Scientists attending an international HIV vaccine conference in Paris are excited about a small number of infected people who don't need treatment.

Researchers have identified about 550 people around the world who have HIV and yet have never become ill.

'How come people can be infected but they control the viral replication?'— Anna Laura Ross

The people can have such low levels of the virus in their blood that it is undetectable by conventional means, even after they became infected, said Bruce Walker, director of a research centre in Boston affiliated with Massachusetts General Hospital, MIT and Harvard University.

"As you sit speaking to one of these people, you get the sense the answer is right there," Walker told CBC News. "We just have to fish it out."

Walker is among growing number of researchers who believe these "elite controller" patients may hold the key that unlocks some of the secrets of why HIV is so difficult to understand.

It is an important area of research, agreed Anna Laura Ross, who heads France's HIV vaccine research unit in Paris.

"How come people can be infected, but they control the viral replication?" Ross asked.

Differences in immune activity

By knowing how these people are protected, "we could really design a vaccine that would specifically target those mechanisms that we have identified before," said Mathias Lichterfeld, who also studies elite controllers at Massachusetts General Hospital.

Controllers appear to have a superior version of dendritic cells, a type of immune cells, that seems to be a point of access for HIV, Lichterfeld told a news conference at an AIDS vaccine conference in Paris on Wednesday.

Some of the dendritic cells in controllers have higher activity of receptors that are entry point in cells, as well as more powerful responses to HIV in another type of immune cell known as CD8 T-cells.

Many controllers share a genetic difference related to the immune system. If researchers understand the mechanism, it could potentially be manipulated in people who didn't inherit it, Walker said.

Still, the mechanisms for suppressing HIV may be very different from those that prevent infection, cautioned Dr. Anthony Fauci, director of the U.S. National Institute for Allergy and Infectious Diseases.

"People need to realize that elite controllers control the virus, but they got infected," Fauci said.

Walker continues to work with 250 private HIV clinics and researchers around the world, including in Canada, to identify more elite controllers. The hope is that their unique genetic qualities could one day lead scientists to a cure for the disease that affects an estimated 33 million people worldwide.