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Regenerative medicine is the process of replacing, engineering or regenerating human cells, tissues or organs to restore or establish function that is lost or missing due to birth defects, diseases, aging, or injury. These approaches can take place outside of the body—to study and generate ‘replacement parts’—or inside the body—to utilize the body’s inherent capacities for repair and regeneration.
Tissue engineering is the practice of combining scaffolds, cells, and biologically active molecules into functional tissues. The goal of tissue engineering is to assemble functional constructs that restore, maintain, or improve damaged tissues or whole organs. Significant progress has been made in engineering human bladders and trachea, as well as other organs. Artificial skin and cartilage are examples of engineered tissues that have been approved by the FDA; however, currently they have limited use in human patients.
Stem cells are the building blocks of our bodies. The highly specialized cells that make up our organs and tissues came from an initial pool of stem cells that formed shortly after fertilization. Throughout our lives, we continue to rely on long-term stem cells to repair injured tissues and replace cells that are lost every day, such as those in our skin, hair, blood, and the lining of our gut.
Stem cells can be broadly defined by two characteristics: their capacity to self-renew (divide in a way that generates more stem cells) and to differentiate (to turn into mature, specialized cells that make up our tissues and organs). Cells can be totipotent (able to give rise to all tissues in an embryo and supporting tissues), pluripotent (able to generate all cells in the body), multipotent (able to generate a few types of cells), or unipotent (able to generate one cell type).
There are 3 main different types of stem cells: embryonic stem cells, adult (tissue-specific) stem cells, and induced pluripotent stem cells:
- Embryonic Stem Cells (ESCs) – Embryonic stem cells are pluripotent stem cells. They are obtained from a very early stage in development, usually the blastocyst stage, which in the human forms about five days after fertilization of an egg. A blastocyst is a mainly hollow ball, barely visible to the naked eye. Inside is a clump of approximately 150 cells, called the inner cell mass, that would eventually form the entire body of the developing animal. ESCs are created by removing the cells from the inner cell mass and growing them in a lab.
Once established, ESCs can be grown indefinitely in a lab if the correct conditions are met. If given the right cues, they can be coaxed to differentiate to a variety of mature, specialized cell types. This makes them very valuable for regenerative medicine. A major research focus is to find ways to generate cells and tissues from ESCs that can be used to test new drugs or to replace damaged organs in patients.
- Adult (tissue-specific) Stem Cells – Adult stem cells are multipotent, usually giving rise to cell types corresponding to the tissues in which they reside (e.g., muscle stem cells give rise to muscle cells). Many tissues contain stem cells that can replace cells that die or restore tissue after injury. Skin, muscle, intestine and bone marrow, for example, each contain their own stem cells. It is not clear whether every adult organ contains stem cells.
- Induced Pluripotent Stem Cells – Induced pluripotent cells (iPSCs) are non-pluripotent cells that were instructed (induced) to become pluripotent. In other words, a cell with a specialized function (e.g., a skin cell) was ‘reprogrammed’ to an unspecialized state similar to that of an embryonic stem cell. You can think of this as erasing the writing from a blackboard, thereby generating a ‘clean slate’ for further instructions. While iPSCs and ESCs share many characteristics they are not identical. iPSCs hold great promise for creating patient- and disease-specific cell lines for research purposes. A great deal of work remains before these methods can be used to generate stem cells suitable for safe and effective therapies.
A bone marrow transplant, also called a hematopoietic stem cell transplant, is a medical procedure used to treat conditions of the blood such as leukemia, sickle cell anemia, or some metabolic conditions. Doctors have been transferring blood stem cells by bone marrow transplant for more than 40 years. This is currently the only FDA-approved stem cell therapy in the USA. Many other stem cell therapies are currently being investigated in clinical trials. For more information about stem cell therapies, refer to the ISSCR ‘Patient Handbook on Stem Cell Therapies’ (http://www.closerlookatstemcells.org/patient-resources).
Information about clinical trials can be found at http://www.clinicaltrials.gov, however, being listed on clinicaltrials.gov does not indicate that the trial is being done under safe or scientifically rigorous conditions.
Stem cell tourism is when patients travel domestically or usually internationally to receive unproven stem cell therapies.
Access Stem Cell Tourism informational video.
Stem cell research contributes to a fundamental understanding of how organisms develop and grow, and how tissues are maintained throughout adult life. This knowledge is required to understand what goes wrong during disease and injury and, ultimately, how these conditions might be treated. Of particular interest in this context is research on human embryonic stem cells, as these cells open a window into unique aspects of human development and biology, and therefore will lead to novel insights into human disease.
Research on human embryonic stem cells, induced pluripotent stem cells (iPSCs) and adult stem cells needs to continue in parallel. All are part of a research effort that seeks to expand our knowledge of how cells function, what fails in the disease process, and how the first stages of human development occur. It is this combined knowledge that will ultimately generate safe and effective therapies.
Start conversations with your friends, family, and co-workers about regenerative medicine. Continue to learn more. Talk to your representatives about regenerative medicine and funding for science. Partner with institutions, like Missouri Cures (http://missouricures.org/) and the Alliance for Regenerative Medicine (http://alliancerm.org/). Support regenerative medicine research at WUSTL (http://medicine.wustl.edu/giving/).
Some exceptional resources, with more in-depth questions and answers:
- International Society for Stem Cell Research (ISSCR) Frequently Asked Questions
- NIH, Regenerative Medicine and Stem Cells
- American Society of Gene & Cell Therapy (ASGCT), Educational Resources on Gene and Cell Therapy
- Harvard Stem Cell Center, StemBook (targeted at persons with some science background)
- Lecture by Sir Martin Evans, Nobel Laureate, Stem Cells: Past, Present & Future
- Educational Resources compiled by Missouri Cures
- Some free courses on iTunesU
- Stem Cell Research by Albert Einstein College of Medicine
- Stem Cells: Policy and Ethics by Stanford University
- Biomedical Engineering by Yale University