Human Cord Blood Progenitors Sustain Thymic T-Cell Development and a Novel Form of Angiogenesis

Angiogenic Factors Correlate with T Cell Immune Reconstitution and Clinical Outcomes after Double-Unit Umbilical Cord Blood Transplantation in Adults

Umbilical cord blood (UCB) is a valuable graft source for allogeneic hematopoietic stem cell transplantation (HSCT) in patients who lack adult donors. UCB transplantation (UCBT) in adults results in delayed immune reconstitution, leading to high infection-related morbidity and mortality. Angiogenic factors and markers of endothelial dysfunction have biologic and prognostic significance in conventional HSCT, but their role in UCBT has not been investigated. Furthermore, the interplay between angiogenesis and immune reconstitution has not been studied. Here we examined whether angiogenic cytokines, angiopoietin-1 (ANG-1) and vascular endothelial growth factor (VEGF), or markers of endothelial injury, thrombomodulin (TM) and angiopoietin-2 (ANG-2), associate with thymic regeneration as determined by T cell receptor excision circle (TREC) values and recovery of T cell subsets, as well as clinical outcomes in adult recipients of UCBT. We found that plasma levels of ANG-1 significantly correlated with the reconstitution of naive CD4+CD45RA+ and CD8+CD45RA+ T cell subsets, whereas plasma levels of VEGF displayed a positive correlation with CD4+CD45RO+ T cells and regulatory T cells and a weak correlation with TRECs. Assessment of TM and ANG-2 revealed a strong inverse correlation of both factors with naive T cells and TRECs. The angiogenic capacity of each patient's plasma, as determined by an in vitro angiogenesis assay, positively correlated with VEGF levels and with reconstitution of CD4+ T cell subsets. Higher VEGF levels were associated with worse progression-free survival and higher risk of relapse, whereas higher levels of TM were associated with chronic graft-versus-host disease and nonrelapse mortality. Thus, angiogenic factors may serve as valuable markers associated with T cell reconstitution and clinical outcomes after UCBT.

Endothelial progenitor cell cotransplantation enhances islet engraftment by rapid revascularization

Impaired revascularization of transplanted islets is a critical problem that leads to progressive islet loss. Since endothelial progenitor cells (EPCs) are known to aid neovascularization, we aimed to enhance islet engraftment by cotransplanting EPCs with islets. Porcine islets, with (islet-EPC group) or without (islet-only group) human cord blood-derived EPCs, were transplanted into diabetic nude mice. The islet-EPC group reached euglycemia by ∼11 days posttransplantation, whereas the islet-only group did not. Also, the islet-EPC group had a higher serum porcine insulin level than the islet-only group. Islets from the islet-EPC group were more rapidly revascularized at the early period of transplantation without increment of final capillary density at the fully revascularized graft. Enhanced revascularization rate in the islet-EPC group was mainly attributed to stimulating vascular endothelial growth factor-A production from the graft. The rapid revascularization by EPC cotransplantation led to better graft perfusion and recovery from hypoxia. EPC cotransplantation was also associated with greater β-cell proliferation, probably by more basement membrane production and hepatocyte growth factor secretion. In conclusion, cotransplantation of EPCs and islets induces better islet engraftment by enhancing the rate of graft revascularization. These findings might provide a directly applicable tool to enhance the efficacy of islet transplantation in clinical practice.

Cord blood-derived hematopoietic stem/progenitor cells: current challenges in engraftment, infection, and ex vivo expansion

Umbilical cord blood has served as an alternative to bone marrow for hematopoietic transplantation since the late 1980s. Numerous clinical studies have proven the efficacy of umbilical cord blood. Moreover, the possible immaturity of cells in umbilical cord blood gives more options to recipients with HLA mismatch and allows for the use of umbilical cord blood from unrelated donors. However, morbidity and mortality rates associated with hematopoietic malignancies still remain relatively high, even after cord blood transplantation. Infections and relapse are the major causes of death after cord blood transplantation in patients with hematopoietic diseases. Recently, new strategies have been introduced to improve these major problems. Establishing better protocols for simple isolation of primitive cells and ex vivo expansion will also be very important. In this short review, we discuss several recent promising findings related to the technical improvement of cord blood transplantation.

Mesenchymal stem cells for the treatment of neurodegenerative disease

Mesenchymal stem cells/marrow stromal cells (MSCs) present a promising tool for cell therapy, and are currently being tested in US FDA-approved clinical trials for myocardial infarction, stroke, meniscus injury, limb ischemia, graft-versus-host disease and autoimmune disorders. They have been extensively tested and proven effective in preclinical studies for these and many other disorders. There is currently a great deal of interest in the use of MSCs to treat neurodegenerative diseases, in particular for those that are fatal and difficult to treat, such as Huntington's disease and amyotrophic lateral sclerosis. Proposed regenerative approaches to neurological diseases using MSCs include cell therapies in which cells are delivered via intracerebral or intrathecal injection. Upon transplantation into the brain, MSCs promote endogenous neuronal growth, decrease apoptosis, reduce levels of free radicals, encourage synaptic connection from damaged neurons and regulate inflammation, primarily through paracrine actions. MSCs transplanted into the brain have been demonstrated to promote functional recovery by producing trophic factors that induce survival and regeneration of host neurons. Therapies will capitalize on the innate trophic support from MSCs or on augmented growth factor support, such as delivering brain-derived neurotrophic factor or glial-derived neurotrophic factor into the brain to support injured neurons, using genetically engineered MSCs as the delivery vehicles. Clinical trials for MSC injection into the CNS to treat traumatic brain injury and stroke are currently ongoing. The current data in support of applying MSC-based cellular therapies to the treatment of neurodegenerative disorders are discussed.

Stemming vision loss with stem cells

Dramatic advances in the field of stem cell research have raised the possibility of using these cells to treat a variety of diseases. The eye is an excellent target organ for such cell-based therapeutics due to its ready accessibility, the prevalence of vasculo- and neurodegenerative diseases affecting vision, and the availability of animal models to demonstrate proof of concept. In fact, stem cell therapies have already been applied to the treatment of disease affecting the ocular surface, leading to preservation of vision. Diseases in the back of the eye, such as macular degeneration, diabetic retinopathy, and inherited retinal degenerations, present greater challenges, but rapidly emerging stem cell technologies hold the promise of autologous grafts to stabilize vision loss through cellular replacement or paracrine rescue effects.

