capacity of 5azaD/TSA-expanded cells is likely because of reversible inhibition of STAT3-dependent DC differentiation. These results suggest that a graft composed of 5azaD/TSA-expanded cells possesses relatively less allostimulatory response but is still capable of generating DC in permissive conditions.

Ultimate Precision: Targeting Cancer but Not Normal Self-replication

Self-replication is the engine that drives all biologic evolution, including neoplastic evolution. A key oncotherapy challenge is to target this, the heart of malignancy, while sparing the normal self-replication mandatory for health and life. Self-replication can be demystified: it is activation of replication, the most ancient of cell programs, uncoupled from activation of lineage-differentiation, metazoan programs more recent in origin. The uncoupling can be physiologic, as in normal tissue stem cells, or pathologic, as in cancer. Neoplastic evolution selects to disengage replication from forward-differentiation where intrinsic replication rates are the highest, in committed progenitors that have division times measured in hours versus weeks for tissue stem cells, via partial loss of function in master transcription factors that activate terminal-differentiation programs (e.g., GATA4) or in the coactivators they use for this purpose (e.g., ARID1A). These loss-of-function mutations bias master transcription factor circuits, which normally regulate corepressor versus coactivator recruitment, toward corepressors (e.g., DNMT1) that repress rather than activate terminal-differentiation genes. Pharmacologic inhibition of the corepressors rebalances to coactivator function, activating lineage-differentiation genes that dominantly antagonize MYC (the master transcription factor coordinator of replication) to terminate malignant self-replication. Physiologic self-replication continues, because the master transcription factors in tissue stem cells activate stem cell, not terminal-differentiation, programs. Druggable corepressor proteins are thus the barriers between self-replicating cancer cells and the terminal-differentiation fates intended by their master transcription factor content. This final common pathway to oncogenic self-replication, being separate and distinct from the normal, offers the favorable therapeutic indices needed for clinical progress.

Hematopoietic Niche - Exploring Biomimetic Cues to Improve the Functionality of Hematopoietic Stem/Progenitor Cells

The adult bone marrow (BM) niche is a complex entity where a homeostatic hematopoietic system is maintained through a dynamic crosstalk between different cellular and non-cellular players. Signaling mechanisms triggered by cell-cell, cell-extracellular matrix (ECM), cell-cytokine interactions, and local microenvironment parameters are involved in controlling quiescence, self-renewal, differentiation, and migration of hematopoietic stem/progenitor cells (HSPC). A promising strategy to more efficiently expand HSPC numbers and tune their properties ex vivo is to mimic the hematopoietic niche through integration of adjuvant stromal cells, soluble cues, and/or biomaterial-based approaches in HSPC culture systems. Particularly, mesenchymal stem/stromal cells (MSC), through their paracrine activity or direct contact with HSPC, are thought to be a relevant niche player, positioning HSPC-MSC co-culture as a valuable platform to support the ex vivo expansion of hematopoietic progenitors. To improve the clinical outcome of hematopoietic cell transplantation (HCT), namely when the available HSPC are present in a limited number such is the case of HSPC collected from umbilical cord blood (UCB), ex vivo expansion of HSPC is required without eliminating the long-term repopulating capacity of more primitive HSC. Here, we will focus on depicting the characteristics of co-culture systems, as well as other bioengineering approaches to improve the functionality of HSPC ex vivo.

Higher-Level Pathway Objectives of Epigenetic Therapy: A Solution to the p53 Problem in Cancer

Searches for effective yet nontoxic oncotherapies are searches for exploitable differences between cancer and normal cells. In its core of cell division, cancer resembles normal life, coordinated by the master transcription factor MYC. Outside of this core, apoptosis and differentiation programs, which dominantly antagonize MYC to terminate cell division, necessarily differ between cancer and normal cells, as apoptosis is suppressed by biallelic inactivation of the master regulator of apoptosis, p53, or its cofactor p16/CDKN2A in approximately 80% of cancers. These genetic alterations impact therapy: conventional oncotherapy applies stress upstream of p53 to upregulate it and causes apoptosis (cytotoxicity)-a toxic, futile intent when it is absent or nonfunctional. Differentiation, on the other hand, cannot be completely suppressed because it is a continuum along which all cells exist. Neoplastic evolution stalls advances along this continuum at its most proliferative points-in lineage-committed progenitors that have division times measured in hours compared with weeks for tissue stem cells. This differentiation arrest is by mutations/deletions in differentiation-driving transcription factors or their coactivators that shift balances of gene-regulating protein complexes toward corepressors that repress instead of activate hundreds of terminal differentiation genes. That is, malignant proliferation without differentiation, also referred to as cancer "stem" cell self-renewal, hinges on druggable corepressors. Inhibiting these corepressors (e.g., DNMT1) releases p53-independent terminal differentiation in cancer stem cells but preserves self-renewal of normal stem cells that express stem cell transcription factors. Thus, epigenetic-differentiation therapies exploit a fundamental distinction between cancer and normal stem cell self-renewal and have a pathway of action downstream of genetic defects in cancer, affording favorable therapeutic indices needed for clinical progress.

