In theory, if such antibodies could be cloned in bulk, a cocktail of enough variants to match all known H.I.V. strains could be given to newly infected patients. That is the equivalent of an immune globulin shot, which was once the only treatment for some diseases, like hepatitis.

But it would be very expensive, and the treatment would have to be given for life. And antiretroviral drugs, which cost pennies to make, do the same thing: prevent the virus from replicating.

However, if a healthy patient could be given a vaccine that would induce his own white blood cells to produce the same cocktail of antibodies, they might knock out any infection that patient got later.

Because the cells that produce antibodies have to go through up to 100 mutations before they make broadly neutralizing ones, Dr. Fauci said, a vaccine to induce that would require many shots, given month after month, to “push” the cells through those mutations. Whether that is possible, let along financially practical, remains to be seen.

Other H.I.V. vaccine experts reacted cautiously to the research, saying it was first-rate work but hedging on its practical implications.

Dr. Louis J. Picker, an H.I.V. vaccine specialist at Oregon Health & Science University, described the work as “a road map to vaccine development, yes — but it’s like one of those maps of the world from the year 1400. We still don’t know how to turn this into a vaccine.”

Dr. Mike McCune III, head of experimental medicine at the University of California, San Francisco, called it “clarifying science, with a lot of data I hadn’t seen before.”

But he said it was not clear if one patient’s immune process could be applied to others.

“Eighty percent of all patients don’t create broadly neutralizing antibodies,” he said. “What do we do for them? Do we know how protective this strategy is against new infections? And would we have to tailor-make batches of vaccine for people with different backgrounds?”