Israel Medical Association Journal

Quantitative chimerism testing has become an indispensable tool for following the course and success of allogeneic hematopoietic stem cell transplants. In this paper, we describe the current laboratory approach to quantitative chimerism testing based on an analysis of short tandem repeats, and explain why performing this analysis longitudinally is important and feasible. Longitudinal analysis focuses on relative changes appearing in the course of sequential samples, and as such exploits the ultimate potential of this intrinsically semi-quantitative platform. Such an analysis is more informative than single static values, less likely to be confused with platform artifacts, and is individualized to the particular patient. It is particularly useful with non-myeloablative conditioning, where mixed chimerism is common. When longitudinal chimerism analysis is performed on lineage-specific subpopulations, the sensitivity, specificity and mechanistic implications of the data are augmented. Importantly, longitudinal monitoring is a routinely feasible laboratory option because multiplex STR-PCR[1] kits are available commercially, and modern software can be used to perform computation, reliability testing, and longitudinal tracking in a rapid, easy to use format. The ChimerTrack© application, a shareware program developed in our laboratory for this purpose, produces a report that automatically summarizes and illustrates the quantitative temporal course of the patient’s chimeric status. Such a longitudinal perspective enhances the value of quantitative chimerism monitoring for decisions regarding immunomodulatory post-transplant therapy. This information also provides unique insights into the biological dynamics of engraftment underlying the fluctuations in the temporal course of a patient’s chimeric status.

Ventricular remodeling and heart failure are the inevitable consequences of myocardial infarction. Current options to cure myocardial infarction and subsequent heart failure suffer from specific limitations. Thus, alternative, additional long-term therapeutic strategies are needed to cure this costly and deadly disease. Cardiac regeneration is a promising new therapeutic option. Through cellular and molecular therapies, the concept of in situ "growing" heart muscle, vascular tissue and manipulating the extracellular matrix environment promises to revolutionize the approach of treating heart disease. Recent studies have suggested that stem cells resident within the bone marrow or peripheral blood can be recruited to the injured heart. The regeneration of damaged heart tissue may include the mobilization of progenitor or stem cells to the damaged area or stimulation of a regenerative program within the organ. There is now evidence accumulating that the heart contains resident stem cells that can be induced to develop into cardiac muscle and vascular tissue. The present review aims to describe the potential, the current status and the future challenges of myocardial regeneration by adult stem cells.

The adult human heart has limited regenerative capacity and, therefore, functional restoration of the damaged heart presents a great challenge. Despite the progress achieved in the pharmacological and surgical treatment of degenerative myocardial diseases, they are still considered a major cause of morbidity and mortality in the western world. Repopulation of the damaged heart with cardiomyocytes represents a novel conceptual therapeutic paradigm but is hampered by the lack of sources for human cardiomyocytes. The recent derivation of pluripotent human embryonic stem cell lines may provide a solution for this cell sourcing problem. This review will focus on the derivation of the hESC[1] lines, their mechanism of self-renewal, and their differentiation to cardiomyocytes. The possible signals and cues involved in the commitment and early differentiation of cardiomyocytes in this model will be discussed as well as the molecular, structural and electrophysiologic characteristics of the generated hESC-derived cardiomyocytes. Finally, the hurdles and challenges toward fully harnessing the potential clinical applications of these unique cells will be described.

Human embryonic stem cells may serve as a potentially endeless source of  transplantable cells to treat various neurologic disorders. Accumulating data have shown the therapeutic value of various neural precursor cell types in experimental models of neurologic diseases. Tailoring cell therapy for specific disorders requires the generation of cells that are committed to specific neural lineages. To this end, protocols have been developed recently for the derivation of dopaminergic neurons, spinal motor neurons and oligodendrocytes from hESC[1]. These protocols recapitulate normal development in culture conditions. However, a novel concept emerging from these studies is that the beneficial effect of transplanted stem cells is not only via cell replacement in damaged host tissue, but also by trophic and protective effects, as well as by an immunomodulatory effect that down-regulates detrimental brain inflammation.

Regenerative medicine concerns the development of cells, tissues and organs for the purpose of restoring function through transplantation.

Stem cell research offers great hope to patients suffering from neuronal damage. Stem cell-based regenerative medicine holds huge potential to provide a true cure for patients affected by a neurodegenerative disease or who have suffered a stroke.

Type 1 diabetes mellitus is caused by an autoimmune destruction of pancreatic islet beta cells, leading to insulin deficiency. Beta-cell replacement is considered the optimal treatment for type 1 diabetes, however it is severely limited by the shortage of human organ donors. An effective cell replacement strategy depends on the development of an abundant supply of beta cells and their protection from recurring immune destruction. Stem/progenitor cells, which can be expanded in tissue culture and induced to differentiate into multiple cell types, represent an attractive source for generation of cells with beta-cell properties: insulin biosynthesis, storage, and regulated secretion in response to physiologic signals. Embryonic stem cells have been shown to spontaneously differentiate into insulin-producing cells at a low frequency, and this capacity could be further enhanced by tissue culture conditions, soluble agents, and expression of dominant transcription factor genes. Progenitor cells from fetal and adult tissues, such as liver and bone marrow, have also been shown capable of differentiation towards the beta-cell phenotype in vivo, or following expression of dominant transcription factors in vitro. These approaches offer novel ways for generation of cells for transplantation into patients with type 1 diabetes.

Intractable forms of autoimmune diseases follow a rapid course, with a significantly shortened life expectancy sometimes comparable to that of malignant diseases. Immunoablative therapy, including high dose cytotoxic agents and hematopoietic autologous stem cell rescue, was recently introduced as an aggressive approach to treat autoimmune diseases that have a rapid course and are resistant to conventional therapy. The most frequent indication for this type of treatment is multiple sclerosis, seconded by systemic sclerosis. The results of immunoablative treatment with documented responses in both diseases are encouraging. The data are mature enough to begin comparative randomized studies of immunoablative versus conventional treatment to validate the benefit of the aggressive approach. A randomized trial involving SSc[1] was recently launched (ASTIS) and a trial involving MS[2] is under preparation. Considerably less experience with immunoablative treatment has been gained in systemic lupus erythematosus, rheumatoid arthritis, and other disorders with an autoimmune pathophysiology. Autologous hematopoietic stem cell transplantation in humans offers more long-lasting immunosuppression than reeducation of lymphocytes. In fact, allogeneic transplantation may replace the whole immune system. However, this attractive approach is still associated with considerable morbidity and mortality and is not yet justified for treatment of automimmune diseases. Non-myeloablative allogeneic transplantation and sub-myeloblative high dose cyclophosphamide without stem cell support are alternative approaches that could be explored in pilot studies.

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