Nor is it clear how the transplanted immune cells stop the existing ones from attacking the new organ.
"It's not clear exactly how protein clumps damage brain cells, " says Pepys.
The cells are encased in a clear, UV and scratch resistant coating.
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Immune cells called macrophages, trying to clear the mess, eventually choke and die, worsening the situation.
Exactly what happens to the windpipe after it is transplanted isn't clear, but researchers believe that placing stem cells, which are capable of developing into different types of body cells, can pick up signals from their environment and integrate with existing tissues.
It is not yet clear how learning triggers the retention of the new brain cells and the laying down of memories.
Walters, one of the principal investigators on the trial, says it will be clear within six weeks of the transplant if the purified cells take root.
Just what causes T cells to malfunction in people with psoriasis isn't entirely clear, although researchers think genetic and environmental factors both play a role.
After her diagnosis, Mulrain's doctors told her to steer clear of all soy foods because these foods could encourage the growth of cancer cells.
And even if it does work, it is not clear how long the implants will keep working, whether they will damage the nerve cells and whether there will be a problem with immune rejection.
It's not clear yet, for example, whether the process will work as efficiently with adult, or older cells, and healthy egg donors may not be as available in some parts of the country as they were in Oregon, where the state allows scientists to compensate donors for their eggs, just as IVF clinics do.
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