Oh, to be a mouse. You'd have been cured of every conceivable cancer and now, you'd have something of a fountain of youth, too, at least for your thymus. A team of researchers has gotten immune-system organs called thymuses in mice to grow, The Economist reports. After the researchers' treatment, the mice's thymuses grew more than twice as large. The thymuses, which normally change in structure and become less efficient as animals age, also returned to a more youthful structure.

This is the first time anybody has been able to get a working organ in a mammal to rejuvenate itself, The Economist reports. It's a step forward for this particular method organ regeneration. Of course, many labs have grown artificial organs in different ways. We've covered everything from a trachea, made from the patient's own stem cells, to 3-D printed organs. Some of these, such as the trachea, have already been used in people.