Biology of human umbilical cord blood-derived hematopoietic stem/progenitor cells

Umbilical Cord Blood Hematopoietic Cells: From Biology to Hematopoietic Transplants and Cellular Therapies

Umbilical cord blood (UCB) is a rich source of hematopoietic stem and progenitor cells that are biologically superior to their adult counterparts. UCB cells can be stored for several years without compromising their numbers or function. Today, public and private UCB banks have been established in several countries around the world. After 35 years since the first UCB transplant (UCBT), more than 50,000 UCBTs have been performed worldwide. In pediatric patients, UCBT is comparable to or superior to bone marrow transplantation. In adult patients, UCB can be an alternative source of hematopoietic cells when an HLA-matched unrelated adult donor is not available and when a transplant is urgently needed. Delayed engraftment (due to reduced absolute numbers of hematopoietic cells) and higher costs have led many medical institutions not to consider UCB as a first-line cell source for hematopoietic transplants. As a result, the use of UCB as a source of hematopoietic stem and progenitor cells for transplantation has declined over the past decade. Several approaches are being investigated to make UCBTs more efficient, including improving the homing capabilities of primitive UCB cells and increasing the number of hematopoietic cells to be infused. Several of these approaches have already been applied in the clinic with promising results. UCB also contains immune effector cells, including monocytes and various lymphocyte subsets, which, together with stem and progenitor cells, are excellent candidates for the development of cellular therapies for hematological and non-hematological diseases.

Fresh Umbilical Cord Blood-A Source of Multipotent Stem Cells, Collection, Banking, Cryopreservation, and Ethical Concerns

Umbilical cord blood (UCB) is a rich source of hematopoietic cells that can be used to replace bone marrow components. Many blood disorders and systemic illnesses are increasingly being treated with stem cells as regenerative medical therapy. Presently, collected blood has been stored in either public or private banks for allogenic or autologous transplantation. Using a specific keyword, we used the English language to search for relevant articles in SCOPUS and PubMed databases over time frame. According to our review, Asian countries are increasingly using UCB preservation for future use as regenerative medicine, and existing studies indicate that this trend will continue. This recent literature review explains the methodology of UCB collection, banking, and cryopreservation for future clinical use. Between 2010 and 2022, 10,054 UCB stem cell samples were effectively cryopreserved. Furthermore, we have discussed using Mesenchymal Stem Cells (MSCs) as transplant medicine, and its clinical applications. It is essential for healthcare personnel, particularly those working in labor rooms, to comprehend the protocols for collecting, transporting, and storing UCB. This review aims to provide a glimpse of the details about the UCB collection and banking processes, its benefits, and the use of UCB-derived stem cells in clinical practice, as well as the ethical concerns associated with UCB, all of which are important for healthcare professionals, particularly those working in maternity wards; namely, the obstetrician, neonatologist, and anyone involved in perinatal care. This article also highlights the practical and ethical concerns associated with private UCB banks, and the existence of public banks. UCB may continue to grow to assist healthcare teams worldwide in treating various metabolic, hematological, and immunodeficiency disorders.

Therapeutic Perspectives for the Clinical Application of Umbilical Cord Hematopoietic and Mesenchymal Stem Cells: Overcoming Complications Arising After Allogeneic Hematopoietic Stem Cell Transplantation

This review focuses on the therapeutic features of umbilical cord blood (UCB) cells as a source for allogeneic hematopoietic stem cell transplantation (aHSCT) in adult and child populations to treat malignant and nonmalignant hematologic diseases, genetic disorders, or pathologies of the immune system, when standard treatment (e.g., chemotherapy) is not effective or clinically contraindicated. In this article, we summarize the immunological properties and the advantages and disadvantages of using UCB stem cells and discuss a variety of treatment outcomes using different sources of stem cells from different donors both in adults and pediatric population. We also highlight the critical properties (total nucleated cell dose depending on HLA compatibility) of UCB cells that reach better survival rates, reveal the advantages of double versus single cord blood unit transplantation, and present recommendations from the most recent studies. Moreover, we summarize the mechanism of action and potential benefit of mesenchymal umbilical cord cells and indicate the most common posttransplantation complications.

Telomeres, Telomerase and Cancer

Telomeres and telomerase play a crucial role in human aging and cancer. Three "drivers" of human aging can be identified. The developmental program encoded in DNA is the primary determinant of lifespan. Faithful execution of the developmental program requires stability of the (epi-)genome which is challenged throughout life by damage to DNA as well as epigenetic 'scars' from error-free DNA repair and stochastic errors made during the establishment and maintenance of the "epigenome". Over time (epi-)mutations accumulate, compromising cellular function and causing (pre-)malignant alterations. Damage to the genome and epigenome can be considered the second "driver" of aging. A third driver of the aging process, important to suppress tumors in long-lived animals, is caused by progressive loss of telomeric DNA. Telomere erosion protects against cancer early in life but limits cell renewal late in life, in agreement with the Antagonistic Pleiotropy theory on the evolutionary origin of aging. Malignant tumors arise when mutations and/or epimutations in cells (clock 2) corrupt the developmental program (clock 1) as well as tumor suppression by telomere erosion (clock 3). In cancer cells clock 3 is typically inactivated by loss of p53 as well as increased expression of telomerase. Taken together, aging in humans can be described by the ticking of three clocks: the clock that directs development, the accumulation of (epi-)mutations over time and the telomere clock that limits the number of cell divisions in normal stem and immune cells.

Cord and peripheral blood erythrocyte analysis by scanning electron microscopy and flow cytometry

INTRODUCTION

Human umbilical cord blood is rich in hematopoietic cells. We aimed to focus on the morphological, biochemical, membrane protein profile and surface protein expression differences of erythrocytes, isolated from cord and adult peripheral blood using techniques such as high-resolution scanning electron microscopy (SEM), gel electrophoresis (SDS-PAGE) and flow cytometry.

METHODS

Adult peripheral blood was collected from consenting adults, and umbilical cord blood was procured from consenting mothers, post-delivery at Medical College, Kolkata. We emphasized on cord and adult peripheral blood erythrocytes' morphological variations using SEM images and protein expression by flow cytometric analysis. Some conventional biochemical analyses such as osmotic fragility of the cell membrane, haemoglobin co-oxidation study and lipid peroxidation assay were done for supporting evidence along with membrane protein content using gel electrophoresis.

