Cloned stem cells may be 鈥測ounger鈥�, 鈥渇itter鈥� and much better at replacing tissue damaged by disease or age than those from other sources. If confirmed, the finding will provide a major boost for therapeutic cloning.
The idea of therapeutic cloning is to take adult cells from a person鈥檚 body, create cloned embryos and extract embryonic stem cells that can turn into a wide range of tissues, all a perfect match for the patient. But recent research suggests that stem cells in adults are just as versatile as embryonic ones, which might make cloning unnecessary.
Now 快猫短视频 has uncovered a patent application that claims cloned stem cells have a big advantage over other stem cells. A team at Advanced Cell Technology (ACT) in Massachusetts, working with Malcolm Moore of the Memorial Sloan-Kettering Cancer Center in New York, cloned skin cells from two cows. They then injected blood-forming stem cells (which also give rise to immune cells) from the cloned fetuses back into the cows. One cow had its immune systems suppressed with drugs.
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The cloned cells seemed to have an amazing ability to take over from adult ones, replacing up to 50 per cent of the cows鈥� blood stem cells after just one infusion, even in the cow whose immune system was untouched.
Autoimmune diseases
The team thinks the stem cells could be 鈥測ounger鈥� and more competitive as a result of cloning. 鈥淲e can confirm that we have had success,鈥� says Robert Lanza of ACT, who declined to comment on details and wanted it made clear that the company did not seek to make the research public prior to journal publication. ACT has been criticised for this before.
The obvious implication is that you could replace the immune system of people with leukaemia or autoimmune diseases such as arthritis. 鈥淚t would be great if we could do this in humans,鈥� says stem cell specialist Diane Krause of Yale University.
She says it is risky to use blood stem cells from a cancer patients鈥� own bone marrow to restore their immune system, as some might be cancerous. And when patients are given bone marrow cells from donors, these can turn on their new host.
The cloned cells could also be modified before being implanted, Lanza says. For example, cells from an HIV patient could be altered to resist the virus.
Regenerative ability
Perhaps most significantly, people who get 鈥測ounger鈥� cells derived by therapeutic cloning might end up with stem cells that have significantly improved repair capabilities. Blood stem cells are known to help repair other organs, though this ability wanes with age. 鈥淲e could introduce cells with regenerative ability,鈥� says Lanza.
The cloned cells may be more vigorous because nuclear transfer 鈥� the key step in cloning 鈥� restores the 鈥渇uses鈥�, or telomeres, on chromosomes, which burn down as cells divide. Of course, a greater ability to divide and regenerate also means a greater risk of the stem cells becoming cancerous. And there is some evidence that cloning can disrupt normal gene expression 鈥� some cloned animals are stillborn or have abnormalities.
Another major issue is the fact that the blood stem cells injected into the cows came from 100-day-old fetuses, since that is when the cells can be found in the liver and can be easily harvested. There is no question of allowing human cloned embryos to grow to that stage to harvest stem cells, but Lanza says ACT and others are trying to derive blood stem cells directly from embryonic ones.
Other experts are reserving judgement until the work is published. 鈥淚t makes me sceptical because I can鈥檛 understand from a patent application what they are doing,鈥� says another stem cell researcher, Dan Kaufman of the University of Minnesota.