Paralysis Resource Guide - (Page 176) RESEARCH THE BIOLOGY OF STEM CELLS: A PRIMER In 1998, scientists isolated pluripotent stem cells from early human embryos and grew them in culture. In the few years since this discovery, evidence has emerged that these stem cells can become almost any of the 200 known specialized cells of the body and, thus, may generate replacement cells to repair or replace cells or tissues that are damaged or destroyed by diseases and disabilities. Meanwhile, as the political process limits research in many areas of stem cells and therapeutic cloning, a flurry of information suggests great potential for adult stem cells. There is tremendous expectation for stem cell therapy; at this time it’s too soon to say just how or when stem cells from any source will be useful for the treatment of disease or trauma. More research for all types of stem cells is needed.What follows is a brief primer on stem cell terminology. Stem cell: a cell from the embryo, fetus, or adult that has, under certain conditions, the ability to reproduce itself for long periods or, in the case of adult stem cells, throughout the life of the organism. It also can give rise to specialized cells that make up the tissues and organs of the body. Pluripotent stem cell: can give rise to the cells that develop from the embryonic germ layers, from which all the cells of the body arise. The only known sources of human pluripotent stem cells are human embryos or fetal tissue destined to be part of the gonads. Embryonic stem cell: derived from an early (4- to 5-day) embryo called the blastocyst. Cells of the inner cell mass can be cultured into embryonic stem cells. Current challenges: to direct differentiation of embryonic stem cells into specialized cell populations; to devise ways to control their proliferation once placed in people. Embryonic germ cell: derived from fetal tissue, specifically from the primordial germ cells that develop into the testes or ovaries. Embryonic stem cells and embryonic germ cells are pluripotent, but they are not identical in their properties. 176
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