RESULTS

Our SEM images indicated clear morphological variations in cord erythrocyte with a higher degree of cellular deformities and difference in membrane texture. Flow cytometric analysis of cord erythrocyte showed a significant difference in CD235a expression than adults. We observed an overexpression of GLUT1 and decreased expression of Band 3 in cord erythrocyte membrane. Our results also showed cord erythrocytes have low osmotic fragility, a slower rate of co-oxidation of cord haemoglobin and a lesser lipid peroxidation level than that of adults.

CONCLUSION

Cord blood erythrocytes have deeper indentations leading to higher flexibility, more oxygen-carrying capacity and less osmotic fragility in comparison with adult erythrocytes. The expression of CD235a and Band 4.5 (GLUT 1) was significantly higher in cord erythrocytes than peripheral adult erythrocytes.

Therapeutic use of red blood cells and platelets derived from human cord blood stem cells

Red blood cells (RBCs) and platelets derived from stem cells are possible solutions to the increasing demand for blood transfusion. Based on the availability of stem cells, their relatively defined differentiation mechanisms, and the massive exploration of induction systems, the generation of RBCs or platelets in vitro from cord blood hematopoietic stem/progenitor cells (CB-HSPCs) has potential for clinical applications. However, information on the clinical translation of stem cell-derived RBCs and platelets in the literature and at the ClinicalTrials.gov website is very limited. The only clinical trial on cultured RBCs, which aimed to assess the lifespan of RBCs cultured in vivo, was reported by Luc Douay and colleagues. Of note, the cultured RBCs they used were derived from autologous peripheral blood HSPCs, and no cultured platelets have been applied clinically to date. However, CB-HSPC-derived megakaryocytes, platelet precursors, have been used in the treatment of thrombocytopenia. A successful phase I trial was reported, followed by phase II and III clinical trials conducted in China. In this review, the gap between the many basic studies and limited clinical trials on stem cell-derived RBCs and platelets is summarized. The possible reasons and solutions for this gap are discussed. Further technological improvements for blood cell expansion and maturation ex vivo and the establishment of biological standards for stem cell derivatives might help to facilitate the therapeutic applications of cultured RBCs and platelets derived from CB-HSPCs in the near future.

Umbilical cord blood transplantation: Still growing and improving

Umbilical cord blood transplantation (UCBT) has been performed in the clinic for over 30 years. The biological and immunological characteristics of umbilical cord blood (UCB) have been re-recognized in recent years. UCB, previously considered medical waste, is rich in hematopoietic stem cells (HSCs), which are naïve and more energetic and more easily expanded than other stem cells. UCB has been identified as a reliable source of HSCs for allogeneic hematopoietic stem cell transplantation (allo-HSCT). UCBT has several advantages over other methods, including no harm to mothers and donors, an off-the-shelf product for urgent use, less stringent HLA match, lower incidence and severity of chronic graft-vs-host disease (GVHD), and probably a stronger graft-vs-leukemia effect, especially for minimal residual disease-positive patients before transplant. Recent studies have shown that the outcome of UCBT has been improved and is comparable to other types of allo-HSCT. Currently, UCBT is widely used in malignant, nonmalignant, hematological, congenital and metabolic diseases. The number of UCB banks and transplantation procedures increased exponentially before 2013. However, the number of UCBTs increased steadily in Asia and China but decreased in the United States and Europe year-on-year from 2013 to 2019. In this review, we focus on the development of UCBT over the past 30 years, the challenges it faces and the strategies for future improvement, including increasing UCB numbers, cord blood unit selection, conditioning regimens and GVHD prophylaxis for UCBT, and management of complications of UCBT.

DNA barcode to trace the development and differentiation of cord blood stem cells (Review)

Umbilical cord blood transplantation was first reported in 1980. Since then, additional research has indicated that umbilical cord blood stem cells (UCBSCs) have various advantages, such as multi-lineage differentiation potential and potent renewal activity, which may be induced to promote their differentiation into a variety of seed cells for tissue engineering and the treatment of clinical and metabolic diseases. Recent studies suggested that UCBSCs are able to differentiate into nerve cells, chondrocytes, hepatocyte-like cells, fat cells and osteoblasts. The culture of UCBSCs has developed from feeder-layer to feeder-free culture systems. The classical techniques of cell labeling and tracing by gene transfection and fluorescent dye and nucleic acid analogs have evolved to DNA barcode technology mediated by transposon/retrovirus, cyclization recombination-recombinase and clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 strategies. DNA barcoding for cell development tracing has advanced to include single cells and single nucleic acid mutations. In the present study, the latest research findings on the development and differentiation, culture techniques and labeling and tracing of UCBSCs are reviewed. The present study may increase the current understanding of UCBSC biology and its clinical applications.

Comparative Analysis of the Biosimilar and Innovative G-CSF Modulated Pathways on Umbilical Cord Blood-Derived Mononuclear Cells

Biosimilars of granulocyte colony-stimulating factor (G-CSF) have been routinely introduced into clinical practice. However, not functional genomics characterization has been performed yet in comparison with the innovator G-CSF. This study aimed to evaluate the transcriptomic changes in an in vitro model of umbilical cord blood cells (UBC) exposed to G-CSF for the identification of their modulated pathways. Umbilical cord blood cells-derived mononuclear cells (MNCs) were treated with biosimilar and innovator G-CSF for further gene expression profiling analysis using a microarray-based platform. Comparative analysis of biosimilar and innovator G-CSF gene expression signatures allowed us to identify the most commonly modulated pathways by both drugs. In brief, we observed predominantly upmodulation of transcripts related to PI3K-Akt, NF-kappaB, and tumor necrosis factor (TNF) signaling pathways as well as transcripts related to negative regulation of apoptotic process among others. In addition, hematopoietic colony-forming cell assays corroborate the G-CSF phenotypic effects over UBC-derived MNCs. In conclusion, our study suggests that G-CSF impacts UBC-derived cells through the modulation of several signaling pathways associated with cell survival, migration, and proliferation. The concordance observed between biosimilar and innovator G-CSF emphasizes their similarity in regards to their specificity and biological responses.

