Ex vivo expanded hematopoietic stem cells overcome the MHC barrier in allogeneic transplantation

Ex vivo expansion of hematopoietic stem cells

Hematopoietic stem cells (HSCs) are multipotent progenitor cells that can differentiate into various mature blood cells and immune cells, thus reconstituting hematopoiesis. By taking advantage of the tremendous potential of HSCs, varied hereditary and hematologic diseases are promised to be alleviated or cured. To solve the contradiction between the growing demand for HSCs in disease treatment and the low population of HSCs in both cord blood and bone marrow, ex vivo HSC expansion along with multiple protocols has been investigated for harvesting adequate HSCs over the past two decades. This review surveys the state-of-the-art techniques for ex vivo HSC self-renewal and provides a concise summary of the effects of diverse intrinsic and extrinsic factors on the expansion of HSCs. The remaining challenges and emerging opportunities in the field of HSC expansion are also presented.

Immune System Influence on Hematopoietic Stem Cells and Leukemia Development

Hematopoietic stem cells (HSCs) are the source for all blood cells, including immune cells, and they interact dynamically with the immune system. This chapter will explore the nature of stem cells, particularly HSCs, in the context of their immune microenvironment. The dynamic interactions between stem cells and the immune system can have profound implications for current and future therapies, particularly regarding a potential "immune-privileged" HSC microenvironment. Immune/stem cell interactions change during times of stress and injury. Recent advances in cancer immunotherapy have overturned the long-standing belief that, being derived from the self, cancer cells should be immunotolerant. Instead, an immunosurveillance system recognizes and eliminates emergent pre-cancerous cells. Only in the context of a failing immunosurveillance system does cancer fully develop. Combined with the knowledge that stem cells or their unique properties can be critically important for cancer initiation, persistence, and resistance to therapy, understanding the unique immune properties of stem cells will be critical for the development of future cancer therapies. Accordingly, the therapeutic implications for leukemic stem cells (LSCs) inheriting an immune-privileged state from HSCs will be discussed. Through their dynamic interactions with a diverse immune system, stem cells serve as the light and dark root of cancer prevention vs. development.

Blocking LAIR1 signaling in immune cells inhibits tumor development

The current immune checkpoint blockade therapy has been successful in treating some cancers but not others. New molecular targets and therapeutic approaches of cancer immunology need to be identified. Leukocyte associated immunoglobulin like receptor 1 (LAIR1) is an immune inhibitory receptor expressing on most immune cell types. However, it remains a question whether we can specifically and actively block LAIR1 signaling to activate immune responses for cancer treatment. Here we report the development of specific antagonistic anti-LAIR1 monoclonal antibodies and studied the effects of LAIR1 blockade on the anti-tumor immune functions. The anti-LAIR1 antagonistic antibody stimulated the activities of T cells, natural killer cells, macrophages, and dendritic cells in vitro. The single-cell RNA sequencing analysis of intratumoral immune cells in syngeneic human LAIR1 transgenic mice treated with control or anti-LAIR1 antagonist antibodies indicates that LAIR1 signaling blockade increased the numbers of CD4 memory T cells and inflammatory macrophages, but decreased those of pro-tumor macrophages, regulatory T cells, and plasmacytoid dendritic cells. Importantly, the LAIR1 blockade by the antagonistic antibody inhibited the activity of immunosuppressive myeloid cells and reactivated T cells from cancer patients in vitro and impeded tumor metastasis in a humanized mouse model. Blocking LAIR1 signaling in immune cells represents a promising strategy for development of anti-cancer immunotherapy.

Development of a novel and synthetic HematoMiR technology that broadly modulates quiescence of stem cells and enhances HSC expansion

Hematopoietic stem cell (HSCs) transplantation is the primary therapeutic modality used to treat hematopoietic disorders. It centers on the capability of a small quantity of HSCs to repopulate whole blood lineages. Along with limited availability of suitable donors, the need for sufficient number of donor HSCs is still challenging in clinical relevance. This has been addressed by ex vivo HSC expansion albeit with partial success, and thus development of an alternative strategy that could improve HSC expansion is required. To that end, we aimed to build HematoMiR, an oligo-based technology that broadly targets HSC quiescence factors. Here, we show that HematoMiRs and their combinations targeting over 50 factors involved in HSC quiescence could induce robust ex vivo murine and human HSC expansion. In particular, HematoMiR-5 treatment enhanced cell cycle through down-regulation of negative cell cycle regulators in HSCs. HematoMiR-5 treated HSPCs had reduced DNA damage during the course of ex vivo expansion. Moreover, HematoMiR-5 treatment led to sustained HSC self-renewal ability and a low apoptosis rate. In addition, HematoMiR-5 expanded HSCs demonstrated successful engraftment and repopulation capacity in the recipient animals. Furthermore, combinatorial treatments of HematoMiR-2 and 5 allowed vigorous ex vivo HSC expansion. These findings demonstrate that novel and synthetic HematoMiR technology is feasible for HSC ex vivo expansion through the sequence-dependent modulation of numerous HSC quiescence modulators.

Induced cell-autonomous neutropenia systemically perturbs hematopoiesis in Cebpa enhancer-null mice

The transcription factor C/EBPa initiates the neutrophil gene expression program in the bone marrow. Knockouts of the Cebpa gene or its +37kb enhancer in mice show two major findings: (1) neutropenia in bone marrow and blood; (2) decrease in long-term hematopoietic stem cell (LT-HSC) numbers. Whether the latter finding is cell autonomous (intrinsic) to the LT-HSCs or an extrinsic event exerted on the stem cell compartment remained an open question. Flow cytometric analysis of the Cebpa +37kb enhancer knockout model revealed that the reduction in LT-HSC numbers observed was proportional to the degree of neutropenia. Single cell transcriptomics of wild type mouse bone marrow showed that Cebpa is predominantly expressed in early myeloid-biased progenitors, but not in LT-HSCs. These observations suggest that the negative effect on LT-HSCs is an extrinsic event caused by neutropenia. We transplanted whole bone marrows from +37kb enhancer deleted mice and found that 40% of the recipient mice acquired full blown neutropenia with severe dysplasia and a significant reduction in the total LT-HSC population. The other 60% showed initial signs of myeloid differentiation defects and dysplasia when they were sacrificed, suggesting they were in an early stage of the same pathological process. This phenotype was not seen in mice transplanted with wild type bone marrow cells. Altogether, these results indicate that Cebpa-enhancer deletion causes cell autonomous neutropenia, which reprograms and disturbs the quiescence of HSCs, leading to a systemic impairment of the hematopoietic process.

Nature or Nurture? Role of the Bone Marrow Microenvironment in the Genesis and Maintenance of Myelodysplastic Syndromes

Myelodysplastic syndrome (MDS) are clonal haematopoietic stem cell (HSC) disorders driven by a complex combination(s) of changes within the genome that result in heterogeneity in both clinical phenotype and disease outcomes. MDS is among the most common of the haematological cancers and its incidence markedly increases with age. Currently available treatments have limited success, with <5% of patients undergoing allogeneic HSC transplantation, a procedure that offers the only possible cure. Critical contributions of the bone marrow microenvironment to the MDS have recently been investigated. Although the better understanding of the underlying biology, particularly genetics of haematopoietic stem cells, has led to better disease and risk classification; however, the role that the bone marrow microenvironment plays in the development of MDS remains largely unclear. This review provides a comprehensive overview of the latest developments in understanding the aetiology of MDS, particularly focussing on understanding how HSCs and the surrounding immune/non-immune bone marrow niche interacts together.

