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Mice reject human embryonic cells – so what?

Friday, 22 August, 2008

Researchers at Stanford University School of Medicine found that mice mounted an immune response after being injected with human embryonic stem cells (hESCs). The result: all the transplanted stem cells—which hold the promise of maturing into several different types of tissue—were dead within a week [from Scientific American].

All of this is leading many to claim that embryonic stem cells won’t work. But that is is big stretch from the data in that study.

First, this study examined human cells implanted into mice. Mice are not the same as humans. The genetic difference there is obviously going to be a factor. That said, it is true that mice have also rejected murine embryonic stem cells (Wu et al 2008), but some research has shown that mice are more likely to develop a tolerance to embryonic cells than to other transplanted tissues (Robertson et al 2007).

Second, scientists already thought this would happen. It is for that reason that the whole concept of therapeutic cloning was considered. If the embryonic cells were genetically identical to the patient, the immune system would likely not attack those cells.

That said, therapeutic cloning still leaves the 16 genes that are present in the egg donor’s mitochondria. It is possible (though, considering that these genes are not cell-surface proteins, unlikely) that this slight difference could still cause an immune response. This has lead some to tout induced pluripotent stem cells as an answer, but those cells are genetically modified in order to induce their pluripotency, so not even they are identical.

I think that both therapeutic cloning and induced pluripotency will be solutions to this immune problem, although I personally would favour the genetic modification of the immune system to stop it being so reckless and killing that which is trying to help. After all, those of us who suffer from autoimmune diseases know that the immune system can quite easily attack cells which are genetically identical to all your other cells.

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