Use of Human Umbilical Cord and Its Byproducts in Tissue Regeneration

The fresh or cryopreserved human umbilical cord (HUC) and its byproducts, such as cells and extracts, have different uses in tissue regeneration. Defining what HUC byproduct is more effective in a particular application is a challenge. Furthermore, the methods of isolation, culture and preservation, may affect cell viability and regenerative properties. In this article, we review the HUC and its byproducts' applications in research and clinical practice. We present our results of successful use of HUC as a patch to treat gastroschisis and its potential to be applied in other conditions. Our in vitro results show an increase in proliferation and migration of human fibroblasts by using an acellular HUC extract. Our goal is to promote standardization of procedures and point out that applications of HUC and its byproducts, as well as the resulting advances in regenerative medicine, will depend on rigorous quality control and on more research in this area.

Past, present, and future efforts to enhance the efficacy of cord blood hematopoietic cell transplantation

Cord blood (CB) has been used as a viable source of hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) in over 35,000 clinical hematopoietic cell transplantation (HCT) efforts to treat the same variety of malignant and non-malignant disorders treated by bone marrow (BM) and mobilized peripheral blood (mPB) using HLA-matched or partially HLA-disparate related or unrelated donor cells for adult and children recipients. This review documents the beginning of this clinical effort that started in the 1980’s, the pros and cons of CB HCT compared to BM and mPB HCT, and recent experimental and clinical efforts to enhance the efficacy of CB HCT. These efforts include means for increasing HSC numbers in single CB collections, expanding functional HSCs ex vivo, and improving CB HSC homing and engraftment, all with the goal of clinical translation. Concluding remarks highlight the need for phase I/II clinical trials to test the experimental procedures that are described, either alone or in combination.

Cord blood research, banking, and transplantation: achievements, challenges, and perspectives

The first hematopoietic transplant in which umbilical cord blood (UCB) was used as the source of hematopoietic cells was performed in October 1988. Since then, significant achievements have been reported in terms of our understanding of the biology of UCB-derived hematopoietic stem (HSCs) and progenitor (HPCs) cells. Over 40,000 UCB transplants (UCBTs) have been performed, in both children and adults, for the treatment of many different diseases, including hematologic, metabolic, immunologic, neoplastic, and neurologic disorders. In addition, cord blood banking has been developed to the point that around 800,000 units are being stored in public banks and more than 4 million units in private banks worldwide. During these 30 years, research in the UCB field has transformed the hematopoietic transplantation arena. Today, scientific and clinical teams are still working on different ways to improve and expand the use of UCB cells. A major effort has been focused on enhancing engraftment to potentially reduce risk of infection and cost. To that end, we have to understand in detail the molecular mechanisms controlling stem cell self-renewal that may lead to the development of ex vivo systems for HSCs expansion, characterize the mechanisms regulating the homing of HSCs and HPCs, and determine the relative place of UCBTs, as compared to other sources. These challenges will be met by encouraging innovative research on the basic biology of HSCs and HPCs, developing novel clinical trials, and improving UCB banking both in the public and private arenas.

Curative approaches for sickle cell disease: A review of allogeneic and autologous strategies

Despite sickle cell disease (SCD) first being reported >100years ago and molecularly characterized >50years ago, patients continue to experience severe morbidity and early mortality. Although there have been substantial clinical advances with immunizations, penicillin prophylaxis, hydroxyurea treatment, and transfusion therapy, the only cure that can be offered is hematopoietic stem cell transplantation (HSCT). In this work, we summarize the various allogeneic curative approaches reported to date and discuss open and upcoming clinical research protocols. Then we consider gene therapy and gene editing strategies that may enable cure based on autologous HSCs.

Immobilisation of Delta-like 1 ligand for the scalable and controlled manufacture of hematopoietic progenitor cells in a stirred bioreactor

Background

Umbilical cord blood provides a source of hematopoietic stem cells for transplantation with immunological and availability advantages over conventional bone marrow sources. Limited cell numbers and slower engraftment from umbilical cord blood units has led to the clinical development of immobilised Notch ligand Delta-Like 1 to promote ex vivo expansion of a rapidly engrafting cell population. However, current immobilisation methods are not simple to scale in a controlled manner.

Results

Delta-Like 1 was immobilised onto streptavidin coated magnetic particles via a heterobifunctionalised polyethylene glycol linker molecule to provide an easily manipulated format of surface protein presentation. CD34⁺ enriched cord blood cells were treated with Delta-Like 1 immobilised particles, and immunophenotypic markers measured to monitor population distributions using cluster identification, characterization, and regression software. The amenability of the approach to scalability was evaluated in a micro-scale stirred tank bioreactor. Surface concentration of Delta-Like 1 was well controlled used differing stoichiometric reagent ratios. Protein immobilisation was a cost effective process and particles were efficiently removed from the final cell product. Immobilised Delta-Like 1 is functional and stimulates qualitatively similar CD34^hi, CD38^lo, CD90^lo, CD133^hi, CD135^hi progenitor expansion in both static culture and scalable stirred culture platforms.

Conclusions

Immobilised Delta-Like 1 in this form has the potential to improve the manufacturing efficiency and control of final ex vivo expanded cell product through compatibility with highly controlled and characterised suspension culture systems.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-017-0383-0) contains supplementary material, which is available to authorized users.

Alternative Donor/Unrelated Donor Transplants for the β-Thalassemia and Sickle Cell Disease

Considerable progress with respect to donor source has been achieved in allogeneic stem cell transplant for patients with hemoglobin disorders, with matched sibling donors in the 1980s, matched unrelated donors and cord blood sources in the 1990s, and haploidentical donors in the 2000s. Many studies have solidified hematopoietic progenitors from matched sibling marrow, cord blood, or mobilized peripheral blood as the best source-with the lowest graft rejection and graft versus host disease (GvHD), and highest disease-free survival rates. For patients without HLA-matched sibling donors, but who are otherwise eligible for transplant, fully allelic matched unrelated donor (8/8 HLA-A, B, C, DRB1) appears to be the next best option, though an ongoing study in patients with sickle cell disease will provide data that are currently lacking. There are high GvHD rates and low engraftment rates in some of the unrelated cord transplant studies. Haploidentical donors have emerged in the last decade to have less GvHD; however, improvements are needed to increase the engraftment rate. Thus the decision to use unrelated cord blood units or haploidentical donors may depend on the institutional expertise; there is no clear preferred choice over the other. Active research is ongoing in expanding cord blood progenitor cells to overcome the limitation of cell dose, including the options of small molecule inhibitor compounds added to ex vivo culture or co-culture with supportive cell lines. There are inconsistent data from using 7/8 or lower matched unrelated donors. Before routine use of these less matched donor sources, work is needed to improve patient selection, conditioning regimen, GvHD prophylaxis, and/or other strategies.