Membrane protein CAR promotes hematopoietic regeneration upon stress

Adult hematopoietic stem cells (HSC) are quiescent most of the time, and how HSC switch from quiescence to proliferation following hematopoietic stress is unclear. Here we demonstrate that upon stress the coxsackievirus and adenovirus receptor CAR (also known as CXADR) is upregulated in HSC and critical for HSC entry into the cell cycle. Wild-type HSC were detected with more rapid repopulation ability than the CAR knockout counterparts. After fluorouracil treatment, CAR knockout HSC had lower levels of Notch1 expression and elevated protein level of Numb, a Notch antagonist. The Notch signaling inhibitor DAPT, dominant negative form of MAML (a transcriptional coactivator of Notch), or dominant negative mutant of LNX2 (an E3 ligase that acts on Numb and binds to CAR), all were capable of abrogating the function of CAR in HSC. We conclude that CAR activates Notch1 signaling by downregulating Numb protein expression to facilitate entry of quiescent HSC into the cell cycle during regeneration.

The Role of Hypoxic Bone Marrow Microenvironment in Acute Myeloid Leukemia and Future Therapeutic Opportunities

Acute myeloid leukemia (AML) is a hematologic malignancy caused by a wide range of alterations responsible for a high grade of heterogeneity among patients. Several studies have demonstrated that the hypoxic bone marrow microenvironment (BMM) plays a crucial role in AML pathogenesis and therapy response. This review article summarizes the current literature regarding the effects of the dynamic crosstalk between leukemic stem cells (LSCs) and hypoxic BMM. The interaction between LSCs and hypoxic BMM regulates fundamental cell fate decisions, including survival, self-renewal, and proliferation capacity as a consequence of genetic, transcriptional, and metabolic adaptation of LSCs mediated by hypoxia-inducible factors (HIFs). HIF-1α and some of their targets have been associated with poor prognosis in AML. It has been demonstrated that the hypoxic BMM creates a protective niche that mediates resistance to therapy. Therefore, we also highlight how hypoxia hallmarks might be targeted in the future to hit the leukemic population to improve AML patient outcomes.

Hematopoietic stem and progenitor cells directly participate in host immune response

The properties of hematopoietic stem and progenitor cells (HSPCs), including self-renewal and pluripotency, have been extensively studied. These features have been explored in the management of several haematological disorders and malignancies. Although their role as precursors of innate immune cells is well understood, little is known about their direct participation in host immune response. In this review, we explicate the direct role of HSPCs in the host immune response and highlight therapeutic options for the infectious disease burden that is currently ravaging the world, including COVID-19.

Overcoming resistance to immunotherapy by teaching old drugs new tricks

Cancer stem cells (CSCs) underlie resistance to therapy. Cancer develops only in the context of failing immunosurveillance, and stem cells occupy immune privileged microenvironments. Recent evidence demonstrates that CSCs borrow immune privilege from their normal counterparts. However, low doses of doxorubicin can target CSCs by restoring anticancer immunity.

A novel murine model of differentiation-mediated cytomegalovirus reactivation from latently infected bone marrow haematopoietic cells

CD34+ myeloid lineage progenitor cells are an important reservoir of latent human cytomegalovirus (HCMV), and differentiation to macrophages or dendritic cells (DCs) is known to cause reactivation of latent virus. Due to its species-specificity, murine models have been used to study mouse CMV (MCMV) latency and reactivation in vivo. While previous studies have shown that MCMV genomic DNA can be detected in the bone marrow (BM) of latently infected mice, the identity of these cells has not been defined. Therefore, we sought to identify and enrich for cellular sites of MCMV latency in the BM haematopoietic system, and to explore the potential for establishing an in vitro model for reactivation of latent MCMV. We studied the kinetics and cellular characteristics of acute infection and establishment of latency in the BM of mice. We found that while MCMV can infect a broad range of haematopoietic BM cells (BMCs), latent virus is only detectable in haematopoietic stem cells (HSCs), myeloid progenitor cells, monocytes and DC-enriched cell subsets. Using three separate approaches, MCMV reactivation was detected in association with differentiation into DC-enriched BMCs cultured in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 4 (IL-4) followed by lipopolysaccharide (LPS) treatment. In summary, we have defined the kinetics and cellular profile of MCMV infection followed by the natural establishment of latency in vivo in the mouse BM haematopoietic system, including the haematopoietic phenotypes of cells that are permissive to acute infection, establish and harbour detectable latent virus, and can be stimulated to reactivate following DC enrichment and differentiation, followed by treatment with LPS.

Development of Small Molecule MEIS Inhibitors that modulate HSC activity

Meis1, which belongs to TALE-type class of homeobox gene family, appeared as one of the key regulators of hematopoietic stem cell (HSC) self-renewal and a potential therapeutical target. However, small molecule inhibitors of MEIS1 remained unknown. This led us to develop inhibitors of MEIS1 that could modulate HSC activity. To this end, we have established a library of relevant homeobox family inhibitors and developed a high-throughput in silico screening strategy against homeodomain of MEIS proteins using the AutoDock Vina and PaDEL-ADV platform. We have screened over a million druggable small molecules in silico and selected putative MEIS inhibitors (MEISi) with no predicted cytotoxicity or cardiotoxicity. This was followed by in vitro validation of putative MEIS inhibitors using MEIS dependent luciferase reporter assays and analysis in the ex vivo HSC assays. We have shown that small molecules named MEISi-1 and MEISi-2 significantly inhibit MEIS-luciferase reporters in vitro and induce murine (LSKCD34^l°^w cells) and human (CD34⁺, CD133⁺, and ALDH^hi cells) HSC self-renewal ex vivo. In addition, inhibition of MEIS proteins results in downregulation of Meis1 and MEIS1 target gene expression including Hif-1α, Hif-2α and HSC quiescence modulators. MEIS inhibitors are effective in vivo as evident by induced HSC content in the murine bone marrow and downregulation of expression of MEIS target genes. These studies warrant identification of first-in-class MEIS inhibitors as potential pharmaceuticals to be utilized in modulation of HSC activity and bone marrow transplantation studies.

c-Myc Inhibitor 10074-G5 Induces Murine and Human Hematopoietic Stem and Progenitor Cell Expansion and HDR Modulator Rad51 Expression

Background:

c-Myc plays a major role in the maintenance of glycolytic metabolism and hematopoietic stem cell (HSC) quiescence.

Objective:

Targeting modulators of HSC quiescence and metabolism could lead to HSC cell cycle entry with concomitant expansion.

