Archive for the ‘stem cells’ Category
Immunology of Stem Cells
Posted by admin in stem cells on June 23rd, 2009
In previous posts,we described general approaches to tackle allo- and autorejection. However, we cannot assume that all stem cell-based therapies will have the same requirements in terms of making them accepted by the recipient, inasmuch as different stem cell types may have different immunological properties. Embryonic stem cells, for instance, have been recently claimed to be “immunoprivileged,” following a series of in vitro and in vivo experiments where both human embryonic stem (huES) cells and their differentiated progeny failed to elicit substantive immune responses. Read the rest of this entry »
Limitations of Islet Transplantation
Posted by admin in stem cells on June 23rd, 2009
Limitations of Islet Transplantation: Engraftment and Long-Term Function
A typical adult pancreas contains approximately one million islets, which represent around 1–2% of the total mass of the organ. It has been estimated that only 50% will survive the harsh process of isolation, with up to 60–80% of the remaining mass perishing in the immediate posttransplantation period due to inflammatory processes not yet fully understood. For instance, it has been shown that islets express tissue factor which may contribute to early islet loss by stimulating coagulation upon their contact with the blood. Considering the many insults that may invariably result in islet cell death from the time of the pancreas procurement to the actual infusion, the fact that only 10% of the transplanted patients are insulin-free 5 years after the procedure is much less surprising than the observation that up to 80% are insulinfree after 1 year. While we define alternative sources of islets that are either plentiful (xenotransplantation) or self-renewable (stem cells), there is an imperative need to “make every islet count” and to minimize their destruction upon implantation. The field of islet cytoprotection is a fertile one, with a large number of chemical gene-based, and protein transduction strategies proven successful in many experimental models. However, it is still necessary to gather much more information Read the rest of this entry »
Remaining Challenges and Clinical Perspectives
Posted by admin in stem cells on June 23rd, 2009
Unlike other potential targets of future stem cell approaches, there is already a current cell therapy for the treatment of type I diabetes. Indeed, islet transplantation has proven successful in inducing insulin independence for at least 1 year after the procedure. Progress in this discipline during the past 20 years has paved the way for stem cell-based therapies. Here we review the current state of the art of islet transplantation and examine the challenges that need to be addressed before a transition is made to stem cell-derived insulin-producing cells, with particular emphasis on the immunological aspects (rejection and autoimmunity) of type I diabetes. Read the rest of this entry »
Directed Liver Transdifferentiation
Posted by admin in stem cells on June 23rd, 2009
One of the earlier attempts at transdifferentiating liver cells into pancreatic beta cells was reported by Ferber and colleagues in 2000. Using a “gain-of-function” strategy, they transferred a constitutively active Pdx1 cassette to recipient mice by means of an adenoviral vehicle . Ectopic expression of the gene was mainly observed in the liver, where it activated the expression of the endogenous genes Insulin 1 and 2 and prohormone convertase 1/3 (PC 1/3). These genes are typically active in beta cells, but not in liver tissue. Plasmatic insulin levels were substantially elevated in treated mice compared with controls treated with an empty virus alone. More strikingly, ectopic insulin expression was found to reduce glucose levels in Read the rest of this entry »
Transdifferentiation
Posted by admin in stem cells on June 23rd, 2009
An alternative to the use of undifferentiated cells is that of reprogramming adult cells from nonpancreatic sources. Of these, the most promising is the liver, whose embryonic development is deeply intertwined with that of the pancreas. Several teams have now proven that the ectopic expression of master pancreatic regulators such as Pdx1 or MafA, among others, can induce the expression of pancreatic markers in liver-derived cells, both in Read the rest of this entry »
Hematopoietic Bone Marrow and Cord Blood Stem Cells
Posted by admin in stem cells on June 21st, 2009
Although hematopoietic stem cells (HSCs) represent a minute percentage of the bone marrow compartment, they are known to reconstitute all blood-forming lineages. HSCs can also be found in the cord blood, which offers an easily bankable source that has already been proven in the clinical arena. More recently, a number of studies have shown that the bone marrow and cord blood host multipotent cells with the ability to differentiate into many different tissues. Certainly, MSCs are one such multipotent cell type, and perhaps the main component of the subpopulations selected for attachment Read the rest of this entry »
Protein Transduction
Posted by admin in stem cells on June 21st, 2009
There are no reports to date on the use of protein transduction for the directed pancreatic differentiation of MSCs. However, Pdx1 has been found to have an antennapedia-like PT domain (pANT) within its sequence. Indeed, purified Pdx1 protein successfully transduced target tissues, including ductal cells (which have been found to be an abundant source of MSCs ) , where they up-regulated the expression of the insulin gene. Even though TAT has proven better than pANT for the delivery of large proteins, the possibility of taking advantage of the native PTD of this and other pancreatic developmental genes without any further manipulation is an attractive one. The reason for the existence of built-in PTDs in transcription factors remains a biological mystery. It has been convincingly shown that nuclear proteins of the engrailed family can be released by “donor” cells and taken up by adjacent cells, which might be indicative of a yet unexplored paracrine function associated with some transcription factors. From a strictly Read the rest of this entry »
Adult Stem Cells and Pancreatic Differentiation
Posted by admin in stem cells on June 21st, 2009
Adult stem cells are found in most tissues, where they are thought to participate in natural turnover and regeneration. Under defined conditions, some of these cells can also be significantly expanded and differentiated along specific lineages. This post is focused on mesenchymal stem cells (MSCs), which can be isolated from virtually every organ of the human body. While MSCs have a wellproven potential to give rise to connective tissues (e.g., bone, cartilage, fat, etc.), their ability to differentiate into endodermal cell types (and particularly insulinproducing beta cells) is Read the rest of this entry »
Human ES Cell Differentiation
Posted by admin in stem cells on June 21st, 2009
The widespread availability of huES cells to most laboratories shortly after their isolation – together with the progressive realization that progress with mouse ES cells might not be immediately translatable to their human counterparts – led to a sudden shift of starting material for pancreatic differentiation experiments. The report that arguably initiated this general move toward huES cells was conducted by Assady and collaborators in 2001. Both in adherent and suspension conditions, spontaneous huES cell differentiation resulted in the generation of insulin-producing cells as early as 2 weeks after the initiation of the protocol (peaking at day 19). Their number was relatively small, as only 60% of the EBs had positive staining and only 1–3% of the cells within these showed cytoplasmic insulin signal. In addition, glucose responsiveness was absent, probably due to the difficulty of detection in such a small representation of cells. Read the rest of this entry »
Genetic Manipulation
Posted by admin in stem cells on June 21st, 2009
In 2000, Soria and colleagues reported a genetic engineering strategy for the development and expansion of ES cell-derived beta cells. In short, they created ES clones that expressed in a stable manner a construct where the neomycin gene (which confers resistance to the drug G418) was placed under the control of the insulin promoter. When these cells were allowed to spontaneously Read the rest of this entry »