Clearance of CMV viremia and survival after double umbilical cord blood transplantation in adults depends on reconstitution of thymopoiesis

Umbilical cord blood grafts are increasingly used as sources of hematopoietic stem cells in adults. Data regarding the outcome of this approach in adults are consistent with delayed and insufficient immune reconstitution resulting in high infection-related morbidity and mortality. Using cytomegalovirus (CMV)-specific immunity as a paradigm, we evaluated the status, mechanism, and clinical implications of immune reconstitution in adults with hematologic malignancies undergoing unrelated double unit cord blood transplantation. Our data indicate that CD8(+) T cells capable of secreting interferon-gamma (IFN-gamma) in a CMV-specific enzyme-linked immunosorbent spot (ELISpot) assay are detectable at 8 weeks after transplantation, before reconstitution of thymopoiesis, but fail to clear CMV viremia. Clearance of CMV viremia occurs later and depends on the recovery of CD4(+)CD45RA(+) T cells, reconstitution of thymopoiesis, and attainment of T-cell receptor rearrangement excision circle (TREC) levels of 2000 or more copies/mug DNA. In addition, overall survival was significantly higher in patients who displayed thymic regeneration and attainment of TREC levels of 2000 or more copies/mug DNA (P = .005). These results indicate that reconstitution of thymopoiesis is critical for long-term clinical outcome in adult recipients of umbilical cord blood transplant. The trial was prospectively registered at http://www.clinicaltrials.gov (NCT00133367).

Cord blood-derived early outgrowth endothelial progenitor cells

The presence of circulating endothelial repopulating cells in the adult human peripheral blood has been proposed since long time ago. In the late 1990s, the putative endothelial progenitor cells (EPCs) were first identified and reported by Asahara and co-workers. Since then, a number of studies have demonstrated that these cells are derived from bone marrow and induce microvascular vasculogenesis and re-endothelialization of injured vessels. Meantime, human umbilical cord blood also gained much attention for the reason of possible additional source to obtain EPCs since cord blood has been shown to contain more number of active hematopoietic stem cells as compared to adult peripheral blood. This review summarizes the aspect of human cord blood-derived EPCs with special focuses into their identity and future clinical application.

Switching-on survival and repair response programs in islet transplants by bone marrow-derived vasculogenic cells

OBJECTIVE

Vascular progenitors of bone marrow origin participate to neovascularization at sites of wound healing and transplantation. We hypothesized that the biological purpose of this bone marrow-derived vascular component is to contribute angiogenic and survival functions distinct from those provided by the local tissue-derived vasculature.

RESEARCH DESIGN AND METHODS AND RESULTS

To address this hypothesis, we investigated the functional impact of bone marrow-derived vascular cells on pancreatic islets engraftment using bone marrow-reconstituted Id1(+/-)Id3(-/-) mice, a model of bone marrow-derived vasculogenesis. We show that, in this model, bone marrow-derived vasculogenic cells primarily contribute to the formation of new blood vessels within islet transplants. In contrast, graft revascularization in a wild-type background occurs by tissue-derived blood vessels only. Using these distinct transplant models in which bone marrow-and tissue-derived vasculature are virtually mutually exclusive, we demonstrate that bone marrow-derived vasculogenic cells exhibit enhanced angiogenic functions and support prompt activation of islets survival pathways, which significantly impact on islets engraftment and function. Moreover, gene profiling of vascular and inflammatory cells of the grafts demonstrate that neovascularization by bone marrow-derived cells is accompanied by the activation of a genetic program uniquely tuned to downregulate harmful inflammatory responses and to promote tissue repair.

CONCLUSIONS

These studies uncover the biological significance of bone marrow-derived vasculogenic cells in the response to injury during transplantation. Enhancing the contribution of bone marrow-derived vasculogenic cells to transplantation sites may help to overcome both limited angiogenic responses of the adult tissue-derived vasculature and untoward effects of inflammation on transplant engraftment.

Endothelial progenitor cells in neovascularization of infarcted myocardium

Historically, revascularization of ischemic tissue was believed to occur through the migration and proliferation of endothelial cells in nearby tissues; however, evidence accumulated in recent years indicates that a subpopulation of adult, peripheral-blood cells, collectively referred to as endothelial progenitor cells (EPCs), can differentiate into mature endothelial cells. After ischemic insult, EPCs are believed to home to sites of neovascularization, where they contribute to vascular regeneration by forming a structural component of capillaries and by secreting angiogenic factors; new evidence indicates that EPCs can also differentiate into cardiomyocytes and smooth-muscle cells. These insights into the molecular and cellular processes of tissue formation suggest that cardiac function may be preserved after myocardial infarction by transplanting EPCs into ischemic heart tissue, thereby enhancing vascular and myocardial recovery. This therapeutic strategy has been effective in animal models of ischemic disorders, and results from randomized clinical trials suggest that cell-based strategies may be safe and feasible for treatment of myocardial infarction in humans and have provided early evidence of efficacy. However, the scarcity of EPCs in the peripheral blood and evidence that several disease states reduce EPC number and/or function have prompted the development of several strategies to overcome these limitations, such as the administration of genetically modified EPCs that overexpress angiogenic growth factors. To optimize therapeutic outcomes, researchers must continue to refine methods of EPC purification, expansion, and administration, and to develop techniques that overcome the intrinsic scarcity and phenotypic deficiencies of EPCs.

