Current Stem Cell Research & Therapy - Volume 3, Issue 4, 2008

Bone marrow, peripheral blood and cord blood are all sources of hematopoietic stem cells for allogeneic transplants. These sources differ in regard to collection methods, cellular content and transplant outcomes. In the related setting, use of peripheral blood stem cells, when compared to bone marrow, results in faster engraftment and may confer a survival benefit in advanced disease but also may lead to an increase in chronic graft-versus-host-disease. While cord blood stem cells are the simplest to collect and allow the greatest flexibility in HLA matching, they contain the lowest stem cell dose leading to the slowest engraftment. In this review, we discuss the advantages and disadvantages of these different stem cell sources as well as areas for further research.

Multiple aldehyde dehydrogenase genes have been identified in many tissues. Aldehyde dehydrogenase class 1A1 (ALDH1A1) has been identified as highly expressed in embryonal tissue as well as in adult stem cells isolated from bone marrow, brain, breast and possibly other tissues. The recent interest in the idea of cancer stem cells (CSC) has resulted in renewed and vigorous interest in aldehyde dehydrogenase activity as a marker for those stem cells as well. It has been known that ALDH activity, which may reflect other ALDH isozymes in addition to ALDH1A1, is important for multiple biological activities including drug resistance, cell differentiation, and oxidative stress response. Purification of viable cells with high ALDH activity has become relatively easy with the availability of flow cytometry based assay. In this review, we examine the data available in regarding the importance of ALDH activity in normal and malignant stem cell functions, and the potential diagnostic and therapeutic implications. We review the available tools that can impact ALDH activity and may have the potential to be used therapeutically, specifically targeting the CSC. We raise questions that need to be investigated before a reasonable therapeutic strategy can be devised that will effectively inhibit ALDH activity.

Neural stem cells are defined as clonogenic cells with self-renewal capacity and the ability to generate all neural lineages. Cells with these characteristics have been isolated from the embryonic and adult Central Nervous System. Numerous reports show that extrinsic factors and intracellular mechanisms may trigger both endogenous and in vitro cultured neural stem cells to differentiate into desired cell outcomes. This plasticity opens new approaches for the use of neural stem cells as a source of cells for replacement therapy in damaged brain. In this review we present the evidence for the involvement of trophic factors, neurotransmitters, second messengers, aminoacids, and factors released by endothelial and glial cells, which have been reported to influence neural stem cells phenotypic choice in vitro and in vivo.

The tremendous need for bone tissue in numerous clinical situations and the limited availability of suitable bone grafts are driving the development of tissue engineering approaches to bone repair. In order to engineer viable bone grafts, one needs to understand the mechanisms of native bone development and fracture healing, as these processes should ideally guide the selection of optimal conditions for tissue culture and implantation. Engineered bone grafts have been shown to have capacity for osteogenesis, osteoconduction, osteoinduction and osteointegration - functional connection between the host bone and the graft. Cells from various anatomical sources in conjunction with scaffolds and osteogenic factors have been shown to form bone tissue in vitro. The use of bioreactor systems to culture cells on scaffolds before implantation further improved the quality of the resulting bone grafts. Animal studies confirmed the capability of engineered grafts to form bone and integrate with the host tissues. However, the vascularization of bone remains one of the hurdles that need to be overcome if clinically sized, fully viable bone grafts are to be engineered and implanted. We discuss here the biological guidelines for tissue engineering of bone, the bioreactor cultivation of human mesenchymal stem cells on three-dimensional scaffolds, and the need for vascularization and functional integration of bone grafts following implantation.

