The Role of Animals in Stem Cell Research

For medical research, as well as for research that explores  the basic processes in the development of organisms and diseases, scientists often rely on

Many research mice are chimeras because they contain both human and mouse cells. Courtesy of Advanced Cell Technology, Inc., Alameda, CA.

animals.  Implanting   human  cells  into  animals such as mice has long been common  practice  in order to test the safety and effectiveness of new drugs,  procedures, and  medical  devices  before clinical  testing  in human  volunteers.  For  stem cell research, scientists use animals to make sure the stem cells are able to incorporate into the tis- sue,  do  not  cause  any  harmful  consequences, and function in concert with the
rest of the body. For example,  before using stem cells to replace the pancreatic  cells that  are destroyed  by type I diabetes in humans,  scientists will transplant human  stem cells into a mouse  to see whether the stem cells yield healthy, insulin-producing cells. If their methods  prove successful in mice, scientists may eventually apply the technology to developing treatments for diabetes in humans.

Animal  studies  can  also  reveal  how  human cells differentiate during normal  development. For  example,   scientists  may  implant   human stem cells into a developing  mouse to observe the processes  involved in building  and organ- izing the  different  tissue  types  that  make  up the human  body.  Scientists  can also trace  the development   and  progression   of  certain  dis- eases within  an animal.  By implanting  human stem cells that lead to a particular disease into a  mouse   blastocyst,   scientists   can   observe when and how the afflicted cells begin to show signs of disease and can test drugs that  might prevent that process.

Organisms  that contain  cells or tissues from another individual   of  the  same  or  a  different  species  are called chimeras. A common  example of a chimera is a  mouse  that  has  been  injected  with  some  human cells so that it can be used for studying a human dis- ease or testing a new drug. A person who has had a blood  transfusion or  a person  who  has  received  a heart  valve  transplant from  a  pig  is  technically  a chimera, as well. The making of chimeras for research has  unique  ethical  implications   that  have  been  the topic of discussions among scientists, ethicists and the public,  especially  when  the  chimeras  contain   both human and animal cells.