May 2003

Human Cloning May be Impossible, New Study Shows

A new study funded in part by the National Institute of Environmental Health Sciences and conducted by a team of researchers at Pittsburgh Development Center has found fundamental flaws in embryonic development that may make therapeutic cloning of primates difficult, and reproductive cloning of primates - including humans - impossible.

The study, which appeared in Science last month, observed basic molecular obstacles that blocked normal cell development despite using four different techniques of nuclear transfer, said Gerald Schatten, Ph.D, senior author.

"The chromosomes do not split properly," Schatten said. "From the very first cell division, development was inappropriate in vital ways."

Schatten is also a professor and vice chair of the department of obstetrics, gynecology and reproductive sciences and of cell biology at the University of Pittsburgh School of Medicine, and director of the Pittsburgh Development Center at the Magee-Women's Research Institute.

NIEHS, the National Institute of Child Health and Human Development, the National Center for Research Resources and private philanthropy funded the study.

According to the report, the study entailed using known methods of nuclear transfer on 716 eggs retrieved from female rhesus macaques. Thirty-three embryos were transferred into surrogates after initial cell division, but no pregnancies resulted. Imaging of DNA and basic cell structure showed that while cell division continued in a superficially normal manner, chromosomal problems existed within each individual cell.

"We used antibodies to tag the cell proteins and DNA so we could track progress," said Calvin Simerly, Ph.D, associate professor of obstetrics, gynecology and reproductive sciences and primary author of the paper. "When cells divide, there are very basic things that are supposed to happen, and they just didn't happen," he said.

Schatten said current techniques like those used to create Dolly the sheep, mice and other domestic animals don't work in nonhuman primates. "I don't want to say that this well never happen. Given enough time and materials, we may discover how to make it work. It just doesn't work now," he said.