Physical characterization of hematopoietic stem cells using multidirectional label-free light scatterings

An experimental setup capable of measuring simultaneous 2D scattered light angular distribution from two directions to study cell morphology without the use of bio-labels was developed. Experiments with hematopoietic stem cells (CD34⁺ cells) show good agreement with detailed numerical simulations of light scattering. Numerical simulations and computer models of cells are used to identify physical features of cells with the largest scattering cross sections. This allows for determination of size, geometry of the nucleus and distribution of mitochondria in hematopoietic stem cells by means of our label-free method.

The LINA Study: Higher Sensitivity of Infant Compared to Maternal Eosinophil/Basophil Progenitors to Indoor Chemical Exposures

Purpose. Enhanced eosinophil/basophil (Eo/B) progenitor cell levels are known to be associated with allergic inflammation and atopy risk. The aim of the present study was to investigate the influence of different indoor exposures on the recruitment and differentiation of Eo/B progenitors in mother-child pairs. Methods. In 68 mother-child pairs of the LINA study peripheral blood mononuclear cells were used to assess Eo/B colony forming units (CFUs). Information about disease outcomes and indoor exposures was obtained from questionnaires. Indoor concentrations of volatile organic compounds (VOCs) were measured by passive sampling. Results. Infant's Eo/B CFUs were positively associated with exposure to tobacco smoke, disinfectants, or VOCs. In contrast, for maternal Eo/B CFUs, only a few associations were seen. Higher numbers of infant Eo/B CFUs were observed in children with wheezing symptoms within the second year of life. Conclusions. We demonstrate that infant's hematopoietic cells seem to respond with more sensitivity to environmental exposure compared to maternal cells. At least in infants, an activation of these hematopoietic cells by environmental exposure could contribute to an enhanced risk for the development of respiratory outcomes.

Stem cell research in Latin America: update, challenges and opportunities in a priority research area

Stem cell research is attracting wide attention as a promising and fast-growing field in Latin America, as it is worldwide. Many countries in the region have defined Regenerative Medicine as a research priority and a focus of investment. This field generates not only opportunities but also regulatory, technical and operative challenges. In this review, scientists from Uruguay, Mexico, Chile, Brazil and Argentina provide their view on stem cell research in each of their countries. Despite country-specific characteristics, all countries share several issues such as regulatory challenges. Key initiatives of each country to promote stem cell research are also discussed. As a conclusion, it is clear that regional integration should be more emphasized and international collaboration, promoted.

Plasma Derived From Human Umbilical Cord Blood Modulates Mitogen-Induced Proliferation of Mononuclear Cells Isolated From the Peripheral Blood of ALS Patients

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by degeneration of motor neurons in the spinal cord and brain. This disease clinically manifests as gradual muscular weakness and atrophy leading to paralysis and death by respiratory failure. While multiple interdependent factors may contribute to the pathogenesis of ALS, increasing evidence shows the possible presence of autoimmune mechanisms that promote disease progression. The potential use of plasma derived from human umbilical cord blood (hUCB) as a therapeutic tool is currently in its infancy. The hUCB plasma is rich in cytokines and growth factors that are required for growth and survival of cells during hematopoiesis. In this study, we investigated the effects of hUCB plasma on the mitogen-induced proliferation of mononuclear cells (MNCs) isolated from the peripheral blood of ALS patients and apoptotic activity by detection of caspase 3/7 expression of the isolated MNCs in vitro. Three distinct responses to phytohemagglutinin (PHA)-induced proliferation of MNCs were observed, which were independent of age, disease duration, and the ALS rating scale: Group I responded normally to PHA, Group II showed no response to PHA, while Group III showed a hyperactive response to PHA. hUCB plasma attenuated the hyperactive response (Group III) and potentiated the normal response in Group I ALS patients, but did not alter that of the nonresponders to PHA (Group II). The elevated activity of caspase 3/7 observed in the MNCs from ALS patients was significantly reduced by hUCB plasma treatment. Thus, study results showing different cell responses to mitogen suggest alteration in lymphocyte functionality in ALS patients that may be a sign of immune deficiency in the nonresponders and autoimmunity alterations in the hyperactive responders. The ability of hUCB plasma to modulate the mitogen cell response and reduce caspase activity suggests that the use of hUCB plasma alone, or with stem cells, may prove useful as a therapeutic in ALS patients.

Preclinical evaluation of the immunomodulatory properties of cardiac adipose tissue progenitor cells using umbilical cord blood mesenchymal stem cells: a direct comparative study

Cell-based strategies to regenerate injured myocardial tissue have emerged over the past decade, but the optimum cell type is still under scrutiny. In this context, human adult epicardial fat surrounding the heart has been characterized as a reservoir of mesenchymal-like progenitor cells (cardiac ATDPCs) with potential clinical benefits. However, additional data on the possibility that these cells could trigger a deleterious immune response following implantation are needed. Thus, in the presented study, we took advantage of the well-established low immunogenicity of umbilical cord blood-derived mesenchymal stem cells (UCBMSCs) to comparatively assess the immunomodulatory properties of cardiac ATDPCs in an in vitro allostimulatory assay using allogeneic mature monocyte-derived dendritic cells (MDDCs). Similar to UCBMSCs, increasing amounts of seeded cardiac ATDPCs suppressed the alloproliferation of T cells in a dose-dependent manner. Secretion of proinflammatory cytokines (IL6, TNFα, and IFNγ) was also specifically modulated by the different numbers of cardiac ATDPCs cocultured. In summary, we show that cardiac ATDPCs abrogate T cell alloproliferation upon stimulation with allogeneic mature MDDCs, suggesting that they could further regulate a possible harmful immune response in vivo. Additionally, UCBMSCs can be considered as valuable tools to preclinically predict the immunogenicity of prospective regenerative cells.

