The first practical application of embryonic stem cells was to provide a way for the gene-targeting trick invented by Dr Capecchi and Dr Smithies to be used to produce adult mice lacking particular genes or knockout mice, as they are now called.

ECONOMIST: The 2007 Nobel science prizes

But scientists still face the challenge of developing the necessary gene therapy and targeting tumours with it.

BBC: Doctors fight tumour drug defences

One problem: Targeting any one defective gene isn't enough.

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It is hoped that gene therapy will have fewer associated side effects by targeting cancer cells.

BBC: Nano-treatment to torpedo cancer

Genasense, which is used in combination with chemotherapy, works by targeting a key "cell suicide" gene called bcl-2 and then inducing cancer cells to kill themselves.

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Benlysta works by targeting a protein called BLISS that came out of HGS' gene databases.

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