Nicotinamide, a SIRT1 inhibitor, inhibits differentiation and facilitates expansion of hematopoietic progenitor cells with enhanced bone marrow homing and engraftment

Novel strategies for improving hematopoietic reconstruction after allogeneic hematopoietic stem cell transplantation or intensive chemotherapy

INTRODUCTION

High-dose conditioning regimens for allogeneic hematopoietic cell transplantation (allo-HCT) as well as intensive poly-chemotherapy for acute myeloid leukemia (AML) induce prolonged periods of neutropenia. The duration of the neutropenia is particularly long following umbilical cord blood transplantation (UCBT). Areas covered: After briefly reviewing the impact of hematopoietic growth factors administration to hasten hematologic reconstitution after allo-HCT or intensive AML chemotherapy, this article summarizes recent approaches that have been investigated to prompt hematologic reconstruction after UCBT or intensive AML chemotherapy. Expert opinion: In the allo-HCT setting, administration of G-CSF or GM-CSF shortened the duration of the neutropenia but failed to decrease infection-related mortality or to improve survival. Novel approaches to hasten hematological reconstruction after UCBT such as double UCBT with expansion of one of the 2 UCB units with Notch ligand, mesenchymal stromal cells, nicotinamide, or StemRegenin 1, co-transplanting a single UCB unit with HLA-haploidentical CD34+ cells, or increasing UCB HSC homing to marrow niches via direct intra bone UCB administration, pulse treatment with dmPGE2 or enforced fucosylation are promising and deserve further investigations in prospective phase III studies. In the AML setting, G-CSF or GM-CSF administration after intensive chemotherapy decreased the duration of the neutropenia without improving survival.

StemCellCKB: An Integrated Stem Cell-Specific Chemogenomics KnowledgeBase for Target Identification and Systems-Pharmacology Research

Given the capacity of self-renewal and multilineage differentiation, stem cells are promising sources for use in regenerative medicines as well as in the clinical treatment of certain hematological malignancies and degenerative diseases. Complex networks of cellular signaling pathways largely determine stem cell fate and function. Small molecules that modulate these pathways can provide important biological and pharmacological insights. However, it is still challenging to identify the specific protein targets of these compounds, to explore the changes in stem cell phenotypes induced by compound treatment and to ascertain compound mechanisms of action. To facilitate stem cell related small molecule study and provide a better understanding of the associated signaling pathways, we have constructed a comprehensive domain-specific chemogenomics resource, called StemCellCKB ( http://www.cbligand.org/StemCellCKB/ ). This new cloud-computing platform describes the chemical molecules, genes, proteins, and signaling pathways implicated in stem cell regulation. StemCellCKB is also implemented with web applications designed specifically to aid in the identification of stem cell relevant protein targets, including TargetHunter, a machine-learning algorithm for predicting small molecule targets based on molecular fingerprints, and HTDocking, a high-throughput docking module for target prediction and systems-pharmacology analyses. We have systematically tested StemCellCKB to verify data integrity. Target-prediction accuracy has also been validated against the reported known target/compound associations. This proof-of-concept example demonstrates that StemCellCKB can (1) accurately predict the macromolecular targets of existing stem cell modulators and (2) identify novel small molecules capable of probing stem cell signaling mechanisms, for use in systems-pharmacology studies. StemCellCKB facilitates the exploration and exchange of stem cell chemogenomics data among members of the broader research community.

Cellular therapy for sickle cell disease

Sickle cell disease (SCD) is a monogenic red cell disorder affecting more than 300 000 annual births worldwide and leading to significant organ toxicity and premature mortality. Although chronic therapies such as hydroxyurea have improved outcomes, more durable therapeutic and curative options are still being investigated. Newer understanding of the disease has implicated invariant natural killer T cells as a critical immune profile that potentiates SCD. Hence, targeting this cell population may offer a new approach to disease management. Hematopoietic stem cell transplant is a curative option for patients with SCD, but the under-representation of minorities on the unrelated donor registry means that this is not a feasible option for more than 75% of patients. Work in this area has therefore focused on increasing the donor pool and decreasing transplant-related toxicities to make this a treatment option for the majority of patients with SCD. This review focuses on the currently available cell and gene therapies for patients with SCD and acknowledges that newer gene-editing approaches to improve gene therapy efficiency and safety are the next wave of potentially curative approaches.