Characterization of the growth modulatory activities of osteoblast conditioned media on cord blood progenitor cells

Engraftment outcomes are strongly correlated with the numbers of hematopoietic stem and progenitor cells (HSPC) infused. Expansion of umbilical cord blood (CB) HSPC has gained much interest lately since infusion of expanded HSPC can accelerate engraftment and improve clinical outcomes. Many novel protocols based on different expansion strategies of HSPC and their downstream derivatives are under development. Herein, we describe the production and properties of serum-free medium (SFM) conditioned with mesenchymal stromal cells derived-osteoblasts (OCM) for the expansion of umbilical CB cells and progenitors. After optimization of the conditioning length, we show that OCM increased the production of human CB total nucleated cells and CD34⁺ cells by 1.8-fold and 1.5-fold over standard SFM, respectively. Production of immature CD34⁺ subpopulations enriched in hematopoietic stem cells was also improved with a shorter conditioning period. Moreover, we show that the growth modulatory activities of OCM on progenitor expansion are regulated by both soluble factors and non-soluble cellular elements. Finally, the growth and differentiation modulatory activities of OCM were fully retained after high dose-ionizing irradiation and highly stable when OCM is stored frozen. In summary, our results suggest that OCM efficiently mimics some of the natural regulatory activities of osteoblasts on HSPC and highlight the marked expansion potentials of SFM conditioned with osteoblasts.

Recent Stem Cell Advances: Cord Blood and Induced Pluripotent Stem Cell for Cardiac Regeneration- a Review

Stem cells are primitive self renewing undifferentiated cell that can be differentiated into various types of specialized cells like nerve cell, skin cells, muscle cells, intestinal tissue, and blood cells. Stem cells live in bone marrow where they divide to make new blood cells and produces peripheral stem cells in circulation. Under proper environment and in presence of signaling molecules stem cells begin to develop into specialized tissues and organs. These unique characteristics make them very promising entities for regeneration of damaged tissue. Day by day increase in incidence of heart diseases including left ventricular dysfunction, ischemic heart disease (IHD), congestive heart failure (CHF) are the major cause of morbidity and mortality. However infracted tissue cannot regenerate into healthy tissue. Heart transplantation is only the treatment for such patient. Due to limitation of availability of donor for organ transplantation, a focus is made for alternative and effective therapy to treat such condition. In this review we have discussed the new advances in stem cells such as use of cord stem cells and iPSC technology in cardiac repair. Future approach of CB cells was found to be used in tissue repair which is specifically observed for improvement of left ventricular function and myocardial infarction. Here we have also focused on how iPSC technology is used for regeneration of cardiomyocytes and intiating neovascularization in myocardial infarction and also for study of pathophysiology of various degenerative diseases and genetic disease in research field.

DECIDER: prospective randomized multicenter phase II trial of low-dose decitabine (DAC) administered alone or in combination with the histone deacetylase inhibitor valproic acid (VPA) and all-trans retinoic acid (ATRA) in patients >60 years with acute myeloid leukemia who are ineligible for induction chemotherapy

Background

Acute myeloid leukemia (AML) is predominantly a disease of older patients with a poor long-term survival. Approval of decitabine (DAC) in the European Union (EU) in 2012 for the treatment of patients with AML ≥65 years marks the potential for hypomethylating agents in elderly AML. Nevertheless the situation is dissatisfactory and the quest for novel treatment approaches, including combination epigenetic therapy is actively ongoing. The given randomized trial should be helpful in investigating the question whether combinations of DAC with the histone deacetylase (HDAC) inhibitor valproic acid (VPA) and/or all-trans retinoic acid (ATRA), which in vitro show a very promising synergism, are superior to the DAC monotherapy. The accompanying translational research project will contribute to find surrogate molecular end points for drug efficacy and better tailor epigenetic therapy. An additional aim of the study is to investigate the prognostic value of geriatric assessments for elderly AML patients treated non-intensively.

