I read about this a few days ago and been searching making sure it wasn't just one place.
To me it's very interesting, I couldn't find the exact site I wanted in English, the reference site was in German, and the test that I originally read was blood from young humans into older rats or mice, can't remember which.
This looks pretty close, though:
https://www.theguardian.com/commentisfree/2014/may/05/blood-transfusions-rejuvenate-mice-humans
To me it's very interesting, I couldn't find the exact site I wanted in English, the reference site was in German, and the test that I originally read was blood from young humans into older rats or mice, can't remember which.
This looks pretty close, though:
https://www.theguardian.com/commentisfree/2014/may/05/blood-transfusions-rejuvenate-mice-humans