Methods and Results:

Here we show that c-Myc inhibitor 10074-G5 treatment leads to 2-fold increase in murine LSKCD34low HSC compartment post 7 days. In addition, c-Myc inhibition increases CD34+ and CD133+ human HSC number. c-Myc inhibition leads to downregulation of glycolytic and cyclindependent kinase inhibitor (CDKI) gene expression ex vivo and in vivo. In addition, c-Myc inhibition upregulates major HDR modulator Rad51 expression in hematopoietic cells. Besides, c-Myc inhibition does not alter proliferation kinetics of endothelial cells, fibroblasts or adipose-derived mesenchymal stem cells, however, it limits bone marrow derived mesenchymal stem cell proliferation. We further demonstrate that a cocktail of c-Myc inhibitor 10074-G5 along with tauroursodeoxycholic acid (TUDCA) and i-NOS inhibitor L-NIL provides a robust HSC maintenance and expansion ex vivo as evident by induction of all stem cell antigens analyzed. Intriguingly, the cocktail of c-Myc inhibitor 10074-G5, TUDCA and L-NIL improves HDR related gene expression.

Conclusion:

These findings provide tools to improve ex vivo HSC maintenance and expansion, autologous HSC transplantation and gene editing through modulation of HSC glycolytic and HDR pathways.

TNF-α Coordinates Hematopoietic Stem Cell Survival and Myeloid Regeneration

Inflammation coordinates tissue regeneration via damaged cell removal and stem cell activation. Hematopoietic stem cells (HSCs) survive inflammatory stress that kills other blood cells, but the mechanisms underlying this effect remain poorly understood. Here, we find that tumor necrosis factor α (TNF-α) acts differently on HSCs and progenitors, thus facilitating hematopoietic clearance and promoting regeneration. We show that while inducing myeloid progenitor apoptosis, TNF-α promotes HSC survival and myeloid differentiation by activating a strong and specific p65-nuclear factor κB (NF-κB)-dependent gene program that primarily prevents necroptosis rather than apoptosis, induces immunomodulatory functions, and poises HSCs for myeloid cell production. These TNF-α-driven mechanisms are critical for HSC response to inflammatory stress but are also hijacked in aged and malignant HSCs. Our results reveal several TNF-α-mediated pro-survival mechanisms unique to HSCs, highlight an important role for necroptosis in HSC killing, and establish TNF-α as a major pro-survival and pro-regeneration factor for HSCs.

Isolation of Murine Hematopoietic Stem Cells

Bone marrow resident hematopoietic stem cells (HSCs) are responsible for the lifetime generation of the wide profusion of blood and immune cell types found in the body. In addition, therapeutically, in the context of bone marrow transplantation, HSCs have been successfully deployed to restore normal blood-forming capacity in patients being treated with high-dose chemotherapy for hematologic malignancies. The known ability of bone marrow transplantation to either restore or reset the immune system and to engender immune tolerance has suggested that HSCs may be applied therapeutically for a wider range of clinical conditions, including immunological/autoimmune disorders and allogeneic organ transplantation. Herein, we describe a flow-cytometry-based method to isolate mouse HSCs for continued experimental investigation into such therapeutic uses.

LILRB4 signalling in leukaemia cells mediates T cell suppression and tumour infiltration

Immune checkpoint blockade therapy has been successful in treating some types of cancer but has not shown clinical benefits for treating leukaemia1. This result suggests that leukaemia uses unique mechanisms to evade this therapy. Certain immune inhibitory receptors that are expressed by normal immune cells are also present on leukaemia cells. Whether these receptors can initiate immune-related primary signalling in tumour cells remains unknown. Here we use mouse models and human cells to show that LILRB4, an immunoreceptor tyrosine-based inhibition motif-containing receptor and a marker of monocytic leukaemia, supports tumour cell infiltration into tissues and suppresses T cell activity via a signalling pathway that involves APOE, LILRB4, SHP-2, uPAR and ARG1 in acute myeloid leukaemia (AML) cells. Deletion of LILRB4 or the use of antibodies to block LILRB4 signalling impeded AML development. Thus, LILRB4 orchestrates tumour invasion pathways in monocytic leukaemia cells by creating an immunosuppressive microenvironment. LILRB4 represents a compelling target for the treatment of monocytic AML.

Prostaglandin E2 Stimulates the Expansion of Regulatory Hematopoietic Stem and Progenitor Cells in Type 1 Diabetes

Hematopoietic stem and progenitor cells (HSPCs) are multipotent stem cells that have been harnessed as a curative therapy for patients with hematological malignancies. Notably, the discovery that HSPCs are endowed with immunoregulatory properties suggests that HSPC-based therapeutic approaches may be used to treat autoimmune diseases. Indeed, infusion with HSPCs has shown promising results in the treatment of type 1 diabetes (T1D) and remains the only “experimental therapy” that has achieved a satisfactory rate of remission (nearly 60%) in T1D. Patients with newly diagnosed T1D have been successfully reverted to normoglycemia by administration of autologous HSPCs in association with a non-myeloablative immunosuppressive regimen. However, this approach is hampered by a high incidence of adverse effects linked to immunosuppression. Herein, we report that while the use of autologous HSPCs is capable of improving C-peptide production in patients with T1D, ex vivo modulation of HSPCs with prostaglandins (PGs) increases their immunoregulatory properties by upregulating expression of the immune checkpoint-signaling molecule PD-L1. Surprisingly, CXCR4 was upregulated as well, which could enhance HSPC trafficking toward the inflamed pancreatic zone. When tested in murine and human in vitro autoimmune assays, PG-modulated HSPCs were shown to abrogate the autoreactive T cell response. The use of PG-modulated HSPCs may thus provide an attractive and novel treatment of autoimmune diabetes.

PD-L1 Expression on Circulating CD34＋ Hematopoietic Stem Cells Closely Correlated with T-cell Apoptosis in Chronic Hepatitis C Infected Patients

Background and Objectives

Lack of understanding of the interplay between hematopoietic stem cells (HSCs) and the immune system has severely hampered stem cell research. Programmed death-1 (PD-L1) has been reported on parenchymal cells in patients with chronically inflamed livers and found to play an essential role in T cell homeostasis regulation. However, the bidirectional interaction between HSCs and lymphocytes remains elusive. Here, we aimed to get more insight into circulating CD34+ HSCs PD-L1 expression and T cell apoptosis in chronic HCV infected patients.

Methods

CD34+ HSCs were isolated and purified by immunomagnetic separation. PD-L1 expression was analyzed by quantitative PCR and flow cytometry. Furthermore, co-culture experiments between CD34+ HSCs and T-lymphocytes were established. T-cell lymphocyte apoptosis in peripheral blood and in cultures was detected.

Results

CD34+ HSCs constitutively express low levels of PD-L1. Its expression is up-regulated in chronic HCV infected patients. Moreover, PD-L1 expression on circulating CD34+ HSCs enhanced T cell apoptosis in peripheral blood and co-culture.

Conclusion

Our results suggest novel bidirectional interplay between HSCs and lymphocytes mediated by PD-L1 expression on CD34+ HSCs. PD-L1 expression correlated with T-cell lymphocyte apoptosis. This may contribute to immunomodulatory properties of HSCs which improves its use for allogeneic transplantation.