Impact of umbilical cord blood-derived mesenchymal stem cells on cardiovascular research

Over the years, cell therapy has become an exciting opportunity to treat human diseases. Early enthusiasm using adult stem cell sources has been tempered in light of preliminary benefits in patients. Considerable efforts have been dedicated, therefore, to explore alternative cells such as those extracted from umbilical cord blood (UCB). In line, UCB banking has become a popular possibility to preserve potentially life-saving cells that are usually discarded after birth, and the number of UCB banks has grown worldwide. Thus, a brief overview on the categories of UCB banks as well as the properties, challenges, and impact of UCB-derived mesenchymal stem cells (MSCs) on the area of cardiovascular research is presented. Taken together, the experience recounted here shows that UCBMSCs are envisioned as attractive therapeutic candidates against human disorders arising and/or progressing with vascular deficit.

Repeated Administrations of Human Umbilical Cord Blood Cells Improve Disease Outcomes in a Mouse Model of Sanfilippo Syndrome Type III B

Sanfilippo syndrome type III B (MPS III B) is an inherited disorder characterized by a deficiency of α- N-acetylglucosaminidase (Naglu) enzyme leading to accumulation of heparan sulfate in lysosomes and severe neurological deficits. We have previously shown that a single administration of human umbilical cord mononuclear cells (hUCB MNCs) into Naglu knockout mice decreased behavioral abnormalities and tissue pathology. In this study, we tested whether repeated doses of hUCB MNCs would be more beneficial than a single dose of cells. Naglu mice at 3 months of age were randomly assigned to either a Media-only group or one of three hUCB MNC treatment groups-single low dose (3 × 106 cells), single high dose (1.8 × 107 cells), or multiple doses (3 × 106 cells monthly for 6 months) delivered intravenously; cyclosporine was injected intraperitoneally to immune suppress the mice for the duration of the study. An additional control group of wild-type mice was also used. We measured anxiety in an open field test and cognition in an active avoidance test prior to treatment and then at monthly intervals for 6 months. hUCB MNCs restored normal anxiety-like behavior in these mice ( p< 0.001). The repeated cell administrations also restored hippocampal cytoarchitecture, protected the dendritic tree, decreased GM3 ganglioside accumulation, and decreased microglial activation, particularly in the hippocampus and cortex. These data suggest that the neuroprotective effect of hUCB MNCs can be enhanced by repeated cell administrations.

Umbilical cord blood-derived mesenchymal stem cells: new therapeutic weapons for idiopathic dilated cardiomyopathy?

Dilated cardiomyopathy is the most frequent etiology of non-ischemic heart failure. In a majority of cases the causal mechanism is unknown, giving rise to the term 'idiopathic' dilated cardiomyopathy (IDCM). Major pathological derangements include patchy interstitial fibrosis, degenerated cardiomyocytes, and dilatation of the cardiac chambers, but recent evidence suggests that disease progression may also have the signature of cardiac endothelial dysfunction. As we better understand the molecular basis of IDCM, novel therapeutic approaches, mainly gene transfer and cell-based therapies, are being explored. Cells with regenerative potential have been extensively tested in cardiac diseases of ischemic origin in both pre-clinical and clinical settings. However, whether cell therapy has any clinical value in IDCM patients is still being evaluated. This article is a concise summary of cell therapy studies for IDCM, with a focus on recent advances that highlight the vascular potential exhibited by umbilical cord blood-derived mesenchymal stem cells (UCBMSCs). We also provide an overview of cardiac vasculature as a key regulator of subjacent myocardial integrity and function, and discuss the potential mechanisms of UCBMSC amelioration of IDCM myocardium. Consideration of these issues shows that these cells are conceivably new therapeutic agents for this complex and elusive human disorder.

Intraarterial transplantation of human umbilical cord blood mononuclear cells is more efficacious and safer compared with umbilical cord mesenchymal stromal cells in a rodent stroke model

INTRODUCTION

Stroke is the second leading cause of death worldwide, claims six lives every 60 seconds, and is a leading cause of adult disability across the globe. Tissue plasminogen activator, the only United States Food and Drug Administration (FDA)-approved drug currently available, has a narrow therapeutic time window of less than 5 hours. In the past decade, cells derived from the human umbilical cord (HUC) have emerged as a potential therapeutic alternative for stroke; however, the most effective HUC-derived cell population remains unknown.

METHODS

We compared three cell populations derived from the human umbilical cord: cord blood mononuclear cells (cbMNCs); cord blood mesenchymal stromal cells (cbMSCs), a subpopulation of cbMNCs; and cord matrix MSCs (cmMSCs). We characterized these cells in vitro with flow cytometry and assessed the cells' in vivo efficacy in a 2-hour transient middle cerebral artery occlusion (MCAo) rat model of stroke. cbMNCs, cbMSCs, and cmMSCs were each transplanted intraarterially at 24 hours after stroke.

RESULTS

A reduction in neurologic deficit and infarct area was observed in all three cell groups; however, this reduction was significantly enhanced in the cbMNC group compared with the cmMSC group. At 2 weeks after stroke, human nuclei-positive cells were present in the ischemic hemispheres of immunocompetent stroke rats in all three cell groups. Significantly decreased expression of rat brain-derived neurotrophic factor mRNA was observed in the ischemic hemispheres of all three cell-treated and phosphate-buffered saline (PBS) group animals compared with sham animals, although the decrease was least in cbMNC-treated animals. Significantly decreased expression of rat interleukin (IL)-2 mRNA and IL-6 mRNA was seen only in the cbMSC group. Notably, more severe complications (death, eye inflammation) were observed in the cmMSC group compared with the cbMNC and cbMSC groups.

CONCLUSIONS

All three tested cell types promoted recovery after stroke, but cbMNCs showed enhanced recovery and fewer complications compared with cmMSCs.

