The U.S. National Institutes of Health retired its controversial program of using chimpanzees for biomedical research. In an email to administrators, NIH Director Francis Collins said Wednesday the remaining 50 chimpanzees held for medical research will be sent to sanctuaries. The NIH also said it would develop a plan to begin resettling the remaining chimps that are supported by, but not owned by, the agency. The NIH scaled back its use of research chimps in 2013, when it released and resettled about 310 after mounting pressure from animal-welfare activists. The agency has received only one application since 2013 to use chimps in research, and it was later withdrawn.