At the end of their conversation, Smith mentioned that he spent 10 hours every night on dialysis, something only a kidney transplant would change. This is still very unusual: only around 500 people in the U.S. donate a kidney to a stranger each year. Together they created the New England Program for Kidney Exchange, a computerized system to match kidney recipients with compatible living donors. In 2007, Roth, Rees and others expanded on the domino chain by creating the first non-simultaneous, extended altruistic donor chain. Still, it required some trust — and it could have “gone terribly,” admits Rees, who founded and runs the Alliance for Paired Kidney Donation.