During the last 10 years we have witnessed the development of a new field in research termed Stem Cell Therapy. Classically, it was considered that cells had a limited division and differentiation ability; however, this dogma was challenged when new exciting results about cell multi/pluripotency were presented to the scientific community. It was found that cells from one adult tissue source were able to originate cells of a very different type. The possibility of transplanting these cells into damaged organs with the aim of substituting sick or dead tissue, triggered many studies to understand the plasticity of the stem cells and their potential in pathological situations. Nowadays, much more is understood about stem cells, although of course, many questions, especially about their mechanism of action, still need to be answered. Their benefit after transplantation has been shown experimentally and even clinically in some cases; however, the degree of stem cell contribution through their own differentiation into the transplanted tissue, has turned out to be generally low, and increasing evidence indicates that a trophic effect must play an important role in such a benefit. A better understanding of the paracrine mechanisms involved could be of great relevance in order to develop new therapies focused on stimulating endogenous cells. On the other hand, more sophisticated methods for cell transplantation combined with bio-engineering techniques have been devised in cardiac disease models. In this review we will try to provide a critical overview of the stem cell studies performed until now and to discuss some of the questions raised about the mechanisms that are involved in their putative reparative effect in cardiovascular diseases, and their origin.

Fish embryonic stem (ES) cells derived from of blastulae (64 cell stage embryo) of Labeo rohita were propagated in culture and retained their ES cell-like properties after cryogenic storage (-196 °C, i.e., liquid nitrogen). Toxic effect of DMSO (dimethyl sulphoxide) on stem cells during preservation process has been reported to restrict therapeutic applications. In this study we reduced the concentration of DMSO and added the non-toxic cryoprotective agent (CPA) trehalose. Cryopreservation of ES cell colonies was done at 5, 25 and 52 passages with 0.2 M trehalose and 0.8 M (DMSO). A combination of both the cryoprotective agents (non-toxic and toxic) demonstrated better survival and recovery of ES cells than the DMSO used alone. Use of this CPA combination in the freezing media gave an optimum viability of more than 83 % in a slow freezing protocol. Trehalose showed a definite advantage over DMSO in terms of viability and intactness of ES cell colonies with evenly distributed morphology. There was no significant difference observed in the expression levels of cell surface markers like stage specific embryonic antigen-1 (SSEA-1) and alkaline phosphatase (ALP) between early and late passages after 60 days of post-thawing. More than 90 % of the ES cell colonies showed extensive expression of ALP and positive expression of SSEA-1 from an early stage of ES cells culture up to passage 52 (in our study) in the presence of leukemia inhibitory factor (LIF) and without feeder cells. Further, thawed ES cells showed a normal karyotype and maintained an undifferentiated state through out the study. This study on ES cell cryopreservation and subsequent retention of stem cell properties without feeder cells using a non-toxic cryoprotectant trehalose would be highly useful for future in vitro differentiation, manipulation of fish ES cells and as a model for mammalian ES cell culture.

In the canonical Notch signaling pathway, intramembrane cleavage by γ-secretase serves to release an intracellular domain of Notch that has activity in the nucleus through binding to transcription factors. In addition, we showed that Notch also supplies signals to Delta, a major Notch ligand, to release the intracellular domain of Delta by γ-secretase from the cell membrane, which then translocates to the nucleus, where it mediates the transcription of specific genes. Therefore, the Notch-Delta signaling pathway is bi-directional and similar mechanisms regulated by γ-secretase are involved in both directions. Recently, it was demonstrated that many type 1 transmembrane proteins including Notch, Delta and amyloid precursor protein (APP) are substrates for γ-secretase and release intracellular domains of these proteins from cell membranes. These observations that the common enzyme, γ-secretase, modulates proteolysis and the turnover of possible signaling molecules have led to the attractive hypothesis that mechanisms similar to the Notch-Delta signaling pathway may widely contribute to γ-secretase-regulated signaling pathways, including APP signaling which leads to Alzheimer's disease. Here, we review the molecular mechanisms of the Notch-Delta signaling pathway in a bi-directional manner, and discuss the recent progress in understanding the biology of γ-secretase-regulated signaling with respect to neurodegeneration.

Is there a clinical future for spermatogonial stem cells? Ellen Goossens and Herman Tournaye. Original citation: Curr Stem Cell Res Ther 2007 Sep; 2(3): 189-95. During the preparation of the manuscript, on the title page, the author's first and last names were interchanged. The correct authors' names appear above. The error is deeply regretted.