17. What kinds of experiments have been done with stem cells and what still needs to be done?
Mouse embryonic stem cells were first described in 1981. The most common types of experiments performed have been to genetically manipulate the DNA within the mouse embryonic stem cells. These experiments have provided a large amount of information on the role that different genes play during mouse development, the formation of different tissues and their role in the adult mouse.

Further, it has been known for years that under the right conditions, mouse embryonic stem cells can contribute to every tissue in the body of the mouse. Experiments that uncovered this phenomenon were conducted by putting mouse embryonic stem cells into a fertilized mouse egg at the blastocyst stage, and examining the mouse that is subsequently generated.

These types of experiments cannot be done with human tissues, thus the potential for human embryonic stem cells must be studied in different ways. The human embryonic stem cells can be studied in vitro (in cell culture conditions) or in special mice that are immune deficient, meaning they will not reject cells from a different species.

Human embryonic stem cells were first described in 1998. The lessons learned from working with mouse embryonic stem cells are rapidly being transferred to human embryonic stem cell systems. Scientists are working hard to understand the properties of these cells and to understand the mechanisms that regulate their differentiation into adult cell types. In addition, many researchers are using these cells to set up models to study early human development and also to provide genetic and cell-based therapies for disease.

To this end, it is hoped to better understand the causes of fetal malformations so they can be treated. It is also hoped that one day we will be able to produce cells in dishes, such as heart, pancreas or brain cells, to replace genetically faulty tissue or tissue damaged as a result of heart attacks, diabetes, spinal cord disorders and Parkinson's disease.

Cell transplantation experiments using mouse models for each of these disorders have been conducted with mouse embryonic stem cells and, in some cases, with human embryonic stem cells. Although it is still in its early days, promising results are emerging.

Hematopoietic stem cells are routinely transplanted following irradiation therapies to treat patients with cancer. Irradiation can destroy the cancer cells, but it also destroys the body's hematopoietic stem cells of the bone marrow leaving the patient without an effective immune system.

In these cases, after irradiation therapy is complete, donor hematopoietic stem cells are transplanted back to the bone marrow to restore the patient's immune system. Experiments involving the transplantation of hematopoietic stem cells to sick fetuses during pregnancy have also been undertaken. These fetuses are generally detected to have genetic defects of their own hematopoietic stem cells. These experiments have been met with some success for the treatment of babies who would have otherwise suffered a range of immunodeficiency disorders, thalassemias and inborn errors of metabolism.

Fetal neural stem cell derivatives have been transplanted to replace damaged cells in experiments aimed at controlling the symptoms of Parkinson's disease. These experiments have been similarly met with some success. Experiments injecting stem cells found in mouse blood vessel walls back into the blood vessels of muscles have been successful in replacing muscle fibers and returning movement to mice with muscle disorders. Mesenchymal stem cells have proven effective in treating mice with genetic liver disease.

Some of the primary experiments that still remain to be performed include those aimed at understanding the factors required to make embryonic stem cells differentiate into the desired cell types; those to understand how to increase the number of stem cells that are accepted by the patient at the correct location in the body during disease; those to reduce host resistance to the new stem cells; and those experiments to ensure that the new stem cells correctly integrate in the body to restore the proper function to the damaged tissue.

18. Can cord blood or stem cells be stored in a bank?
Human cord blood, neural stem cells and human embryonic stem cell banks have been established in various countries and are currently being expanded. Cord blood, like bone marrow, is stored as a source of hematopoietic stem cells for the treatment of specific genetic and acquired diseases in allogeneic stem-cell transplantation therapies.

Neural stem cells, which are derived from aborted fetuses, are stored in banks for the potential treatment of brain specific diseases. Embryonic stem cell banks have also been established for the potential treatment of a wide variety of genetic and acquired diseases, ranging from neural to blood to pancreatic to heart to skin.

Prior to banking, quality control procedures check for: chromosomal abnormalities, the ability of the stem cells to undergo the freeze-thawing processes, the immune compatibility of the stem cells with patients potentially requiring the cells, the presence of viruses within the stem cells that may cause disease, the ability of the stem cells to give rise to the required adult cell types when required, and the ability of the stem cell numbers to be increased to useful amounts.

19. What is regenerative medicine?
The goal of regenerative medicine is to repair organs or tissues that are damaged by disease, aging or trauma, so that function can be restored, or at least improved. Using this definition, most medical acts can be considered "regenerative," except those that are aimed at prevention of disease such as vaccination.

The term regenerative medicine is used nowadays to describe medical acts, treatments and research that use stem cells (either adult or embryonic) to restore the function of organs or tissues. This can be achieved in different ways; first, by administering stem cells, or specific cells that are derived from stem cells in the laboratory; or second, by administering drugs that coax stem cells that are already present in tissues to more efficiently repair the involved tissue.

Currently, the only routinely applied medical practice using stem cells is for bone marrow transplantation. The use of human embryonic stem cells for therapy is still in its developing stages, but is showing promising experimental results.

20. How many human embryonic stem cell lines are there?
The available number of human embryonic stem cell lines is a matter of some debate. Originally, it was stated that there were at least 60 lines. However, most of those were not adequately characterized and only a minority (8 to 10) are currently widely accepted as true human embryonic stem cells. Detailed information on the cell lines that are available through the National Institutes of Health Human Stem Cell Registry can be found at http://stemcells.nih.gov.