Current Stem Cell Research & Therapy - Volume 5, Issue 4, 2010

In children, cancers are the deadliest of diseases and second only to accidents as the leading cause of death. The deadliest of the brain cancers are the malignant gliomas. Approximately two-thirds of children can survive less malignant types of brain cancers, however, in ~67% of these survivors recurs under the current regimes of surgery followed by administration of high doses toxic drugs and exposure to high doses of radiation. Even more distressing is that fortunate survivors are generally left with life-long cognitive disabilities. A new medical approach is desperately needed. Stem cells, with their natural ability to seek out brain tumors, could be used to accurately deliver therapy directly to the cancer sparing normal tissues for suppression of tumor growth. Despite exciting initial reports, clinical potency of stem cell therapy in animal brain tumor models has to date proven disappointing. Attempts to extrapolate the animal study results to humans are stymied by the fact that stem cells are heterogeneous, resulting in differences in their efficacy. Indeed, therapeutic success relies on an effective strategy to select for a stem cell sub-population within some particular stage of the development at which they are competitive and capable of targeting brain tumors. To improve this during developmental path, concept of a ‘therapeutic window’ is proposed. The “therapeutic window” for stem cells or more specifically a “biochemical therapeutic window” can be determined from biochemical assays and a “biological therapeutic window” from biological assays or even a molecular window from genetic description. Taken together, we can use selective processes to generate more effective stem cells to treat cancers as is clearly needed today.

About 30 years ago circulating endothelial cells (CEC) were first observed in peripheral blood. Since then CEC have been established as a reliable indicator of vascular injury and damage and more sophisticated detection techniques, such as immunomagnetic isolation and fluorescence-activated cell sorting (FACS), have become available. However even today there remains controversy as to the best approach to isolate and enumerate these cells. Here, we review the isolation and enumeration of CEC with an emphasis on CD146- driven immunomagnetic isolation and FACS as the two competing techniques. We describe advantages and pitfalls of both approaches. Moreover, we provide a list of clinical studies in this field and describe the possible clinical utility of CEC as a surrogate marker for vascular damage and dysfunction. In addition, we review the phenotype of CEC and discuss mechanisms of detachment. Recent evidence has also revealed interesting interactions between CEC and healthy endothelium in vitro although the relevance of these findings for human vascular disease in vivo remains unclear. Finally, we highlight differences between circulating endothelial cells and endothelial progenitor cells. In summary, CEC must be regarded as a sensitive and specific marker of endothelial damage as well as a potential mediator in vascular disease.

Systemic available circulating cells play a role in cardiac maintenance and ameliorate cardiac recovery and repair after myocardial infarction. However, only a small number of cells will be incorporated during cardiac damage. Cell mobilization, homing to the ischemic myocardium and engraftment are complex processes depending on many adhesion molecules, proteases, chemokines and their receptors. Physiologic and pathophysiologic circumstances, cytokines, chemokines and certain drugs are able to influence these processes. For cardiovascular regeneration, understanding how mobilization and homing of blood derived cells is regulated and can be modulated as well as identification of cell populations able to regenerate the heart or reduce damage after myocardial infarction is essential for the development of successful cell based therapies.

The discovery of several sources of hepatic progenitors in extra-hepatic organs and tissues, both in animal models and in humans, supports opportunities to isolate, grow and expand them in vitro. Microenvironment factors involved in regulating proliferation and commitment of liver cell precursors have been identified and better characterization of liver stem cell pathobiology would greatly improve the understanding of liver differentiation/ regeneration processes, especially those leading to hepatocarcinogenesis. The goal of these researches has been to discover the most available, suitable and easy-to-use pluripotent stem cells (PSC) sources for cell-based therapies in genetic and acquired liver diseases, therapies which to date have required liver transplantation, This report reviews the efforts, so far, to either investigate the presence of PSC in hepatic and extra-hepatic districts or evaluate their capacity to differentiate in vitro and to restore in vivo liver function.