Methods/Design

DECIDER is a prospective, randomized, observer blind, parallel group, multicenter, Phase II study with a 2x2 factorial design. The primary endpoint is objective best overall response (complete remission (CR) and partial remission (PR)). The target population is AML patients aged 60 years or older and unfit for standard induction chemotherapy. Patients are randomized to one of the four treatment groups: DAC alone or in combination with VPA or ATRA or with both add-on drugs. One interim safety analysis was planned and carried out with the objective to stop early one or more of the treatment arms in case of an unacceptable death rate. This analysis showed that in all treatment arms the critical stopping rule was not reached. No important safety issues were observed. The Data Monitoring Committee (DMC) recommended continuing the study as planned. The first patient was included in December 2011. A total of 189 out of 200 planned patients were randomized since then (status 31.12.2014).

Trial registration

ClinicalTrials.gov identifier: NCT00867672 (registration date 23.03.2009); German clinical trials registry number: DRKS00000733 (registration date 19.04.2011).

Ex vivo expansion of human mobilized peripheral blood stem cells using epigenetic modifiers

BACKGROUND

Epigenetic modifications likely control the fate of hematopoietic stem cells (HSCs). The chromatin-modifying agents (CMAs), 5-aza-2'-deoxycytidine (5azaD) and trichostatin A (TSA), have previously been shown to expand HSCs from cord blood and marrow. Here we assessed whether CMA can also expand HSCs present in growth factor-mobilized human peripheral blood (MPB).

STUDY DESIGN AND METHODS

5azaD and TSA were sequentially added to CD34+ MPB cells in the presence of cytokines, and the cells were cultured for 9 days.

RESULTS

After culture, a 3.6 ± 0.5-fold expansion of CD34+CD90+ cells, a 10.1 ± 0.5-fold expansion of primitive colony-forming unit (CFU)-mix, and a 2.2 ± 0.5-fold expansion of long-term cobblestone-area-forming cells (CAFCs) was observed in 5azaD/TSA-expanded cells. By contrast, cells cultured in cytokines without 5azaD/TSA displayed no expansion; rather, a reduction in CD34+CD90+ cells (0.7 ± 0.1-fold) and CAFCs (0.3 ± 0.1-fold) from their initial numbers was observed. Global hypomethylation corresponding with increased transcript levels of several genes implicated in HSC self-renewal, including HOXB4, GATA2, and EZH2, was observed in 5azaD/TSA-expanded MPB cells in contrast to controls. 5azaD/TSA-expanded MPB cells retained in vivo hematopoietic engraftment capacity.

CONCLUSION

MPB CD34+ cells from donors can be expanded using 5azaD/TSA, and these expanded cells retain in vivo hematopoietic reconstitution capacity. This strategy may prove to be potentially useful to augment HSC numbers for patients who fail to mobilize.

Decitabine suspends human CD34+ cell differentiation and proliferation during lentiviral transduction

Efficient ex vivo transduction of hematopoietic stem cells (HSCs) is encumbered by differentiation which reduces engraftment. We hypothesized that inhibiting DNA methyltransferase with decitabine would block differentiation of transduced CD34+ cells under cytokine stimulation and thus improve transduction efficiency for engrafting HSCs. Human CD34+ cells in cytokine-containing media were treated with or without decitabine for 24 or 48 hours, and then these cells were transduced with a GFP-expressing lentiviral vector. Utilizing decitabine pre-treatment for 48 hours, we observed an equivalent percentage of successfully transduced cells (GFP-positivity) and a higher percentage of cells that retained CD34 positivity, compared to no decitabine exposure. Cell proliferation was inhibited after decitabine exposure. Similar results were observed among CD34+ cells from six different donors. Repopulating activity was evaluated by transplantation into NOD/SCID/IL2Rγnull mice and demonstrated an equivalent percentage of GFP-positivity in human cells from decitabine-treated samples and a trend for higher human cell engraftment (measured 20-24 weeks after transplantation), compared to no decitabine exposure. In conclusion, ex vivo decitabine exposure inhibits both differentiation and proliferation in transduced human CD34+ cells and modestly increases the engraftment ability in xenograft mice, while the transduction efficiency is equivalent in decitabine exposure, suggesting improvement of lentiviral transduction for HSCs.

