One of the themes in Dracula movies is that, by making two neat holes in the neck of a nubile cutie and having a swig of blood, the evil count gets another lease of life. It's an old story and an old idea that young blood can rejuvenate old people. Irish poet W.B. Yeats [prev] adopted a variation on the theme by getting injections of a concoction made from monkey testes so that he could more effectively lech after Maude Gonne and/or her daughter Iseult. Or maybe not, it seems more likely that Yeats allowed a quack to give him a vasectomy to conserve his precious bodily fluids and hence his potency. TA rich seam in medical research is devoted to understanding the process of aging so that it can be slowed for rich white men. Senescence might be defined as the progressive breakdown of the delicate homeostatic balances that keep human physiology on the straight and narrow: failures to compensate for changes leads to deficits and wild fluctuations in the set point of things that doctors can measure: heart rate, blood-pressure, glucose levels, oxygen concentration, enzyme activity and hormonal balance.
About a generation before Bram Stoker wrote Dracula (1897), a French physiologist called Paul Bert carried out a peculiar vivisection experiment in which he cut the skin of two mice and sewed them together so that they shared a circulatory system. The science of parabiosis was thus invented. It was found that some active principle in the blood of a young mouse could extend the life of its older sewing partner. The reciprocal was also true: the young mouse paired with a crumbly one tended to live a shorter life. That's a peculiar experiment with an interesting result. Regardless of how interesting the result, most institutional ethics committees would have difficulty authorising such an experiment today. Work in this century has tended to use blood by syringe rather than connecting two circulatory systems. And there is almost as much flim-flam and dodgy science about the promise of parabiosis as there is about nutty diets. Caveat emptor, if you shell out money to make yourself young again.
This month, there was a report in Nature in which human umbilical cord blood (young) was infused into elderly mice to see if some of the manifestations of aging can be reversed. I suspect that the thing which is most distressing for old people is that they get a bit leaky down there. But because the scientists live in their heads they tend to concentrate on deficits in memory, cognition and problem solving. Well it turns out the young human blood helps old mice run mazes quicker and more reliably and that goes along with changes in the hippocampus - a part of the brain responsible for memory. Old human blood doesn't help in this matter. They then went on a fishing expedition to identify proteins which were more concentrated in human umbilical cord blood than in adult human blood. This generated a panel of 66 possibles. It is a statistical certainty that, if you look at a great many proteins, you will find some that are up-in-umbilical in all the samples you have time and money to process. But many of these 'hits' will be false positives - statistical artifacts from multiple testing. If you toss 10 coins 10,000 times you'll get about a dozen cases of HHHHHHHHHH but you wouldn't thereby suspect that the coins are biased.
Nevertheless, one of the 66 proteins - TIMP2 - was able to reliably work the trick on improved maze-solving when purified from blood. Any blood. Once you've identified the active principal in the old vs young test, it doesn't matter where it comes from. You can clone it into yeast and churn the stuff out in a vat. They really haven't much clue about how or why TIMP2 has this useful property but speculate that it might help certain growth hormones cross the blood-brain barrier and start to work on neurons in the hippocampus. But that's okay, the current finding to solid enough and sufficiently interesting that the researchers will have no difficulty in securing funding for further experiments. Even in a political milieu which is quite anti-science there are plenty of rich old white men in the Trump administration who will speak up on behalf of promising gerontological research.