New lines are free of animal feeder cells.

Scientists have for the first time created a line of human stem cells without using animal cells, a potential source of contaminants. The breakthrough raises hopes that researchers can grow cells that are safe for human therapy.

Most available stem cell lines, including those approved for US federal funding, were either generated or grown on animal feeder cells, a nourishing scaffold often used to support the cells. Scientists have been concerned that these animal products could pass viruses or other contaminants to the human cells, making them unfit for clinical use. In January, scientists announced that at least one of the Bush-approved stem cell lines was contaminated with an animal sugar (Nat. Med. 11, 228–232; 2005).

Researchers had previously developed ways to grow embryonic stem cells without using animal cells (Nat. Methods 2, 185–191; 2005), but had yet to create a new cell line without the feeder cells. Robert Lanza and colleagues at Advanced Cell Technology in Worcester, Massachusetts, announced in March that they have derived a new cell line free of any animal cells or serum. They extracted stem cells from a human embryo and grew them on a specially created sterile protein matrix. The cells maintained their ability to grow into different types of tissues, even after six months in the undifferentiated state. That report was published online in The Lancet.