Using human embryonic stem (ES) cells in research is controversial, and adult stem cells have been proposed as a potential alternative. The debate was fuelled by recent landmark experiments that bring us closer to stem-cell therapy. Catherine Verfaillie's group found adult stem cells in mice and men “that [seem] to have all the versatility of embryonic stem cells” (The New York Times), and thus overturned “the dogma that animal development proceeds in one irreversible direction, from the unspecialized [zygote] to the highly specialized cells of an adult body” (Washington Post). When injected into early mouse embryos, these adult stem cells that come from bone marrow contribute to many tissue types and can make up to 40% of all cells. Importantly, they “do not form a spontaneous tumor known as a teratoma [...] and they could in many cases be derived from the patient” (The New York Times), eliminating a risk of immune rejection.

So has ES-cell research become superfluous? Those who “have been battling to end all human embryonic research because it requires the destruction of five-day-old embryos” (Financial Times) might argue that it has; however, experiments from Ron McKay's group, published at the same time, prove otherwise. “McKay's team was able to turn mouse [ES] cells into dopamine-producing neurons — the kind that would be needed to correct the devastating effects of Parkinson's disease” (New Scientist).

It is not clear how close we really are to stem-cell-based therapy. Although some say that “clinical trials could begin in 12 to 18 months” (The New York Times), others wonder “how scientists would be able to produce enough adult cells in the laboratory to use widely for medical treatments ”(Financial Times).