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Statement on Nuclear Transfer and Human Reproductive Cloning

The American Society of Hematology (ASH) urges support for nuclear transfer (NT) research while backing efforts to prohibit the cloning of a human being.


Human embryonic stem cells offer a great deal of promise in treating disease and disability. NT is an experimental tool that utilizes human embryonic stem cells to expand their potential power as a human therapeutic and reveal new insights into human disease. With NT, investigators extract the nucleus of a patient’s somatic cell (such as a heart, brain, liver, or pancreas cell) and transplant it into an unfertilized egg that has been stripped of its own nucleus. The unfertilized egg—with the nucleus and genetic material from another cell—is coaxed to grow for five to six days into an early-stage embryo, which contains stem cells. The stem cells are harvested and grown as a new stem cell line, which can be utilized for scientific investigation and hopefully, in the future, into new blood, heart, brain, nerve, liver, kidney, or insulin-producing cells for therapeutic uses.

One issue with potential embryonic stem cell therapies is that patients may reject transplants that are not derived from their own DNA. Stem cells created through NT could be made to match the patient’s genetic makeup and would presumably be readily incorporated into the patient’s body. Thus, NT research provides scientists a means for harnessing the power of stem cells while circumventing the rejection issues associated with non-genetic matches.

Scientists will also be able to develop genetic tools to study disease through the NT technique. NT can create specialized embryonic stem cell lines from the somatic cell nuclei of patients with complex genetic diseases. These lines are needed to study how these diseases affect the growth and development of other cells and tissues.

To realize the full potential of this research, scientists must be able to use today and tomorrow’s technological advances to genetically manipulate the embryonic stem cell.

The cloning of a human being or human reproductive cloning would begin with the same process as NT but would involve the illegal and ethically untenable step of taking the early-stage embryo and implanting it in a womb, thereby allowing it to develop into a fetus. NT research has nothing to do with the cloning of human beings.

Current Challenges

Unfortunately, “cloning” is a term that has become associated in the current lexicon with both NT and rogue efforts to create a genetically identical human being. Every day, scientists do many kinds of cloning of genetic material in cells, most of which is a commonly accepted part of medical research.

The major issue facing the field is informing interested parties that there is a profound distinction between human reproductive cloning and NT research. Investigators need to educate the public and policymakers that human reproductive cloning cannot occur without the implantation of an embryo in a womb. In contrast to human reproductive cloning, NT involves stimulating an unfertilized egg cell to begin dividing. Once the cell begins dividing, stem cells can be extracted five to six days later and used for research.

ASH Policy

ASH strongly supports federal funding of NT research and believes that it is a critical tool for scientists to fully develop the future promise of stem cell research and ultimately help patients with deadly and debilitating diseases. NT is a powerful technique that allows scientists to study differences between normal and diseased cells, so that future treatments can be discovered. With the appropriate public oversight and under strict National Institutes of Health federal research guidelines, the Society believes that NT is fundamental to improving scientists’ understanding of how stem cells and other cells develop. New knowledge derived from NT will accelerate the search for new treatments for some of the world’s most complex diseases.

In addition, NT will allow scientists to create new embryonic stem cell lines that advance the full investigation of the genetic causes of disease. To move cell biology and stem cell research forward, investigators will need to create new stem cells that contain genetic disease genes to study how these diseases affect the growth and development of other cells and tissues. Researchers will also be better equipped to focus their research efforts on a broad array of diseases through NT. With many diseases more prevalent in people with particular backgrounds, NT permits investigators to explore embryonic stem cell lines with certain racial and ethnic characteristics to ensure that valuable research moves forward in those disease-specific areas.

Moreover, ASH ardently opposes human reproductive cloning and actively supports efforts to implement a complete ban on the practice by creating and enforcing strict new policies that supplement current Food and Drug Administration regulations.

ASH vigorously supports NT research while firmly denouncing any attempts at human reproductive cloning. The Society remains committed to moving stem cell science forward to help patients.

Founded in 1958, ASH represents nearly 13,000 clinicians and scientists committed to the study and treatment of blood and blood-related diseases. These diseases encompass malignant hematologic disorders such as leukemia, lymphoma, and myeloma; and non-malignant conditions including anemia and hemophilia; and congenital disorders such as sickle cell anemia and thalassemia. In addition, hematologists have been pioneers in the fields of bone marrow transplantation, gene therapy, and many drugs for the prevention and treatment of heart attacks and strokes.