The aim is to see whether or not this can usefully change the balance of signaling molecules to, say, spur greater stem cell activity. There has been a trial in Alzheimer's patients, but some signs in animal studies that transfusions from young to old don't do much. It seems useful to speed up the process of determining whether or not transfusions are an interesting line of research, or something that only looked promising. That means more patients and larger trial populations, which Ambrosia is working on.

These transfusion initiatives are one of a number of outgrowths of parabiosis research in mice. Heterochronic parabiosis is the name given to connecting the circulatory systems of an old and a young individual. The older mouse shows a modest rejuvenation in a number of measures of aging, and the younger mouse shows some greater signs of aging - though most of the focus here has been on the old mouse. In recent years this technique has been used to search for potentially actionable differences in levels of specific signal molecules circulating in the bloodstream. For example, stem cell activity declines with aging, and this is likely governed by signaling processes. If levels of the most relevant molecules could be adjusted in old individuals, it might be possible to produce benefits that look quite similar to those of stem cell therapies: increased regeneration and tissue maintenance. This class of approach puts damaged, aged cells back to work, and does little to address causes of aging based on accumulation of metabolic waste, such as cross-links that stiffen blood vessels, but to the degree that it can improve health it is probably worthy of further investigation in the same way as stem cell therapy was back in the day.

One potential shortcut to the production of therapies is to perform transfusions: deliver young blood or young plasma to old individuals. I call this a potential shortcut because it really is still very uncertain as to (a) whether or not the whole process works in humans anywhere near as well as it works in mice, and (b) whether or not transfusions will recapture the effects of parabiosis to a useful degree. The evidence in mice suggests so far that it may not. It is possible to paint all sorts of scenarios in which the fact that old and young cells are in contact, feeding signals to one another in a feedback loop, is necessary to produce beneficial changes in the old individual. It is also possible to imagine signals with a short half-life, that won't be recaptured in transfusions, or changes in the old environment that are based on an increased level of specific signal molecules. That increased level won't be changed in the slightest by the arrival of some amount of young blood plasma. Only reduced levels are likely to be impacted that way.

In any case, testing and perhaps ruling out the fast path of transfusions seems like a fair plan. If it works, it will draw in more funding to build the better option of manipulating signal molecule levels directly. It if doesn't work, that result will direct scientists to focus on more productive lines of research and development. There is some grumbling from the expected quarters over the structuring of this present initiative by Ambrosia, but getting it done is better than not getting it done. The data will be useful in the sense that only sizable effects are interesting, and thus before and after data for participants will be convincing. Marginal effects, of the sort in which it would have been useful to have a control group to establish whether or not any benefits actually resulted, would mean that this probably isn't worth further exploration. Still, this well demonstrates the fact that many scientists who work within the heavily regulated, slow, and repressive system of medical development really don't like it when people try to get things done more rapidly and more inventively. To the extent that it closes down productive avenues, this is a dangerous attitude.

Recent commentary suggests that none of the results so far are either large enough or extensive enough to definitively be something other than the placebo effect, chance, or other items such as a patient making lifestyle changes. I think there is some skepticism regarding the potential effectiveness of transfusions of young blood in any case; the data is somewhat mixed, and underlying theory on what is going on still in flux. Recent research suggests that the effects observed in parabiosis studies of mice with joined circulatory systems are due to a dilution of harmful factors in old blood rather than a delivery of helpful factors from young blood, for example. If the case, that would mean that transfusions should produce very limited results at best. Still, obtaining data is the important thing, and that is what is being done here. Those complaining the loudest should put in the work to raise funds and run a study they way they would prefer to.