Taking from a comment above: "Remarkably, the microenvironmental change and the functional decline of mid-old cells could be reversed by a young cell-originate

Taking from a comment above: "Remarkably, the microenvironmental change and the functional decline of mid-old cells could be reversed by a young cell-originated protein, SLIT2" I wonder then if this could be the magical factor in the blood of younger people. If there is indeed one or a small set of factors that induce the positive effects of young blood transfusions, then that type of "rejuvenation" becomes available to everyone and without any ethical issue.