Human Being Semi-Cloned

"All the news we feel like printing"

The Klarreich Occasionally

Vol. IV, No. 1

September 8, 2002

HUMAN BEING SEMI-CLONED

"Dazzling breakthrough," researchers say

In what experts hail as a major step forward for fertility research, scientists have "semi-cloned" a human being: they have created an infant whose genome contains exactly half the original donor's genes, plus half the genes of another human donor.

The discovery could mean that billions of people who have not conceived children through laboratory fertilization techniques could become parents, reproductive experts say.

"This is the biggest thing to happen in reproductive science since Dolly was cloned," says Raymond Silber, a fertility researcher at Beth Israel Deaconess Medical Center in Boston, referring to the sheep that was cloned in 1997 by scientists at the Roslyn Institute near Edinburgh. "Its potential is almost unlimited."

Unlike regular cloning, which has been plagued with technical difficulties, semi-cloning is a simple, inexpensive procedure that uses only technologies at hand, says Anthony Petronio of the University of Washington in Seattle, who led the team that performed the study.

An unfertilized human egg cell contains only half as much DNA-the basic building block of genes-as a full human cell. In normal cloning, scientists remove the egg's partial DNA and replace it with a complete set of DNA from an adult human cell. The resulting embryo thus contains exactly the same genetic material as its "parent."

The new technique does not require the delicate and dangerous step of removing the egg's DNA. Instead of inserting DNA from an adult cell, the researchers inserted an entire human cell from a specialized class of cells called sperm, which like egg cells contain only half the normal amount of DNA. "It was a brilliant idea," says Kenneth Murphy, a geneticist at Stanford University in Palo Alto, California.

The embryos the team produced contained DNA that was a perfect 50-50 mix of DNA from the two people who contributed the egg and sperm. "That, to me, is the most amazing thing in what they have done," Murphy says. "I would never have imagined beforehand that they could get that kind of precise split."

In clinical trials, semi-cloned babies proved even healthier than cloned babies, the team reported in this week's issue of Nature.

As with cloned infants, embryos produced via semi-cloning must still mature for nine months inside a woman's uterus, Petronio says. "If a man wishes to have a child by this method, he must find a woman who is, so to speak, willing." The procedure could work well for married couples, he suggests.

Semi-cloning will never take the place of full cloning, experts caution. "The procedure requires a sperm cell from a male and an egg cell from a female, which is a pretty restrictive scenario," Murphy says. And the baby produced will not be an exact copy of another human being, he points out, a fact many would-be parents might view as off-putting.

As with other advances in fertility research, semi-cloning is fraught with ethical issues. "One worry is that people might try to create 'designer' babies," warns George Dixon, a medical ethicist at the University of Maryland, College Park. "They might purposely choose spouses who are intelligent and attractive, in the hopes of producing intelligent and attractive babies."

Ethical problems or not, the simplicity of the procedure means it is here to stay, experts agree. "This is by far the easiest way fertility experts have found so far to produce healthy babies," Silber says. "Let's do it."