When Dolly the cloned sheep was born 20 years ago on July 5, many hailed mankind’s new-found mastery over DNA as a harbinger of medical miracles, such as laboratory-grown transplant organs. Others feared a “Brave New World” of identical humans farmed for spare parts. As it turns out, neither came to pass.
Human cloning—complicated, risky, and ethically contentious—has largely been replaced as the holy grail of regenerative medicine by other technologies, according to a report from the global news agency AFP.
“It has not lived up to the hype,” Rosario Isasi of the University of Miami’s Institute for Bioethics and Health Policy told AFP. “It was like a ‘eureka’ moment: that we will finally be able to understand more about the mechanisms of disease, be able to maybe use it as a treatment for infertility. But that has not happened.”
Arguably the world’s most famous sheep, Dolly was the first mammal cloned using a technique called somatic-cell nuclear transfer (SCNT). The process involves removing the DNA-containing nucleus of a cell other than an egg or sperm—a skin cell, for example—and implanting it into an unfertilized egg from which the nucleus has been removed.
In Dolly’s case, the gene-encoding cell was taken from a mammary gland, which saw the ewe named for buxom country singer Dolly Parton. Once transferred, the egg reprograms the mature DNA back to an embryonic state with the aid of an electric jolt, and starts dividing to form a single-parent embryo.
Apart from ethical objections raised to the creation of carbon-copy people, safety is a key concern. In animals, only a handful of cloned embryos survive to birth, and many have health problems later.
In therapeutic cloning, scientists harvest stem cells from a very early-stage embryo—called a blastocyst—a hollow ball of approximately 100 to 200 cells. Coaxing these “blank” juvenile cells into becoming specialized liver or blood cells, for example, holds the promise of curing disease or repairing damaged organs. If grown from the patient’s own DNA, the risk of transplant rejection is dramatically reduced.
But producing stem cells this way involves destroying embryos, another moral quagmire. And while a handful of scientists have succeeded in creating stem cells through SCNT, none has been grown into a functional human organ.
While cloning may not have found a direct application in medicine, it has yielded many spinoff technologies, experts say.
“The whole field has moved to IPS [induced pluripotent stem] cell research,” said Julian Savulescu, the head of Oxford University’s Uehiro Center for Practical Ethics.
IPS cells are created by stimulating mature, already- specialized cells back into a juvenile state—basically cloning without the need for an embryo. The discovery is the new focus of regenerative medicine, although the jury is out as to whether IPS cells work as well as embryonic ones.
Another spinoff is mitochondrial gene transfer, a new way of planting parental DNA into a healthy egg to create an embryo free of harmful mutations carried by the mother.
Source: Medical Xpress; July 5, 2016.