Cellular therapies represent a new frontier in the treatment of neurological disease. Mesenchymal stem cells (MSCs), which can be harvested from bone marrow, adipose tissue, and umbilical cord blood, among many other sources, possess several qualities which may be used to treat diseases of the central nervous system. MSCs migrate to sites of malignancy, a property which may be used for the treatment of brain cancer. MSCs possess immunosuppressive properties, which may be used for the treatment of neurological disorders with an inflammatory etiology. Finally, MSCs restore injured neural tissue, a property which may be used for the treatment of neural injury. Approximately 23 clinical trials have been completed to date, with many more ongoing, and all have been listed in this review. The long-term safety of MSC-based therapies is not well established, and continues to be one major limitation to clinical translation. More broadly, only a small minority of clinical trials have employed rigorous designs that include prospective randomization, patients from multiple centers, clinically-relevant and reproducible endpoints, and adequate long-term follow-up. These limitations must be addressed before MSCs can enter widespread clinical use. Nevertheless, MSCs represent a promising new approach to treating diseases of the central nervous system that are traditionally associated with morbid outcomes. With additional pre-clinical and clinical studies that focus on their potential benefits as well as dangers, MSCs may one day find translation to clinical use in the setting of neurological disease.

While the use of biologics as adjuncts for spine surgery is growing annually stem cells have yet to be approved for this clinical application. Stem cells have the unique ability to differentiate into a variety of musculoskeletal tissues including bone or cartilage. Moreover they have been shown to secrete growth factors that promote matrix repair and regeneration and can down regulate inflammation and immune cell functions. It is these combined activities that make stem cells attractive candidates for advancing current techniques in spine surgery and possibly mitigating those pathologies responsible for tissue degeneration and failure thereby minimising the need for surgical intervention at a later date. This review focuses on the characteristics of progenitor cells from different sources and explores their potential as adjuncts for both current and future applications in spine surgery. Where possible we draw on the experimental outcomes from our own preclinical studies using adult mesenchymal progenitor stem cells, as well as related studies by others to support our contention that stem cell based therapies will play a significant role in spine surgery in the future.

Cellular therapy for patients with diabetes is receiving great attention among scientists and clinicians. Bone marrow is considered one of the rich sources of stem cells. However, the limited availability of bone marrow donors precludes its use for all the suitable patients. Human umbilical cord blood (HUCB) is being increasingly used as an alternative source of stem cells for cell-based therapy for malignant and nonmalignant diseases. HUCB is preferred to bone marrow because of its easy availability, low potential for graft-versushost disease and tumorigenicity as well as infectious complications. Furthermore, no immunosuppression is required. In vitro and in vivo studies have shown that HUCB-derived stem cells can differentiate into insulin-secreting β-cells. Administration of HUCB cells has been shown to improve blood glucose levels in diabetic animals. The first use of autologous HUCB transfusion in type 1 diabetic children is showing promise in reducing the daily requirement of insulin dose and the maintenance of near normoglycemia over a short period of time. The time has come for more clinical trials using autologous and allogenic cord blood transfusion to treat diabetes mellitus.

Umbilical cord blood (UCB) is an alternative source of haematopoietic progenitors for transplantation in the treatment of haematological malignancies, marrow failure, immunodeficiencies, hemoglobinopathies and inherited metabolic diseases. It has greatly contributed to increase the feasibility to transplantation for many patients in need. To date, more than 20,000 UCB transplants have been performed on children and adults, and more than 400,000 UCB units are available in more than 50 public CB banks. One of the most important objectives of banks is to cryopreserve and store high quality UCB units. Volume reduction is a usual process in cord blood banking that has some advantages as reducing the storage space and the DMSO quantity in final product. Volume reduction methodology must guarantee high cell recovery and red blood cell (RBC) depletion by reducing the UCB units to a standard volume. Hydroxyethyl starch (HES) sedimentation was the first method developed for this purpose by the New York Cord Blood Bank and implemented in many banks worldwide. The semi-automated top and bottom system, usually used for blood fractionation was further developed to simplify and short the process. Later, automatic devices as SEPAX and AXP have been developed in last years specifically for UCB volume reduction purpose. This review critically analyses the advantages and disadvantages of the different procedures. All of them have been used in Valencia Cord Blood Bank along 10 years. In general, automatic devices are preferred because of compliance with cGTP, closed systems, higher reproducibility and less influence of technician.

Dendritic cells (DC) are important antigen presenting cells (APC) which induce and control the adaptive immune response. In spleen alone, multiple DC subsets can be distinguished by cell surface marker phenotype. Most of these have been shown to develop from progenitors in bone marrow and to seed lymphoid and tissue sites during development. This study advances in vitro methodology for haematopoiesis of dendritic-like cells from progenitors in spleen. Since spleen progenitors undergo differentiation in vitro to produce these cells, the possibility exists that spleen represents a specific niche for differentiation of this subset. The fact that an equivalent cell subset has been shown to exist in spleen also supports that hypothesis. Studies have been directed at investigating the specific functional role of this novel subset as an APC accessible to blood-borne antigen, as well as the conditions under which haematopoiesis is initiated in spleen, and the type of progenitor involved.