SHP-1 regulates hematopoietic stem cell quiescence by coordinating TGF-β signaling

Cell cycle quiescence is critical for hematopoietic stem cell (HSC) maintenance. TGF-β signaling in bone marrow niche has been identified in regulating HSC quiescence; however, the intrinsic regulatory mechanisms remain unclear. This study reports that Shp-1 knockout HSCs have attenuated quiescence and impaired long-term self-renewal. SHP-1-activated HSCs are surrounded by megakaryocytes, which regulate HSC quiescence by producing TGF-β1. Mechanistically, SHP-1 interacts with the immunoreceptor tyrosine-based inhibition motif on TGF-β receptor 1 and is critical for TGF-β signaling activation in HSCs. Functionally, Shp-1 knockout HSCs do not respond to TGF-β-enforced HSC quiescence regulation, both in vitro and in vivo. Therefore, we identify TGF-β-SHP-1 as a novel intrinsic regulatory mechanism for HSC quiescence maintenance.

CAMKs support development of acute myeloid leukemia

Background

We recently identified the human leukocyte immunoglobulin-like receptor B2 (LILRB2) and its mouse ortholog-paired Ig-like receptor (PirB) as receptors for several angiopoietin-like proteins (Angptls). We also demonstrated that PirB is important for the development of acute myeloid leukemia (AML), but exactly how an inhibitory receptor such as PirB can support cancer development is intriguing.

Results

Here, we showed that the activation of Ca (2+)/calmodulin-dependent protein kinases (CAMKs) is coupled with PirB signaling in AML cells. High expression of CAMKs is associated with a poor overall survival probability in patients with AML. Knockdown of CAMKI or CAMKIV decreased human acute leukemia development in vitro and in vivo. Mouse AML cells that are defective in PirB signaling had decreased activation of CAMKs, and the forced expression of CAMK partially rescued the PirB-defective phenotype in the MLL-AF9 AML mouse model. The inhibition of CAMK kinase activity or deletion of CAMKIV significantly slowed AML development and decreased the AML stem cell activity. We also found that CAMKIV acts through the phosphorylation of one of its well-known target (CREB) in AML cells.

Conclusion

CAMKs are essential for the growth of human and mouse AML. The inhibition of CAMK signaling may become an effective strategy for treating leukemia.

Electronic supplementary material

The online version of this article (10.1186/s13045-018-0574-8) contains supplementary material, which is available to authorized users.

Maturation of hematopoietic stem cells from prehematopoietic stem cells is accompanied by up-regulation of PD-L1

Tober et al. show that hematopoietic stem cells (HSCs) that mature from pre-HSCs in vivo in the fetal liver, versus ex vivo, are not molecularly equivalent. Although both express cell surface programmed death ligand 1 (PD-L1), it is not required for the engraftment of fetal HSCs into adult recipients.

Hematopoietic stem cells (HSCs) mature from pre-HSCs that originate in the major arteries of the embryo. To identify HSCs from in vitro sources, it will be necessary to refine markers of HSCs matured ex vivo. We purified and compared the transcriptomes of pre-HSCs, HSCs matured ex vivo, and fetal liver HSCs. We found that HSC maturation in vivo or ex vivo is accompanied by the down-regulation of genes involved in embryonic development and vasculogenesis, and up-regulation of genes involved in hematopoietic organ development, lymphoid development, and immune responses. Ex vivo matured HSCs more closely resemble fetal liver HSCs than pre-HSCs, but are not their molecular equivalents. We show that ex vivo–matured and fetal liver HSCs express programmed death ligand 1 (PD-L1). PD-L1 does not mark all pre-HSCs, but cell surface PD-L1 was present on HSCs matured ex vivo. PD-L1 signaling is not required for engraftment of embryonic HSCs. Hence, up-regulation of PD-L1 is a correlate of, but not a requirement for, HSC maturation.

Sickle cells produce functional immune modulators and cytotoxics

Sickle erythrocytes' (SSRBCs) unique physical adaptation to hypoxic conditions renders them able to home to hypoxic tumor niches in vivo, shut down tumor blood flow and induce tumoricidal responses. SSRBCs are also useful vehicles for transport of encapsulated drugs and oncolytic virus into hypoxic tumors with enhanced anti-tumor effects. In search of additional modes for arming sickle cells with cytotoxics, we turned to a lentiviral β-globin vector with optimized Locus Control Region/β-globin coding region/promoter/enhancers. We partially replaced the β-globin coding region of this vector with genes encoding T cell cytolytics, perforin and granzyme or immune modulating superantigens SEG and SEI. These modified vectors efficiently transduced Sca⁺ ckit^- Lin^- hematopoietic stem cells (HSCs) from humanized sickle cell knockin mice. Irradiated mice reconstituted with these HSCs displayed robust expression of transgenic RNAs and proteins in host sickle cells that was sustained for more than 10 months. SSRBCs from reconstituted mice harboring SEG/SEI transgenes induced robust proliferation and a prototypical superantigen-induced cytokine reaction when exposed to human CD4+/CD8+ cells. The β-globin lentiviral vector therefore produces a high level of functional, erythroid-specific immune modulators and cytotoxics that circulate without toxicity. Coupled with their unique ability to target and occlude hypoxic tumor vessels these armed SSRBCs constitute a potentially useful tool for treatment of solid tumors.

Evaluation of proinflammatory and immunosuppressive cytokines in blood and bone marrow of healthy hematopoietic stem cell donors

INTRODUCTION

Cytokine composition of bone marrow microenvironment in comparison to blood is poorly explored. The goal of this study was to investigate the levels of cytokines present in peripheral blood and bone marrow of healthy hematopoietic stem cells donors. The data obtained on this subject with addition to cytometric analysis can provide new insight into the hematopoietic stem cells microenvironment.

METHODOLOGY

Study consisted of cytokine concentration analysis performed by ELISA tests of peripheral blood of healthy peripheral blood stem cells donors and bone marrow of healthy bone marrow donors. Additionally we have tested the expression of CD47 and CD274 proteins on the surface of hematopoietic stem cells by the flow cytometry analysis.

RESULTS

The results has shown different composition of analyzed cytokines (IL-1 β, IL-2, IL-4, IL-6, IL-10, IL-17A, TGF-β1, IFN-γ and TNF-α) present in bone marrow and blood of stem cells donors. The hematopoietic stem cells in peripheral blood are subjected to higher levels of proinflammatory cytokines whilst the lower level of those cytokines in bone marrow with a very high level of TGF-β1 which possibly creates a more immunosuppressive environment. The IL-10 level was significantly higher in peripheral blood of PBSC donors after the administration of mobilizing factor (G-CSF). The percentage of CD47+HSCs was significantly higher in bone marrow compared to peripheral blood of mobilized donors.

Inhibitory Effect of Mesenchymal Stem Cell Co-Culture on Erythroid Differentiation of K562 Cells Compared to The Control Group

OBJECTIVE

Bone marrow mesenchymal stem cells (BMMSCs) reside in the bone marrow and control the process of hematopoiesis. They are an excellent instrument for regenerative treatment and co-culture with hematopoietic stem cells (HSCs).

