The blood contains founder cells that spend a lifetime making new blood cells. As we age, they start making mistakes: immunity weakens, and blood cancer becomes more common. To figure out exactly what breaks down, scientists collected 186,000 of these cells from 28 healthy people, from infants to the elderly. For each cell, they looked at which genes were switched on and saw how their activity changes over the years.
Using 55 genes from two main programs, the computer was taught to determine a cell's age. It is off by only 3 years, which is like guessing a person's age from a photograph. Then this method was applied to blood cancer cells from 90 patients. In some patients, the cancer cells looked "younger" than their actual age. Such patients lived an average of 8.6 months, while those whose cells matched their age lived 13.1 months. So "young" cancer cells are more dangerous.
Now doctors can use this clock to better predict how cancer will behave in a particular patient. And scientists can use it to test whether new drugs help slow down the aging of blood cells.
The aging clock's error was just 3 years across a range from 4 weeks after conception to 77 years, which is comparable to the accuracy of predicting age from a photograph of a face.
The idea of an "aging clock" echoes the film "In Time" (2011), where people have a countdown of life on their arm. Here the clock is hidden inside cells, and it can be "tweaked" by influencing molecular programs.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.