CASE 3 YOU, FROM A TO T: YOUR PERSONAL GENOME

Stem cells play a prominent role in regenerative medicine, which aims to use the natural processes of cell growth and development to replace diseased or damaged tissues. Stem cells are already used in bone marrow transplantation and may someday be used to treat Parkinson’s disease, Alzheimer’s disease, heart failure, certain types of diabetes, severe burns and wounds, and spinal cord injury.

At first, it seemed as though the use of embryonic stem cells gave the greatest promise for regenerative medicine because of their pluripotency. This approach proved ethically controversial because obtaining embryonic stem cells requires the destruction of human blastocysts—that is, early-stage embryos. A major breakthrough occurred in 2006 when Japanese scientists demonstrated that adult cells can be reprogrammed by activation of just a handful of genes, most of them encoding transcription factors or chromatin proteins. The reprogrammed cells were pluripotent and were therefore called induced pluripotent stem cells (iPS cells).

The success rate was only about one iPS cell per thousand, and the genetic engineering technique required the use of viruses that can sometimes cause cancer. Nevertheless, the result was regarded as spectacular. Other researchers soon found other genes that could be used to reprogram adult cells into pluripotent or multipotent stem cells, and still other investigators developed virus-free methods for delivering the genes. In recent years, researchers have even discovered small organic molecules that can reprogram adult cells.

This kind of reprogramming opens the door to personalized stem cell therapies. The goal is to create stem cells derived from the adult cells of the individual patient. Since these cells contain the patient’s own genome, problems with tissue rejection are minimized or eliminated (Chapter 43). There remains much to learn before therapeutic use of induced stem cells becomes routine. Researchers will face challenges such as increasing the efficiency of reprogramming, verifying that reprogramming is complete, making sure that the reprogrammed cells are not prone to cancer, and demonstrating that the reprogrammed cells differentiate as they should. Nevertheless, researchers hope that someday soon your own cells containing your personal genome could be reprogrammed to restore cells or organs damaged by disease or accident.