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IT鈥橲 now possible to grow human embryonic stem cells that are guaranteed free of any animal diseases.

Stem cells taken from early embryos can develop into any type of cell, so in theory you could use them to replace the nerve cells that die in people with Parkinson鈥檚, or the failing insulin-producing cells in those with diabetes. But until now, biologists could only grow them in combination with cells from mouse fetuses, and often cow serum too.

That way there鈥檚 a risk of animal diseases being passed on to humans. 鈥淣o one in their right mind would try and develop a cell product that was xeno-derived,鈥� says Chris Juttner of BresaGen, a stem cell company based in Adelaide. The US government, however, will only fund embryonic cell research if it is restricted to 78 cell lines created before 8 August 2001, all of which were grown with animal cells and could harbour animal pathogens.

Now Ariff Bongso鈥檚 team at the National University of Singapore have managed to replace the mouse cells and cow serum with muscle cells from human fetuses and human serum screened for diseases such as HIV. The team鈥檚 embryonic stem cells look and behave just like ESCs produced using mouse 鈥渇eeder鈥� cells (Nature Biotechnology, DOI:10.1038/nbt726).

鈥淚f they truly have derived cell lines that are pathogen-free, every one will be trying to repeat it,鈥� Juttner says.

Bongso鈥檚 team is getting advice from stem cell experts at the FDA to improve safety even more, by screening cells for other diseases such as vCJD. Because of ethical concerns, they are also trying to grow ESCs using adult muscle and skin cells instead of fetal muscle cells.

But there are still many hurdles to overcome. Unlike adult stem cells, for instance, undifferentiated ESCs can form tumours when injected into the body.