Can We Reverse the Ageing Process by Putting Young Blood into Older People?

On an August morning in 2008, Tony Wyss-Coray sat in a conference room at the Veterans Affairs hospital in Palo Alto, California, waiting for his lab’s weekly meeting to begin. Wyss-Coray, a professor of neurology at Stanford University, was leading a young group of researchers who studied ageing and neurodegeneration. As a rule, the gatherings were forgettable affairs – the incremental nature of scientific progress does not lend itself to big surprises. But a lab member scheduled to speak that day had taken on a radical project, and he had new results to share.

Saul Villeda, an ebullient PhD student with slick black hair and a goatee, had spent the past year engrossed in research that called to mind the speculative medical science of the middle ages. He was investigating whether the old and frail could be rejuvenated by infusions of blood from the young. The hypothesis was not as absurd as it might sound.

Villeda had conducted pilot studies with pairs of surgically conjoined mice that shared a blood supply for several weeks. Young mice received blood...