Concise review: ex vivo expansion of cord blood-derived hematopoietic stem and progenitor cells: basic principles, experimental approaches, and impact in regenerative medicine

Hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) play key roles in the production of mature blood cells and in the biology and clinical outcomes of hematopoietic transplants. The numbers of these cells, however, are extremely low, particularly in umbilical cord blood (UCB); thus, ex vivo expansion of human UCB-derived HSCs and HPCs has become a priority in the biomedical field. Expansion of progenitor cells can be achieved by culturing such cells in the presence of different combinations of recombinant stimulatory cytokines; in contrast, expansion of actual HSCs has proved to be more difficult because, in addition to needing recombinant cytokines, HSCs seem to deeply depend on the presence of stromal cells and/or elements that promote the activation of particular self-renewal signaling pathways. Hence, there is still controversy regarding the optimal culture conditions that should be used to achieve this. To date, UCB transplants using ex vivo-expanded cells have already been performed for the treatment of different hematological disorders, and although results are still far from being optimal, the advances are encouraging. Recent studies suggest that HSCs may also give rise to nonhematopoietic cells, such as neural, cardiac, mesenchymal, and muscle cells. Such plasticity and the possibility of producing nonhematopoietic cells at the clinical scale could bring new alternatives for the treatment of neural, metabolic, orthopedic, cardiac, and neoplastic disorders. Once standardized, ex vivo expansion of human HSCs/HPCs will surely have a positive impact in regenerative medicine.

Double umbilical cord blood transplantation for hematological malignancies: a long-term analysis from the SFGM-TC registry

Allogeneic hematopoietic stem cell (HSC) transplantation is a curative treatment for many hematologic malignancies for which umbilical cord blood (UCB) represents an alternative source of HSCs. To overcome the low cellularity of one UCB unit, double UCB transplantation (dUCBT) has been developed in adults. We have analyzed the outcome of 136 patients who underwent dUCBT reported to the SFGM-TC registry between 2005 and 2007. Forty-six patients received myeloablative regimens, and 90 patients received reduced-intensity conditioning regimens. There were 84 cases of leukemia, 17 cases of non-Hodgkin lymphoma, 11 cases of myeloma, and 24 other hematologic malignancies. At transplantation, 40 (29%) patients were in complete remission. At day 60 after transplantation, the cumulative incidence of neutrophil recovery was 91%. We observed one UCB unit domination in 88% of cases. The cumulative incidence of day 100 acute graft-versus-host disease, chronic graft-versus-host disease, transplant-related mortality, and relapse at 2 years were 36%, 23%, 27%, and 28% respectively. After a median follow-up of 49.5 months, the 3-year probabilities of overall and progression-free survival were 41% and 35%, respectively, with a significant overall survival advantage when male cord engrafted male recipients. We obtained a long-term plateau among patients in complete remission, which makes dUCBT a promising treatment strategy for these patients.

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

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

Comparative in vitro analysis of different hematopoietic cell populations from human cord blood: in search of the best option for clinically oriented ex vivo cell expansion

BACKGROUND

Ex vivo expansion of hematopoietic stem and progenitor cells has become a priority in the experimental hematology arena. In this study we have obtained different hematopoietic cell populations from umbilical cord blood and simultaneously assessed their proliferation and expansion kinetics. Our main goal was to determine which one of these cell populations would be more suitable for clinical-grade ex vivo expansion.

STUDY DESIGN AND METHODS

By using immunomagnetic-negative selection and cell sorting, five cell populations were obtained: unseparated mononuclear cells (MNCs; I); two lineage-negative cell populations, one enriched for CD34+ CD38+ cells (II) and the other enriched for CD34+ CD38- cells (III); and two CD34+ cell fractions purified by fluorescence-activated cell sorting, one containing CD34+ CD38+ cells (IV) and the other containing CD34+ CD38- cells (V). The kinetics of such populations were analyzed in both relative and absolute terms.

RESULTS

No expansion was observed in Population I; in contrast, significant increments in the numbers of both progenitor and stem cells were observed in cultures of Populations II to V. Population V (reaching 12,800-fold increase in total cells; 1280-fold increase in CD34+ cells; 490-fold increase in colony-forming cells; and 12-fold increase in long-term culture-initiating cells) showed the highest proliferation and expansion potentials.

CONCLUSION

Our study suggests that the cell fraction containing greater than 98% CD34+ CD38- cells would be the ideal one for large-scale ex vivo expansion; however, based on our data, it seems that, except for MNCs, all other cell populations could also be used as input cell fractions.

In vitro biology of human hematopoietic stem and progenitor cells

Hematopoietic stem and progenitor cells from human umbilical cord blood have been the focus of both basic and clinical research during the last 20 years. It has been clearly demonstrated that such sells possess higher proliferation and expansion potentials, as compared to their adult counterparts, and their capacity to reconstitute the hematopoietic system of mammals has also been shown. Different In vitro systems have been used to characterize the biology of these hematopoietic cells and some culture methods are being currently used to expand the numbers of such cells for clinical purposes.

The dose-response effect of acute intravenous transplantation of human umbilical cord blood cells on brain damage and spatial memory deficits in neonatal hypoxia-ischemia

Despite the beneficial effects of cell-based therapies on brain repair shown in most studies, there has not been a consensus regarding the optimal dose of human umbilical cord blood cells (HUCBC) for neonatal hypoxia-ischemia (HI). In this study, we compared the long-term effects of intravenous administration of HUCBC at three different doses on spatial memory and brain morphological changes after HI in newborn Wistar rats. In addition, we tested whether the transplanted HUCBC migrate to the injured brain after transplantation. Seven-day-old animals underwent right carotid artery occlusion and were exposed to 8% O(2) inhalation for 2 h. After 24 h, randomly selected animals were assigned to four different experimental groups: HI rats administered with vehicle (HI+vehicle), HI rats treated with 1×10(6) (HI+low-dose), 1×10(7) (HI+medium-dose), and 1×10(8) (HI+high-dose) HUCBC into the jugular vein. A control group (sham-operated) was also included in this study. After 8 weeks of transplantation, spatial memory performance was assessed using the Morris water maze (MWM), and subsequently, the animals were euthanized for brain morphological analysis using stereological methods. In addition, we performed immunofluorescence and polymerase chain reaction (PCR) analyses to identify HUCBC in the rat brain 7 days after transplantation. The MWM test showed a significant spatial memory recovery at the highest HUCBC dose compared with HI+vehicle rats (P<0.05). Furthermore, the brain atrophy was also significantly lower in the HI+medium- and high-dose groups compared with the HI+vehicle animals (P<0.01; 0.001, respectively). In addition, HUCBC were demonstrated to be localized in host brains by immunohistochemistry and PCR analyses 7 days after intravenous administration. These results revealed that HUCBC transplantation has the dose-dependent potential to promote robust tissue repair and stable cognitive improvement after HI brain injury.

