Tuesday, July 12, 2005
Pluripotent Stem Cells from Dead Embryos
From a scientific perspective, there is no published study showing that it is possible to generate an embryonic stem cell line from a non-dividing, “dead” embryo in rodents, non-human primates or humans. If stem cell lines could be derived from such embryos, the resulting cell line would have to be carefully checked for karyotypic (genetic) abnormalities or other defects, which may have been the underlying cause of the embryo’s lack of development. This research will require that clear criteria be established to determine when a “non-dividing embryo” is dead.
Finally, the Dickey Amendment to the Department of Health and Human Services (DHHS) appropriations act prohibits the use of funds appropriated to DHHS to support the creation of a human embryo for research purposes or research in which a human embryo is destroyed, discarded, or subjected to risk of injury or death greater than that allowed under Federal requirements for fetuses in utero. Applicability of this prohibition would have to be analyzed before NIH could fund research on this technique using human embryos.
Pluripotent Stem Cells from Biopsied Blastomeres
From a scientific perspective, NIH is not aware of any published scientific data that confirms the establishment of hESC lines from a single cell removed from an 8-cell stage embryo. We are aware of the published research of Dr. Yury Verlinsky at the Reproductive Genetics Institute in Chicago that showed that a hESC line can be derived by culturing a human morula-staged embryo (Reproductive BioMedicine Online, 2004 Vol. 9, No. 6, 623-629, Verlinsky, Strelchenko, et al). It is also worth noting, however, that in these experiments, the entire morula was plated and used to derive the hESC lines. The human morula is generally composed of 10-30 cells and is the stage (Day 4) that immediately precedes the formation of the blastocyst (Day 5). It is not known whether a hESC line can be created from a single cell or a few cells because these cells appear to require close contact with surrounding cells for survival and for maintenance of the pluripotent state. Even with the hESCs derived from the inner cell mass of the human blastocyst, the odds of starting a hESC line from a single cell are poor, perhaps one in 20 tries. Thus, the odds of being able to start with a single cell from an 8-cell or morula stage embryo are likely to be challenging.
NIH believes that such experiments might be pursued in animals, including non-human primates. Experiments in animal model systems could be conducted to determine whether it is possible to derive hESCs from a single cell of the 8-cell or morula stage embryo. To date, NIH is aware of only two published reports where scientists developed mouse stem cell lines from individual blastomeres. NIH also does not know whether these experiments have been tried and failed in other animals and/or humans and, therefore, have not been reported in the literature. NIH explored whether there have been any attempts to use single cells from the 8-cell or morula stage of an animal embryo to start embryonic stem cell lines by consulting with scientists that are currently conducting related embryo research. From these discussions, these scientists believe it is worth attempting experiments using a single cell from an early stage embryo or cells from a morula of a non-human primate to establish an embryonic stem cell line. If this approach is successful, the resulting stem cell lines would, of course, have to be validated for genetic stability, pluripotency, and unlimited self-renewal — all cardinal features of embryonic stem cell lines generated from blastocysts by culturing the inner cell mass.
NIH concludes that the possibility of establishing a hESC line from an 8-cell or morula stage embryo can only be determined with additional research. NIH would welcome the receipt of investigator-initiated grant applications on this topic using animal embryos. As with all grant applications, such proposals would be judged for scientific merit by peer review and then will be awarded research funds if sufficient funds are available.
Live births resulting from human embryos that undergo PGD and are subsequently implanted seem to suggest that this procedure does not harm the embryo; however, there are some reports that some embryos do not survive this procedure. In addition, long-term studies are needed to determine whether this procedure produces subtle injury to children born following PGD. This experiment in human embryos at either the morula or the blastocyst stage would require evaluations of not only normal birth but also unknown long-term risks to the person even into adulthood.
Moreover, there are a number of questions to be resolved with regard to the nature of the cells removed from the 8-cell stage embryo. If the cells removed at this stage are totipotent (and most scientists would agree they are), then it might be argued that these cells are themselves embryos, i.e., having the potential to undertake all of the life functions of the adult. It is possible, however, that one could put these cells in an environment in which they will not continue to develop and, under these conditions, they would no longer be embryos.
As with the Landry-Zucker proposal, applicability of the Dickey Amendment would have to be analyzed before NIH could fund research on human embryos.
Pluripotent Stem Cells from Biological Artifacts
From a scientific perspective, Dr. Janet Rossant at Mount Sinai Hospital in Toronto has identified a gene essential for normal trophoblast development/function in a mouse model system. However, no one has demonstrated that it is possible to execute the sequence of steps proposed by Dr. Hurlbut and obtain a pluripotent, genetically stable stem cell line. Embryonic stem cell derivations would need to undergo pilot experiments, first in rodents and then in non-human primates, to prove that this approach has merit and is technically feasible. If created, the stem cell lines would, of course, have to be validated as authentic, with all the properties associated with self-renewing, pluripotent embryonic stem cell lines.
Dr. Hurlbut’s proposed approach to deriving hESCs is dependent upon the widespread acceptance of his assertion that the genetically modified entity created using his procedure is not, in fact, a human embryo.
There are no limitations on any pilot studies performed in rodents or non-human primates. Limits of Federal funding of research for any extension of this approach to humans would require an analysis of the applicability of the Dickey Amendment.
Pluripotent Stem Cells by Reprogramming Somatic Cells
From a scientific perspective, it may be possible at some time in the future to culture populations of somatic cells in the laboratory and reverse their differentiating process, enabling them to become pluripotent. Scientists may also identify the molecules in cells such as embryonic stem cells that are responsible for maintaining cells in a pluripotent state and use these factors to dedifferentiate somatic cells. This proposal would raise ethical issues if the dedifferentiation process were to proceed too far and create a totipotent cell (a cloned human zygote). Research conducted with somatic cells can be conducted with appropriated funds since no human embryos are involved, unless the dedifferentiation process proceeds too far and results in the creation of a cell equivalent to a zygote.
NIH places a high priority on support for research using embryonic and non-embryonic stem cells that will also be useful for basic, translational, and clinical studies. The NIH is very grateful for your continued support. I look forward to working with you to advance this and all fields of biomedical research. I will be happy to try to answer any questions that you and the Subcommittee might have.
Last Revised: July 13, 2005