Current Stem Cell Research & Therapy - Volume 3, Issue 2, 2008

Haploidentical hematopoietic stem cell transplantation from a mismatched family member is an alternative treatment for transplant candidates who lack a HLA-matched related or an appropriate unrelated donor. One of main obstacles to successful haploidentical transplantation is slow immune reconstitution which significantly increases the risk of opportunistic infections, graft-vs-host-disease and disease relapse. Immune reconstitution is conventionally estimated by phenotypic recovery of immune cells according to lineage and/or by in vitro evidence of cell function. The limitations of these approaches include the sensitivity and specificity of phenotype markers, the availability of antibodies, the instability of long-term cell culture and the laborious nature of cell-function assays. Investigators have sought alternative approaches that are more sensitive, specific and simple, and that allow high-throughput testing for use in clinical transplantation. In this mini-review, we briefly introduce the concept of “molecular monitoring of immune-reconstitution” and discuss recent progress in this field achieved by our laboratory and other groups. We also propose future directions for clinical research incorporating these novel concepts.

Umbilical cord blood (UCB) has become an alternative source of hematopoietic progenitors (HSC) for transplantation. Although most CB transplants have been performed in children, unrelated donor-cord blood transplants in adults have been growing steadily in recent years. HSC content of CB units influence significantly the transplantation outcome, as shown by many clinical studies. UCB banks are fundamental to support this increasing clinical activity and one of their main goals must be to store good quality units. Strategies for increasing HSC content of UCB units are reviewed and also its influence on transplantation outcome. Our bank selected the UCB units for cryopreservation on the basis of their total nucleated cells (TNC) and CD34+ cells content. We also reviewed the results of our UCB bank program.

Mannose-binding lectin (or mannan-binding lectin, MBL) may have an influence on susceptibility to infection in patients given chemotherapy to induce remission or as conditioning before stem cell transplantation. The most surprising finding reported from an inconsistent literature was the observation that mbl-2 gene mutations in donors could influence the risk of serious infections in recipients of allogeneic stem cell transplants. This could be explained if leukocytes in the stem cell preparations (or their derivatives) were able to synthesize and secrete MBL, but the available evidence seems to exclude that possibility. An alternative mechanism could involve MBL binding to autologous cells and inducing immunological maturation of those cells. MBL can certainly bind to various cell types via surface glycoconjugates and the possible significance of this for MBL replacement therapy will be discussed.

As a novel neurotherapeutic strategy, stem cell transplantation has received considerable attention. However, little focus of this attention has been devoted to the probabilities of success of stem cell therapies for specific neurological disorders. Given the complexities of the cellular organization of the nervous system and the manner in which it is assembled during development, it seems unlikely that a cellular replacement strategy will succeed for any but the simplest of neurological disorders in the near future. A general strategy for stem cell transplantation to prevent or minimize neurological disorders is much more likely to succeed. The lysosomal storage diseases represent the quintessential neurodegenerative diseases for which preventative stem cell transplantation will both likely succeed and set the stage for therapeutic approaches to other neurodegenerative diseases.

Inositol phospholipid signaling pathways have begun to emerge as important players in stem cell biology and bone marrow transplantation [1-4]. The SH2-containing Inositol Phosphatase (SHIP) is among the enzymes that can modify endogenous mammalian phosphoinositides. SHIP encodes an isoform specific to pluripotent stem (PS) cells [5,6] plays a role in hematopoietic stem (HS) cell biology [7,8] and allogeneic bone marrow (BM) transplantation [1,2,9,10]. Here I discuss our current understanding of the cell and molecular pathways that SHIP regulates that influence PS/HS cell biology and BM transplantation. Genetic models of SHIP-deficiency indicate this enzyme is a potential molecular target to enhance both autologous and allogeneic BM transplantation. Thus, strategies to reversibly target SHIP expression and their potential application to stem cell therapies and allogeneic BMT are also discussed.

