Sheep normally live to be 11 or 12. Dolly was 6 and a half and lame with arthritis. She was euthanised due to a lung condition.
The institute's Dr. Harry Griffin said Dolly had suffered from a virus-induced lung cancer that was also diagnosed in the past few months in other sheep housed with Dolly
She might not have gotten the infection and cancer as a result of being a clone. It is not clear that being a clone contributed to her early death. Though one scientist who was involved in research on Dolly says her clone status did contribute to her early death.
Professor Rudolf Jaenisch, who in March 2001 co-wrote an article with Dolly's creator Professor Ian Wilmut for the journal Science titled "Don't Clone Humans!" said that the death "is exactly what was expected: clones will die early".
How could her status as a clone contribute to her early death? Dolly had short telomere caps on her chromosomes.
The researchers found that Dolly's telomeres were shorter than other 3-year-old sheep, suggesting she is genetically older than her birth date.
The telomeres of chromosomes shrink with age losing 100-200 base pairs in length every time a cell divides. Shorter telomeres have recently been demonstrated to correlate with shorter life expectancy in humans. This strongly suggests that Dolly's problems stem from her shorter telomeres. Certainly her immune system would be less vigorous as a result of shortened telomeres.
However, as scientists cloning cows at Advanced Cell Technology have demonstrated, cloning of cells from an older organism does not always lead to shorter telomeres in the cloned offspring.
Moreover, when the scientists examined skin cells from the clones, they found that the telomeres were longer than those of the original senescent cells and even longer than those of typical newborn calves. One cloned cow that's now 2 years old has the telomeres of a calf, says Lanza.
ACT might be using a technique that is part of their proprietary cloning technology to achieve better cloning outcomes.
Worcester, MA, November 22, 2001 – Advanced Cell Technology, Inc. (ACT) and its subsidiary Cyagra, Inc. today reported that its proprietary cloning technology has been used to produce healthy and normal adult animals. ACT evaluated 30 cattle cloned from proliferating skin cells. Twenty-four (80%) of the clones were vigorous and remained alive and healthy one to four years later (by comparison, survival to adulthood normally ranges from 84% to 87%). Results of general health screens, physical examination and immune function were normal for all clones, including laboratory analysis on blood and urine, biochemistry, and behavioral responses. "We haven't observed any of the genetic defects, immune deficiencies or other abnormalities reported in the popular or scientific press," said Robert Lanza, M.D., Vice-President of Medical & Scientific ACT. "All of the data collected reinforce the view that these animals were clinically and phenotypically normal." The report will be published in next week's issue of SCIENCE (November 30, 2001), titled "Cloned Cattle Can Be Healthy and Normal" by ACT and its collaborators at the Mayo Clinic, Trans Ova Genetics, Em Tran and the University of Pennsylvania.
ACT has also done therapeutic cloning experiments where they cloned old cows, extracted cells from the embryo, and then injected the embryo cells back into the old cattle. These cells became major sources of blood immune system cells in the old cattle.
He said that 170 days later the injected cells had survived and were thriving in the blood of the cattle. When put into lab dishes, they grew abundantly, much as young fetal cells do.
This is an important experiment because ACT was able to take cells from an old cow and from them make cells that were much younger that could be injected back into the same cow to rejuvenate the cow's aged immune system. The problem with this approach is that since it involves the creation of an embryo it is considered morally objectionable by many and quite possibly will be outlawed by the US Congress.
An experiment with fetal cells was recently done in the UK where instead of cloning to create a source of cells aborted fetuses were used. The fetuses provided eye stem cells that improved the eyesight of sufferers of retinitis pigmentosa.
Transplants of fetal eye tissue seem to have improved the vision of two out of four people with a degenerative eye disease. It is too early to be sure the improvements are real and lasting, but on the strength of the results the team pioneering the surgery has asked regulators for permission to carry out further operations.
The ACT therapeutic cloning experiment to rejuvenate aged cow immune systems and the experiment with aborted fetus eye stem cells both demonstrate the therapeutic potential of cells derived from embryos (whether pluripotent or not). Work on adult stem cells so far has not produced cell lines with all the same advantages. On the bright side these experiments are demonstrating the enormous future therapeutic potential for cell therapies. However, regardless of how one feels personally about the use of therapeutic cloning or aborted fetuses stem cell sources, enough people have ethical objections to these approaches that the quickest way scientifically to the development of many useful cell therapies is likely to be legally blocked in at least some countries.
|Share |||Randall Parker, 2003 February 14 07:34 PM Aging Reversal|