SIRT1 is a critical regulator of K562 cell growth, survival, and differentiation

Inhibition of histone deacetylases (HDACi) has emerged as a promising approach in the treatment of many types of cancer, including leukemias. Among the HDACs, Class III HDACs, also known as sirtuins (SIRTs), are unique in that their function is directly related to the cell's metabolic state through their dependency on the co-factor NAD(+). In this study, we examined the relation between SIRTs and the growth, survival, and differentiation of K562 erythroleukemia cells. Using a mass spectrometry approach we previously developed, we show that SIRT expression and deacetylase activity in these cells changes greatly with differentiation state (undifferentiated vs. megakaryocytic differentiation vs. erythroid differentiation). Moreover, SIRT1 is crucially involved in regulating the differentiation state. Overexpression of wildtype (but not deacetylase mutant) SIRT1 resulted in upregulation of glycophorin A, ~2-fold increase in the mRNA levels of α, γ, ε, and ζ-globins, and spontaneous hemoglobinization. Hemin-induced differentiation was also enhanced by (and depended on) higher SIRT1 levels. Since K562 cells are bipotent, we also investigated whether SIRT1 modulation affected their ability to undergo megakaryocytic (MK) differentiation. SIRT1 was required for commitment to the MK lineage and subsequent maturation, but was not directly involved in polyploidization of either K562 cells or an already-MK-committed cell line, CHRF-288-11. The observed blockage in commitment to the MK lineage was associated with a dramatic decrease in the formation of autophagic vacuoles, which was previously shown to be required for K562 cell MK commitment. Autophagy-associated conversion of the protein LC3-I to LC3-II was greatly enhanced by overexpression of wildtype SIRT1, further suggesting a functional connection between SIRT1, autophagy, and MK differentiation. Based on its clear effects on autophagy, we also examined the effect of SIRT1 modulation on stress responses. Consistent with results of prior studies, we found that SIRT1 silencing modestly promoted drug-induced apoptosis, while overexpression was protective. Furthermore, pan-SIRT inhibition mediated by nicotinamide pre-treatment substantially increased imatinib-induced apoptosis. Altogether, our results suggest a complex role for SIRT1 in regulating many aspects of K562 cell state and stress response. These observations warrant further investigation using normal and leukemic primary cell models. We further suggest that, ultimately, a well-defined mapping of HDACs to their substrates and corresponding signaling pathways will be important for optimally designing HDACi-based therapeutic approaches.

Optimizing autologous cell grafts to improve stem cell gene therapy

Over the past decade, stem cell gene therapy has achieved unprecedented curative outcomes for several genetic disorders. Despite the unequivocal success, clinical gene therapy still faces challenges. Genetically engineered hematopoietic stem cells are particularly vulnerable to attenuation of their repopulating capacity once exposed to culture conditions, ultimately leading to low engraftment levels posttransplant. This becomes of particular importance when transduction rates are low or/and competitive transplant conditions are generated by reduced-intensity conditioning in the absence of a selective advantage of the transduced over the unmodified cells. These limitations could partially be overcome by introducing megadoses of genetically modified CD34(+) cells into conditioned patients or by transplanting hematopoietic stem cells hematopoietic stem cells with high engrafting and repopulating potential. On the basis of the lessons gained from cord blood transplantation, we summarize the most promising approaches to date of increasing either the numbers of hematopoietic stem cells for transplantation or/and their engraftability, as a platform toward the optimization of engineered stem cell grafts.

Progress and obstacles towards generating hematopoietic stem cells from pluripotent stem cells

PURPOSE OF REVIEW

Human pluripotent stem cells (PSCs) have the potential to provide an inexhaustible source of hematopoietic stem cells (HSCs) that could be used in disease modeling and in clinical applications such as transplantation. Although the goal of deriving definitive HSCs from PSCs has not been achieved, recent studies indicate that progress is being made. This review will provide information on the current status of deriving HSCs from PSCs, and will highlight existing challenges and obstacles.

RECENT FINDINGS

Recent strides in HSC generation from PSCs has included derivation of developmental intermediates, identification of transcription factors and small molecules that support hematopoietic derivation, and the development of strategies to recapitulate niche-like conditions.

SUMMARY

Despite considerable progress in defining the molecular events driving derivation of hematopoietic progenitor cells from PSCs, the generation of robust transplantable HSCs from PSCs remains elusive. We propose that this goal can be facilitated by better understanding of the regulatory pathways governing HSC identity, development of HSC supportive conditions, and examining the marrow homing properties of PSC-derived HSCs.

