What are stem cells? Stem cells have the ability to renew themselves and act as the body's repair system by replenishing many types of cells in the body. When a stem cell divides, each new cell has the potential to remain a stem cell or become another type of more specific cell, such as a heart muscle cell, a red blood cell, or a brain cell. Because of the unique regeneration and repair nature of stem cells, scientists study them to understand the role of genes in human development, see how infections attack human cells, learn how environmental factors affect cell growth, and find treatments and cures for diseases such as cancer, Alzheimer's, Parkinson's, juvenile diabetes, and spinal cord injuries.