A compelling proof-of-principle demonstration of this approach lies in the report of a successful transplant of an HIV-1-infected individual with bone marrow from a donor with a mutation in the HIV-1 coreceptor CCR5, which resulted in a repopulation of peripheral CD4+ T cells with donor cells resistant to HIV-1 infection, thereby allowing the discontinuation of antiretroviral therapy without viral rebound [21]. The gene discussed is CCR5; the disease is HIV-1 infection.