Epigenetic reprogramming induces the expansion of cord blood stem cells

Cord blood (CB) cells that express CD34 have extensive hematopoietic capacity and rapidly divide ex vivo in the presence of cytokine combinations; however, many of these CB CD34+ cells lose their marrow-repopulating potential. To overcome this decline in function, we treated dividing CB CD34+ cells ex vivo with several histone deacetylase inhibitors (HDACIs). Treatment of CB CD34+ cells with the most active HDACI, valproic acid (VPA), following an initial 16-hour cytokine priming, increased the number of multipotent cells (CD34+CD90+) generated; however, the degree of expansion was substantially greater in the presence of both VPA and cytokines for a full 7 days. Treated CD34+ cells were characterized based on the upregulation of pluripotency genes, increased aldehyde dehydrogenase activity, and enhanced expression of CD90, c-Kit (CD117), integrin α6 (CD49f), and CXCR4 (CD184). Furthermore, siRNA-mediated inhibition of pluripotency gene expression reduced the generation of CD34+CD90+ cells by 89%. Compared with CB CD34+ cells, VPA-treated CD34+ cells produced a greater number of SCID-repopulating cells and established multilineage hematopoiesis in primary and secondary immune-deficient recipient mice. These data indicate that dividing CB CD34+ cells can be epigenetically reprogrammed by treatment with VPA so as to generate greater numbers of functional CB stem cells for use as transplantation grafts.

Differential effects of epigenetic modifiers on the expansion and maintenance of human cord blood stem/progenitor cells

Epigenetic therapies, including DNA methyltransferase and histone deacetylase (HDAC) inhibitors, are increasingly being considered to treat hematological malignancies, but their effects on normal hematopoietic stem cells (HSCs) remain largely unexplored. We compared the effects of several HDAC inhibitors, including valproic acid (VPA) and trichostatin A (TSA), alone or in combination with 5-aza-2'-deoxycytidine (5azaD) on the expansion of HSCs. VPA induced the highest expansion of CD34+CD90+ cells and progenitor cells compared with other HDAC inhibitors or the sequential addition of 5azaD/TSA in culture. Xenotransplantation studies demonstrated that VPA prevents HSC loss, whereas 5azaD/TSA treatment leads to a net expansion of HSCs that retain serial transplantation ability. 5azaD/TSA-mediated HSC expansion was associated with increased histone acetylation and transient DNA demethylation, which corresponded with higher gene transcript levels. However, some genes with increased transcript levels lacked changes in methylation. Importantly, a global microarray analysis revealed a set of differentially expressed genes in 5azaD/TSA- and VPA-expanded CD34+ cells that might be involved in the expansion and maintenance of transplantable HSCs, respectively. In summary, our data indicate that treatment of HSCs with different chromatin-modifying agents results in either the expansion or maintenance of HSCs, an observation of potential therapeutic importance.

Small molecule-based approaches to adult stem cell therapies

There is considerable interest in the development of stem cell-based strategies for the treatment of a broad range of human diseases, including neurodegenerative, autoimmune, cardiovascular, and musculoskeletal diseases. To date, such regenerative approaches have focused largely on the development of cell transplantation therapies using cells derived from pluripotent embryonic stem cells (ESCs). Although there have been exciting preliminary reports describing the efficacy of ESC-derived replacement therapies, approaches involving ex vivo manipulated ESCs are hindered by issues of mutation, immune rejection, and ethical controversy. An alternative approach involves direct in vivo modulation or ex vivo expansion of endogenous adult stem cell populations using drug-like small molecules. Here we describe chemical approaches to the regulation of somatic stem cell biology that are yielding new biological insights and that may ultimately lead to innovative new medicines.

Stem cell bioengineering strategies to widen the therapeutic applications of haematopoietic stem/progenitor cells from umbilical cord blood

Umbilical cord blood (UCB) transplantation has observed a significant increase in recent years, due to the unique features of UCB haematopoietic stem/progenitor cells (HSCs) for the treatment of blood-related disorders. However, the low cell numbers available per UCB unit significantly impairs the widespread use of this source for transplantation of adult patients, resulting in graft failure, delayed engraftment and delayed immune reconstitution. In order to overcome this issue, distinct approaches are now being considered in clinical trials, such as double-UCB transplantation, intrabone injection or ex vivo expansion. In this article the authors review the current state of the art, future trends and challenges on the ex vivo expansion of UCB HSCs, focusing on culture parameters affecting the yield and quality of the expanded HSC grafts: novel HSC selection schemes prior to cell culture, cytokine/growth factor cocktails, the impact of biochemical factors (e.g. O2 ) or the addition of supportive cells, e.g. mesenchymal stem/stromal cell (MSC)-based feeder layers) were addressed. Importantly, a critical challenge in cellular therapy is still the scalability, reproducibility and control of the expansion process, in order to meet the clinical requirements for therapeutic applications. Efficient design of bioreactor systems and operation modes are now the focus of many bioengineers, integrating the increasing 'know-how' on HSC biology and physiology, while complying with the GMP standards for the production of cellular products, i.e. through the use of commercially available, highly controlled, disposable technologies.