MATERIALS AND METHODS

In this experimental study, K562 cell lines were either treated with butyric acid and co-cultured with MSCs, or cultivated in a conditioned medium from MSCs plus butyric acid for erythroid differentiation. We used the trypan blue dye exclusion assay to determine cell counts and viability in each group. For each group, we separately assessed erythroid differentiation of the K562 cell line with Giemsa stain under light microscopy, expression of specific markers of erythroid cells by flowcytometry, and erythroidspecific gene expressions by real-time polymerase chain reaction (RT-PCR).

RESULTS

There was enhandced erythroid differentiation of K562 cells with butyric acid compared to the K562 cell line co-cultured with MSCs and butyric acid. Erythroid differentiation of the K562 cell line cultivated in conditioned medium with butyric acid was higher than the K562 cell line co-cultured with MSCs and butyric acid, but less than K562 cell line treated with butyric acid only.

CONCLUSION

Our results showed that MSCs significantly suppressed erythropoiesis. Therefore, MSCs would not be a suitable optimal treatment strategy for patients with erythroid leukemia.

Fasting selectively blocks development of acute lymphoblastic leukemia via leptin-receptor upregulation

New therapeutic approaches are needed to treat leukemia effectively. Dietary restriction regimens, including fasting, have been considered for the prevention and treatment of certain solid tumor types. However, whether and how dietary restriction affects hematopoietic malignancies is unknown. Here we report that fasting alone robustly inhibits the initiation and reverses the leukemic progression of both B cell and T cell acute lymphoblastic leukemia (B-ALL and T-ALL, respectively), but not acute myeloid leukemia (AML), in mouse models of these tumors. Mechanistically, we found that attenuated leptin-receptor (LEPR) expression is essential for the development and maintenance of ALL, and that fasting inhibits ALL development by upregulation of LEPR and its downstream signaling through the protein PR/SET domain 1 (PRDM1). The expression of LEPR signaling-related genes correlated with the prognosis of pediatric patients with pre-B-ALL, and fasting effectively inhibited B-ALL growth in a human xenograft model. Our results indicate that the effects of fasting on tumor growth are cancer-type dependent, and they suggest new avenues for the development of treatment strategies for leukemia.

CD274 promotes cell cycle entry of leukemia-initiating cells through JNK/Cyclin D2 signaling

Background

CD274 (programmed death ligand 1, also known as B7H1) is expressed in both solid tumors and hematologic malignancies and is of critical importance for the escape of tumor cells from immune surveillance by inhibiting T cell function via its receptor, programmed death 1 (PD-1). Increasing evidence indicates that functional monoclonal antibodies of CD274 may potently enhance the antitumor effect in many cancers. However, the role of CD274 in leukemia-initiating cells (LICs) remains largely unknown.

Methods

We established an MLL-AF9-induced acute myeloid leukemia (AML) model with wild-type (WT) and CD274-null mice to elucidate the role of CD274 in the cell fates of LICs, including self-renewal, differentiation, cell cycle, and apoptosis. RNA sequencing was performed to reveal the potential downstream targets, the results of which were further validated both in vitro and in vivo.

Results

In silico analysis indicated that CD274 level was inversely correlated with the overall survival of AML patients. In Mac-1⁺/c-Kit⁺ mouse LICs, CD274 was expressed at a much higher level than in the normal hematopoietic stem cells (HSCs). The survival of the mice with CD274-null leukemia cells was dramatically extended during the serial transplantation compared with that of their WT counterparts. CD274 deletion led to a significant decrease in LIC frequency and arrest in the G1 phase of the cell cycle. Interestingly, CD274 is not required for the maintenance of HSC pool as shown in our previous study. Mechanistically, we demonstrated that the levels of both phospho-JNK and Cyclin D2 were strikingly downregulated in CD274-null LICs. The overexpression of Cyclin D2 fully rescued the loss of function of CD274. Moreover, CD274 was directly associated with JNK and enhanced the downstream signaling to increase the Cyclin D2 level, promoting leukemia development.

Conclusions

The surface immune molecule CD274 plays a critical role in the proliferation of LICs. The CD274/JNK/Cyclin D2 pathway promotes the cell cycle entry of LICs, which may serve as a novel therapeutic target for the treatment of leukemia.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-016-0350-6) contains supplementary material, which is available to authorized users.

Sorting protein VPS33B regulates exosomal autocrine signaling to mediate hematopoiesis and leukemogenesis

Certain secretory proteins are known to be critical for maintaining the stemness of stem cells through autocrine signaling. However, the processes underlying the biogenesis, maturation, and secretion of these proteins remain largely unknown. Here we demonstrate that many secretory proteins produced by hematopoietic stem cells (HSCs) undergo exosomal maturation and release that is controlled by vacuolar protein sorting protein 33b (VPS33B). Deletion of VPS33B in either mouse or human HSCs resulted in impaired exosome maturation and secretion as well as loss of stemness. Additionally, VPS33B deficiency led to a dramatic delay in leukemogenesis. Exosomes purified from either conditioned medium or human plasma could partially rescue the defects of HSCs and leukemia-initiating cells (LICs). VPS33B co-existed in exosomes with GDI2, VPS16B, FLOT1, and other known exosome markers. Mechanistically, VPS33B interacted with the GDI2/RAB11A/RAB27A pathway to regulate the trafficking of secretory proteins as exosomes. These findings reveal an essential role for VPS33B in exosome pathways in HSCs and LICs. Moreover, they shed light on the understanding of vesicle trafficking in other stem cells and on the development of improved strategies for cancer treatment.

Shared target antigens on cancer cells and tissue stem cells: go or no-go for CAR T cells?

INTRODUCTION

Adoptive therapy with chimeric antigen receptor (CAR) T cells redirected towards CD19 produces remissions of B cell malignancies, however, it also eradicates healthy B cells sharing the target antigen. Such 'on-target off-tumor' toxicity raises serious safety concerns when the target antigen is also expressed by tissue stem cells, with the risk of lasting tissue destruction. Areas covered: We discuss CAR T cell targeting of activation antigens versus lineage associated antigens on the basis of recent experimental and animal data and the literature in the field. Expert commentary: Targeting an activation associated antigen which is transiently expressed by stem cells seems to be safe, like CAR T cells targeting CD30 spare CD30⁺ hematopoietic stem and progenitor cells while eliminating CD30⁺ lymphoma cells, whereas targeting lineage associated antigens which increase in expression during cell maturation, like folate receptor-β and CD123, is of risk to destruct tissue stem cells.

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.

