Two H.I.V.-infected patients in Boston who had bone-marrow transplants for blood cancers have apparently been virus-free for weeks since their antiretroviral drugs were stopped, researchers at an international AIDS conference announced Wednesday.

The patients’ success echoes that of Timothy Ray Brown, the famous “Berlin patient,” who has shown no signs of resurgent virus in the five years since he got a bone-marrow transplant from a donor with a rare mutation conferring resistance to H.I.V.

The Boston cases, like Mr. Brown’s, are of no practical use to the 34 million people in the world who have H.I.V. but neither blood cancer nor access to premier cancer-treatment hospitals.

But AIDS experts still find the Boston cases exciting because they are another step in the long and so-far-fruitless search for a cure. They offer encouragement to ambitious future projects to genetically re-engineer infected patients’ cells to be infection-resistant. At least two teams are already experimenting with variants on this idea, said Dr. Steven G. Deeks, an AIDS researcher at the University of California, San Francisco.