Methods of ex vivo expansion of human cord blood cells: challenges, successes and clinical implications

More than 40,000 unrelated cord blood transplantations (UCBT) have been performed worldwide as treatment for patients with malignant or non-malignant life threatening hematologic disorders. However, low absolute numbers of hematopoietic stem and progenitor cells (HSPCs) within a single cord blood unit has remained a limiting factor for this transplantation modality, particularly in adult recipients. Further, because UCB contains low numbers of mostly naïve T cells, immune recovery after UCBT is slow, predisposing patients to severe infections. Other causes of UCBT failure has included graft-versus-host disease (GVHD) and relapse of the underlying disease. In this article, we first review the current landscape of cord blood engineering aimed at improving engraftment. This includes approaches of UCB-HSPCs expansion and methods aimed at improving UCB-HSCPs homing. We then discuss recent approaches of cord blood engineering developed to prevent infection [generation of multivirus-specific cytotoxic T cells (VSTs) from UCB], relapse [transduction of UCB-T cells with tumor-specific chimeric receptor antigens (CARs)] and GVHD (expansion of regulatory T cells from UCB). Although many of these techniques of UCB engineering remain currently technically challenging and expensive, they are likely to revolutionize the field of UCBT in the next decades.

Increased Engraftment of Human Short Term Repopulating Hematopoietic Cells in NOD/SCID/IL2rγnull Mice by Lentiviral Expression of NUP98-HOXA10HD

Techniques to expand human hematopoietic stem cells ex-vivo could be beneficial to the fields of clinical hematopoietic stem cell transplantation and gene therapy targeted at hematopoietic stem cells. NUP98-HOXA10HD is a relatively newly discovered fusion gene that in mouse transplant experiments has been shown to increase numbers of hematopoietic stem cells. We evaluated whether this fusion gene could be used to expand engrafting human primitive CD34+ cells in an immunodeficient mouse model. Gene transfer was achieved using a lentiviral based vector. The engraftment of mobilized peripheral blood human CD34+ cells grown in culture for one week after gene transfer was evaluated 3–4 months after transplant and found to be 2–3 fold higher in the NUP98-HOXA10HD groups as compared to controls. These data suggest an expansive effect at least at the short term human repopulating cell level. Further evaluation in long term repopulating models and investment in a NUP98-HOXA10HD protein seems worthy of consideration. Additionally, the results here provide strong impetus to utilize NUP98-HOXA10HD as a tool to search for underlying genes and pathways involved in hematopoietic stem cell expansion that can be enhanced and have an even more potent expansive effect.

Cord blood transplant for acute myeloid leukaemia

Umbilical cord blood is a haematopoietic progenitor cell source for patients with acute myeloid leukaemia (AML), other haematological malignancies and metabolic diseases who can be cured by allogeneic haematopoietic cell transplantation, but who do not have a human leucocyte antigen compatible related or unrelated donor. Although the first cord blood transplants were done in children, there are currently more cord blood transplants performed in adults. In this review, we explore the history of umbilical cord blood transplantation, paediatric and adult outcome results, and novel trends to improve engraftment and reduce infection. Umbilical cord blood transplantation cures approximately 30-40% of adults and 60-70% of children with AML. Controversial issues, including the use of double versus single cord blood units for transplantation, optimal cord blood unit selection, infection prophylaxis, conditioning regimens and graft versus host disease prophylaxis, will be reviewed. Finally, comparison to other graft sources, cost, access to care, and the ideal graft source are discussed.

Hematopoietic stem cell expansion and generation: the ways to make a breakthrough

Hematopoietic stem cell transplantation (HSCT) is the first field where human stem cell therapy was successful. Flooding interest on human stem cell therapy to cure previously incurable diseases is largely indebted to HSCT success. Allogeneic HSCT has been an important modality to cure various diseases including hematologic malignancies, various non-malignant hematologic diseases, primary immunodeficiency diseases, and inborn errors of metabolism, while autologous HSCT is generally performed to rescue bone marrow aplasia following high-dose chemotherapy for solid tumors or multiple myeloma. Recently, HSCs are also spotlighted in the field of regenerative medicine for the amelioration of symptoms caused by neurodegenerative diseases, heart diseases, and others. Although the demand for HSCs has been growing, their supply often fails to meet the demand of the patients needing transplant due to a lack of histocompatible donors or a limited cell number. This review focuses on the generation and large-scale expansion of HSCs, which might overcome current limitations in the application of HSCs for clinical use. Furthermore, current proof of concept to replenish hematological homeostasis from non-hematological origin will be covered.