Novel source of human hematopoietic stem cells from peritoneal dialysis effluents

Hematopoietic stem cells (HSCs) hold great promise for the treatment of various diseases and blood disorders. However, limited availability of these cells has hampered their applications in clinical and biological research. Here we have identified a new source of autologous human HSCs in peritoneal dialysis (PD) effluents from patients with end stage renal diseases (ESRDs). Cells isolated from PD effluents contain a Lin-/CD34+/CD38-/CD90+ sub-population and can repopulate NOD/SCID/gamma-/- mice in serial transplantation. Differing from cord blood HSCs, PD-derived HSCs have high tendencies to repopulate peritoneal cavity and spleen with myeloid cells and B lymphocytes. Repopulating HSCs also reside in peritoneal cavities in mice. The isolation of HSCs from peritoneal cavities provides a novel and promising source of autologous and functional HSCs for stem cell research and possible clinical use.

The ITIM-containing receptor LAIR1 is essential for acute myeloid leukaemia development

Conventional strategies are not particularly successful in treatment of leukemia, and identification of signaling pathways crucial to the activity of leukemia stem cells will provide targets for the development of new therapies. Here we report that certain receptors containing the immunoreceptor tyrosine-based inhibition motif (ITIM) are crucial for the development of acute myeloid leukemia (AML). Inhibition of expression of the ITIM-containing receptor LAIR1 does not affect normal hematopoiesis but abolishes leukemia development. LAIR1 induces activation of SHP-1, which acts as a phosphatase-independent signaling adaptor to recruit CAMK1 for activation of downstream CREB in AML cells. The LAIR1/SHP-1/CAMK1/CREB pathway sustains the survival and self-renewal of AML stem cells. Intervention in the signaling initiated by ITIM-containing receptors such as LAIR1 may result in successful treatment of AML.

Concise review: workshop review: understanding and assessing the risks of stem cell-based therapies

The field of stem cell therapeutics is moving ever closer to widespread application in the clinic. However, despite the undoubted potential held by these therapies, the balance between risk and benefit remains difficult to predict. As in any new field, a lack of previous application in man and gaps in the underlying science mean that regulators and investigators continue to look for a balance between minimizing potential risk and ensuring therapies are not needlessly kept from patients. Here, we attempt to identify the important safety issues, assessing the current advances in scientific knowledge and how they may translate to clinical therapeutic strategies in the identification and management of these risks. We also investigate the tools and techniques currently available to researchers during preclinical and clinical development of stem cell products, their utility and limitations, and how these tools may be strategically used in the development of these therapies. We conclude that ensuring safety through cutting-edge science and robust assays, coupled with regular and open discussions between regulators and academic/industrial investigators, is likely to prove the most fruitful route to ensuring the safest possible development of new products.

IGF-IR determines the fates of BCR/ABL leukemia

Background

The tyrosine kinase receptor insulin-like growth factor 1 receptor (IGF-IR) contributes to the initiation and progression of many types of malignancies. We previously showed that IGF-2, which binds IGF-IR, is an extrinsic factor that supports the ex vivo expansion of hematopoietic stem cells (HSCs). We also demonstrated that IGF-IR is not required for HSC activity in vivo.

Methods and results

Here we investigated the role of IGF-IR in chronic myeloid leukemia (CML) using the retroviral BCR/ABL transplantation mouse model. Existing antibodies against IGF-IR are not suitable for flow cytometry; therefore, we generated a fusion of the human IgG Fc fragment with mutant IGF-2 that can bind to IGF-IR. We used this fusion protein to evaluate mouse primary hematopoietic populations. Through transplantation assays with IGF-IR⁺ and IGF-IR⁻ cells, we demonstrated that IGF-IR is expressed on all mouse HSCs. The expression of IGF-IR is much higher on CML cells than on acute lymphoblastic leukemia (ALL) cells. The depletion of IGF-IR expression in BCR/ABL⁺ cells led to the development of ALL (mostly T cell ALL) but not CML. Lack of IGF-IR resulted in decreased self-renewal of the BCR/ABL⁺ CML cells in the serial replating assay.

Conclusion

IGF-IR regulates the cell fate determination of BCR/ABL⁺ leukemia cells and supports the self-renewal of CML cells.

ANGPTL7 regulates the expansion and repopulation of human hematopoietic stem and progenitor cells

Successful expansion of hematopoietic stem cells would benefit the use of hematopoietic stem cell transplants in the clinic. Several angiopoietin-like proteins, including angiopoietin-like 7, can support the activity of hematopoietic stem cells. However, effects of ANGPTL7 on human hematopoietic stem cells and the downstream signaling cascade activated by ANGPTL7 are poorly understood. Here, we established a human hematopoietic stem and progenitor cell-supportive mouse fetal liver cell line that specifically expressed the Angptl7 protein. Furthermore, we found ANGPTL7 is capable of stimulating human hematopoietic stem and progenitor cell expansion and increasing the repopulation activities of human hematopoietic progenitors in xenografts. RNA-sequencing analysis showed that ANGPTL7 activated the expression of CXCR4, HOXB4 and Wnt downstream targets in human hematopoietic progenitors. In addition, chemical manipulation of Wnt signaling diminished the effects of ANGPTL7 on human hematopoietic stem and progenitor cells in culture. In summary, we identify the secreted growth factor ANGPTL7 as a regulator of both human hematopoietic stem and progenitor cell expansion and regeneration.

Hematopoietic stem cell niche maintenance during homeostasis and regeneration

The bone marrow niche has mystified scientists for many years, leading to widespread investigation to shed light into its molecular and cellular composition. Considerable efforts have been devoted toward uncovering the regulatory mechanisms of hematopoietic stem cell (HSC) niche maintenance. Recent advances in imaging and genetic manipulation of mouse models have allowed the identification of distinct vascular niches that have been shown to orchestrate the balance between quiescence, proliferation and regeneration of the bone marrow after injury. Here we highlight the recently discovered intrinsic mechanisms, microenvironmental interactions and communication with surrounding cells involved in HSC regulation, during homeostasis and in regeneration after injury and discuss their implications for regenerative therapy.

Sustained Engraftment of Cryopreserved Human Bone Marrow CD34(+) Cells in Young Adult NSG Mice

Hematopoietic stem cells (HSCs) are defined by their ability to repopulate the bone marrow of myeloablative conditioned and/or (lethally) irradiated recipients. To study the repopulating potential of human HSCs, murine models have been developed that rely on the use of immunodeficient mice that allow engraftment of human cells. The NSG xenograft model has emerged as the current standard for this purpose allowing for engraftment and study of human T cells. Here, we describe adaptations to the original NSG xenograft model that can be readily implemented. These adaptations encompass use of adult mice instead of newborns and a short ex vivo culture. This protocol results in robust and reproducible high levels of lympho-myeloid engraftment. Immunization of recipient mice with relevant antigen resulted in specific antibody formation, showing that both T cells and B cells were functional. In addition, bone marrow cells from primary recipients exhibited repopulating ability following transplantation into secondary recipients. Similar results were obtained with cryopreserved human bone marrow samples, thus circumventing the need for fresh cells and allowing the use of patient derived bio-bank samples. Our findings have implications for use of this model in fundamental stem cell research, immunological studies in vivo and preclinical evaluations for HSC transplantation, expansion, and genetic modification.

