Safety of Induced Pluripotent Stem Cells Gets a Boost

Safety of Induced Pluripotent Stem Cells Gets a Boost

Previous suspicions of an immune response to replacement tissues have been pre-mature. New data published in the journal Nature, suggests rejecting previous studies about possible side effects.

In 2007, scientists reported that a person’s cells could be reprogrammed to an embryo-like state, and therefore could form any type of cell in the body. Scientists immediately imagined utilizing those “induced pluripotent stem (iPS) cells” to create any type of body cells, thereby treating a range of diseases. It was a notable invention with the hope of creainge an endless supply of genetically matched replacement tissues to treat a range of diseases such as Parkinson’s.

[quote_right]Induced stem cells are stem cells artificially derived from other cell types (e.g: somatic, reproductive, pluripotent etc.) through a process of epigenetic reprogramming.[/quote_right]

Later, in 2011 scientists at the University of California, San Diego, raised concerns about the side effects of iPS cells, finding that they induced immune responses in the mice from which they were derived.

Led by Professor Yang Xu, researchers created iPS cells from mouse skin cells and transplanted them into genetically identical mice. The cells were attacked by the immune system of the recipient mice. This was in contrast to transplants using embryonic stem cells (ES cells), which were not destroyed by the immune system of mice.

The recent study published last month in the journal Nature, rejects that conclusion. Led by Masumi Abe, a geneticist at the National Institute of Radiological Sciences in Chiba, Japan, researchers have injected iPS cells from mice back into genetically identical mice. For comparison, just like in the previous study, they injected other mice with ES cells. Yet unlike the 2011 study, the team found no differences between the immune responses of each group.

In the 2011 study, direct transplantation of the iPS cells resulted in the formation of teratomas – non-malignant tumors. This was used to indicate the pluripotency of the iPS cells, but this could also have caused the cells to be attacked and destroyed by the immune system of the mice.

Instead, Dr Abe and his team in a new study, first transformed iPS cells into other cell types such as skin and bone marrow tissue before these were transplanted into mice.

Dr Abe’s team did that by fusing either iPSCs or ESCs to mouse embryos, which then developed into chimeric mice containing diverse cell types that had differentiated from the stem cells. They then transplanted skin from these animals onto genetically identical mice. The transplants from both groups did just as well after 2 months, showing that iPSCs trigger negligible immune responses, no more than ESCs do. Bone marrow transplants showed the same pattern.

Technical differences between the two contradicting studies make it difficult to assess whether iPSCs are truly safe from immune attacks.

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