By Pallab Ghosh
BBC News, science correspondent
A UK company is applying for permission to transplant stem cells made from human foetal tissue into the brains of stroke patients.
Stem cells are taken from aborted foetuses
Guildford-based ReNeuron has told the BBC it has convincing lab evidence that the cells could potentially regenerate brain cells damaged by a stroke.
It has applied to the US Food and Drug Administration to carry out human trials on 12 stroke patients.
However, opponents have said it is a "sick proposal".
The ReNeuron team have successfully extracted stem cells from the developing brain area of a 12 week old aborted foetus.
These cells have begun to specialise into brain cells and have the ability to rapidly generate brain tissue.
According to Dr Eric Miljan, Reneuron's head of stem cell discovery, when the foetal stem cells were injected into the brains of rats in which a stroke had been induced their movement recovered.
Tests showed that blood flow and brain activity were restored in the damaged area.
Dr Miljan said: "We're very excited. There have been a battery of tests. There have been a series of animal safety experiments. And they work.
" We feel that we are ready to go into patient trials."
The company is to submit its research results to the FDA, and if the human trial is approved it could begin early next year.
But the regulators will want to be satisfied that the trials will be safe and hold out a realistic chance of doing some good.
In particular they will want to look closely at a crucial part of the treatment which involves genetically modifying the foetal brain cells.
The researchers incorporate a gene called c-myc which is associated with normal cell division.
However, when there are abnormalities with cells the gene can be involved in the uncontrollable replication of cells and lead to cancer.
ReNeuron say they have safely harnessed this property by modifying this gene to make its action fully controllable.
They add the modified version of the gene so that it can cause a small number of foetal stem cells to multiply when a chemical is added. In effect, this provides a biochemical way of photocopying the cells.
The replication stops once the chemical is taken away.
Michael Hunt, ReNeuron's CEO, said: "We have proven with reams of experimental data that the system is fully controllable.
"We have also shown that the cells we grow using this system show absolutely no abnormalities throughout the growth process.
"It is very important for us to be able to demonstrate these safety characteristics before moving our therapy forward into stroke patients."
Reneuron's idea is to produce unlimited quantities of stem cells from just one foetal tissue sample.
According to Dr Miljan, this makes their treatment potentially commercially viable and ethically more acceptable.
"We only take one single piece of tissue and for that we can grow up enough cells to potentially treat all eligible patients.
"And we never have to go back to that tissue again. We can provide a renewable source of cells in order to treat a large patient population."
Joe Corner, of the UK's stroke Association, said the research was "very interesting".
He said: "The Holy grail for stroke research has been to find a way of regenerating the damaged part of the brain.
"Until now its been thought that the damage was irreversible.
"Most treatments and therapies have relied on teaching the patient to use different parts of their brain through physiotherapy.
"But we are beginning to see some promising signs in potential stem cell treatments and ReNeuron's approach does seem very exciting."
However, John Smeaton, director of the Society for the Protection of Unborn Children, was completely opposed to the research.
He said: "It's a sick proposal. It involves cannibalising an unborn child.
"It's an unethical in every way - killing one member of the human race to help another. We are totally opposed to this."