Life in perpetuity will be secured by “rejuvenative medicine” — repairing the body by developing new tissues and organs as the old ones wear out — and nanotechnology, says Dr. William A. Haseltine, CEO of Human Genome Sciences.He sees rejuvenative medicine growing out of “regenerative medicine,” which will unfold in four phases.

1. The first phase is using the body’s own signaling factors to stimulate healing processes. Human Genome Sciences has discovered a wound-healing factor, keratinocyte growth factor-2, which causes three layers of skin to form. It regenerates the connective tissues and induces new blood vessels to grow into the healed area.

2. The second phase “kicks in when the body is injured beyond the point of repair, at which point you want to put in a new organ,” he said. Tissue engineers have already learned to grow sheets of skin and have started to produce three-dimensional structures, like bladders and blood vessels. These are constructed with mature cells grown on special matrices outside the body. In the future, they may use the patient’s own adult stem cells.

3. The third stage is the use of embryonic stem cells for “rejuvenative medicine” — replacing all the body’s adult stem cells as their powers start to fade.

4. In the fourth phase, nanotechnology will merge with biological systems. Artificial devices are likely to improve to the point that they will eventually interface with evolution’s form of engineering.