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108th Congress

arrow indicating current page Session I | Session II

Stem Cell Research

Ronald McKay, Ph.D.
Senior Investigator, National Institute of Neurological Disorders and Stroke
May 22, 2003

Mr. Chairman, Senator Harkin, and Members of the Subcommittee, I am pleased to appear before you today to testify about human embryonic stem cell research. Human embryonic stem (ES) cells have been proposed as a limitless source for the many specific cell types of the adult body. Cells obtained in this way will likely have many uses in the future, including the development of new cell therapies for degenerative diseases. There is wide agreement on the potential importance of knowledge about stem cells but much of this information comes from work on mouse ES cells. In the last few months, published reports have shown that mouse ES cells can generate cells of the skin, blood, brain and pancreas. Even in the mouse system there are technical questions we do not fully understand but there is no doubt that mouse ES cells can be used to generate many somatic cell types.

There is clear evidence that human ES cells will form teratomas, complex mixtures of different cells, but much less is known about efficiently generating specific cell types. There are encouraging published reports of a preliminary nature but the research and biotech communities still needs to demonstrate that human ES cells can rapidly generate large numbers of a specific cell type of clinical interest. The recent wider access to human ES cells made possible by the President's decision of August 9, 2001 will accelerate progress on this question and I am confident that procedures for making some of the human cells that most interest us will be reported in detail in the next few months.

As this area is new and rapidly developing, the major technical barriers that may slow our progress are not understood. However, some of the potential difficulties can be anticipated. The human ES cells may be difficult to grow and differentiate. Their genome may be unstable. The different cells may show very different properties resulting from their genetic origin. There may be unexpected difficulties in taking the cells to a point where they are clinically relevant. And once we have obtained the differentiated cells, it may be difficult to integrate these cells with the other cells of the body.

All of these possibilities may be influenced by the history of the cell line. There are several variables that differ when human ES cells were first placed in culture by different research teams around the world. But in the first wave of work most success was obtained by growing the human cells in the company of a supporting mouse cell. This procedure was derived from data showing that mouse ES cells grow well in the presence of another cell type, a fibroblast. We do not know the exact reason for the effects of this interaction. Workers in the field still actively discuss whether one or another type of mouse fibroblast is more effective. Recent work suggests that the beneficial effects of mouse cells can be replaced by human cells or by introducing specific chemicals into the environment that supports the human cells. There are many possible ways that differences in the growth conditions could influence the properties of the human ES cells. But there are two simple questions that must be asked: Can we accurately measure these effects of these different growth conditions and do they cause irreversible harm to the human ES cell lines?

The answer to the first question is yes, but as we have discussed above, we are still developing the techniques to accurately measure all the interesting properties of human ES cells. So today, we cannot compare precisely the properties of cells grown under different conditions. A detailed answer to the second question depends on having access to these techniques. However, it is clear that any major irreversible change would immediately influence the use of an existing cell lines. The genome carries biological information through time so it is important to establish if the ES cells carry alterations in their own genes or harbor genes from other organisms that significantly affect their properties. Many cells carry pathogens that would have no practical consequences but we are explicitly concerned that the human ES cells have acquired significant genetic changes from any stage of their previous history.

These problems have been clearly stated by the biomedical research community in discussions held by the NIH Stem Cell Task Force. The NIH response to these concerns is outlined in Dr. Zerhouni's statement but it might be useful for me to amplify on the resources and role of the Human ES Cell Characterization Unit that Dr. Zerhouni has asked me to direct. The ES Unit has been established to directly compare the cell lines that are available on the NIH stem cell registry. The groups holding intellectual property rights have agreed to allow the ES Cell Unit to compare the available cells and provide open access to this information. Space has been renovated, equipment is being purchased and we hope to have a core team of four scientists at work in 3 or 4 weeks. We are building strong contacts with scientists in this country and overseas to acquire additional eligible cells. This work is monitored by a committee that includes senior investigators at other medical research facilities. This project has been actively sponsored by Dr. Zerhouni, the Director of the Intramural Research Program, Dr. Gottesman and Dr. Battey. We will compare ES cells with adult stem cells that may be pluripotent and move quickly to analyze as many of the critical features of these cells as possible. The genetic composition of these cells will be one of several measures that we use to define the cells. Our immediate goal is to rapidly develop the Human ES Cell Unit as a source of high-quality information that will allow informed use of these cells.

In this statement, I have placed the specific issue of mouse feeder in cells in the wider context of characterizing human ES cells. New data confirms that human ES cells can differentiate to cells of great clinical interest. We are all aware that there are many potential sources of problems as we move forward with this exciting technology. Should we find that the currently available cells carry irreversible changes that restrict their value, this information will be discussed openly without delay. But this specific issue is only one of many that we must address as we explore the potential of human ES cells. I am confident that the National Institutes of Health, here in Bethesda, will contribute both technical information and sound advice to the world-wide effort needed to harness the benefits of stem cells.

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