NCPA - National Center for Policy Analysis

Clone Failure

April 18, 2003

Reproductive cloning of primates, including humans, may be impossible using currently available techniques, say researchers. Somatic cell nuclear transfer (SCNT) in nonhuman primates could accelerate medical research by contributing identical animals for research and clarifying the potential therapeutic uses of embryonic stem cells.

U.S. researchers investigated the development of cells resulting from nuclear transfer in 724 eggs retrieved from female rhesus macaques. Their study showed that cell division was abnormal when four different techniques for nuclear transfer were used to clone primate cells:

  • Although 33 embryos were transferred into 16 surrogates after initial cell division, no pregnancies resulted, compared with seasonably variable 28 percent to 66 percent pregnancy rates using assisted reproduction techniques.
  • Imaging of DNA and basic cell structures showed abnormalities in the replication and splitting of chromosomes, even though cell division seemed to occur normally at a superficial level.

The scientists say that "primate nuclear transfer appears to be challenged by stricter molecular requirements for mitotic spindle assembly than in other mammals."

There has only been one report of rhesus births after embryonic cell nuclear transfer, and that report has not been replicated.

Source: Calvin Simerly et al., "Molecular Correlates of Primate Nuclear Transfer Failures," Science magazine, April 11, 2003; "Human Cloning May Be Impossible," British Medical Journal, April 19, 2003.

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