Stem Cells Made from Cloned Human Embryos

Cell lines made by two separate teams could boost the prospects of patient-specific therapies

This colony of embryonic stem cells, created from a type 1 diabetes patient, is one of the first to be cloned from an adult human. Credit:Bjarki Johannesson, NYSCF

Two research groups have independently produced human embryonic stem-cell lines from embryos cloned from adult cells. Their success could reinvigorate efforts to use such cells to make patient-specific replacement tissues for degenerative diseases, for example to replace pancreatic cells in patients with type 1 diabetes. But further studies will be needed before such cells can be tested as therapies.

The first stem-cell lines from cloned human embryos were reported in May last year by a team led by reproductive biology specialist Shoukhrat Mitalipov of the Oregon Health & Science University in Beaverton (see 'Human stem cells created by cloning'). Those cells carried genomes taken from fetal cells or from cells of an eight-month-old baby, and it was unclear whether this would be possible using cells from older individuals. (Errors were found in Mitalipov's paper, but were not deemed to affect the validity of its results.)

Now two teams have independently announced success. On 17 April, researchers led by Young Gie Chung and Dong Ryul Lee at the CHA University in Seoul reported inCell Stem Cellthat they had cloned embryonic stem-cell (ES cell) lines made using nuclei from two healthy men, aged 35 and 75. And in a paper published onNature's website today, a team led by regenerative medicine specialist Dieter Egli at the New York Stem Cell Foundation Research Institute describes ES cells derived from a cloned embryo containing the DNA from a 32-year-old woman with type 1 diabetes. The researchers also succeeded in differentiating these ES cells into insulin-producing cells.

Nuclear transfer To produce the cloned embryos, all three groups used an optimized version of the laboratory technique called somatic-cell nuclear transfer (SCNT), where the nucleus from a patient's cell is placed into an unfertilized human egg which has been stripped of its own nucleus. This reprograms the cell into an embryonic state. SCNT was the technique used to create the first mammal cloned from an adult cell, Dolly the sheep, in 1996.

The studies show that the technique works for adult cells and in multiple labs, marking a major step. It's important for several reasons, says Robin Lovell-Badge, a stem-cell biologist at the MRC National Institute for Medical Research in London.

At present, studies to test potential cell therapies derived from ES cells are more likely to gain regulatory approval than those testing therapies derived from induced pluripotent stem (iPS) cells, which are made by adding genes to adult cells to reprogram them to an embryonic-like state. Compared with iPS cells, ES cells are less variable, says Lovell-Badge. Therapies for spinal-cord injury and eye disease using non-cloned ES cells have already been tested in human trials. But while many ES cell lines have been made using embryos left over from fertility treatments, stem cells made from cloned adult cells are genetically matched to patients and so are at less risk of being rejected when transplanted.

Ethically fraught Lovell-Badge says cloned embryos could also be useful in other ways, in particular to improve techniques for reprogramming adult cells and to study cell types unique to early-stage embryos, such as those that go on to form the placenta.

Few, however, expect a huge influx of researchers making stem cells from cloned human embryos. The technique is expensive, technically difficult and ethically fraught. It creates an embryo only for the purpose of harvesting its cells. Obtaining human eggs also requires regulatory clearance to perform an invasive procedure on healthy young women, who are paid for their time and discomfort.

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Stem Cells Made from Cloned Human Embryos