Two-dimensional polymer-based cultures expand cord blood-derived hematopoietic stem cells and support engraftment of NSG mice

Currently, ex vivo expansion of hematopoietic stem cells (HSC) is still insufficient. Traditional approaches for HSC expansion include the use of stromal cultures, growth factors, and/or bioreactors. Biomaterial-based strategies provide new perspectives. We focus on identifying promising two-dimensional (2D) polymer candidates for HSC expansion. After a 7-day culture period with cytokine supplementation, 2D fibrin, poly(D,L-lactic-co-glycolic acid; Resomer® RG503), and Poly(ɛ-caprolactone; PCL) substrates supported expansion of cord blood (CB)-derived CD34⁺ cells ex vivo. Fibrin cultures achieved the highest proliferation rates (>8700-fold increase of total nuclear cells, p<0.001), high total colony-forming units (3.6-fold increase, p<0.001), and highest engraftment in NSG mice (7.69-fold more donor cells compared with tissue culture polysterene, p<0.001). In addition, the presence of multiple human hematopoietic lineages such as myeloid (CD13⁺), erythroid (GypC⁺), and lymphoid (CD20⁺/CD56⁺) in murine transplant recipients confirmed the multilineage engraftment potential of fibrin-based cultures. Filopodia development in fibrin-expanded cells was a further indicator for superior cell adhesion capacities. We propose application of fibrin, Resomer® RG503, and PCL for future strategies of CB-CD34⁺ cell expansion. Suitable polymers for HSC expansion might also be appropriate for future drug discovery applications or for studies aimed to develop hematological therapies.

Valproic acid triggers erythro/megakaryocyte lineage decision through induction of GFI1B and MLLT3 expression

Histone deacetylase inhibitors represent a family of targeted anticancer compounds that are widely used against hematological malignancies. So far little is known about their effects on normal myelopoiesis. Therefore, in order to investigate the effect of histone deacetylase inhibitors on the myeloid commitment of hematopoietic stem/progenitor cells, we treated CD34(+) cells with valproic acid (VPA). Our results demonstrate that VPA treatment induces H4 histone acetylation and hampers cell cycle progression in CD34(+) cells sustaining high levels of CD34 protein expression. In addition, our data show that VPA treatment promotes erythrocyte and megakaryocyte differentiation. In fact, we demonstrate that VPA treatment is able to induce the expression of growth factor-independent protein 1B (GFI1B) and of mixed-lineage leukemia translocated to chromosome 3 protein (MLLT3), which are crucial regulators of erythrocyte and megakaryocyte differentiation, and that the up-regulation of these genes is mediated by the histone hyperacetylation at their promoter sites. Finally, we show that GFI1B inhibition impairs erythroid and megakaryocyte differentiation induced by VPA, while MLLT3 silencing inhibits megakaryocyte commitment only. As a whole, our data suggest that VPA sustains the expression of stemness-related markers in hematopoietic stem/progenitor cells and is able to interfere with hematopoietic lineage commitment by enhancing erythrocyte and megakaryocyte differentiation and by inhibiting the granulocyte and mono-macrophage maturation.

Angptl4 maintains in vivo repopulation capacity of CD34+ human cord blood cells

OBJECTIVES

Methods to expand hematopoietic stem cells (HSCs) ex vivo encompass an attractive approach that would substantially broaden the clinical applicability of HSCs derived from cord blood (CB). Recently, members of the angiopoietin-like (Angptl) family of growth factors were shown to expand both murine and human HSCs. Specifically, Angptl5 has been implicated in the expansion of human NOD/SCID-repopulating cells (SRCs) ex vivo. Here, we sought to evaluate the potential of additional Angptls to expand human SRCs from CB. Additionally, the purpose of this study was to evaluate the reproducibility of Angptl-mediated expansion of SRCs across independent experiments.

METHODS

Human CD34(+) cells from CB were cultured in vitro for eleven or 8 d in the presence or absence of Angptls. The reconstitution capacity of expanded cells was subsequently measured in vivo by transplantation into NOD/SCID or NSG mice and compared with that of uncultured cells.

