evidence: A German man has probably been cured of HIV, a medical milestone achieved by only six other people in the more than 40 years since the AIDS epidemic began. [...] As with all previous cases of potential HIV cure, experts are eager to temper public excitement with a caveat: The treatment that apparently thwarted the virus in the seven patients will ever be available to only a select few. All contracted HIV and later developed blood cancer, which demanded stem cell transplants to treat the malignancy. [...] In five of the seven cases of definite or possible HIV cure, doctors found donors who had rare, natural defects in both copies of a gene that gives rise to a particular protein, called CCR5, on the surface of immune cells. Most HIV strains attach to that protein to infect cells. Without functional CCR5 proteins, immune cells are HIV-resistant.