Science has honored stem cell research as its 1999 "Breakthrough of the Year." This year, scientists published more than a dozen landmark papers on the remarkable abilities of stem cells, which can reproduce while in their immature state and also become more specialized tissues. The work raises hopes of dazzling medical applications and also forces scientists to reconsider fundamental ideas about how cells grow up.
Late last year, two teams announced that they had managed to keep embryonic and fetal human cells at their maximum potential, ready to be steered into becoming any kind of cell in the body. Such stem cells may one day be used to treat human diseases in all sorts of ways, from repairing damaged nerves to growing new heart and liver tissue in the laboratory. Despite that promise, many voices in society have raised objections to using stem cells derived from human embryos, a debate that is sure to continue into 2000 and beyond.
But another astonishing development that occurred in 1999 may ease the ethical dilemma. In defiance of decades of accepted wisdom, researchers this year found that stem cells from adults retain the youthful ability to become different kinds of tissues. In January, Italian and U.S. scientists reported that stem cells taken from the brains of mice could take up residence in the bloodstream and bone marrow and become mature blood cells; other researchers found that cells taken from the bone marrow could become liver cells. That means signals in the immediate environment can in some cases override a cell's history, and that nature allows developing cells far more freedom than scientists had imagined. Research groups are now speeding ahead with work on adult stem cells, hoping to discover whether their promise will rival that of stem cells from embryos or fetuses.
As basic research leaped forward this year, biomedical scientists sought new ways to use stem cells to help people. For example, researchers found that healthy bone marrow stromal cells, which give rise to bone, could strengthen bones and prevent fractures when injected into three children with the bone-weakening disease osteogenesis imperfecta. Another group injected bone and muscle stem cells into mice that lacked the protein dystrophin--missing in patients with Duchenne's muscular dystrophy--and within 2 weeks the animals produced the missing protein. Applications of embryonic or fetal cells could be even more dramatic. Missouri researchers this month reported that mouse embryonic stem cells could help restore some movement to the limbs of partially paralyzed rats.
At the same time, ethical debates about using human embryos in experiments sprang up in all sorts of public forums. Several countries took steps toward promoting the research. A French high court advised lifting that country's ban on human embryo research, for example, and a U.S. presidential advisory panel recommended that public funds be available for all types of stem cell research. In proposed rules released this month, the National Institutes of Health is a bit more restrictive, prohibiting researchers from using federal funds to derive cell lines from an embryo but allowing them to work with certain cell lines created using private funds (ScienceNOW, 1 December). With dramatic results from the lab and growing public acceptance, the stem cell field is poised for progress.
For full coverage of the Breakthrough of the Year, enhanced with references and links, go to the Science Web site.