Novel Techniques for Ex Vivo Expansion of Cord Blood: Clinical Trials

Cord blood (CB) provides an excellent alternative source of hematopoietic progenitor cells (HPC) for patients lacking human leukocyte antigen-matched peripheral blood or bone marrow graft for transplantation. However, due to the limited cell dose in CB graft, it is associated with prolonged time to engraftment, risk of graft rejection, infections, and treatment-related mortality. To increase the cell dose, a variety of ex vivo expansion techniques have been developed. Results of traditional methods of CB expansion using cytokines alone were disappointing. Expanding CB cells with mesenchymal progenitor cells led to sizeable increase in graft content and improved engraftment. Other methods used HPC-differentiation blockers, such as nicotinamide analogs, copper chelators, inducing constitutive Notch signaling, or an aryl hydrocarbon receptor antagonist (StemReginin1). Many of these methods lead to substantial expansions of total nucleated cells and CD34(+) cells, and significantly improved time to neutrophil or platelet engraftment in patients transplanted with the expanded products compared to the recipients of unmanipulated CBT. These studies differ not only in the expansion method but also with regards to the cytokines used, patient population, conditioning regimens, and transplantation practices, to name a few. Some of these methods employed expansion of a portion of CB unit in the setting of single CBT, while others in the setting of double CBT. Here, we review various procedures used for CB expansion and highlight some of the key differences. Novel methods of improving engraftment that aim at improving bone marrow homing potential of CB cells are not reviewed.

Ex vivo expansion of hematopoietic stem cells

Ex vivo expansion of hematopoietic stem cells (HSCs) would benefit clinical applications in several aspects, to improve patient survival, utilize cord blood stem cells for adult applications, and selectively propagate stem cell populations after genetic manipulation. In this review we summarize and discuss recent advances in the culture systems of mouse and human HSCs, which include stroma/HSC co-culture, continuous perfusion and fed-batch cultures, and those supplemented with extrinsic ligands, membrane transportable transcription factors, complement components, protein modification enzymes, metabolites, or small molecule chemicals. Some of the expansion systems have been tested in clinical trials. The optimal condition for ex vivo expansion of the primitive and functional human HSCs is still under development. An improved understanding of the mechanisms for HSC cell fate determination and the HSC culture characteristics will guide development of new strategies to overcome difficulties. In the future, development of a combination treatment regimen with agents that enhance self-renewal, block differentiation, and improve homing will be critical. Methods to enhance yields and lower cost during collection and processing should be employed. The employment of an efficient system for ex vivo expansion of HSCs will facilitate the further development of novel strategies for cell and gene therapies including genome editing.

SIRT1 and Neural Cell Fate Determination

During the development of the central nervous system (CNS), neurons and glia are derived from multipotent neural stem cells (NSCs) undergoing self-renewal. NSC commitment and differentiation are tightly controlled by intrinsic and external regulatory mechanisms in space- and time-related fashions. SIRT1, a silent information regulator 2 (Sir2) ortholog, is expressed in several areas of the brain and has been reported to be involved in the self-renewal, multipotency, and fate determination of NSCs. Recent studies have highlighted the role of the deacetylase activity of SIRT1 in the determination of the final fate of NSCs. This review summarizes the roles of SIRT1 in the expansion and differentiation of NSCs, specification of neuronal subtypes and glial cells, and reprogramming of functional neurons from embryonic stem cells and fibroblasts. This review also discusses potential signaling pathways through which SIRT1 can exhibit versatile functions in NSCs to regulate the cell fate decisions of neurons and glia.

Improving the outcome of umbilical cord blood transplantation through ex vivo expansion or graft manipulation

The outcome of umbilical cord blood transplantation for adult patients with hematologic malignancies now rivals that of matched unrelated donor transplantation. However, relatively low lymphocyte and hematopoietic stem and progenitor cell dose is a source of significant morbidity and mortality. Multiple strategies are now being studied to overcome these limitations. One strategy involves ex vivo expansion of the umbilical cord blood unit before transplantation. Ex vivo expansion has the potential to increase the number of lymphocytes, committed progenitors and long-term repopulating hematopoietic stem cells. Increasing the numbers of lymphocytes and committed progenitor cells will address the issue of delayed hematopoietic recovery after umbilical cord blood transplantation. Increasing the hematopoietic stem cell content will improve the availability of adequately sized and matched cord blood units for transplantation. It may also eliminate the need for dual umbilical cord blood transplantation for those without an adequately sized single umbilical cord blood graft. The second strategy involves exposure of the umbilical cord blood graft to compounds aimed at improving homing and engraftment following transplantation. Such a strategy may also address the problem of slow hematopoietic recovery as well as the increased risk of graft failure. Many of these strategies are now being tested in late-phase multi-center clinical trials. If proven cost-effective and efficacious, they may alter the landscape of donor options for allogeneic stem cell transplantation.

