Problems Using Stem Cells for Heart Disease
There are a number of studies either completed, or underway, that are using allogeneic stem cells as a treatment strategy for cardiovascular disease. Whilst many studies have made use of the patients’ own stem cells, some have used foetal, embryonic, and umbilical cord stem cells to treat acute heart disease in animals, and in humans with varying results. Researchers at the Texas Heart Institute are concerned that the assumption of immunotolerance and immunosuppression for such stem cells is faulty and dangerous and cite evidence of stem cells gaining immune potency in vivo (Buja and Vela, 2010). The researchers point to a growing body of evidence showing that stem cells do induce a response by the Major Histocompatibility Complex where they were previously thought to be immunologically inert (Kofidis, et al, 2005). This is thought to be particularly problematic if injected into an area of inflammation where plentiful immune system components are already present (Buja and Vela, 2010).
Heart Inflammation and Stem Cells
One observed effect of stem cell infusion is a lymphohistiocytic inflammatory reaction that is exaggerated by the use of xenogeneic stem cells (Yang, 2007). This is of concern for those using stem cells to treat acute myocardial infarction as this newly damaged tissue is already inflamed. Another concern is that this immune system reaction may actually accelerate the destruction of the injected stem cells with Yasuda (et al, 2005) finding that only around half of the stem cells injected into damaged heart tissue survived after an hour and that just 9% remained after 4 weeks. There does not seem to be evidence of the injected stem cells triggering an autoimmune response affecting existing stem cells in the heart tissue, although this has not yet been investigated so remains a, largely theoretical, possibility.
Immune Reactions to Stem Cell Transplants
Unfortunately, worries over the immune system’s reaction to stem cells does not stop at embryonic or cord blood stem cells as some researchers are now observing similar problems with mesenchymal stem cells. Poncelet (et al, 2007) noted the difference in immune response between allogeneic mesenchymal stem cells used in vivo and in vitro for ischaemic myocardial tissue. When injected into the damaged hearts of pigs, the stem cells elicited both a cellular and humoral response despite having displayed no proliferative T-cell response in the laboratory. Many of the assumptions made from laboratory work on the immune response to stem cells may then be considered incomplete at best, and perhaps dangerously incorrect when applied in a living organism. More animals are likely to be used up in research on this issue and some concerns may arise over the prematurity of human clinical trials of stem cell treatments for inflammatory diseases and states in particular.
Rapid Stem Cell Therapy Progression Disconcerting
The rapid progression over the past five years from initial laboratory tests to full blown human clinical trials is unusual in terms of most treatment developments and some scientists are concerned that there is considerable confusion over what has actually been learnt from all the research so far. Dinsmore’s (2008) critical analysis of stem cells and cardiac repair points out that tissue repair and regeneration is not a simple process and that “[u]nderstanding cells, the signals they respond to, and the keys to appropriate survival and tissue formation are orders of magnitude more complicated than understanding the pathways targeted by most drugs.”
Animals in Stem Cell Research
The necessity of sacrificing animal models in the laboratory to examine cell survival has been a major obstruction for much of this research, and it is also becoming more widely recognized that animal models are not necessarily an accurate prediction of the behaviour or stem cell medicine in human patients. The development of stem cell technology able to track stem cells and DNA, using quantum dots for example, may aid researchers in this field and prevent the need for histological analysis of the heart after treatment.
Related Topics –> Critical Limb Ischaemia and Endothelial Progenitor Cell Research
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