Aug. 18, 2011
Like an out of control youth, embryonic stem cells can wreak havoc with tissue damage and tumor formation. Their inability to make appropriate, mature cells that can function in an adult body is also a problem. Scientists at UCLA have found that cells derived from pluripotent stem cells are developmentally very immature, and do not resemble the adult cell types that they would theoretically replace in a transplant. The immaturity was seen in cell derivatives from both embryonic stem cells and induced pluripotent stem (iPS) cells. The data indicate that pluripotent stem cells such as embryonic stem cells are inappropriate substitutes for adult stem cells in patient treatments.
One goal of the UCLA study was to address the ongoing question of just how closely iPS cells resemble embryonic stem cells. The researchers derived several different cell types from both human embryonic stem cells and human iPS cells--neuronal cells, hepatocytes (liver cells), and fibroblasts (common in skin and connective tissue.) The progeny of the human pluripotent stem cells were compared to each other by gene expression patterns, functionality and appearance. The authors noted that the two cell types "make nearly identical progeny", with essentially no difference between them, again indicating that iPS cells can substitute for embryonic stem cells in laboratory studies.
But when the scientists compared the cells made from pluripotent stem cells to normal human tissue cells, there were significant differences in gene expression patterns. Cells made from embryonic stem cells and iPS cells had not turned off many of the genes normally expressed only in growing, pluripotent stem cells. According to senior author Dr. William Lowry, this could be very problematic, since some of those same pluripotency genes are expressed during cancer development. The cells derived from embryonic stem cells were developmentally very immature, and were most similar to cells less than six weeks after conception, in the earliest stages of human development. Lowry said:
"What we found, looking at gene expression, was that the cells we derived were similar to cells found in early fetal development and were functionally much more immature than cells taken from human tissue. This finding may lead to exciting new ways to study early human development, but it also may present a challenge for transplantation, because the cells you end up with are not something that's indicative of a cell you'd find in an adult or even in a newborn baby."
Other groups have previously documented similar results, that embryonic stem cells produce immature cells, and that embryonic stem cell derivatives are inappropriate for use in transplants. This new study published in the journal Cell Research shows the developmental level to be very immature. These are critical discrepancies that could be lethal during transplantation, again indicating that embryonic stem cell derivatives are inappropriate for therapies.
Meanwhile, adult stem cells continue to treat over 50,000 patients a year around the globe.
Adult stem cells remain the gold standard for actual patient treatments.