Failures In Primate Cloning May Signal Impossibility Of Human Reproductive Cloning

In therapeutic cloning, limited cell division is induced in an unfertilized egg cell to produce embryonic stem cells. In reproductive cloning, an egg cell with a donor nucleus is implanted into a living surrogate female in an attempt to make a successful pregnancy.

"The chromosomes do not split properly," said Dr. Schatten, who also is professor and vice chairman of the departments of obstetrics, gynecology and reproductive sciences and of cell biology at the University of Pittsburgh School of Medicine. "From the very first cell division, development is inappropriate in vital ways."

In the current study, Dr. Schatten and his colleagues used known methods of nuclear transfer on 724 eggs retrieved from female rhesus macaques. Although 33 embryos were transferred into surrogates after initial cell division, no pregnancies were established. Imaging of DNA and basic cell structure revealed 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 that we could track progress," said Calvin Simerly, Ph.D., associate professor of obstetrics, gynecology and reproductive sciences at Pitt and the paper's first author. "When cells divide, there are very basic things that are supposed to happen, and they just didn't happen."

Among the key structures involved in cell division is the mitotic spindle, which functions to precisely align and separate chromosomes. However, in cells originating as a result of nuclear-transfer, examination of spindle configuration revealed chaotic structures and unequal chromosome counts. Even the most basic proteins involved in spindle formation were absent or inadequate, said Dr. Simerly, who also is an investigator with the Pittsburgh Development Center.

"Current techniques such as those used to create Dolly the sheep, mice and other domestic animals do not work in nonhuman primates," added Dr. Schatten. "I don't want to say that this will never happen. Given enough time and materials, we may discover how to make it work. It just doesn't work now."

In addition to Drs. Schatten and Simerly, other researchers who contributed to the study are Christopher Navara, Ph.D.; Kowit-Yu Chong, Ph.D.; Laura Hewitson, Ph.D.; Gabriella Gosman, M.D.; Saviero Capuano, D.V.M.; and Christopher Payne, B.S., all of the Pittsburgh Development Center; Tanja Dominko, D.V.M., Ph.D., CellThera, Worcester, Mass.; and Duane Compton, Ph.D., Dartmouth Medical School, Hanover, N.H.

The study was funded in part by the National Institute of Child Health and Human Development; the National Center for Research Resources; National Institute of Environmental Health Sciences; and private philanthropy.