Imprinted genes are expressed predominantly or exclusively from one allele only. This mode of gene expression makes the regulation of imprinted genes susceptible to epigenetic insults, which may in turn lead to disease. There is compelling experimental evidence that certain aspects of assisted reproductive technology (ART) such as in vitro cell culture may have adverse effects on the regulation of epigenetic information in mammalian embryos, including the disruption of imprinted genes and epigenetic regulators. Moreover, in humans, disorders of genomic imprinting have been reported in children conceived by ART. The derivation and in vitro culture of embryonic stem (ES) cells are potential points of origin for epigenetic abnormalities. There is evidence that defects of genomic imprinting occur in mouse embryonic stem cells, with similar data now emerging in related studies in non-human primate and human ES cells. It is therefore pertinent to rigorously assess the epigenetic status of all stem cells and their derivatives prior to their therapeutic use in humans. Focusing on the stability of genomic imprinting, this review discusses the current evidence for epigenetic disruption in mammalian embryonic stem cells in light of the epigenetic disruption observed in ART-derived mammalian embryos.

The successful establishment of human embryonic stem cell (hESC) lines has raised high expectation for their future applications. The major focus of hESC research has been on their potential use in replacement therapies. However, the most immediate application of hESCs may be in establishment of humanised in vitro tests, which have potential to reduce problems of interspecies variations in safety assessments. Improved prediction of human hazard would increase patient safety and reduce the number of laboratory animals needed for toxicological and safety pharmacological testing, leading to improved efficiency of drug discovery and development in term of cost and time. The current review describes some of the newest research programmes on the use of hESCs for safety evaluations of conventional drugs. It provides an overview of the possible impact of hESCs and their derivates on regulatory drug safety assessments and discusses the potential effects on the product pipeline organisation. The review additionally summarizes initiatives in establishing quality criteria for hESC expansion and differentiation. Such criteria are necessary in order to achieve high standardisation and throughput of pharmacological and toxicological tests. Finally, it will discuss the actions needed to scientifically prove the relevance and reliability of safety tests based on hESCs.

Mesenchymal stem cells (MSCs) are multipotent cells that arise from the mesenchyme during development. They reside in the bone marrow close to hematopoietic stem cell niches allowing them to maintain bone marrow homeostasis and to regulate the maturation of both hematopoietic and non-hematopoietic cells. MSCs possess an extensive potential to proliferate and differentiate e.g. into osteoblasts, osteocytes, adipocytes and chondrocytes. Nevertheless, there still are some open questions about the complex process of MSC differentiation involving different transcription factors and signaling pathways, which will be discussed in this review. We also shortly introduce the characteristics and function of bone-forming osteoblasts and their role in angiogenesis. MSCs are of interest in clinical applications, since they can be easily isolated from bone marrow aspirates and expanded in vitro. When the source of osteoprogenitors is compromised, cell-based therapies could provide a novel way to repair bone defects. Indeed, there is an increasing interest in the use of MSCs and more differentiated cells in clinical applications for bone repair, which will be introduced in this review. A major section of the review is dedicated to the functions of osteocytes in the regulation of bone remodeling. Finally, we present an original hypothesis about the possible role of osteocytes in future bone tissue engineering.

In this review we focus on epidermal stem cells in the normal regeneration of the skin as well as in wounded and psoriatic skin. Furthermore, we discuss current data supporting the idea of cancer stem cells in the pathogenesis of skin carcinoma and malignant melanoma. Epidermal stem cells present in the basal layer of the interfollicular epidermis and in the bulge region of the hair follicle play a critical role for normal tissue maintenance. In wound healing, multipotent epidermal stem cells contribute to re-epithelization. It is possible that defects in growth control of either epidermal stem cells or transit amplifying cells constitute a primary pathogenetic factor in the epidermal hyperproliferation seen in psoriasis. In cutaneous malignancies mounting evidence supports a stem cell origin in skin carcinoma and malignant melanoma and a possible existence of cancer stem cells.