CELLS that might cause cancer can now be extracted from transplants grown
from embryonic stem cells, removing a major barrier to this kind of tissue
repair. What鈥檚 more, if things go wrong, the entire transplant could be ordered
to self-destruct.
Stem cells derived from embryos could revolutionise medicine by allowing
scientists to grow new tissue, such as neurons or heart muscle to repair damaged
brains and hearts. Stem cells taken from adults have already shown promise, and
embryonic stem cells (ESCs) can develop into an even wider range of tissue
types. But there is a major problem with this approach.
At the moment, specialised tissues grown from ESCs are always contaminated
with stem cells that have not differentiated into any specialised cell type.
When transplanted into mice, these cells often cause a form of tumour called a
teratoma. The fear is that the same thing could happen in humans given
transplants grown from ESCs.
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鈥淚t鈥檚 a real worry,鈥� says Nissim Benvenisty, a geneticist at the Hebrew
University in Jerusalem. 鈥淲e don鈥檛 want to transplant even a few embryonic stem
肠别濒濒蝉.鈥�
So Benvenisty and his colleagues linked the gene for a jellyfish protein
called green fluorescent protein to the control region of another gene that is
only expressed in stem cells. They then put this into human ESCs. When tissues
are grown from these cells, any remaining stem cells fluoresce green in UV
light. A machine called a cell sorter can then separate them out.
鈥淭his is very important,鈥� says Austin Smith of the Centre for Genome Research
in Edinburgh. Similar techniques are used with mice, but doing it with human
ESCs is a significant step forward, he says.
The technique could also be adapted to pick out other cell types. 鈥淔or
research, it鈥檚 a wonderful tool,鈥� Benvenisty told a conference on stem cells in
London last week.
But in case patients or regulators have qualms about transplants containing a
jellyfish gene, Benvenisty鈥檚 team has also created fluorescent antibodies that
can bind to particular cell types. This allows the marked cells to be removed by
cell-sorting machines without any genetic engineering.
Similar methods are already being used to hunt down any cancer cells
remaining in the blood of leukaemia patients who are in remission. 鈥淚 think
eventually this will be the procedure of choice,鈥� says Benvenisty.
He also has a back-up plan. His team is inserting 鈥渟uicide鈥� genes into human
ESCs that make them self-destruct when exposed to an antibiotic. So if a
transplant goes awry, or shows signs of becoming cancerous, it could be killed
off with a short course of drugs. 鈥淚f there are side effects, we can eliminate
the cells,鈥� says Benvenisty.