Researchers Clone First Embryonic Fibroblasts from Adult Skin Cells
ARTICLE IN BRIEF
- ✓ Investigators successfully used somatic cell nuclear transfer to produce a handful of viable blastocyst-stage embryos using nuclei from differentiated adult cells.
Scientists at a private research firm in California have cloned the first embryonic stem cells using genetic material from an adult donor's mature skin cells. Moreover, they used a technique that does not rely on potentially mutagenic viruses to insert the adult's DNA into healthy eggs from a fertility clinic.
Andrew French, PhD, and his colleagues at Stemagen Corp. in La Jolla, and Genesis Genetics Institute in Detroit, successfully used somatic cell nuclear transfer (SCNT) to produce a handful of viable blastocyst-stage embryos using nuclei from differentiated adult cells. The findings were published online Jan. 17 ahead of print in the journal Stem Cells.
Tests confirmed that three new embryos were genetically identical to the adult donor, according to Stemagen chief executive officer and researcher Samuel Wood, MD, PhD. Dr. Wood co-authored the paper and donated the skin cells from which the embryos were cloned.
The practical value of this process in treating diseases remains unclear, however. The finding comes just months after researchers in the U.S. and Japan reported similar progress in cloning stem cells from adults using a different technique — induced pluripotent stem cells (iPS) — in which genes are used to reprogram skin cells, or retroviruses deliver DNA into the inner cell mass of an embryo. (See Neurology Today's “Stem Cells Created Without Human Embryos — What Does It Mean for Embryonic Stem-Cell Research?” Dec. 18, 2007.)
Although human data are limited, animal studies suggest using viruses and foreign genes elevates the risk of cell mutation and cancer.
The Stemagen researchers developed five blastocysts from 29 healthy eggs donated by individuals at a local reproductive sciences center. Two were confirmed to be clones based on DNA “fingerprinting” — procedures used to detect the presence of the skin cell donor DNA in the blastocyst. A third was confirmed by additional mitochondrial DNA (mtDNA) analysis, which revealed the presence of oocyte donor mtDNA without any oocyte donor nuclear DNA.
The blastocyst, a thin-walled, hollow structure containing a cluster of between 70 to 100 individual cells called the inner cell mass, from which an embryo develops, is formed early in embryonic development, typically within the first week after fertilization.
Genetic material in the remaining two blastocysts did not amplify to the extent required for analysis, which the authors attributed to technical difficulties.
The study is one of several breakthrough papers published within the past six months demonstrating that cells from an adult can be induced to grow into cloned embryonic pluripotent stem cells. Observers believe these findings could help relieve the ethical gridlock surrounding the funding of research using stem cells from unwanted human embryos donated in fertility clinics. In addition, they contend that using genetically identical stem cells in novel therapies would eliminate the risk of rejection or other immune system problems — that is, the patient's body could accept the cloned embryonic cells as its own.
In an accompanying editorial, Rita Pilar Cervera, PhD, and Miodrag Stojkovic, PhD, of the Cellular Reprogramming Laboratory at the Centro de Investigación Príncipe Felipe in Valencia, Spain, said SCNT offers clear advantages over iPS and should be the focus of research aiming to develop entire stem cell lines.
“Currently, it has been proposed that human embryonic stem cells could be derived from different embryo stages of development, and even from arrested embryos and a single blastomere. Once a NTSC line is obtained, not only are a huge number of cells available for all the studies required to prove the identity of each clone, but also these cells can be used by a different laboratory to prove repeatability,” they said.
“[At] this early stage of development, we do not consider iPS cells a substitute for SCNT. … the use of genes and retroviruses known to cause cancer in mammals and retroviruses known to have the ability to disrupt the normal DNA function and stimulate the birth of cancer cells makes questionable any possible application of iPS in regenerative medicine, especially cell therapy,” they said.
“Although some proponents of reprogramming argue that these problems are purely technical and easily surmountable, it is vital to maintain the pace of research on more controversial fronts, such as the use of human oocytes in SCNT,” they continued.
Nonetheless, the editorialists cautioned that both approaches are still in very early stages of development and there are many questions that remain unanswered.
PROOF OF CONCEPT
“No one has done this conclusively before, and this study provides better documentation than ever before,” said Steven Goldman, MD, PhD, professor of neurology and chief of the Division of Cell and Gene Therapy at the University of Rochester in New York. “But it's still early in the game,” he told Neurology Today in a telephone interview. Dr. Goldman was not involved in the study.
Dr. Goldman, the Dean Zutes Chair and director of the Center for Translational Neuromedicine at Rochester, noted that the researchers started with 29 healthy eggs but were only able to prove conclusively that one ultimately yielded a blastocyst genetically identical to the donor fibroblast, while two more were “probable” clones. “This is a proof of concept,” he said, “but it's one thing to prove a concept and another to scale it up to clinical application.”
He added that he was perplexed that the researchers stopped short of actually collecting viable stem cells from the inner cell mass and trying to create a cell line.
“The real proof of establishing human somatic cell nuclear transfer as a means of creating patient-specific stem cell lines is in harvesting cells from the cloned blastocyst and then propagating them as pluripotent stem cells,” Dr. Goldman said. “That's the usual gold standard for this type of stem cell research. This work is certainly a step in that direction, but they stopped at the most important stage. It's possible that they may have tried to grow blastocyst-directed inner cell mass cells and failed, or that they couldn't obtain a stable stem cell line, but that's just a guess.”
WHAT HAPPENS IN SOMATIC CELL NUCLEAR TRANSFER?
In somatic cell nuclear transfer, investigators remove the nucleus of an egg containing the cell's DNA, replacing it with the nucleus of the foreign adult cell. The egg immediately begins “reprogramming” the inserted nucleic material into a stem cell containing the same DNA as the adult donor's. Once an electrical current is applied, the cells begin dividing. After enough cells have developed (around 100), they form a blastocyst, the earliest stage of embryonic development and a potential source of stem cells with the same DNA as the adult donor.