RESULTS

We report here that Angptl4 functions to maintain SRC activity of CD34(+) CB-derived cells ex vivo as assayed in NOD/SCID and NSG mice. However, all Angptls tested, including Angptl1, Angptl4, and Angptl5, were associated with variation between experiments.

CONCLUSION

Our findings indicate that Angptl4 and Angptl5 can lead to increased engraftment capacity of SRCs, but more frequently, these factors are associated with maintenance of SRC activity during ex vivo culture. Thus, Angptl-mediated expansion of SRCs ex vivo is associated with more interexperimental variation than previously thought. We conclude that Angptls would be useful in instances where there is a need to maintain HSCs ex vivo, such as during transduction for gene therapy applications.

Effect of AGM and fetal liver-derived stromal cell lines on globin expression in adult baboon (P. anubis) bone marrow-derived erythroid progenitors

This study was performed to investigate the hypothesis that the erythroid micro-environment plays a role in regulation of globin gene expression during adult erythroid differentiation. Adult baboon bone marrow and human cord blood CD34+ progenitors were grown in methylcellulose, liquid media, and in co-culture with stromal cell lines derived from different developmental stages in identical media supporting erythroid differentiation to examine the effect of the micro-environment on globin gene expression. Adult progenitors express high levels of γ-globin in liquid and methylcellulose media but low, physiological levels in stromal cell co-cultures. In contrast, γ-globin expression remained high in cord blood progenitors in stromal cell line co-cultures. Differences in γ-globin gene expression between adult progenitors in stromal cell line co-cultures and liquid media required cell-cell contact and were associated with differences in rate of differentiation and γ-globin promoter DNA methylation. We conclude that γ-globin expression in adult-derived erythroid cells can be influenced by the micro-environment, suggesting new potential targets for HbF induction.

Concise review: Multidimensional regulation of the hematopoietic stem cell state

Hematopoietic stem cells (HSCs) are characterized by their unique function to produce all lineages of blood cells throughout life. Such tissue-specific function of HSC is attributed to their ability to execute self-renewal and multilineage differentiation. Accumulating evidence indicates that the undifferentiated state of HSC is characterized by dynamic maintenance of chromatin structures and epigenetic plasticity. Conversely, quiescence, self-renewal, and differentiation of HSCs are dictated by complex regulatory mechanisms involving specific transcription factors and microenvironmental crosstalk between stem cells and multiple compartments of niches in bone marrows. Thus, multidimensional regulatory inputs are integrated into two opposing characters of HSCs-maintenance of undifferentiated state analogous to pluripotent stem cells but execution of tissue-specific hematopoietic functions. Further studies on the interplay of such regulatory forces as "cell fate determinant" will likely shed the light on diverse spectrums of tissue-specific stem cells.

Ex vivo expansion of umbilical cord blood: where are we?

Since the first successful clinical use of umbilical cord blood (UCB) in 1988, UCB grafts have been used for over 20,000 patients with both malignant and non-malignant diseases. UCB has several practical advantages over other transplantable graft sources. For example, the ease of procurement, the absence of donor risks, the reduced risk of transmissible infections, and the availability for immediate use make UCB an appealing graft choice. However, UCB grafts suffer from a few limitations related to the limited cell dose available for transplantation in each UCB unit and to defects in UCB stem cell homing. These limitations lead to increased post-transplant complications. In this review, we focus on the issue of limited cell dose in UCB units and discuss the possible approaches to overcome this limitation. We also summarize the various cellular pathways that have been explored to expand UCB units.

Human umbilical cord is a unique and safe source of various types of stem cells suitable for treatment of hematological diseases and for regenerative medicine

Cord blood (CB) is a rich source of hematopoietic stem cells (HSCs) and for this reason CB transplantation has been used successfully for the treatment of some malignant and nonmalignant diseases. However, this technique is limited by the relatively low number of HSCs present in each CB unit and by the delayed engraftment of platelets and neutrophils. To bypass these obstacles efforts have been made to develop strategies to expand CB HSCs in vitro for transplantation. CB is also an important source of other stem cells, including endothelial progenitors, mesenchymal stem cells (MSCs), very small embryonic/epiblast-like (VSEL) stem cells, and unrestricted somatic stem cells (USSC), potentially suitable for use in regenerative medicine. For some of these stem cell populations, such as MSCs, clinical studies have been started and for other stem cell populations potential clinical applications have been identified and clinical studies will follow. In addition to CB, other parts of umbilical cord, such as the Wharton's jelly, or tissues strictly linked such as the placenta are also rich sources of stem cells.