Cord blood stem and progenitor cells

Cord blood has served as a source of hematopoietic stem and progenitor cells for successful repopulation of the blood cell system in patients with malignant and nonmalignant disorders. It was information on these rare immature cells in cord blood that led to the first use of cord blood for transplantation. Further information on these cells and how they can be manipulated both in vitro and in vivo will likely enhance the utility and broadness of applicability of cord blood for treatment of human disease. This chapter reviews information on the clinical and biological properties of hematopoietic stem and progenitor cells, as well as the biology of endothelial progenitor cells, and serves as a source for the methods used to detect and quantitate these important functional cells. Specifically, methods are presented for enumerating human cord blood myeloid progenitor cells, including granulocyte-macrophage (CFU-GM), erythroid (BFU-E), and multipotential (CFU-GEMM or CFU-Mix) progenitors, and their replating potential; hematopoietic stem cells, as assessed in vitro for long-term culture-initiating cells (LTC-ICs), cobblestone area-forming cells (CAFCs), and myeloid-lymphoid-initiating cells (ML-ICs), and as assessed in vivo for nonobese diabetic (NOD)/severe combined immunodeficient (SCID) mouse repopulating cells (SRCs); and high and low proliferative potential endothelial progenitor cells (EPCs).

Stem cell therapy for the treatment of heart failure

PURPOSE OF REVIEW

Congestive heart failure is a complex clinical syndrome resulting from myocardial dysfunction that impairs the cardiovascular system's function. Medical and surgical therapy both still result in a large number of patients with very few options and persistent ventricular dysfunction. The major process to reverse ventricular remodeling would be the enhancement of regeneration of cardiac myocytes, as well as the stimulation of neovascularization within the affected area of the myocardium. This can be achieved by introducing progenitor cells that are capable of differentiating into cardiac myocytes, or that promote neovascularization and restore the normal characteristics of myocardium environment. A number of issues remain as to the type of cells, delivery, timing, and mechanisms involved, however.

RECENT FINDINGS

There have been a number of clinical trials in patients with heart failure that have been based on animal data related to stem cell therapy. Most have utilized whole bone marrow cells or myoblasts. The majority of the studies demonstrate an improvement in ventricular function, reduction in scarring, and improvement in symptoms. Some trials have shown no improvement at all.

SUMMARY

This review examines the bench-to-bedside developments of stem cell therapy related to congestive heart failure.

Systemic inhibition of tumour angiogenesis by endothelial cell-based gene therapy

Angiogenesis and post-natal vasculogenesis are two processes involved in the formation of new vessels, and both are essential for tumour growth and metastases. We isolated endothelial cells from human blood mononuclear cells by selective culture. These blood outgrowth cells expressed endothelial cell markers and responded correctly to functional assays. To evaluate the potential of blood outgrowth endothelial cells (BOECs) to construct functional vessels in vivo, NOD-SCID mice were implanted with Lewis lung carcinoma cells subcutaneously (s.c.). Blood outgrowth endothelial cells were then injected through the tail vein. Initial distribution of these cells occurred throughout the lung, liver, spleen, and tumour vessels, but they were only found in the spleen, liver, and tumour tissue 48 h after injection. By day 24, they were mainly found in the tumour vasculature. Tumour vessel counts were also increased in mice receiving BOEC injections as compared to saline injections. We engineered BOECs to deliver an angiogenic inhibitor directly to tumour endothelium by transducing them with the gene for human endostatin. These cells maintained an endothelial phenotype and decreased tumour vascularisation and tumour volume in mice. We conclude that BOECs have the potential for tumour-specific delivery of cancer gene therapy.

Progenitor cells and retinal angiogenesis

Nothing more dramatically captures the imagination of the visually impaired patient or the ophthalmologist treating them than the possibility of rebuilding a damaged retina or vasculature with "stem cells." Stem cells (SC) have been isolated from adult tissues and represent a pool of cells that may serve to facilitate rescue/repair of damaged tissue following injury or stress. We propose a new paradigm to "mature" otherwise immature neovasculature or, better yet, stabilize existing vasculature to hypoxic damage. This may be possible through the use of autologous bone marrow (BM) or cord blood derived hematopoietic SC that selectively target sites of neovascularization and gliosis where they provide vasculo- and neurotrophic effects. We have demonstrated that adult BM contains a population of endothelial and myeloid progenitor cells that can target activated astrocytes, a hallmark of many ocular diseases, and participate in normal developmental, or injury-induced, angiogenesis in the adult. Intravitreal injection of these cells from mice and humans can prevent retinal vascular degeneration ordinarily observed in mouse models of retinal degeneration; this vascular rescue correlates with functional neuronal rescue as well. The use of autologous adult BM derived SC grafts for the treatment of retinal vascular and degenerative diseases represents a novel conceptual approach that may make it possible to "mature" otherwise immature neovasculature, stabilize existing vasculature to hypoxic damage and/or rescue and protect retinal neurons from undergoing apoptosis. Such a therapeutic approach would obviate the need to employ destructive treatment modalities and would facilitate vascularization of ischemic and otherwise damaged retinal tissue.

Cell therapy and gene therapy using endothelial progenitor cells for vascular regeneration

The isolation of endothelial progenitor cells (EPCs) derived from adult bone marrow (BM) was an epoch-making event for the recognition of "neovessel formation" occurring as physiological and pathological responses in adults. The finding that EPCs home to sites of neovascularization and differentiate into endothelial cells (ECs) in situ is consistent with "vasculogenesis," a critical paradigm well described for embryonic neovascularization, but proposed recently in adults, in which a reservoir of stem or progenitor cells contributes to vascular organogenesis. EPCs have also been considered as therapeutic agents to supply the potent origin of neovascularization under pathological conditions. Considering the regenerative implications, gene modification of stem cells has advantages over conventional gene therapy. Ex vivo gene transfection of stem cells may avoid administration of vectors and vehicles into the recipient organism. Stem cells isolated from adults may exhibit age-related, genetic, or acquired disease-related impairment of their regenerative ability. Transcriptional or enzymatic gene modification may constitute an effective means to maintain, enhance, or inhibit EPCs' capacity to proliferate or differentiate. This chapter provides an update of EPC biology as well as EPCs' potential use for therapeutic regeneration.

Contribution of endothelial progenitors and proangiogenic hematopoietic cells to vascularization of tumor and ischemic tissue

PURPOSE OF REVIEW

During the last several years, a substantial amount of evidence from animal as well as human studies has advanced our knowledge of how bone marrow derived cells contribute to neoangiogenesis. In the light of recent findings, we may have to redefine our thinking of endothelial cells as well as of perivascular mural cells.

