Tissue engineering is an interdisciplinary field that applies the principles of engineering and life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function or a whole organ. There has been substantial progress to growing livers and kidneys.
What if you could go beyond growing whole, healthy replacement organs and grow new, young healthy replacements for all tissues of the body ? How long could someone live if everything was relatively easy to replace ? How long could the brain stay healthy if there was no deterioration in the function of any organ or system (immune, nervous etc…) of the body ? Stem cells would also be used to provide supplies of cells for more frequent rejuvenated cells. Especially for blood.
Extreme surgery could also be an interesting possibility. there is work to modify the life /death boundary to enable suspension of the body for hours with a healthy revival. Combining this with the repair of spinal cord injuries could enable extreme surgery where the head and brain are suspended during a brain or head transplant to a healthy body.
Increasing the ability of the human body to regenerate (more like the capabilities of a salamander) would also help with the issue of spinal cord repair and with possibilities for life extension.
Successfully treating diseases of the brain would help the extreme tissue engineering and replacement path have a higher maximum amount of life extension.