No Synergistic Effect of Cotransplantation of MSC and Ex Vivo TPO-Expanded CD34(+) Cord Blood Cells on Platelet Recovery and Bone Marrow Engraftment in NOD SCID Mice

After cord blood (CB) transplantation, early platelet recovery in immune-deficient mice is obtained by expansion of CB CD34(+) cells with thrombopoietin (TPO) as single growth factor. Moreover, improvement of hematopoietic engraftment has been shown by cotransplantation of mesenchymal stem cells (MSC). We investigated whether a combination of both approaches would further enhance the outcome of CB transplantation in NOD SCID mice. NOD SCID mice were transplanted with either CB CD34(+) cells, CD34(+) cells with MSC, TPO-expanded CD34(+) cells or TPO-expanded CD34(+) cells with MSC. We analyzed human platelet recovery in the peripheral blood (PB) from day 4 after transplantation onward and human bone marrow (BM) engraftment at week 6. The different transplants were assessed in vitro for their migration capacity and expression of CXCR4. TPO expansion improved the early platelet recovery in the PB of the mice. Cotransplantation of MSC with CD34(+) cells improved BM engraftment and platelet levels in the PB 6 weeks after transplantation. Combining TPO expansion and MSC cotransplantation, however, neither resulted in a more efficient early platelet recovery, nor in a better BM engraftment, nor even very low or absent BM engraftment occurred. In vitro, MSC boosted the migration of CD34(+) cells, suggesting a possible mechanism for the increase in engraftment. Our results show that cotransplantation of MSC with TPO-expanded CD34(+) cells at most combines, but does not increase the separate advantages of these different strategies. A combination of both strategies even adds a risk of non engraftment.

Histone deacetylase III as a potential therapeutic target for the treatment of lethal sepsis

BACKGROUND

We have recently demonstrated that inhibition of histone deacetylase (HDAC) Class I, II, and IV with nonspecific HDAC inhibitors improves survival in a mouse model of lethal cecal ligation and puncture (CLP). However, the consequence of HDAC Class III inhibition is unknown in this model. The aims of the present study were to explore the effect of EX-527, a selective Sirtuin 1 (SIRT1) inhibitor, on survival in the lethal model of CLP-sepsis and to assess the impact of the treatment on inflammatory cytokine production, coagulopathy, and bone marrow atrophy during severe sepsis.

METHODS

For Experiment I, C57BL/6J mice were subjected to CLP and, 1 hour later, intraperitoneally injected with either EX-527 dissolved in dimethyl sulfoxide (DMSO) or DMSO only. Survival was monitored for 10 days. For Experiment II, 1 hour after CLP animals were randomly treated with (1) DMSO vehicle and (2) EX-527. Peritoneal fluid and blood samples were collected for measurement of cytokines, and blood was also used to evaluate coagulation status using thrombelastography. In addition, long bones (femurs and tibias) were examined to determine morphologic changes in the marrow by hematoxylin and eosin staining. For Experiment III, normal primary splenocytes were cultured and treated with lipopolysaccharide in the presence or absence of EX-527 to assess cytokine production.

RESULTS

EX-527 significantly improved survival (50% vs. 0% survival as compared to vehicle, p = 0.0007) and attenuated levels of cytokines tumor necrosis factor α and interleukin 6 in the blood and the peritoneal fluid compared with the vehicle control. It also decreased tumor necrosis factor α and interleukin 6 production by splenocytes in vitro. Selective inhibition of SIRT1 was associated with significant improvements in fibrin cross-linkage, platelet function, and clot rigidity but had no significant impact on the clot initiation parameters. Moreover, inhibition of SIRT1 was associated with a significant decrease in bone marrow atrophy.

CONCLUSION

Selective inhibition of Class III HDAC SIRT1 significantly improves survival, attenuates cytokine levels and sepsis-associated coagulopathy, and decreases bone marrow atrophy in a lethal mouse septic model.

Augmenting antitumor immune responses with epigenetic modifying agents

Epigenetic silencing of immune-related genes is a striking feature of the cancer genome that occurs in the process of tumorigenesis. This phenomena impacts antigen processing and antigen presentation by tumor cells and facilitates evasion of immunosurveillance. Further modulation of the tumor microenvironment by altered expression of immunosuppressive cytokines impairs antigen-presenting cells and cytolytic T-cell function. The potential reversal of immunosuppression by epigenetic modulation is therefore a promising and versatile therapeutic approach to reinstate endogenous immune recognition and tumor lysis. Pre-clinical studies have identified multiple elements of the immune system that can be modulated by epigenetic mechanisms and result in improved antigen presentation, effector T-cell function, and breakdown of suppressor mechanisms. Recent clinical studies are utilizing epigenetic therapies prior to, or in combination with, immune therapies to improve clinical outcomes.

