They could be used to build an artificial artery in a test tube or the stem cells could be injected straight into the heart and they could form within it.

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Dr Reynolds, and others, have shown that under the influence of suitable growth factors, stem cells can lead full lives in a test tube.

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The way to test whether a particular cell is a stem cell, therefore, is to grow it individually.

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Egli and other stem cell scientists are eager to replicate the process, to test how reliable and robust it is, and hurdles still remain before the technique is standardized.

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Geron had injected stem cells into the spine of a small number of spinal patients to test safety.

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Sure enough, he found that the only cells that could produce new tumors in the test tube were the ones with CD133--strong circumstantial evidence that defective stem cells were the growth factor in brain cancer.

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Embryonic stem cells have also caught the eye of drug companies, which aim to use them to test potential drugs for effectiveness and toxicity.

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