Efficacy of vorinostat in a murine model of polycythemia vera

The discovery of the JAK2V617F mutation in most patients with Ph-negative myeloproliferative neoplasms has led to the development of JAK2 kinase inhibitors. However, JAK2 inhibitor therapy has shown limited efficacy and dose-limiting hematopoietic toxicities in clinical trials. In the present study, we describe the effects of vorinostat, a small-molecule inhibitor of histone deacetylase, against cells expressing JAK2V617F and in an animal model of polycythemia vera (PV). We found that vorinostat markedly inhibited proliferation and induced apoptosis in cells expressing JAK2V617F. In addition, vorinostat significantly inhibited JAK2V617F-expressing mouse and human PV hematopoietic progenitors. Biochemical analyses revealed significant inhibition of phosphorylation of JAK2, Stat5, Stat3, Akt, and Erk1/2 in vorinostat-treated, JAK2V617F-expressing human erythroleukemia (HEL) cells. Expression of JAK2V617F and several other genes, including GATA1, KLF1, FOG1, SCL, C/EPBα, PU.1, and NF-E2, was significantly down-regulated, whereas the expression of SOCS1 and SOCS3 was up-regulated by vorinostat treatment. More importantly, we observed that vorinostat treatment normalized the peripheral blood counts and markedly reduced splenomegaly in Jak2V617F knock-in mice compared with placebo treatment. Vorinostat treatment also decreased the mutant allele burden in mice. Our results suggest that vorinostat may have therapeutic potential for the treatment of PV and other JAK2V617F-associated myeloproliferative neoplasms.

Histone deacetylase inhibitors in cell pluripotency, differentiation, and reprogramming

Histone deacetylase inhibitors (HDACi) are small molecules that have important and pleiotropic effects on cell homeostasis. Under distinct developmental conditions, they can promote either self-renewal or differentiation of embryonic stem cells. In addition, they can promote directed differentiation of embryonic and tissue-specific stem cells along the neuronal, cardiomyocytic, and hepatic lineages. They have been used to facilitate embryo development following somatic cell nuclear transfer and induced pluripotent stem cell derivation by ectopic expression of pluripotency factors. In the latter method, these molecules not only increase effectiveness, but can also render the induction independent of the oncogenes c-Myc and Klf4. Here we review the molecular pathways that are involved in the functions of HDAC inhibitors on stem cell differentiation and reprogramming of somatic cells into pluripotency. Deciphering the mechanisms of HDAC inhibitor actions is very important to enable their exploitation for efficient and simple tissue regeneration therapies.

Chemical biology in stem cell research

Stem cells are offering a considerable range of prospects to the biomedical research including novel platforms for disease models and drug discovery tools to cell transplantation and regenerative therapies. However, there are several obstacles to overcome to bring these potentials into reality. First, robust methods to maintain stem cells in the pluripotent state should be established and factors that are required to direct stem cell fate into a particular lineage should be elucidated. Second, both allogeneic rejection following transplantation and limited cell availability issues must be circumvented. These challenges are being addressed, at least in part, through the identification of a group of chemicals (small molecules) that possess novel activities on stem cell biology. For example, small molecules can be used both in vitro and/or in vivo as tools to promote proliferation of stem cells (self-renewal), to direct stem cells to a lineage specific patterns (differentiation), or to reprogram somatic cells to a more undifferentiated state (de-differentiation or reprogramming). These molecules, in turn, have provided new insights into the signaling mechanisms that regulate stem cell biology, and may eventually lead to effective therapies in regenerative medicine. In this review, we will introduce recent findings with regards to small molecules and their impact on stem cell self-renewal and differentiation.

p53-Independent, normal stem cell sparing epigenetic differentiation therapy for myeloid and other malignancies

Cytotoxic chemotherapy for acute myeloid leukemia (AML) usually produces only temporary remissions, at the cost of significant toxicity and risk for death. One fundamental reason for treatment failure is that it is designed to activate apoptosis genes (eg, TP53) that may be unavailable because of mutation or deletion. Unlike deletion of apoptosis genes, genes that mediate cell cycle exit by differentiation are present in myelodysplastic syndrome (MDS) and AML cells but are epigenetically repressed: MDS/AML cells express high levels of key lineage-specifying transcription factors. Mutations in these transcription factors (eg, CEBPA) or their cofactors (eg., RUNX1) affect transactivation function and produce epigenetic repression of late-differentiation genes that antagonize MYC. Importantly, this aberrant epigenetic repression can be redressed clinically by depleting DNA methyltransferase 1 (DNMT1, a central component of the epigenetic network that mediates transcription repression) using the deoxycytidine analogue decitabine at non-cytotoxic concentrations. The DNMT1 depletion is sufficient to trigger upregulation of late-differentiation genes and irreversible cell cycle exit by p53-independent differentiation mechanisms. Fortuitously, the same treatment maintains or increases self-renewal of normal hematopoietic stem cells, which do not express high levels of lineage-specifying transcription factors. The biological rationale for this approach to therapy appears to apply to cancers other than MDS/AML also. Decitabine or 5-azacytidine dose and schedule can be rationalized to emphasize this mechanism of action, as an alternative or complement to conventional apoptosis-based oncotherapy.