RECENT FINDINGS

Inflammatory hematopoietic cells, such as macrophages, have been shown to promote neoangiogenesis during tumor growth and wound healing. Dendritic cells, B lymphocytes, monocytes, and other immune cells have also been found to be recruited to neoangiogenic niches and to support neovessel formation. These findings have led to the concept that subsets of hematopoietic cells comprise proangiogenic cells that drive adult revascularization processes. While evidence of the importance of endothelial progenitor cells in adult vasculogenesis increased further, the role of these comobilized hematopoietic cells has been intensely studied in the last few years.

SUMMARY

Angiogenic factors promote mobilization of vascular endothelial growth factor receptor 1-positive hematopoietic cells through matrix metalloproteinase-9 mediated release of soluble kit-ligand and recruit these proangiogenic cells to areas of hypoxia, where perivascular mural cells present stromal-derived factor 1 (CXCL-12) as an important retention signal. The same factors are possibly involved in mobilization of vascular endothelial growth factor receptor 2-positive endothelial precursors that may participate in neovessel formation. The complete characterization of mechanisms, mediators and signaling pathways involved in these processes will provide novel targets for both anti and proangiogenic therapeutic strategies.

Tumor stromal-derived factor-1 recruits vascular progenitors to mitotic neovasculature, where microenvironment influences their differentiated phenotypes

Mechanisms underlying tumor vasculogenesis, the homing and engraftment of bone marrow-derived vascular progenitors, remain undefined. We hypothesized that tumor cell-secreted factors regulate vasculogenesis. We studied vasculogenic and nonvasculogenic intracranial murine gliomas. A PCR screen identified stromal-derived factor-1 (SDF-1/CXCL12) and vascular endothelial growth factor (VEGF) expression by vasculogenic glioma cells and spontaneously arising vasculogenic tumors in NF1+/-:Trp53+/- mice, but not by nonvasculogenic glioma cells. Enforced SDF-1, not VEGF, expression in nonvasculogenic cells caused vasculogenesis. Combined SDF-1 and VEGF expression augmented vasculogenesis over SDF-1 expression alone. Blocking SDF-1 receptor CXCR4 reduced short-term homing and long-term engraftment of vascular progenitors. Implanting tumor cells secreting SDF-1 was therefore necessary and sufficient to incorporate marrow-derived precursors into tumor endothelium. SDF-1 seemed to exert these effects by acting locally intratumorally and did not cause an efflux of marrow-derived progenitors into circulation. Tumor microenvironment determined additional fates of marrow-derived cells. Hypoxia, observed with ectopic s.c. murine tumors at levels approximating that of intracranial human glioblastoma, interacted with tumor-secreted SDF-1 to expand engrafted vascular progenitor differentiated phenotypes to include pericytes as well as endothelium. In contrast, less hypoxic orthotopic intracranial murine gliomas contained only marrow-derived endothelium without marrow-derived pericytes. Furthermore, we found that vasculogenesis is significant for tumors because it generates endothelium with a higher mitotic index than endothelium derived from local sources. Although CXCR4 blockade selectively targeted endothelium generated by vasculogenesis, completely inhibiting vessel formation may require combination therapy targeting locally derived and marrow-derived endothelium.

Stem cell biology for vascular regeneration

The isolation of endothelial progenitor cells (EPCs) derived from bone marrow (BM) was one epoch-making event for the recognition of neovessel formation in adults occurring as physiological and pathological responses. The finding that EPCs home to sites of neovascularization and differentiate into endothelial cells (ECs) in situ is consistent with vasculogenesis, a critical paradigm that has been well described for embryonic neovascularization, but proposed recently in adults in which a reservoir of stem or progenitor cells contribute to vascular organogenesis. EPCs have also been considered as therapeutic agents to supply the potent origin of neovascularization under pathological conditions. This chapter highlights an update of EPC biology as well as its potential use for therapeutic regeneration.

Isolation and Angiogenesis by Endothelial Progenitors in the Fetal Liver

Endothelial progenitor cells (EPCs) have significant therapeutic potential. However, the low quantity of such cells available from bone marrow and their limited capacity to proliferate in culture make their use difficult. Here, we present the first definitive demonstration of the presence of true EPCs in murine fetal liver capable of forming blood vessels in vivo connected to the host's vasculature after transplantation. This population is particularly interesting because it can be obtained at high yield and has a high angiogenic capacity as compared with bone marrow-derived EPCs. The EPC capacity is contained within the CD31+Sca1+ cell subset. We demonstrate that these cells are dependent for survival and proliferation on a feeder cell monolayer derived from the fetal liver. In addition, we describe a novel and easy method for the isolation and ex vivo proliferation of these EPCs. Finally, we used gene expression profiling and tandem mass spectrometry proteomics to examine the fetal liver endothelial progenitors and the feeder cells to identify possible proangiogenic growth factor and endothelial differentiation-associated genes.

Surgical treatment for congestive heart failure with autologous adult stem cell transplantation: a prospective randomized study

BACKGROUND

Autologous adult stem cell transplantation has been touted as the latest tool in regenerative medical therapy. Its potential for use in cardiovascular disease has only recently been recognized. A randomized study was conducted with a novel epicardial technique to deploy stem cells as an adjuvant to conventional revascularization therapy in patients with congestive heart failure.

METHODS

After institutional review board and government approval, adult autologous stem cell transplantation (CD34+) was performed in patients with ischemic cardiomyopathy and an ejection fraction of less than 35% who were scheduled for primary off-pump coronary artery bypass grafting. Preoperatively, the patients underwent echocardiography, stress thallium imaging single photon emission computed tomography, and cardiac catheterization to identify ischemic regions of the heart and to guide in the selection of stem cell injection sites. The patients were prospectively randomized before the operative therapy was performed. Patient follow-up was 1, 3, and 6 months with echocardiography, single photon emission computed tomography, and angiography.

