Germline Intervention

Seeds of Contention

Stuart Newman, Ph.D.
Professor of Cell Biology and Anatomy
New York Medical College

Most discussions of human stem cells in the public media have focused on two categories: embryonic stem (ES) cells and adult stem cells. ES cells are derived from early-stage embryos produced in vitro. While they are the more versatile of the two categories in their ability to give rise to a wide range of cell types (a characteristic known as "multipotency"), their use in experimental studies and potentially in therapies has proven contentious. The best-known reservations concerning ES cells are based on their source - human embryos produced by in vitro fertilization. But their potential, if subjected to certain experimental manipulations, has also raised ethical concerns. ES cells can be combined with non-human embryos and, in principle, be brought to full-term, forming part-human organisms known as "chimeras." Moreover, with appropriate extracellular packaging, ES cells can be used to form a complete human embryo, and ultimately a full-term individual. ES cells, of course, are much easier to manipulate genetically than single-celled embryos, potentially facilitating germ line (i.e., inheritable) genetic engineering.

Adult stem cells are the category presumed to be non-controversial. While they are, in general, not as prolific as ES cells in their capacity to differentiate into numerous cell types, they are still useful therapeutically because no one patient needs more than a limited range of replacement tissues. Their limited potential also disqualifies them for uses in embryo or chimera construction. Most importantly, few belief systems would preclude the harvesting the cells of a person's own body for the purpose of curing that individual of an illness, were this shown to be feasible.

A new article in the journal Nature,¹ however, puts a crimp in this neat division between contentious and non-contentious stem cells. This study, the joint work of several research groups at University of Gottingen, Germany, used adult mice to show that a previously known population of cells from the mature testis, so-called spermatogonial stem cells (responsible for maintaining sperm production throughout the life of a male), are capable of being transformed in vitro into an actively dividing multipotent cell type that, as far as can be judged, is identical in all respects to ES cells. Around the same time that the Göttingen study was announced, a California biotech company, PrimGen, claimed that it had isolated similar "multipotent adult germ line stem cells" (maGSC) from testicular biopsies of human males.

As maGS cells are indeed derived from the adult body, and are in this sense "adult stem cells," they are likely to escape scrutiny by those, including the U.S. government, whose opposition to the production of ES cells focuses on their source in human embryos. Nonetheless, because of their biological similarity to ES cells, maGSC are subject to the same questionable uses, including production of human-animal chimeras and full-term humans, with or without experimental gene modifications, who are disconnected from the familial and social nexus.

¹K. Guan, K. Nayernia, L.S. Maier, S. Wagner, R. Dressel, J.H. Lee, J. Nolte, F. Wolf, M. Li, W. Engel, G. Hasenfuss, Pluripotency of Spermatogonial Stem Cells from Adult Mouse Testis, 440 Nature 1199-1203 (2006).