Fetal bovine bone marrow is a rich source of CD34+ hematopoietic progenitors with myelo-monocytic colony-forming activity

The CD34 glycoprotein is an important marker of hematopoietic stem cells. We used a polyclonal rabbit anti-bovine CD34 antibody to stain fetal and adult bovine bone marrow cells. Flow cytometry revealed a low side scatter (SSC(low)) population of cells that were CD34(+) but negative for leukocyte lineage markers CD11b, CD14 or CD2. Hematopoietic colony assays with CD34(+) and CD34(-) bone marrow cells suggested that the colony-forming potential in SSC(low) bone marrow cells was confined to the CD34(+) fraction. In contrast, this population was not enriched for cells expressing high aldehyde dehydrogenase activity, a metabolic marker that has been used to characterize hematopoietic stem cells. Thus, the CD34 antigen can be used to identify and isolate bovine bone marrow cells exhibiting clonogenic potential in vitro. Moreover, the proportion of CD34(+) cells is very high in fetal bovine bone marrow, indicating it as a rich source of hematopoietic progenitors.

Multiple intravenous administrations of human umbilical cord blood cells benefit in a mouse model of ALS

BACKGROUND

A promising therapeutic strategy for amyotrophic lateral sclerosis (ALS) is the use of cell-based therapies that can protect motor neurons and thereby retard disease progression. We recently showed that a single large dose (25 × 10⁶ cells) of mononuclear cells from human umbilical cord blood (MNC hUCB) administered intravenously to pre-symptomatic G93A SOD1 mice is optimal in delaying disease progression and increasing lifespan. However, this single high cell dose is impractical for clinical use. The aim of the present pre-clinical translation study was therefore to evaluate the effects of multiple low dose systemic injections of MNC hUCB cell into G93A SOD1 mice at different disease stages.

METHODOLOGY/PRINCIPAL FINDINGS

Mice received weekly intravenous injections of MNC hUCB or media. Symptomatic mice received 10⁶ or 2.5 × 10⁶ cells from 13 weeks of age. A third, pre-symptomatic, group received 10⁶ cells from 9 weeks of age. Control groups were media-injected G93A and mice carrying the normal hSOD1 gene. Motor function tests and various assays determined cell effects. Administered cell distribution, motor neuron counts, and glial cell densities were analyzed in mouse spinal cords. Results showed that mice receiving 10⁶ cells pre-symptomatically or 2.5 × 10⁶ cells symptomatically significantly delayed functional deterioration, increased lifespan and had higher motor neuron counts than media mice. Astrocytes and microglia were significantly reduced in all cell-treated groups.

CONCLUSIONS/SIGNIFICANCE

These results demonstrate that multiple injections of MNC hUCB cells, even beginning at the symptomatic disease stage, could benefit disease outcomes by protecting motor neurons from inflammatory effectors. This multiple cell infusion approach may promote future clinical studies.

Direct contact of umbilical cord blood endothelial progenitors with living cardiac tissue is a requirement for vascular tube-like structures formation

The umbilical cord blood derived endothelial progenitor cells (EPCs) contribute to vascular regeneration in experimental models of ischaemia. However, their ability to participate in cardiovascular tissue restoration has not been elucidated yet. We employed a novel coculture system to investigate whether human EPCs have the capacity to integrate into living and ischaemic cardiac tissue, and participate to neovascularization. EPCs were cocultured with either living or ischaemic murine embryonic ventricular slices, in the presence or absence of a pro-angiogenic growth factor cocktail consisting of VEGF, IGF-1, EGF and bFGF. Tracking of EPCs within the cocultures was performed by cell transfection with green fluorescent protein or by immunostaining performed with anti-human vWF, CD31, nuclei and mitochondria antibodies. EPCs generated vascular tube-like structures in direct contact with the living ventricular slices. Furthermore, the pro-angiogenic growth factor cocktail reduced significantly tubes formation. Coculture of EPCs with the living ventricular slices in a transwell system did not lead to vascular tube-like structures formation, demonstrating that the direct contact is necessary and that the soluble factors secreted by the living slices were not sufficient for their induction. No vascular tubes were formed when EPCs were cocultured with ischaemic ventricular slices, even in the presence of the pro-angiogenic cocktail. In conclusion, EPCs form vascular tube-like structures in contact with living cardiac tissue and the direct cell-to-cell interaction is a prerequisite for their induction. Understanding the cardiac niche and micro-environmental interactions that regulate EPCs integration and neovascularization are essential for applying these cells to cardiovascular regeneration.

Novel measurements of mammary stem cells in human umbilical cord blood as prospective predictors of breast cancer susceptibility in later life

BACKGROUND

The size of the breast stem-cell pool could underlie the intrauterine roots of breast cancer. We studied whether breast stem cells exist in umbilical cord blood and if they correlate with hematopoietic stem-cell measurements that have been positively associated with perinatal risk factors for breast cancer.

SUBJECTS AND METHODS

We isolated mononuclear cells from umbilical cord blood of 170 singleton full-term pregnancies and determined, by reverse transcription polymerase chain reaction, the presence of genes of putative breast epithelial stem-cell/progenitor markers [including epithelial cell adhesion molecule (EpCAM), CD49f (α6-integrin), CD117 (c-kit receptor), CD24, and CD29 (β1-integrin)]. By immunocytochemistry, we colocalized protein expressions of EpCAM+CD49f+, CD49f+CD24+, and CD24+CD29+. We correlated concentrations of putative breast stem-cell/progenitor subpopulations, quantified by flow cytometry, with concentrations of hematopoietic stem cells.

