The Future for Stem Cell Research Robin Lovell-Badge Division of Developmental Genetics, MRC National Institute for Medical Research Nature 2001; 414: Park, Ji-Yoon

Contents 1. Introduction 2. Background A. What are Stem Cells? A. What are Stem Cells? B. Properties of Human ES Cells B. Properties of Human ES Cells 3. Where do embryonic stem cells come from? 3. Where do embryonic stem cells come from? 4. Why are embryonic stem cells important? 4. Why are embryonic stem cells important? 5. How might embryonic stem cells be used to treat disease? 5. How might embryonic stem cells be used to treat disease? 6. Why not derive stem cells from adults? 6. Why not derive stem cells from adults? What are the benefits of studying embryonic stem cells?

What are embryonic stem cells?  Embryonic stem cells » s tem cells are the newest "hot" topic in biological research » are undifferentiated cells that are unlike adult cell » have the ability to choose between prolonged self-renewal & differentiation » fate choice; highly regulated by intrinsic signals & the external environment » only found naturally in the early stages of embryonic development and are totipotent » they have the ability to form any adult cell - undifferentiated embryonic stem cells can proliferate indefinitely in culture - they could potentially provide an unlimited source of specific, clinically important adult cells such as bone, muscle, liver or blood cell

Properties of Human ES Cells  Relatively flat, compact colonies that easily dissociate into single cells in trypsin or in Ca 2+ - and Mg 2+ - free medium  Grow more slowly than mouse ES cells  Population-doubling time: ~ 36 hrs, / mouse ES cells: ~12hrs  In vitro culture requirements for undifferentiated growth » mouse - LIF(leukemia inhibitory factor) » human - feeder layers & serum / or serum-free media, bFGF » fibroblast feeder layers: prevent differentiation of human ES cells  Remarkably stable karyotypes » normal XX and XY karyotype » model of the study of developmental biology mechanism  Expression of high levels of telomerase » maintain their length, is highly correlated with immortality in human cell line

Where do embryonic stem cells come from? Where do embryonic stem cells come from?  Human embryonic stem cells » are derived from fertilized embryos less than a week old » using 14 blastocysts obtained from donated, surplus embryos produced by in vitro fertilization » James Thomson established five independent stem cell lines in November 1998 » This was the first time human embryonic stem cells had been successfully isolated and cultured  The cell lines » capable of prolonged, undifferentiated proliferation in culture » maintained the ability to develop into a variety of specific cell types, including neural, gut, muscle, bone and cartilage cells.

Why are embryonic stem cells important?  Drug discovery » The ability to grow pure populations of specific cell types - offers a proving ground for chemical compounds that may have medical importance - treating specific cell types with chemicals and measuring their response offers a short-cut to sort out chemicals that can be used to treat the diseases - would permit the rapid screening of hundreds of thousands of chemicals that must now be tested through much more time-consuming processes  Benefits » offer insights into developmental events that cannot be studied directly in humans in utero or fully understood through the use of animal models » knowledge of normal development could ultimately allow the prevention or treatment of abnormal human development

How might embryonic stem cells be used to treat disease?  The ability to grow human tissue of all kinds opens the door to treating a range of cell-based diseases and to growing medically important tissues that can be used for transplantation purposes.

Why not derive stem cells from adults?  There are several approaches now in human clinical trials that utilize mature stem cells (such as blood-forming cells, neuron-forming cells and cartilage- forming cells)  because adult cells are already specialized, their potential to regenerate damaged tissue is very limited:  Adults do not have stem cells in many vital organs, so when those tissues are damaged, scar tissue develops. Only embryonic stem cells, which have the capacity to become any kind of human tissue, have the potential to repair vital organs.  adult stem cells are difficult to grow in the lab and their poetntial to reproduce diminishes with age.  Studies of adult stem cells are important and will provide valuable insights into the use of stem cell in transplantation procedures.

What are the benefits of studying embryonic stem cells?  They have the potential to treat or cure a myriad of diseases, including Parkinson's, Alzheimer's, diabetes, heart disease, stroke, spinal cord injuries and burns.  Understand what leads cells to specialization in order to direct cells to become particular types of tissue.  To study the potential of immune rejection of the cells, and how to overcome that problem.

Derivation of human ES cell lines

In vitro differentiation of human ES cells under a variety of conditions

Pluripotency of mouse embryonic stem (ES) cells Fig 1.a, Aggregates of mouse ES cells forming embryoid bodies. The dark staining shows expression of Sox2 in the less differentiated cells, whereas the rind of differentiated endoderm is unstained. (Image courtesy of A. Avilion). b, Histological section of a teratocarcinoma derived from mouse ES cells. Many different cell types are found, all formed from the ES cells, including representatives of all three germ layers. (Image courtesy of M. Parsons.) c, The ultimate test of pluripotentiality: a chimaera made by injecting ES cells into a blastocyst. The pigmented areas reveal the contribution of ES cell derivatives to the skin, but all tissues are composed of a mixture of ES and host embryo derivatives. Even a single ES cell can give a chimaera like this.

Fig 2. A small primary neurosphere, obtained from one or a few cells from the dorsal telencephalon of a 14.5-d.p.c. mouse embryo, which has been grown in culture for 21 days. This is stained with DAPI (blue) to reveal nuclei and with both SOX2 (green) and Nestin (red) to reveal neural progenitor cells. Many, if not all, of these cells have properties of neural stem cells. (Figure courtesy of E. Remboutsika.)

Tissue derivatives of all three EG layers differentiated from human ES cells in vivo

Definition Somatic cell - cell of the body other than egg or sperm. Somatic cell nuclear transfer - the transfer of a cell nucleus from a somatic cell into an egg from which the nucleus has been removed. Stem cells - cells that have the ability to divide for indefinite periods in culture and to give rise to specialized cells. Pluripotent - capable of giving rise to most tissues of an organism. Totipotent - having unlimited capability. Totipotent cells have the capacity to specialize into extraembryonic membranes and tissues, the embryo, and all postembryonic tissues and organs.