Acute promyelocytic leukemia (APL) is a distinct subset of acute myeloid leukemia. An abnormal fusion gene, PML/RARA is detected in approximately 98% of patients with APL. PML/RARA confers long-term self-renewal properties to promyelocytes. All-trans retinoic acid (ATRA) and arsenic trioxide (ATO), which are the major molecularly targeted therapies in APL, affect the PML/RARA fusion protein and cause differentiation and apoptosis of APL cells. Although the leukemia-initiating cells of APL may be present in a myeloid progenitor committed compartment, the precise population of those remains to be elucidated. However, recent studies have demonstrated the effect of ATRA and ATO on APL leukemia-initiating cells. Through these studies, we can understand more deeply how current clinical therapies lead to long-lasting remission of APL. ATRA and ATO have improved the prognosis of APL patients and have changed the role of hematopoietic stem cell transplantation (HSCT). At present, HSCT is not indicated for patients with APL in first complete remission, and considered for patients with relapsed APL. In this review, we discuss the three main topics as follows: the leukemia- initiating cells in APL, the current state-of-the-art treatment for newly diagnosed and relapsed APL, and the role of HSCT in APL patients.

Leukemia is a heterogeneous disorder of bone marrow (BM) failure syndrome where normal hematopoiesis gets altered due to transformation of either the normal hematopoietic cell or the hematopoietic microenvironment or both. Scientists have tried for decades to understand leukemia development in the context of therapeutic strategies. The existence of “leukemic stem cells” and their possible role in leukemogenesis have only recently been identified and it has changed the perspective with regard to new approaches for treating the disease. However the relationship between leukemic stem cells (LSCs) and leukemogenesis requires further investigation. In this present study, we have experimentally induced leukemia in mice by means of N-N´ Ethylnitrosourea (ENU) to investigate the alterations in normal bone marrow cellular phenotype and associated changes in the stromal hematopoietic microenvironment under the event of leukemic disease progression. We have identified a significant decrease in the normal HSC phenotype in terms of Sca1 and c-kit receptor expression and subsequent sharp increase in certain leukemic cell specific receptor expression like CD123, CXCR4 and CD44 in the leukemic bone marrow. The decreased HSC receptor (Sca1 and c-kit) expression profile with concurrent increase in the expression of leukemic cell specific receptors (CD123, CXCR4, CD44) by the bone marrow cells of leukemic mice may account for the possible transformation of the normal hematopoietic cells that is necessary for the disease initiation and progression. Some of these receptors like CXCR4 and CD44 are also known to play an important role in maintaining leukemic cells and their complex crosstalk with the surrounding stromal microenvironment. Thus up-regulation in CXCR4 and CD44 receptor expression essentially pointed towards the stroma dependent surveillance of the leukemic bone marrow cells in leukemia. Leukemic bone marrow cells documented a rapid generation of stromal feeder layer in culture. The rapid stroma generation further supported the fact that leukemic stromal microenvironment gets altered in possible ways to support leukemic cell generation and fueling leukemogenesis. The study presented here, has tried to hint at exploring new therapeutic strategies by not only identifying the expression profile of cell surface receptors unique to cells involved in leukemic progression but also targeting the specific components of the stromal microenvironment that would facilitate therapeutic management of the disease.

Stem cells are undifferentiated cells that renew themselves while simultaneously producing differentiated tissue- or organspecific cells through asymmetric cell division. The appreciation of the importance of stem cells in normal tissue biology has prompted the idea that cancers may also develop from a progenitor pool (the “cancer stem cell (CSC) hypothesis”), and this idea is gaining increasing acceptance among scientists. CSCs are sub-populations of cancer cells responsible for tumor initiation, differentiation, recurrence, metastasis, and drug resistance. First identified in the hematopoietic system, CSCs have also been discovered in solid tumors of the breast, colon, pancreas, and brain. Recently, the tissue-specific stem cells of the normal urothelium have been proposed to reside in the basal layer, and investigators have isolated phenotypically similar populations of cells from urothelial cancer cell lines and primary tumors. Herein, we review the CSC hypothesis and apply it to explain the development of the two different types of bladder cancer: noninvasive (“superficial”) carcinoma and invasive carcinoma. We also examine potential approaches to identify CSCs in bladder cancer as well as therapeutic applications of these findings. While exciting, the verification of the existence of CSCs in bladder cancer raises several new questions. Herein, we identify and answer some of these questions to help readers better understand bladder cancer development and identify reasonable therapeutic strategy for targeting stem cells.