The blastocyst stage is a developmental step in which the embryo resembles a hollow, fluid-filled cavity surrounded by a single layer of cells. Called the inner cell mass, this layer contains embryonic stem cells. Growth of a cloned nonhuman primate egg to the blastocyst stage is farther along the developmental spectrum than ever achieved before, Gerald Schatten, Ph.D., director of the Pittsburgh Development Center at Magee-Womens Research Institute, and his colleagues report.

Therapeutic Cloning and Embryonic Stem Cells

Calvin Simerly, Ph.D., associate professor of obstetrics, gynecology and reproductive sciences at the University of Pittsburgh School of Medicine and the study’s first author, presented the findings on December 6 at Cell Biology 2004 in Washington, D.C.

“We’ve made improvements by adapting some of the Korean methods and have been able to overcome some of the hurdles we were seeing before,” said Dr. Schatten, senior author of the study and professor of obstetrics, gynecology and reproductive sciences and cell biology and physiology in Pitt’s School of Medicine. “This is a significant step forward and gives us hope for eventually being able to derive embryonic stem cells through therapeutic 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 transferred into a living surrogate female in an attempt to make a successful pregnancy.

Stem cells are believed to be a key ingredient in the body’s self-repair system -- blank slates that can develop into multiple cell types, such as nerve, blood, bone or muscle. Stem cell-based approaches may hold promise for treating or curing diabetes, Parkinson’s disease, amyotrophic lateral sclerosis (ALS), heart disease, stroke, spinal cord injury and genetic diseases. Scientists believe that embryonic stem cells may have the most versatility in potential cell-based treatments, but intensive research continues on both embryonic and adult-derived stem cells.

Dr. Schatten and his colleagues are focusing much of their research on strategies to derive embryonic stem cells from nonhuman primates. Such cells could be used as a template for human embryonic stem cell study, and answer many questions about how embryonic stem cells work and whether they can be used safely and effectively against disease or injury.

Molecular Barrier Broken

The Pittsburgh team also is attempting to clone nonhuman primates as a way to generate better research models for human disease so that studies can obtain more accurate results with fewer animals.

While the current study represents significant progress, many barriers to cloning nonhuman primates remain.

Reporting in the journal Science in April 2003, Drs. Schatten, Simerly and their colleagues described fundamental flaws they observed in nonhuman primate embryonic development despite using the techniques of nuclear transfer that had resulted in successful cloning of Dolly the sheep, mice and other domestic animals.

In the 2003 study, researchers found basic molecular obstacles that blocked normal cell development, such as absent or deficient proteins, chaotic mitotic spindle structures and misaligned chromosomes. While cell division superficially seemed normal, chromosomal problems existed within each individual cell.

The most recent study appears to have broken that impasse.

“We’ve had better development to the blastocyst stage in laboratory culture, which may help us to achieve cloned primate embryonic stem cells,” said Dr. Simerly. “There are primate embryonic stem cells now, but no cloned primate embryonic stem cells.”