Ex-vivo expansion of red blood cells: how real for transfusion in humans?

Blood transfusion is indispensable for modern medicine. In developed countries, the blood supply is adequate and safe but blood for alloimmunized patients is often unavailable. Concerns are increasing that donations may become inadequate in the future as the population ages prompting a search for alternative transfusion products. Improvements in culture conditions and proof-of-principle studies in animal models have suggested that ex-vivo expanded red cells may represent such a product. Compared to other cell therapies transfusion poses the unique challenge of requiring great cell doses (2.5×10(12) cells vs 10(7) cells). Although production of such cell numbers is theoretically possible, current technologies generate red cells in numbers sufficient only for safety studies. It is conceived that by the time these studies will be completed, technical barriers to mass cell production will have been eliminated making transfusion with ex-vivo generated red cells a reality.

Histone deacetylase inhibition enhances self renewal and cardioprotection by human cord blood-derived CD34 cells

Background

Use of peripheral blood- or bone marrow-derived progenitors for ischemic heart repair is a feasible option to induce neo-vascularization in ischemic tissues. These cells, named Endothelial Progenitors Cells (EPCs), have been extensively characterized phenotypically and functionally. The clinical efficacy of cardiac repair by EPCs cells remains, however, limited, due to cell autonomous defects as a consequence of risk factors. The devise of “enhancement” strategies has been therefore sought to improve repair ability of these cells and increase the clinical benefit.

Principal Findings

Pharmacologic inhibition of histone deacetylases (HDACs) is known to enhance hematopoietic stem cells engraftment by improvement of self renewal and inhibition of differentiation in the presence of mitogenic stimuli in vitro. In the present study cord blood-derived CD34⁺ were pre-conditioned with the HDAC inhibitor Valproic Acid. This treatment affected stem cell growth and gene expression, and improved ischemic myocardium protection in an immunodeficient mouse model of myocardial infarction.

Conclusions

Our results show that HDAC blockade leads to phenotype changes in CD34⁺ cells with enhanced self renewal and cardioprotection.

Inhibition of histone deacetylases by Trichostatin A leads to a HoxB4-independent increase of hematopoietic progenitor/stem cell frequencies as a result of selective survival

BACKGROUND

DNA and chromatin modifications are critical mediators in the establishment and maintenance of cell type-specific gene expression patterns that constitute cellular identities. One type of modification, the acetylation and deacetylation of histones, occurs reversibly on lysine ε-NH₃(+) groups of core histones via histone acetyl transferases (HAT) and histone deacetylases (HDAC). Hyperacetylated histones are associated with active chromatin domains, whereas hypoacetylated histones are enriched in non-transcribed loci.

METHODS

We analyzed global histone H4 acetylation and HDAC activity levels in mature lineage marker-positive (Lin(+)) and progenitor lineage marker-negative (Lin⁻) hematopoietic cells from murine bone marrow (BM). In addition, we studied the effects of HDAC inhibition on hematopoietic progenitor/stem cell (HPSC) frequencies, cell survival, differentiation and HoxB4 dependence.

RESULTS

We observed that Lin⁻ and Lin(+) cells do not differ in global histone H4 acetylation but in HDAC activity levels. Further, we saw that augmented histone acetylation achieved by transient Trichostatin A (TSA) treatment increased the frequency of cells with HPSC immunophenotype and function in the heterogeneous pool of BM cells. Induction of histone hyperacetylation in differentiated BM cells was detrimental, as evidenced by preferential death of mature BM cells upon HDAC inhibition. Finally, TSA treatment of BM cells from HoxB4(-/-) mice revealed that the HDAC inhibitor-mediated increase in HPSC frequencies was independent of HoxB4.

CONCLUSIONS

Overall, these data indicate the potential of chromatin modifications for the regulation of HPSC. Chromatin-modifying agents may provide potential strategies for ex vivo expansion of HPSC.