Human somatic cell nuclear transfer (cloning).

Within 2 years of the announced birth in 1997 of Dolly, the lamb cloned from the mam-mary cells of an adult ewe, research groups announced that they had cloned mice and calves by using differentiated somatic cells (1– 3). In the cloning technique used to produce Dolly, the nucleus of a somatic cell of the ewe was transferred to a sheep oocyte from which the nucleus had been removed, and the cells were fused through electrofusion to produce offspring that shared the genome of the original ewe. Research into the science of reproductive somatic cell nuclear transfer (SCNT) is proceeding as investigators clone additional species by using the original and related methods. The prospect of using reproductive SCNT to produce human beings has evoked extensive debate among lawmakers, academicians, religious leaders, international and national agencies , professional societies, and others. Whether human reproductive SCNT will ever be undertaken will depend on such factors as the safety and efficacy of the procedure, presence or absence of governmental regulation, perceptions of procreative rights, adherence to a voluntary moratorium against human cloning, consumer interest, and the intensity and extent of ethical objections. Reproductive SCNT in laboratory animals has heretofore been inefficient in that relatively few births have resulted from many attempts. It also has been associated with harmful side effects in calves and with high fetal and neonatal death rates (4, 5). Although concerns about fetal and neonatal safety alone would make reproductive SCNT unethi-cal for humans at present, improvements in animal cloning indicate that safety concerns may be only a temporary barrier to reproductive SCNT in humans. Moreover, researchers have proposed using SCNT to generate embry-onic stem cells for persons who need tissue or organ transplants, which raises issues not addressed in this report (6). If undertaken, the development of SCNT for such therapeutic purposes, in which embryos are not transferred for pregnancy, is likely to produce knowledge that could be used to achieve reproductive SCNT (7). Although consensus about the ethical acceptability of reproductive SCNT does not and may never exist, it is appropriate to think prospectively about the ethical issues that reproductive SCNT would raise if preclinical data suggested the procedure were safe and effective and researchers sought to conduct human trials (8). Ongoing debates about the ethics of reproductive SCNT have revealed that some observers regard human reproductive SCNT as morally unacceptable in all circumstances, others see merit in …