Several groups had already found genetically engineered mice that begin expressing Yamanaka factors in adulthood show reversal of certain aging symptoms.To explore an approach that might lead to a more practical treatment for people, San Diego–based company Rejuvenate Bio injected elderly (124-week-old) mice with adeno-associated viruses (AAVs) carrying genes for three of the factors, collectively known as OSK.These animals lived another 18 weeks on average, compared with 9 weeks for a control group, the company reported in a preprint on bioRxiv this month.To see whether the epigenetic degradation was reversible, the researchers injected some of these elderly seeming mice with AAVs carrying OSK genes, which Sinclair’s group recently reported could reverse loss of vision in aging rodents.Molecular biologist Wolf Reik, director of the Altos Cambridge Institute of Science (opened last year by rejuvenation-focused company Altos Labs), praised the sophistication and thoroughness of the Harvard team’s study, but says the team’s indirect way of inducing epigenetic changes with dramatic DNA breaks that could have other effects makes it hard to prove those changes are what’s causing aging."