Generation of a lentiviral vector producer cell clone for human Wiskott-Aldrich syndrome gene therapy

We have developed a producer cell line that generates lentiviral vector particles of high titer. The vector encodes the Wiskott-Aldrich syndrome (WAS) protein. An insulator element has been added to the long terminal repeats of the integrated vector to limit proto-oncogene activation. The vector provides high-level, stable expression of WAS protein in transduced murine and human hematopoietic cells. We have also developed a monoclonal antibody specific for intracellular WAS protein. This antibody has been used to monitor expression in blood and bone marrow cells after transfer into lineage negative bone marrow cells from WAS mice and in a WAS negative human B-cell line. Persistent expression of the transgene has been observed in transduced murine cells 12–20 weeks following transplantation. The producer cell line and the specific monoclonal antibody will facilitate the development of a clinical protocol for gene transfer into WAS protein deficient stem cells.

Expansion and homing of umbilical cord blood hematopoietic stem and progenitor cells for clinical transplantation

The successful expansion of hematopoietic stem and progenitor cells (HSPCs) from umbilical cord blood (UCB) for transplantation could revolutionize clinical practice by improving transplantation-related outcomes and making available UCB units that have suboptimal cell doses for transplantation. New cytokine combinations appear able to promote HSPC growth with minimal differentiation into mature precursors and new agents, such as insulin-like growth factor-binding protein 2, are being used in clinical trials. Molecules that simulate the HSPC niche, such as Notch ligand, have also shown promise. Further improvements have been made with the use of mesenchymal stromal cells, which have made possible UCB expansion without a potentially deleterious prior CD34/CD133 cell selection step. Chemical molecules, such as copper chelators, nicotinamide, and aryl hydrocarbon antagonists, have shown excellent outcomes in clinical studies. The use of bioreactors could further add to HSPC studies in future. Drugs that could improve HSPC homing also appear to have potential in improving engraftment times in UCB transplantation. Technologies to expand HSPC from UCB and to enhance the homing of these cells appear to have attained the goal of accelerating hematopoietic recovery. Further discoveries and clinical studies are likely to make the goal of true HSPC expansion a reality for many applications in future.

Advances in umbilical cord blood manipulation-from niche to bedside

The use of umbilical cord blood (UCB) as an alternative haematopoietic cell source in lieu of bone marrow for haematopoietic reconstitution is increasingly becoming a mainstay treatment for both malignant and nonmalignant diseases, as most individuals will have at least one available, suitably HLA-matched unit of blood. The principal limitation of UCB is the low and finite number of haematopoietic stem and progenitor cells (HSPC) relative to the number found in a typical bone marrow or mobilized peripheral blood allograft, which leads to prolonged engraftment times. In an attempt to overcome this obstacle, strategies that are often based on native processes occurring in the bone marrow microenvironment or 'niche' have been developed with the goal of accelerating UCB engraftment. In broad terms, the two main approaches have been either to expand UCB HSPC ex vivo before transplantation, or to modulate HSPC functionality to increase the efficiency of HSPC homing to the bone marrow niche after transplant both of which enhance the biological activities of the engrafted HSPC. Several early phase clinical trials of these approaches have reported promising results.

Background and future considerations for human cord blood hematopoietic cell transplantation, including economic concerns

Cord blood (CB) has been used since 1988 as a source of hematopoietic stem cells (HSCs) and progenitor cells for hematopoietic cell transplantation (HCT) to treat patients with malignant and nonmalignant disorders. CB has both advantages and disadvantages when compared with other tissue sources of HSCs such as bone marrow and mobilized peripheral blood, which are also being used in the setting of HCT. This short review focuses on some historical information, as well as current efforts that are being assessed to enhance the efficacy of CB HCT. Also of importance are the costs of CB, and the feasibility and economics of using such to be identified, and newly confirmed improvements worldwide for the greatest number of patients. In this context, simple methods that would not necessarily entail the need for selected cell-processing facilities to ex vivo expand or improve the CB graft's functional activity may be of interest, with one such possibility being the use of an orally active inhibitor of the enzyme dipeptidylpeptidase 4, alone or in combination with other new and innovative approaches for improving HSC engraftment and in vivo repopulating capability of CB.