RESULTS

Mammary stem-cell phenotypes were identified in umbilical cord blood. The measured EpCAM+ subpopulation was positively correlated with concentrations of CD34+ and CD34+CD38- hematopoietic stem cells (both P=0.006). Additionally, EpCAM+CD49f+ and CD49f+CD24+ subpopulations were positively correlated to the CD34+ cells (P=0.03 and 0.008, respectively).

CONCLUSION

The positive association between measurable breast and hematopoietic stem cells in human umbilical cord blood suggests plausible mechanisms for a prenatal influence on breast cancer risk.

Umbilical cord blood: lessons learned and lingering challenges after more than 20 years of basic and clinical research

During the last 23 years, cord blood research has played important roles both in experimental and clinical hematology. Cord blood-derived hematopoietic stem and progenitor cells have been shown to possess particular biological features and their study has been very important in our understanding of hematopoietic development. Today, >20,000 umbilical cord blood (UCB) transplants have been performed worldwide and ∼460,000 UCB units are being stored in >47 UCB banks worldwide. Here a brief overview on some of the most relevant issues regarding cord blood research is presented.

Very small embryonic-like stem cells: biology and therapeutic potential for heart repair

Very small embryonic-like stem cells (VSELs) represent a population of extremely small nonhematopoietic pluripotent cells that are negative for lineage markers and express Sca-1 in mice and CD133 in humans. Their embryonic-like characteristics include the expression of markers of pluripotency; the ability to give rise to cellular derivatives of all three germ-layers; and the ability to form embryoid-like bodies. Indeed, quiescent VSELs may represent the remnants of epiblast-derived cells in adult organs. After tissue injury, including acute myocardial infarction (MI), bone marrow-derived VSELs are mobilized into the peripheral blood and home to the damaged organ. Given the ability of VSELs to differentiate into cardiomyocytes and endothelial cells, and their ability to secrete various cardioprotective growth factors/cytokines, VSELs may serve as an ideal cellular source for cardiac repair. Consistently, transplantation of VSELs after an acute MI improves left ventricular (LV) structure and function, and these benefits remain stable during long-term follow-up. Although the mechanisms remain under investigation, effects of secreted factors, regeneration of cellular constituents, and stimulation of endogenous stem/progenitors may play combinatorial roles. The purpose of this review is to summarize the current evidence regarding the biologic features of VSELs, and to discuss their potential as cellular substrates for therapeutic cardiac repair.

A novel method for human hematopoietic stem/progenitor cell isolation from umbilical cord blood based on immunoaffinity aqueous two-phase partitioning

A novel cell separation process based on immunoaffinity aqueous two phase systems is presented to isolate and purify CD34(+) stem/progenitor cells directly from the whole umbilical cord blood (UCB). A system, composed of polyethylene glycol and dextran, was evaluated for the selective recovery of CD34(+) cells from UCB. A monoclonal antibody against the CD34 surface antigen was used for the direct partitioning of CD34(+) cells in UCB to the PEG-rich phase. The initial population of CD34(+) cells (0.2% of the initial sample) was enriched to values up to 42% in a single partitioning step, while the majority of contaminant cells were partitioned to the dextran-rich phase (1.37 × 10(-2) < K(P) < 2.76 × 10(-2)). This novel selection method allowed a recovery yield of 95% of CD34(+) cells with a purification factor of 245 and is expected to pave a new way to purify hematopoietic stem/progenitor cells for use in a variety of clinical settings.

Design, characterization and application of a minibioreactor for the culture of human hematopoietic cells under controlled conditions

The in vitro culture of human hematopoietic cells has recently received considerable attention due to its clinical importance. Most studies of the culture and expansion of hematopoietic cells have been performed in static cultures but only very few reports exist on the use of bioreactors where strict control of environmental variables is maintained. In this work, the design, characterization and application of a fully instrumented minibioreactor for the culture of human hematopoietic cells from umbilical cord blood is presented. The system consists of a stirred- tank reactor where cells are maintained in suspension in an homogeneous environment and without the need of a stromal feeding layer. The minibioreactor was coupled to a data acquisition and control system which continuously monitored pH, dissolved oxygen and redox potential. When operated at 75 rpm with a hanging magnetic bar (impeller-to-tank diameter ratio of 0.57), the dead and mixing times were 120 and 80 s, respectively, and the maximum response rate and volumetric oxygen transfer coefficient were 0.8 mM O2 hr-1, and 1.8 hr-1, respectively. Such characteristics allowed a tight control of pH(until day 11) and dissolved oxygen at predetermined set-points, and up to a 7-fold expansion of hematopoietic progenitors was possible in cultures maintained at 20% dissolved oxygen with respect to air saturation. Growth phase and cell concentration could be inferred on- line through determinations of oxygen uptake rate and culture redox potential. Oxygen uptake rate increased during exponential growth phase to a maximum of 40 muM hr-1. Such an increase closely followed the increase in concentration of hematopoietic progenitors. In contrast, culture redox potential decreased during exponential growth phase and then increased during death phase. The designed system permits not only the maintenance of controlled environmental conditions and on-line identification of fundamental culture parameters, but also the application of control strategies for improving expansion of hematopoietic cells.

MHC class II deficiency cured by unrelated mismatched umbilical cord blood transplantation: case report and review of 68 cases in the literature

MHC class II deficiency is a rare and fatal form of primary combined immunodeficiency caused by a lack of T-cell-dependent humoral and cellular immune response to foreign antigens, which can only be cured by allogenic stem cell transplantation. In the literature search, we identified 68 cases of HSCT in MHC class II deficiency in the last 14 yr. Pre- and post-transplant MHC class II deficiency is complicated by overwhelming viral infections, a high incidence of GvHD, and graft failure with a poor overall survival rate below 50%. We report an eight-month-old boy presenting with severe respiratory infections and chronic diarrhea, whose sister died at the age of four yr from septicemia. MHC II deficiency was caused by an RFXANK-mutation and treated successfully by 4/6 mismatched unrelated CBT after a myeloablative conditioning regimen based on anti-thymocyte globulin, busulfane, fludarabine, and cyclophosphamide. At present, our patient is well with full immune reconstitution 3(4/12) yr after CBT. CB may represent an alternative source of stem cells for children with MHC class II deficiency without a suitable donor.