Concerns over the mutations that occur when adult cells are reprogrammed into induced pluripotent stem cells has caused scientists to step back and take a second look at this technology. Can such a technology be used to treat human patients safely?
Some cells in our bodies lack nuclei. For example, platelets and red blood cells do not have nuclei, and therefore, they lack a human genome. If red blood cells can be made from pluripotent stem cells, they could potentially treat patients who suffer from anemia. The red blood cells will not harbor any mutations because they do not have DNA. Thus, induced pluripotent stem cells could potentially be used to treat patients.
A paper in Stem Cells and Development by Jessica Dias and colleagues in the laboratory of Igor Slukvin at the University of Wisconsin, Madison has reported the generation of red blood cells from human induced pluripotent stem cells (J. Dias, et al., Stem Cells and Dev 20, no 9 (2011): 1639-47).
To make red blood cells from induced pluripotent stem cells (iPSCs), they made human iPSCs from skin cells called “fibroblasts” that were taken from new-born babies. They made they iPSCs with methods that did not use viruses. Instead they placed in the fibroblasts, small circles of DNA that contained all the genes necessary to create iPSCs. These small circles of DNA are called “episomes.” and they can create iPSCs without maintaining themselves in the cells. That is to say, once the episomes convert the adult cells into iPSCs, they are lost and do contaminate the genome of the iPSCs.
After making iPSCs, they grew them for seven days with two other cells; human embryonic stem cells and a mouse bone marrow cell line called OP9. This combination converted the iPSCs into bone marrow stem cells. The bone marrow stem cells were isolated and cultured for five days with chemicals that are known to push bone marrow stem cells to become red blood cells. These chemicals (erythropoietin, stem cell factor, thrombopoietin, interleukin-3, dexamethasone, insulin, interleukin-6, and iron), drove the stem cells to become red blood cell-like cells. Because these cells were also grown under conditions that prevented them from attaching they grew and differentiated. After five days, the cells were maintained on another mouse bone marrow cells line called MS5 cells.
Dias and her colleagues also used an alternative technique that worked just as well that did not include isolating the bone marrow stem cells, but subjected the cells to a Percoll centrifugation that also isolated the differentiating cells from the other cells. This technique seemed faster and less troublesome.
Neither of these techniques could be employed if these cells were to be used for human treatments. The use of animal cells lines could contaminate the iPSCs with animal viruses or animal proteins. Both of these would cause the human immune system to react adversely to the cells (Martin MJ, Muotri A, Gage F, Varki A. Human embryonic stem cells express an immunogenic nonhuman sialic acid.Nat Med. 2005 Feb;11(2):228-32). Therefore, some other protocol will need to be devised if this type of treatment is employed for anemic humans.
Nevertheless, this culture did generate red blood cells that expressed mainly embryonic and fetal types of hemoglobin. While there was some adult hemoglobin made, it was the minority molecule. All of the cells produced by this cell culture system were of the same type as those that produce red blood cells (erythroid), and not of those that make white blood cells (myeloid). This shows that it is feasible to make red blood cells from iPSCs, and it might even be feasible to produce them in a culture system that makes large quantities of them. Other uses for culture systems like this could include making red blood cells to grow malarial parasites for drug research. Clearly this is a remarkable discovery that may lead to a source of red blood cells for patients and laboratories alike.