The blood in our body is constantly renewed, like water in a river. But with age, the source of this river, the blood stem cells, begins to run dry. Scientists found a way to take an adult human cell and return it to a newborn state.
First the cell is reprogrammed: it forgets what it used to be and becomes similar to an embryonic cell. Then a blood stem cell is grown from it. Such a cell was transplanted into mice, and after some time its descendants were taken and transplanted into other mice. After two transplantations, the cells were still young, even though their "real" age, counting the donor, could be more than sixty years.
So far the experiments are only in mice, but if the method works in humans, it will be possible to create stocks of young blood stem cells. Then transplantation will become more accessible and safer, because there will be no need to wait for a donor and worry about their age.
The Horvath epigenetic clocks used in the work were calibrated on thousands of human tissue samples and can predict age to within a few years. Here they showed that cells that went through reprogramming and two transplants remain younger than seven years, even though their "real" age, counting the donor and the time in culture, could exceed 60 years.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.