RESULTS

There were 20 patients enrolled in the study. Ten patients had successful subepicardial transplantation of autologous stem cells into ischemic myocardium. The other 10 patients, the control group, only had off-pump coronary artery bypass grafting. There were 8 male and 2 female subjects in each group. The median number of grafts performed was 1 in both groups. On angiographic follow-up, all grafts were patent at 6 months. The ejection fractions of the off-pump coronary artery bypass grafting group versus the off-pump coronary artery bypass grafting plus stem cell transplantation group were as follows: preoperative, 30.7% +/- 2.5% versus 29.4% +/- 3.6%; 1 month, 36.4% +/- 2.6% versus 42.1% +/- 3.5%; 3 months, 36.5% +/- 3.0% versus 45.5% +/- 2.2%; and 6 months, 37.2% +/- 3.4% versus 46.1% +/- 1.9% (P < .001). There were no perioperative arrhythmias or neurologic or ischemic myocardial events in either group.

CONCLUSIONS

Autologous stem cell transplantation led to significant improvement in cardiac function in patients undergoing off-pump coronary artery bypass grafting for ischemic cardiomyopathy. Further investigation is required to quantify the optimal timing and specific cellular effects of the therapy.

Bone marrow-derived lin(-)c-kit(+)Sca-1+ stem cells do not contribute to vasculogenesis in Lewis lung carcinoma

The development of tumor vasculature is thought to occur through two complementary processes: sprouting angiogenesis from preexisting blood vessels of the host, and vasculogenesis, which involves the spontaneous development of vessels through specific recruitment, differentiation, and vascular incorporation of circulating endothelial cells (EC), endothelial progenitor cells (EPC), or potentially bone marrow-derived cells. Recent reports, however, have challenged the belief that bone marrow-derived cells contribute to tumor neovascularization, claiming an exclusive role for sprouting angiogenesis in tumor blood vessel development. In the present study, we explored the recruitment behavior of bone marrow-derived lin(-)c-kit(+)Sca-1+ stem cells to subcutaneously implanted Lewis lung carcinoma in a syngeneic bone marrow transplantation model. We observed that although lin(-)c-kit(+)Sca-1+ and their derived cells demonstrate significant recruitment to carcinomas in vivo, they do not appear to functionally contribute to tumor neovascularization. Furthermore, our results support the hypothesis that new vessel formation in carcinomas occurs primarily through endothelialization from adjacent and preexisting vasculature.

Tumor necrosis factor promotes human T-cell development in nonobese diabetic/severe combined immunodeficient mice

A major problem after clinical hematopoietic stem cell transplantations is poor T-cell reconstitution. Studying the mechanisms underlying this concern is hampered, because experimental transplantation of human stem and progenitor cells into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice usually results in low T-lymphocyte reconstitution. Because tumor necrosis factor alpha (TNFalpha) has been proposed to play a role in T-lineage commitment and differentiation in vitro, we investigated its potential to augment human T-cell development in vivo. Administration of TNF to irradiated NOD/SCID mice before transplantation of human mononuclear cells from either cord blood or adult G-CSF-mobilized peripheral blood (MPBL) led 2-3 weeks after transplantation to the emergence of human immature CD4(+)CD8(+) double-positive T-cells in the bone marrow (BM), spleen, and thymus, and in this organ, the human cells also express CD1a marker. One to 2 weeks later, single-positive CD4(+) and CD8(+) cells expressing heterogenous T-cell receptor alpha beta were detected in all three organs. These cells were also capable of migrating through the blood circulation. Interestingly, human T-cell development in these mice was associated with a significant reduction in immature lymphoid human CD19(+) B cells and natural killer progenitors in the murine BM. The human T cells were mostly derived from the transplanted immature CD34(+) cells. This study demonstrates the potential of TNF to rapidly augment human T lymphopoiesis in vivo and also provides clinically relevant evidence for this process with adult MPBL progenitors.

Biology of cord blood cells and future prospects for enhanced clinical benefit

Cord blood (CB) has served as a clinically beneficial source of hematopoietic stem (HSC) and progenitor (HPC) cells for transplantation and correction of a large number of malignant and non-malignant disorders. The capacity of CB to perform these functions is intimately related to the quality and quantity of HSC and HPC present in CB. This review covers the biology of HSC and HPC, efforts to expand these cells ex vivo for enhanced clinical utility that has thus far not been very successful, and recent studies on attempts to enhance the homing and engrafting capability of HSC as an alternative means for more effective use of the limited numbers of CB cells collected. This review also highlights the presence in CB of mesenchymal stem cells, unrestricted somatic stem cells, endothelial progenitor cells and immune cells. The presence and biology of these non-HSC/HPC may open up future possibilities for additional clinical benefit of CB, a product considered mainly for discard before its clinical transplantation potential was realized in the late 1980s.

The role of angiopoietins in the development of endothelial cells from cord blood CD34+ progenitors

Circulating endothelial progenitors contribute to neovascularization at sites of injury and tumorigenesis in postnatal life. Yet, the molecular mechanisms initiating the endothelial developmental program of these precursors remain elusive. Here we provide evidence that endothelial development from progenitors circulating in human cord blood requires angiopoietins, a set of growth factors also involved in vascular branching during embryogenesis. We show that cord blood cells with the potential for endothelial development reside in a CD34(+)CD11b+ subset capable of autonomously producing and binding angiopoietins. Functionally, endogenous angiopoietin-1 regulates initial endothelial cell commitment, whereas angiopoietin-2 enhances expansion of the endothelial cell progeny. These findings suggest a role for angiopoietins as regulators of endothelial development from circulating progenitors and imply a function of angiopoietins at distinct developmental steps in postnatal angiogenesis.

