Stem cells are primitive cells that can differentiate into cell types including embryonic stem cells, adult stem cells and umbilical cord blood stem cells. These cells divide ,regenerate themselves and change to the specialized cells such as neurons, chondrocytes, hepatocytes and osteoblasts. Stem cells are able to treat different disease in the future, such as diabetes, arthritis and spinal cord injury but problems with the host immune response, cancer and infection that must be resolved.