Stem Cells

What are Stem Cells?

Stem cells are cells with the ability to divide many times and to give rise to specialized cells. We are excited about stem cells because we can make lots of them and we can make them into specialized cells for therapeutics and research.


People are made of different types of tissues. Tissues include your brain, liver, pancreas and intestines. Tissues are made up of specialized cells. Liver cells make up the liver, insulin-producing cells and other cells make up the pancreas and so on. A goal of regenerative medicine is to deliver fresh cells, as a therapy, to tissues that are diseased, or to make replacement tissues from scratch, starting with fresh cells and engineering them into a tissue in the lab.

Tissue regeneration occurs naturally in your body, every day. Cells in certain tissues live and function for a few days, in other tissues for a few months, and in other tissues, such as the brain, for many years. When cells naturally die off, they are usually replaced by normal regeneration processes that keep your tissues functioning properly. A goal of the Institute for Regenerative Medicine (IRM) at the University of Pennsylvania is to understand how natural regeneration processes occur, so that we can replicate the processes in the lab and generate cells for therapeutic or research purposes.

There are two kinds of natural regeneration processes. Some tissues, like the liver, have their specialized cells divide as needed, in order to balance natural cell death with regeneration. For other tissues, like the skin, blood, and intestines, their specialized cells usually don’t replicate. Instead, these tissues naturally have their own types of stem cells. The stem cells can divide many times and give rise to specialized cells as needed, to keep the tissues healthy.

In diseased or injured tissues, cells work improperly, die too early, and are not replaced fast enough by natural regeneration processes. Even the stem cells that naturally occur in tissues can fail to function, or to keep up with the demands of natural regeneration. That’s why we need new sources of cells, and why the IRM develops therapies to replace diseased cells with healthy cells.


There is a difficulty in obtaining adult cells, even adult stem cells, for tissue regeneration, for they grow poorly in a lab. Embryonic stem (ES) cells provide a solution, because they grow well inany lab and can make any type of cell.These types of stem cells originate in a fertilized egg and can be isolated before the embryonic stage. An alternative to embryonic stem cells are induced pluripotent stem (iPS) cells. These cells are derived from adult biopsy cells and induced with four embryo genes. The ES or iPS cells can then be made into specialized cells, and inserted into tissues to replace diseased cells.

The IRM is currently using stem cells and cell therapy for patient-specific research, where biopsy cells from a person with genetic or terminal diseases can be used to create iPS cells to study the onset of disease in the lab and approaches to therapeutics. The research being done in our labs every day is working to alleviate human suffering and disease.