Zhao et al. Nature.
Embryonic stem cells are associated with numerous ethical dilemmas. The creation of equivalents of ES cells through retrodifferentiation led to a new area of research that does not require destruction of life. Specifically, it was discovered that any adult cell can be transfected with several genes, which results in the cell taking the phenotype and function of cells that appear to be very similar to embryonic stem cells. These cells can give rise to any tissue that embryonic stem cells give rise to, and unfortunately, like embryonic stem cells for teratomas (tumors). We made a video to explain this http://www.youtube.com/watch?v=_RLlUdJLy74.
One of the most exciting medical properties of iPS cells is that they can be made from a donor and theoretically the cells and their differentiated offspring should not be rejected by the donor. This would allow for generation of compatible cells, without the need for immune suppression. However, a recent study suggests that this may not be the case.
In the study (Zhao et al. Immunogenicity of induced pluripotent stem cells. Nature. 2011 May 13) investigators assessed the ability of embryonic stem cells and induced pluripotent stem cells (iPS) to stimulate immune responses using inbred, genetically identical mice. They found that embryonic stem cells (ESCs) derived from C57BL/6 (B6) mice can efficiently form teratomas (an aggressive type of tumor) in B6 mice (syngeneic) without any evident immune rejection. However, when allogeneic ESCs from 129/SvJ mice where transplanted into B6 mice, they were rapidly rejected by the B6 immune system. This by itself is interesting because transplantation of adult stem cells, mesenchymal stem cells, does not lead to rejection when transplanted between mouse strains.
When B6 mouse embryonic fibroblasts (MEFs) were reprogrammed into iPSCs by either retroviral approach (ViPSCs) or a novel episomal approach (EiPSCs) that causes no genomic integration and transplanted into B6 mice rejection was observed. Specifically, the retrovirally-generated iPS cells were more immunogenic than those generated by the novel episomal method. Rejection of both types of iPS cells was characterized by T cell infiltration.
Global gene expression analysis of teratomas formed by B6 ESCs and EiPSCs demonstrated that several iPS genes were expressed that contributed to immunogenicity. According to the authors “these findings indicate that, in contrast to derivatives of ESCs, abnormal gene expression in some cells differentiated from iPSCs can induce T-cell-dependent immune response in syngeneic recipients.”