I think a more practical approach would be eukaryotic cells, since they generally tend to be able to hold more DNA(instructions) and protect it better within the nucleus, probably modified human cells, that can easily travel through the bloodstream. If they've the human genome(updated and optimized), with a few additional artificial chromosomes(carrying additional error correction and maintenance genes, additional anti-cancer genes, and general mechanisms to ensure indefinite lifespan.), as they traveled through the body they could go about replacing most any cell and getting rid of extracellular junk. Since neurons likely have to be repaired in place, some mechanisms to deliver replacement chromosomes and destroy existing ones(after copying epigenetic information if necessary.) would likely be included.
The only thing that would have to be done is to alter the immune system, by using the training mechanics that protect the body's cells from immune attack, such that it does not attack these altered cells carrying and producing novel|foreign proteins. Once this is done the immune system will not attack the proteins produced by the additional chromosomes and the altered|optimized ones from the human genome, they would be recognized as self not foreign.
Evolution requires a certain rate of error|mutation to work, thus a lower rate simply cannot evolve(it can only be designed), but this rate is extremely unlikely to be the lowest physically possible for DNA. It is likely that utilizing our knowledge we can engineer error-correction and repair mechanisms that are far superior, so that we can keep the code pretty much indefinitely intact. If this is so, immortal cells can be created(multiple copies would be used to compare|error-correct and undo any mutation, mutations that would be far rarer if the replication and repair was even more precise... thus mutations would for all purposes practically not accumulate through time.). In any event pretty much all cells and organs can be replaced wholly(organs preferably replaced cell-by-cell through a regeneration mechanism, rather than surgically.) with optimized cells and thus rejuvenated. The only organ that would be a bit problematic would be the brain, but even here chromosome transfusion|replacement should be enough to rejuvenate it(obviously adding a few neurons from time to time to compensate for those lost to injury|disease or any cause. Theoretically the new optimized replacement cells would not only be far more resistant to anything thrown at it, but could leave some sort of tracer substance in the unlikely case it died, such that it indicated replacement was necessary and also to what places it was connected.).
Theoretically, one could receive updated cells|models with more optimal codes as they are designed and brought to market. Such cells would travel through the body replacing older model cells with the more optimal ones and doing chromosome transfusion|replacement in the brain(say to allow the brain to better resist lack of oxygen in an emergency.). Thus one could imagine version 1.0, 2.0, 3.0, etc.
With this even the negligible-senescence|Agelessness of some creatures should not only be obtainable but surpassable.
Edited by Cameron, 31 January 2010 - 01:41 PM.
LongeCity
