Scientists at two private U.S. companies are attempting to clone embryos for the purpose of harvesting medically useful cells. One company is focusing on cloning human cells, while the other is attempting to create embryos that are part human and part cow. Their work and progress are sure to focus public attention on the ethics of cloning.

Michael West, the president of Advanced Cell Therapeutics of Worcester, Mass. -- the company involved in the human-cow research -- says that European regulators make a distinction between "therapeutic cloning" and "reproductive cloning."

• In the former, the embryos are cloned for their valuable cells, while reproductive cloning would involve an embryo which would actually be implanted in a womb and grow into a baby.

• Young human embryos are essentially balls of a few hundred cells, says Rick Weiss of the Washington Post -- without a nervous system or any human characteristics.

• He says that many scientists believe an embryo does not become a person until it is at least 14 days old -- when the first evidence of a nervous system appears.

• Within such an understanding, experimentation on five- to 10-day-old human embryos could result in stem cell tissues to replace failing tissues in people.

West says these distinctions should calm the fears of those who envision the goal being the creation of full-scale human-cow hybrids. He says "a lot of this debate is over mental images that words like 'embryo' portray."

Experts say that in the U.S., regulatory efforts relevant to human embryo research and cloning have not attained that level of subtle distinction. Caught between the desire not to support anything resembling abortion and an equally strong desire not to interfere with medical research, Congress has repeatedly failed to muster the votes necessary to pass legislation relating to cloning in the private sector. At present, federal funds cannot be used to create embryos for harvest.

Source: Rick Weiss, "Embryo Work Raises Specter of Human Harvesting," Washington Post, June 14, 1999.