Umbilical cord blood expansion with nicotinamide provides long-term multilineage engraftment

BACKGROUND

Delayed hematopoietic recovery is a major drawback of umbilical cord blood (UCB) transplantation. Transplantation of ex vivo-expanded UCB shortens time to hematopoietic recovery, but long-term, robust engraftment by the expanded unit has yet to be demonstrated. We tested the hypothesis that a UCB-derived cell product consisting of stem cells expanded for 21 days in the presence of nicotinamide and a noncultured T cell fraction (NiCord) can accelerate hematopoietic recovery and provide long-term engraftment.

METHODS

In a phase I trial, 11 adults with hematologic malignancies received myeloablative bone marrow conditioning followed by transplantation with NiCord and a second unmanipulated UCB unit. Safety, hematopoietic recovery, and donor engraftment were assessed and compared with historical controls.

RESULTS

No adverse events were attributable to the infusion of NiCord. Complete or partial neutrophil and T cell engraftment derived from NiCord was observed in 8 patients, and NiCord engraftment remained stable in all patients, with a median follow-up of 21 months. Two patients achieved long-term engraftment with the unmanipulated unit. Patients transplanted with NiCord achieved earlier median neutrophil recovery (13 vs. 25 days, P < 0.001) compared with that seen in historical controls. The 1-year overall and progression-free survival rates were 82% and 73%, respectively.

CONCLUSION

UCB-derived hematopoietic stem and progenitor cells expanded in the presence of nicotinamide and transplanted with a T cell-containing fraction contain both short-term and long-term repopulating cells. The results justify further study of NiCord transplantation as a single UCB graft. If long-term safety is confirmed, NiCord has the potential to broaden accessibility and reduce the toxicity of UCB transplantation.

TRIAL REGISTRATION

Clinicaltrials.gov NCT01221857.

FUNDING

Gamida Cell Ltd.

Enhancement in efferocytosis of oxidized low-density lipoprotein-induced apoptotic RAW264.7 cells through Sirt1-mediated autophagy

Macrophages play a key role in atherosclerotic plaque formation and rupture. These phagocytic cells are important in the scavenging of modified lipoproteins, unwanted or dead cells and cellular debris through efferocytosis. Sirtuin1 (Sirt1), a member of the conserved sirtuin family and a key regulator in the progression of atherosclerosis exerts protective effects by regulating autophagy, a well-known survival mechanism. Inhibition of autophagy may also result in defective efferocytosis. This study aimed to investigate the effect of Sirt1 on the efferocytosis of oxidized low-density lipoprotein (ox-LDL)-induced apoptotic RAW264.7 cells through upregulation of autophagy. The apoptotic cells were incubated with high and low concentrations of Sirt1 activator resveratrol (RSV) and Sirt1 inhibitor nicotinamide (NAM) as well as autophagy inhibitor 3-methyladenine (3-MA) + low concentration RSV. Apoptosis was determined by flow cytometry (FCM) of annexin-V/propidium iodide (AV/PI) dual staining. Total proteins were extracted and protein levels were detected through western blot analysis. The ox-LDL uptake and efferocytosis of apoptotic RAW264.7 cells were detected by oil red O staining and calculation of the phagocytic index of apoptotic RAW264.7 cells. The expression of Sirt1 and autophagy marker proteins was simultaneously increased with the stimulation of low concentration RSV (all P<0.05) and decreased in low and high NAM groups (all P<0.05), compared with the control group. Efferocytosis was highest in the low concentration RSV group (P<0.001) and relatively lower in the low and high concentration NAM groups (both P<0.05) compared with the control group, which was similar to the change in the expression of Sirt1 and autophagy marker proteins. The results showed that the efferocytosis of apoptotic RAW264.7 cells was significantly improved with the upregulation of Sirt1-mediated autophagy. Therefore, Sirt1 may serve as a novel therapeutic target for the treatment of atherosclerosis.

Profiling deacetylase activities in cell lysates with peptide arrays and SAMDI mass spectrometry

The development of arrays that can profile molecular activities in cells is important to understanding signaling pathways in normal and pathological settings. While oligonucleotide arrays are now routinely used to profile global gene expression, there is still a lack of tools for profiling enzyme activities in cell lysates. This paper describes the combination of peptide arrays formed on self-assembled monolayers and mass spectrometry to provide a label-free approach for identifying patterns of enzyme activities in cell lysates. The approach is demonstrated by profiling lysine deacetylase (KDAC) activities in cell lysates of the CHRF megakaryocytic (Mk) cell line. Class-specific deacetylase inhibitors were used to show that terminal Mk differentiation of CHRF cells is marked by a pronounced decrease in sirtuin activity and by little change in activity of KDACs 1-11. This work establishes a platform that can be used to identify changes in global activity profiles of cell lysates for a wide variety of enzymatic activities.

