Individual “banks” of immune cells taken from pigs might one day be used to boost our own immune systems or to fight HIV and cancer. Our immune system’s T-cells, which play a key role in fighting off diseases, are sharpened during childhood to attack particular pathogens after encountering them. This flexibility diminishes after a child reaches young adulthood, but researchers at a US university have come up with a way to revive it. According to them, if a human’s immune cells are transferred into a young pig, they could be brought up to maximum effectiveness (as in a child’s body), then implanted back into the person they came from. The research team has already had success with experiments where human stem cells were injected into developing pig foetuses; when the piglets were born, the injected cells had multiplied and matured into a diverse range of human T-cells, alongside the pig’s own immune cells, that were shown to be fully functional. The chief researcher envisions this approach eventually being used to make human cells that fight specific diseases. The necessary technology is available now to introduce the technique widely, provided that regulatory authorities can be convinced that it can be safely tested in humans. However, the fear is that dormant pig viruses buried in their DNA could be spread to humans. Another potential danger is that human- derived cells might pick up surface molecules from the pig. This could make the transferred cells themselves targets for immune destruction. The pigs might also produce too few human cells to fight disease.