Vasculogenic potential of long term repopulating cord blood progenitors

In the adult, involvement of bone marrow-derived circulating endothelial progenitor cells (EPCs) in tissue revascularization (vasculogenesis) and the cooperation of hematopoietic cell subsets in supporting this process have been described in different experimental animal models. However, the effective contribution of such cells in restoring organ vascularization in a clinical setting needs to be clarified. In this study, a mouse transplantation model was engrafted by human cord blood hematopoietic stem and progenitor cells to follow the behavior of donor-derived endothelial and hematopoietic cells in the presence of a localized source of an angiogenic inducer. Human endothelial markers (CD31+/CD45-, VE-cadherin+) were always detectable in the bone marrow of transplanted mice, while they were only randomly detectable in peripheral neovascularization sites. To investigate the ability of human transplanted hematopoietic stem cells to support new vessel formation in response to altered homeostatic conditions, chimeric mice were further treated by systemic injection of human mononuclear cells (MNCs). Our data indicate that MNC administration in transplanted mice enhances vasculogenesis in the newly formed vessels. Taken together these results suggest that human-derived EPCs, long-term engrafting a xenotransplantation model, have hematopoietic and endothelial developmental potential, which can be modulated by altering the physiological conditions of host microenvironment.

Human NK cell development in NOD/SCID mice receiving grafts of cord blood CD34+ cells

Definition of the cytokine environment, which regulates the maturation of human natural killer (NK) cells, has been largely based on in vitro assays because of the lack of suitable animal models. Here we describe conditions leading to the development of human NK cells in NOD/SCID mice receiving grafts of hematopoietic CD34+ precursor cells from cord blood. After 1-week-long in vivo treatment with various combinations of interleukin (IL)-15, flt3 ligand, stem cell factor, IL-2, IL-12, and megakaryocyte growth and differentiation factor, CD56+CD3- cells were detected in bone marrow (BM), spleen, and peripheral blood (PB), comprising 5% to 15% of human CD45+ cells. Human NK cells of NOD/SCID mouse origin closely resembled NK cells from human PB with respect to phenotypic characteristics, interferon (IFN)-gamma production, and cytotoxicity against HLA class 1-deficient K562 targets in vitro and antitumor activity against K562 erythroleukemia in vivo. In the absence of growth factor treatment, CD56+ cells were present only at background levels, but CD34+CD7+ and CD34-CD7+ lymphoid precursors with NK cell differentiation potential were detected in BM and spleen of chimeric NOD/SCID mice for up to 5 months after transplantation. Our results demonstrate that limitations in human NK cell development in the murine microenvironment can be overcome by treatment with NK cell growth-promoting human cytokines, resulting in the maturation of IFN-gamma-producing cytotoxic NK cells. These studies establish conditions to explore human NK cell development and function in vivo in the NOD/SCID mouse model.

Therapeutic stem and progenitor cell transplantation for organ vascularization and regeneration

Emerging evidence suggests that bone marrow-derived endothelial, hematopoietic stem and progenitor cells contribute to tissue vascularization during both embryonic and postnatal physiological processes. Recent preclinical and pioneering clinical studies have shown that introduction of bone marrow-derived endothelial and hematopoietic progenitors can restore tissue vascularization after ischemic events in limbs, retina and myocardium. Corecruitment of angiocompetent hematopoietic cells delivering specific angiogenic factors facilitates incorporation of endothelial progenitor cells (EPCs) into newly sprouting blood vessels. Identification of cellular mediators and tissue-specific chemokines, which facilitate selective recruitment of bone marrow-derived stem and progenitor cells to specific organs, will open up new avenues of research to accelerate organ vascularization and regeneration. In addition, identification of factors that promote differentiation of the progenitor cells will permit functional incorporation into neo-vessels of specific tissues while diminishing potential toxicity to other organs. In this review, we discuss the clinical potential of vascular progenitor and stem cells to restore long-lasting organ vascularization and function.

Angiogenic factors reconstitute hematopoiesis by recruiting stem cells from bone marrow microenvironment

The mechanism by which angiogenic factors recruit bone marrow (BM)-derived quiescent endothelial and hematopoietic stem cells (HSCs) is not known. Here, we report that functional vascular endothelial growth factor receptor-1 (VEGFR1, Flt-1) is expressed on a subpopulation of human CD34(+) and mouse Lin-Sca-1(+)c-Kit(+) BM-repopulating stem cells, conveying signals for recruitment of HSCs and reconstitution of hematopoiesis. Inhibition of VEGFR1 signaling, but not VEGFR2 (Flk-1, KDR), blocked HSC cell cycling, differentiation and hematopoietic recovery after BM suppression, resulting in the demise of the treated mice. Plasma elevation of placental growth factor (PlGF), which signals through VEGFR1, but not VEGFR2, restored hematopoiesis during the early and late phases following BM suppression. The mechanism whereby PlGF enhanced early phases of BM recovery was mediated directly through rapid chemotaxis of readily available VEGFR1(+) BM-repopulating and progenitor cells. The late phase of hematopoietic recovery was driven by PlGF-induced upregulation of matrix metalloproteinase-9 (MMP-9) in the BM, mediating the release of soluble Kit-ligand (sKitL). sKitL increased proliferation and motility of HSCs and progenitor cells, thereby augmenting hematopoietic recovery. PlGF promotes recruitment of VEGFR1(+) HSCs from a quiescent to a proliferative microenvironment within the BM, favoring differentiation, mobilization, and reconstitution of hematopoiesis.

Molecular pathways regulating mobilization of marrow-derived stem cells for tissue revascularization

Adult bone marrow is a rich reservoir of hematopoietic and vascular stem and progenitor cells. Mobilization and recruitment of these cells are essential for tissue revascularization. Physiological stress, secondary to tissue injury or tumor growth, results in the release of angiogenic factors, including vascular endothelial growth factor (VEGF), which promotes mobilization of stem cells to the circulation, contributing to the formation of functional vasculature. VEGF interacts with its receptors, VEGFR2 and VEGFR1, expressed on endothelial and hematopoietic stem cells, and thereby promotes recruitment of these cells to neo-angiogenic sites, accelerating the revascularization process. The mobilization of stem cells from marrow is a dynamic process, regulated by shear stress imparted by blood flow, and the activation of metalloproteinases that induce the release of 'Kit ligand', facilitating egress from the marrow to the circulation. Identification of the molecular pathways that support the proliferation and differentiation of vascular stem and progenitor cells will open up new avenues for the design of clinical trials to accelerate tissue vascularization and organogenesis.