A motif in LILRB2 critical for Angptl2 binding and activation

A better understanding of the interaction between extrinsic factors and surface receptors on stem cells will greatly benefit stem cell research and applications. Recently, we showed that several angiopoietin-like proteins (Angptls) bind and activate the immune inhibitory receptor human leukocyte immunoglobulin (Ig)-like receptor B2 (LILRB2) to support ex vivo expansion of hematopoietic stem cells (HSCs) and leukemia development. However, the molecular basis for the interaction between Angptls and LILRB2 was unclear. Here, we demonstrate that Angptl2 expressed in mammalian cells forms high-molecular-weight species and that ligand multimerization is required for activation of LILRB2 for downstream signaling. A novel motif in the first and fourth Ig domains of LILRB2 was identified that is necessary for the receptor to be bound and activated by Angptl2. The binding of Angptl2 to LILRB2 is more potent than and not completely overlapped with the binding of another ligand, HLA-G. Immobilized anti-LILRB2 antibodies induce a more potent activation of LILRB2 than Angptl2, and we developed a serum-free culture containing defined cytokines and immobilized anti-LILRB2 that supports a net expansion of repopulating human cord blood HSCs. Our elucidation of the mode of Angptl binding to LILRB2 enabled the development of a new approach for ex vivo expansion of human HSCs.

Hypoxia and metabolic properties of hematopoietic stem cells

SIGNIFICANCE

The effect of redox signaling on hematopoietic stem cell (HSC) function is not clearly understood.

RECENT ADVANCES

A growing body of evidence suggests that adult HSCs reside in the hypoxic bone marrow microenvironment or niche during homeostasis. It was recently shown that primitive HSCs in the bone marrow prefer to utilize anaerobic glycolysis to meet their energy demands and have lower rates of oxygen consumption and lower ATP levels. Hypoxia-inducible factor-α (Hif-1α) is a master regulator of cellular metabolism. With hundreds of downstream target genes and crosstalk with other signaling pathways, it regulates various aspects of metabolism from the oxidative stress response to glycolysis and mitochondrial respiration. Hif-1α is highly expressed in HSCs, where it regulates their function and metabolic phenotype. However, the regulation of Hif-1α in HSCs is not entirely understood. The homeobox transcription factor myeloid ecotropic viral integration site 1 (Meis1) is expressed in the most primitive HSCs populations, and it is required for primitive hematopoiesis. Recent reports suggest that Meis1 is required for normal adult HSC function by regulating the metabolism and redox state of HSCs transcriptionally through Hif-1α and Hif-2α.

CRITICAL ISSUES

Given the profound effect of redox status on HSC function, it is critical to fully characterize the intrinsic, and microenvironment-related mechanisms of metabolic and redox regulation in HSCs.

FUTURE DIRECTIONS

Future studies will be needed to elucidate the link between HSC metabolism and HSC fates, including quiescence, self-renewal, differentiation, apoptosis, and migration.

Profilin 1 is essential for retention and metabolism of mouse hematopoietic stem cells in bone marrow

How stem cells interact with the microenvironment to regulate their cell fates and metabolism is largely unknown. Here we demonstrated that the deletion of the cytoskeleton-modulating protein profilin 1 (pfn1) in hematopoietic stem cell (HSCs) led to bone marrow failure, loss of quiescence, and mobilization and apoptosis of HSCs in vivo. A switch from glycolysis to mitochondrial respiration with increased reactive oxygen species (ROS) level was also observed in HSCs on pfn1 deletion. Importantly, treatment of pfn1-deficient mice with the antioxidant N-acetyl-l-cysteine reversed the ROS level and loss of quiescence of HSCs, suggesting that the metabolism is mechanistically linked to the cell cycle quiescence of stem cells. The actin-binding and proline-binding activities of pfn1 are required for its function in HSCs. Our study provided evidence that pfn1 at least partially acts through the axis of pfn1/Gα13/EGR1 to regulate stem cell retention and metabolism in the bone marrow.

IGF binding protein 2 is a cell-autonomous factor supporting survival and migration of acute leukemia cells

BACKGROUND

The role of IGF binding protein 2 (IGFBP2) in cancer development is intriguing. Previously we identified IGFBP2 as an extrinsic factor that supports the activity of hematopoietic stem cells (HSCs).

METHODS AND RESULTS

Here we investigated the role of IGFBP2 in in human leukemia cells and in the retroviral AML1-ETO9a transplantation acute myeloid leukemia (AML) mouse model.

RESULTS

IGFBP2 is highly expressed in certain human AML and acute lymphoblastic leukemia (ALL) cells. Inhibition of expression of endogenous IGFBP2 in human leukemia cells led to elevated apoptosis and decreased migration and, consistently, to decreased activation of AKT and other signaling molecules. We also studied the effects of IGFBP2 knockout in the retroviral AML1-ETO9a transplantation AML mouse model. The deletion of IGFBP2 in donor AML cells significantly decreased leukemia development in transplanted mice. Lack of IGFBP2 resulted in upregulation of PTEN expression and downregulation of AKT activation, in the mouse AML cells. The treatment of IGFBP2 deficient AML cells with a PTEN inhibitor restored the wild-type colony forming ability. The deletion of IGFBP2 also led to decreased AML infiltration into peripheral organs and tissues, suggesting that IGFBP2 is required for the migration of AML cells out of bone marrow.

CONCLUSION

IGFBP2 is a critical cell-autonomous factor that promotes the survival and migration of acute leukemia cells.

Comparison of the Ex Vivo Expansion of UCB-Derived CD34+ in 3D DBM/MBA Scaffolds with USSC as a Feeder Layer

OBJECTIVE(S)

Ex vivo expansion of hematopoitic stem cells is an alternative way to increase umbilical cord blood (UCB)-CD34+ cells for bone marrow transplantation. For this purpose demineralized bone matrix (DBM) and mineralized bone allograft (MBA) as two scaffolds based on bone matrix and stem cell niche, were simultaneously used to enhance the effect of human mesenchymal progenitor cells (MPCs) - unrestricted somatic stem cells (USSCs) - as a feeder layer.

MATERIALS AND METHODS

USSCs were isolated and characterized by morphological and immunological analysis then seeded on both scaffolds as a feeder layer. UCB-CD34(+) were isolated by MACS method and were co-culture expanded by USSC in 3D and 2D environments. After 3 weeks expansion, cells were counted and were assessed by karyotype, flow cytometry, clonogenic activity, and long-term culture-initiating cells (LTC-IC).

RESULTS

Co-culture expansion in DBM and MBA was 29.22-fold and 27.77-fold, no significant differences in colony and LTC-IC were obtained. Maximum number of colonies belonged to the day 14 with the 73% CFU-GM (Colony Forming Unit- Granulocyte/Macrophage) in contrast to the day 0 which was BFU-E/CFU-E (Burst/Colony Forming Unit-Erythroid). Flow cytometry indicated that the percentage of CD34+ marker was decreased in USSC co-culture and the highest percentage was observed in simple 2D culture.

CONCLUSION

Because of acid extraction in the DBM production process, mineral materials were removed and the protein background that was more flexible was presented. Therefore these results suggest that USSC-DBM can be a suitable ex vivo mimicry niche by intensifying of surface/volume ratio and supporting the stem cell differentiation and expansion.

