US scientists have successfully created cloned primate embryos for the first time and used them to make embryonic stem cells. Their work is published in the early online issue of the journal Nature.
Researchers at the Oregon National Primate Research Center (ONPRC) based at Oregon Health & Science University (OHSU) in Portland, Oregon, in collaboration with a number of other biomedical research organizations, have successfully produced monkey embryonic stem cells by using a new method to remove the nucleus of the eggs being used.
The research was led by Dr Shoukhrat Mitalipov, director of the OHSU research team and assistant scientist at the Reproductive Sciences Division of ONPRC, the Oregon Stem Cell Center and the department of Obstetrics and Gynecology of OHSU. Dr Don Wolf of the ONPRC also played a significant role in the project.
The achievement is said to have brought the likelihood of human therapeutic cloning a step closer, although there is still a long way to go. The success of the team at OHSU comes after nearly ten years of failed attempts, and the researchers are not quite sure why this particular experiment succeeded.
Embryonic stem (ES) cells are like “master cells” that have the potential to generate any cell in the body.
Scientists believe that one day it will be possible to create human ES cells that are genetically identical to the cells of a patient by transferring genetic material from cells of the patient to an egg stripped of its nucleus and then using it to grow ES cells in the lab to insert back into the patient.
This would open the door to cure or alleviate the symptoms of many degenerative diseases because then the patient’s immune system would not try to attack the foreign material but recognise it as its own, allowing the introduced ES cells to grow new cells to replace the diseased ones.
“Many scientists believe that embryonic stem cells hold great promise for treating a variety of diseases including Parkinson’s disease, multiple sclerosis, cardiac disease and spinal cord injuries,” said Mitalipov, adding that, using their advanced methods meant that years from now it could be conceivable that patients might receive:
“Therapeutic embryonic stem cells developed from their very own cells; meaning that there would be no concerns about transplant rejection.”
“Another noteworthy aspect of this research is that it does not involve the use of fertilized embryos, a topic which has been the source of a significant ethical debate in this country,” added Mitalipov.
In 2004 a Korean scientist, Woo Suk Hwang, claimed to have created cloned ES cells from humans, but his results were later found to be fake.
This latest study by the OHSU team, led by Shoukhrat Mitalipov, comes after nearly 10 years of research to achieve reproductive cloning in primates, using some 15,000 eggs over that time. Eventually the team switched from reproductive cloning to try to produce cloned ES cells instead, potentially not such a big step.
Mitalipov and colleagues managed to create cloned mouse embryos before moving on to monkeys. Their success came when they used the DNA of skin cells from rhesus macaque monkeys to make embryos from which they were able to extract ES cells three days later. They used a new way to remove the nuclear material of the host egg before introducing the skin DNA.
The researchers said their success is down to the use of specialized imaging software called the Oosight Spindle Imaging System. This system lets them look into the structure of the eggs’s nuclear material, thus allowing them to remove it more precisely. Previous attempts using less sophisticated technology had resulted in damaged eggs that did not divide and grow properly. This clean extraction is the first step in the process of nuclear transfer.
Mitalipov and colleagues used skin cells from a a nine-year-old male rhesus macaque monkey called Semos. Using the Oosight system they located and precisely removed the nuclear material attached to the egg’s spindle fibres and inserted the skin cell nuclei into the nucleus-free eggs.
From this they were able to grow two ES cell lines, whose DNA they were able to match to the DNA from the male skin cell donor monkey to verify they were a direct clone.
However, the success is not straigthforward and there were many failed attempts. Over 304 monkey eggs (oocytes) from 14 female rhesus monkeys were used to produce just 2 ES cell lines, and the researchers said they don’t know the reason why these particular two cell lines worked while the others did not.
Primate-cloning researcher Gerald Schatten, who has been working on reproductive cloning for years, said in a Nature news article in the same issue as the study, that while the work of the OHSU team was “a highly significant achievement”, the rate of success is still very low.
Mitalipov explained that it is early days, and now that the study has proved it can be done, the next step is to refine the process to make it more efficient and increase the success rate:
“This is the next step for our research team as other scientists continue to investigate the promise of stem cell therapies,” he said.
“Producing primate embryonic stem cells by somatic cell nuclear transfer.”
J. A. Byrne, D. A. Pedersen, L. L. Clepper, M. Nelson, W. G. Sanger, S. Gokhale, D. P. Wolf, S. M. Mitalipov. Nature advance online publication 14 November 2007.
doi:10.1038/nature06357
Written by: Catharine Paddock