Angiogenesis in hematologic malignancies and its clinical implications

Angiogenesis is defined as a neoformation of blood vessels of capillary origin. Hematopoiesis is closely linked with angiogenesis, for they share a common ancestor, the hemangioblast. Although it is well established that growth in solid tumors is dependent on angiogenesis, its role in hematologic malignancies has not yet been clarified. In this review, the direct evidence, ie, increased microvessel density, and the indirect evidence, ie, elevated level of angiogenic factors or overexpression of messenger RNA or protein of angiogenic factors, for and against the role of angiogenesis in the development and progression of hematologic malignancies are presented.

Adapted NOD/SCID model supports development of phenotypically and functionally mature T cells from human umbilical cord blood CD34(+) cells

The NOD-LtSZ scid/scid (NOD/SCID) repopulation assay is the criterion for the study of self-renewal and multilineage differentiation of human hematopoietic stem cells. An important shortcoming of this model is the reported absence of T-cell development. We studied this aspect of the model and investigated how it could be optimized to support T-cell development. Occasionally, low-grade thymic engraftment was observed in NOD/SCID mice or Rag2(-/-)gamma(c)(-/-) mice. In contrast, the treatment of NOD/SCID mice with a monoclonal antibody against the murine interleukin-2R beta, (IL-2R beta) known to decrease natural killer cell activity, resulted in human thymopoiesis in up to 60% of the mice. T-cell development was phenotypically normal and resulted in polyclonal, mature, and functional CD1(-) TCR alpha beta (+) CD4(+) or CD8(+) single-positive T cells. In mice with ongoing thymopoiesis, peripheral T cells were observed. TREC analysis showed that T cells with a naive phenotype (CD45RA(+)) emerged from the thymus. In approximately half of these mice, the peripheral T cells included a pauciclonal outgrowth of CD45RO(+) cells. These data suggest that all elements of a functional immune system were present in these animals.

A broad T-cell repertoire diversity and an efficient thymic function indicate a favorable long-term immune reconstitution after cord blood stem cell transplantation

Cord blood (CB) is used increasingly as a source of hematopoietic stem cells because of a lower risk of acute and chronic graft-versus-host disease (GVHD). However, there is some concern regarding the ability to adequately reconstitute host immune response due to the immaturity and naivety of CB T cells. This study was designed to evaluate T-cell reconstitution using combined approaches of phenotyping, analysis of alphabeta T-cell receptor (TCR) diversity, and assessment of ex vivo thymic function by measuring TCR rearrangement excision circles (TRECs). Ten patients who underwent CB transplantation for high-risk hematologic disorders were compared to a reference group of 19 age- and GVHD-matched patients who underwent transplantation with non-T cell-depleted bone marrow from an HLA-identical sibling donor. TREC values correlated with the relative number of naive T cells and with TCR repertoire polyclonality. During the first year after transplantation, TCR repertoires were highly abnormal and TREC values low in both groups. Notably, 2 years after transplantation onward TREC values as well as TCR diversity were higher in CB recipients than in recipients of bone marrow transplants. These data indicate an efficient thymic regeneration pathway from CB lymphoid progenitors despite the low number of cells infused compared to bone marrow, arguing for a complete clinical immune recovery after CB transplantation.

NK cells recover early and mediate cytotoxicity via perforin/granzyme and Fas/FasL pathways in umbilical cord blood recipients

Umbilical cord blood (UCB) is now widely accepted as a source of stem cells in patients with malignant hematologic and genetic disorders. We have recently reported that in a series of 30 pediatric UCB transplant recipients comparable outcome to that anticipated with other unrelated stem cell sources. In our series, however, the probability of GVHD for grade III-IV was 9% and no UCB recipient developed chronic GVHD. The reason for the low incidence of GVHD after UCB transplantation is not fully understood. Because functional NK cells are among the first population of lymphocytes to be detected in UCB transplant recipients, 2 months post-transplant on average, we wanted to establish whether NK cells could be implicated in reducing the risk of GVHD. Here, we confirm that early NK cells detected in UCB transplant recipients activate the granzyme/perforin lytic pathway and, in addition, they can mediate Fas/Fas ligand (FasL) activity, a finding not previously reported. Both pathways develop simultaneously and are detectable months before the other lymphocytes, notably CD8 are fully functional. Our contention, therefore, is that the low GVHD observed in UCB recipients may be partially due to early NK cells.

Donor stromal cells from human blood engraft in NOD/SCID mice

Little is known about the presence, frequency, and in vivo proliferative potential of stromal cells within blood-derived hematopoietic transplants. In this study, nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice were injected with human CD34+ peripheral blood cells (PBCs) or cord blood cells (CBCs, either enriched for CD34 or density-gradient separated mononuclear cells). Flow cytometric analysis 5 to 11 weeks after transplantation revealed the presence of a human lymphomyeloid hematopoiesis within the murine bone marrow. Immunohistochemical staining of bone marrow cell suspensions using human-specific antibodies showed human cells staining positive for human fibroblast markers, human von Willebrand factor (vWF) and human KDR (vascular endothelial growth factor receptor-2) in mice transplanted with CD34+ PBCs or CBCs, with mean frequencies between 0.6% and 2.4%. In stromal layers of bone marrow cultures established from the mice, immunohistochemical staining using human-specific antibodies revealed flattened reticular cells or spindle-shaped cells staining positive with human-specific antifibroblast antibodies (mean frequency, 2.2%). Cell populations of more rounded cells stained positive with human-specific antibodies recognizing CD34 (1.5%), vWF (2.2%), and KDR (1.6%). Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis and subsequent complementary DNA sequencing detected transcripts of human KDR (endothelial specific) and human proline hydroxylase-α (fibroblast specific) within the bone marrow and spleen of transplanted mice. Analysis of nontransplanted control mice yielded negative results in immunocytochemistry and RT-PCR. Cells expressing endothelial and fibroblast markers were also detected in the grafts before transplantation, and their numbers increased up to 3 log in vivo after transplantation. These results indicate that stromal progenitor cells are present in human cytokine-mobilized peripheral blood or cord blood that engraft in NOD/SCID mice.