Mice lacking ANGPTL8 (Betatrophin) manifest disrupted triglyceride metabolism without impaired glucose homeostasis

Angiopoietin-like protein (ANGPTL)8 (alternatively called TD26, RIFL, Lipasin, and Betatrophin) is a newly recognized ANGPTL family member that has been implicated in both triglyceride (TG) and glucose metabolism. Hepatic overexpression of ANGPTL8 causes hypertriglyceridemia and increased insulin secretion. Here we examined the effects of inactivating Angptl8 on TG and glucose metabolism in mice. Angptl8 knockout (Angptl8(-/-)) mice gained weight more slowly than wild-type littermates due to a selective reduction in adipose tissue accretion. Plasma levels of TGs of the Angptl8(-/-) mice were similar to wild-type animals in the fasted state but paradoxically decreased after refeeding. The lower TG levels were associated with both a reduction in very low density lipoprotein secretion and an increase in lipoprotein lipase (LPL) activity. Despite the increase in LPL activity, the uptake of very low density lipoprotein-TG is markedly reduced in adipose tissue but preserved in hearts of fed Angptl8(-/-) mice. Taken together, these data indicate that ANGPTL8 plays a key role in the metabolic transition between fasting and refeeding; it is required to direct fatty acids to adipose tissue for storage in the fed state. Finally, glucose and insulin tolerance testing revealed no alterations in glucose homeostasis in mice fed either a chow or high fat diet. Thus, although absence of ANGPTL8 profoundly disrupts TG metabolism, we found no evidence that it is required for maintenance of glucose homeostasis.

mTOR complex 1 plays critical roles in hematopoiesis and Pten-loss-evoked leukemogenesis

The mechanistic target of rapamycin (mTOR) pathway serves as a key sensor of cellular-energetic state and functions to maintain tissue homeostasis. Hyperactivation of the mTOR pathway impairs hematopoietic stem cell (HSC) function and is associated with leukemogenesis. However, the roles of the unique mTOR complexes (mTORCs) in hematopoiesis and leukemogenesis have not been adequately elucidated. We deleted the mTORC1 component, regulatory-associated protein of mTOR (Raptor), in mouse HSCs and its loss causes a nonlethal phenotype characterized by pancytopenia, splenomegaly, and the accumulation of monocytoid cells. Furthermore, Raptor is required for HSC regeneration, and plays largely nonredundant roles with rapamycin-insensitive companion of mTOR (Rictor) in these processes. Ablation of Raptor also significantly extends survival of mice in models of leukemogenesis evoked by Pten deficiency. These data delineate critical roles for mTORC1 in hematopoietic function and leukemogenesis and inform clinical strategies based on chronic mTORC1 inhibition.

The Alpha Stem Cell Clinic: a model for evaluating and delivering stem cell-based therapies

Cellular therapies require the careful preparation, expansion, characterization, and delivery of cells in a clinical environment. There are major challenges associated with the delivery of cell therapies and high costs that will limit the companies available to fully evaluate their merit in clinical trials, and will handicap their application at the present financial environment. Cells will be manufactured in good manufacturing practice or near-equivalent facilities with prerequisite safety practices in place, and cell delivery systems will be specialized and require well-trained medical and nursing staff, technicians or nurses trained to handle cells once delivered, patient counselors, as well as statisticians and database managers who will oversee the monitoring of patients in relatively long-term follow-up studies. The model proposed for Alpha Stem Cell Clinics will initially use the capacities and infrastructure that exist in the most advanced tertiary medical clinics for delivery of established bone marrow stem cell therapies. As the research evolves, they will incorporate improved procedures and cell preparations. This model enables commercialization of medical devices, reagents, and other products required for cell therapies. A carefully constructed cell therapy clinical infrastructure with the requisite scientific, technical, and medical expertise and operational efficiencies will have the capabilities to address three fundamental and critical functions: 1) fostering clinical trials; 2) evaluating and establishing safe and effective therapies, and 3) developing and maintaining the delivery of therapies approved by the Food and Drug Administration, or other regulatory agencies.

Proteins and small molecules for cellular regenerative medicine

Regenerative medicine seeks to understand tissue development and homeostasis and build on that knowledge to enhance regeneration of injured tissues. By replenishing lost functional tissues and cells, regenerative medicine could change the treatment paradigm for a broad range of degenerative and ischemic diseases. Multipotent cells hold promise as potential building blocks for regenerating lost tissues, but successful tissue regeneration will depend on comprehensive control of multipotent cells-differentiation into a target cell type, delivery to a desired tissue, and integration into a durable functional structure. At each step of this process, proteins and small molecules provide essential signals and, in some cases, may themselves act as effective therapies. Identifying these signals is thus a fundamental goal of regenerative medicine. In this review we discuss current progress using proteins and small molecules to regulate tissue regeneration, both in combination with cellular therapies and as monotherapy.

Hematopoietic stem cells: interplay with immunity

Ample evidence indicated that hematopoietic stem cells (HSCs) receive signaling from infection or other immune responses to adjust their differentiation and self-renewal. More recent reports also suggested that, while the bone marrow microenvironment or niche may provide the immune privilege for HSCs, HSCs can present surface immune inhibitors per se to suppress innate immunity and adaptive immunity to evade potential immune surveillance and attack. These findings support the hypothesis that HSCs are capable of interacting with the immune system as signal "receivers" and signal "providers". On the one hand, HSCs are capable of directly sensing the signals from the immune system through their surface receptors to modulate their self-renewal and differentiation ("in" signaling); on the other hand, HSCs display surface immune inhibitory molecules to evade the attack from the innate and adaptive immune systems ("out" signaling). The continuing investigation of the interplay between HSCs and immunity may lead to the open-up of a new research filed - the immunology of stem cells.

Meis1 regulates the metabolic phenotype and oxidant defense of hematopoietic stem cells

The role of Meis1 in leukemia is well established, but its role in hematopoietic stem cells (HSCs) remains poorly understood. Previously, we showed that HSCs use glycolytic metabolism to meet their energy demands. However, the mechanism of regulation of HSC metabolism, and the importance of maintaining this distinct metabolic phenotype on HSC function has not been determined. More importantly, the primary function of Meis1 in HSCs remains unknown. Here, we examined the effect of loss of Meis1 on HSC function and metabolism. Inducible Meis1 deletion in adult mouse HSCs resulted in loss of HSC quiescence, and failure of bone marrow repopulation after transplantation. While we previously showed that Meis1 regulates Hif-1α transcription in vitro, we demonstrate here that loss of Meis1 results in down-regulation of both Hif-1α and Hif-2α in HSCs. This resulted in a shift to mitochondrial metabolism, increased reactive oxygen species production, and apoptosis of HSCs. Finally, we demonstrate that the effect of Meis1 knockout on HSCs is entirely mediated through reactive oxygen species where treatment of the Meis1 knockout mice with the scavenger N-acetylcystein restored HSC quiescence and rescued HSC function. These results uncover an important transcriptional network that regulates metabolism, oxidant defense, and maintenance of HSCs.