Sirt1 ablation promotes stress-induced loss of epigenetic and genomic hematopoietic stem and progenitor cell maintenance

Loss of Sirt1 causes increased Hoxa9 expression and expansion of HSPC subsets under hematopoietic stress, resulting in increased DNA damage and exhaustion of long-term progenitors.

The (histone) deacetylase Sirt1 is a mediator of genomic and epigenetic maintenance, both of which are critical aspects of stem cell homeostasis and tightly linked to their functional decline in aging and disease. We show that Sirt1 ablation in adult hematopoietic stem and progenitor cells (HSPCs) promotes aberrant HSPC expansion specifically under conditions of hematopoietic stress, which is associated with genomic instability as well as the accumulation of DNA damage and eventually results in a loss of long-term progenitors. We further demonstrate that progenitor cell expansion is mechanistically linked to the selective up-regulation of the HSPC maintenance factor and polycomb target gene Hoxa9. We show that Sirt1 binds to the Hoxa9 gene, counteracts acetylation of its histone target H4 lysine 16, and in turn promotes polycomb-specific repressive histone modification. Together, these findings demonstrate a dual role for Sirt1 in HSPC homeostasis, both via epigenetic regulation of a key developmental gene and by promoting genome stability in adult stem cells.

Administration of nicotinamide does not increase platelet levels in mice

Elucidating ways to enhance megakaryopoiesis in vivo would have therapeutic applications for thrombocytopenia and transfusion medicine. Nicotinamide has been shown to enhance endomitosis in megakaryocytes cultured in vitro, suggesting that it may be beneficial for the production of platelets in culture. We hypothesized that regular injections of nicotinamide in mice would also increase platelets in vivo. However, we found that platelet counts were reduced by about 25% with daily injections of nicotinamide. Altering the schedule, duration, or nicotinamide dose did not improve platelet production. Consistent with lower platelet levels, nicotinamide also tended to decrease megakaryocyte frequency in sternum and spleen sections, as well as colony formation in vitro by bone marrow progenitor cells. However, there was no effect on the fraction or ploidy of CD41(+) cells harvested from bone marrow. Together, our results suggest that, although nicotinamide increases polyploidization of megakaryocytes in culture, it does not have translatable effects in vivo.

Development of gene therapy for thalassemia

Retroviral vector-mediated gene transfer into hematopoietic stem cells provides a potentially curative therapy for severe β-thalassemia. Lentiviral vectors based on human immunodeficiency virus have been developed for this purpose and have been shown to be effective in curing thalassemia in mouse models. One participant in an ongoing clinical trial has achieved transfusion independence after gene transfer into bone marrow stem cells owing, in part, to a genetically modified, dominant clone. Ongoing efforts are focused on improving the efficiency of lentiviral vector-mediated gene transfer into stem cells so that the curative potential of gene transfer can be consistently achieved.

Umbilical cord blood graft enhancement strategies: has the time come to move these into the clinic?

Umbilical cord blood (UCB) is an attractive stem cell graft option for patients who need allogeneic hematopoietic stem cell support, but lack a suitable HLA-matched donor. However, the limited number of hematopoietic progenitor cells in a single cord blood unit can lead to an increased risk of graft failure, delayed hematological recovery and prolonged immunosuppression, particularly in adult patients. Several strategies to overcome these potential limitations are being evaluated. In this review, we discuss promising ex vivo manipulations to enhance cord blood engraftment capacity such as culture of UCB cells with stimulatory cytokines and growth factors, mesenchymal cells, Notch ligand, copper chelators, prostaglandins, complement components, nicotinamide and CD26/DPPIV inhibitors. All these approaches are now in early clinical trials. However, despite the fact that several cord blood enhancement strategies have resulted in increased numbers of progenitor cells and faster neutrophil recovery, the ability of these techniques to significantly shorten engraftment time and permit the use of cord units with low numbers of total nucleated cells, or accomplish reliable engraftment with a single cord, have yet to be convincingly demonstrated. The ultimate clinical value of ex vivo cord blood expansion or manipulation has not been defined yet, and the current data do not permit predicting which technology will prove to be the optimal strategy. Nevertheless, expectations remain high that eventually ex vivo enhancement will be able to improve clinical outcomes and significantly extend the applicability of UCB transplantation.