Donor stromal cells from human blood engraft in NOD/SCID mice

Little is known about the presence, frequency, and in vivo proliferative potential of stromal cells within blood-derived hematopoietic transplants. In this study, nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice were injected with human CD34+ peripheral blood cells (PBCs) or cord blood cells (CBCs, either enriched for CD34 or density-gradient separated mononuclear cells). Flow cytometric analysis 5 to 11 weeks after transplantation revealed the presence of a human lymphomyeloid hematopoiesis within the murine bone marrow. Immunohistochemical staining of bone marrow cell suspensions using human-specific antibodies showed human cells staining positive for human fibroblast markers, human von Willebrand factor (vWF) and human KDR (vascular endothelial growth factor receptor-2) in mice transplanted with CD34+ PBCs or CBCs, with mean frequencies between 0.6% and 2.4%. In stromal layers of bone marrow cultures established from the mice, immunohistochemical staining using human-specific antibodies revealed flattened reticular cells or spindle-shaped cells staining positive with human-specific antifibroblast antibodies (mean frequency, 2.2%). Cell populations of more rounded cells stained positive with human-specific antibodies recognizing CD34 (1.5%), vWF (2.2%), and KDR (1.6%). Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis and subsequent complementary DNA sequencing detected transcripts of human KDR (endothelial specific) and human proline hydroxylase-α (fibroblast specific) within the bone marrow and spleen of transplanted mice. Analysis of nontransplanted control mice yielded negative results in immunocytochemistry and RT-PCR. Cells expressing endothelial and fibroblast markers were also detected in the grafts before transplantation, and their numbers increased up to 3 log in vivo after transplantation. These results indicate that stromal progenitor cells are present in human cytokine-mobilized peripheral blood or cord blood that engraft in NOD/SCID mice.

Infection by porcine endogenous retrovirus after islet xenotransplantation in SCID mice

Animal donors such as pigs could provide an alternative source of organs for transplantation. However, the promise of xenotransplantation is offset by the possible public health risk of a cross-species infection. All pigs contain several copies of porcine endogenous retroviruses (PERV), and at least three variants of PERV can infect human cell lines in vitro in co-culture, infectivity and pseudotyping experiments. Thus, if xenotransplantation of pig tissues results in PERV viral replication, there is a risk of spreading and adaptation of this retrovirus to the human host. C-type retroviruses related to PERV are associated with malignancies of haematopoietic lineage cells in their natural hosts. Here we show that pig pancreatic islets produce PERV and can infect human cells in culture. After transplantation into NOD/SCID (non-obese diabetic, severe combined immunodeficiency) mice, we detect ongoing viral expression and several tissue compartments become infected. This is the first evidence that PERV is transcriptionally active and infectious cross-species in vivo after transplantation of pig tissues. These results show that a concern for PERV infection risk associated with pig islet xenotransplantation in immunosuppressed human patients may be justified.

Cocultivation of umbilical cord blood cells with endothelial cells leads to extensive amplification of competent CD34+CD38- cells

OBJECTIVE

In this report, methods to expand the number of human cord blood hematopoietic stem cells were explored.

MATERIALS AND METHODS

CD34+ cord blood cells were expanded in the presence of various cytokine combinations in either a stroma-free cell culture system or a preformed porcine microvascular endothelial cell layer. After 7 to 21 days, stem cell number and function were monitored. In addition, the replicative history of stem cells was tracked using the fluorescent dye, PKH26.

RESULTS

With the addition of various cytokine combinations, total cellular expansion was equivalent for both culture systems, although the endothelial cell-based system contained statistically greater numbers of CD34+ cells. By day 21, the endothelial-based system receiving the FLT3L, SCF, IL-6, and GM-CSF cytokine combination contained five-fold greater numbers of CD34+ than the stroma cell-free culture cell system. Endothelial-based cultures receiving these four cytokines plus megakaryocyte growth and development factor produced a 640-fold expansion of CD34+CD38- cells as compared to a four-fold expansion in the stroma-free system. The number of progenitor cells generated was similar with both systems, yet the greatest degree of expansion of cobblestone area-forming cells was observed in the endothelial based cultures (11-fold vs four-fold). Virtually all CD34+ and CD34+CD38+ cells expanded in the presence of endothelial cells had undergone self replication by day 10, yet stromal cell-free cultures contained a significant number (4.8%) of quiescent cells. Identical numbers of re-isolated cord blood CD34+ cells expanded in both systems exhibited a similar ability to engraft and generate cells belonging to multiple hematopoietic lineages in human fetal bones implanted in immunodeficient mice.

CONCLUSIONS

These results suggest that the use of preformed endothelial cell monolayers might permit the ex vivo generation of sufficient numbers of cord stem cells to serve as successful grafts for adult transplant recipients.

Transplanted cord blood-derived endothelial precursor cells augment postnatal neovascularization

Endothelial precursor cells (EPCs) have been identified in adult peripheral blood. We examined whether EPCs could be isolated from umbilical cord blood, a rich source for hematopoietic progenitors, and whether in vivo transplantation of EPCs could modulate postnatal neovascularization. Numerous cell clusters, spindle-shaped and attaching (AT) cells, and cord-like structures developed from culture of cord blood mononuclear cells (MNCs). Fluorescence-trace experiments revealed that cell clusters, AT cells, and cord-like structures predominantly were derived from CD34-positive MNCs (MNC(CD34+)). AT cells and cell clusters could be generated more efficiently from cord blood MNCs than from adult peripheral blood MNCs. AT cells incorporated acetylated-LDL, released nitric oxide, and expressed KDR, VE-cadherin, CD31, and von Willebrand factor but not CD45. Locally transplanted AT cells survived and participated in capillary networks in the ischemic tissues of immunodeficient nude rats in vivo. AT cells thus had multiple endothelial phenotypes and were defined as a major population of EPCs. Furthermore, laser Doppler and immunohistochemical analyses revealed that EPC transplantation quantitatively augmented neovascularization and blood flow in the ischemic hindlimb. In conclusion, umbilical cord blood is a valuable source of EPCs, and transplantation of cord blood-derived EPCs represents a promising strategy for modulating postnatal neovascularization.