New clues found to symptom-free HIV

There's still no vaccine for HIV, but researchers have made inroads in discovering new clues to why a minority of infected people can carry the virus without symptoms.

Only about one in 300 people infected appear to have an immune system that can naturally suppress the virus's replication, and thus they carry low levels of the virus, the study said. Specific genetic variations may be responsible for this uncommon response to HIV, this study published in the journal Science found.

"This tells us that the immune system is definitely involved in people getting infected and not progressing," said study co-author Dr. Florencia Pereyra, who established International HIV Controllers Study, which has enrolled more than 1,500 people with HIV who have shown a natural ability to control the virus. "It really helps us focus a lot of research."

In this study, an international team of researchers looked at the genome of nearly 1,000 "controllers" - people who can naturally control the virus in their system - and 2,600 individuals with progressive HIV infections.

They found that there are small variants in a protein called HLA-B that may be response for the ability to control the virus well. In people with particular differences in five components of this protein, called amino acids, the immune response against HIV is stronger.

Here's how Pereyra explains it: Imagine that there's a factory worker who grabs a piece of the virus, shows it out the window and says, “Hey, there’s this virus in here." That's the cue for the immune system to come in and attack. The hand of the factory worker represents the HLA molecule in this analogy.

In people who have specific differences in the "hands," their T-cells, blood cells that protect against infections, appear to stop the virus from following the destructive course seen in most HIV-positive people. Some have lived symptom-free for more than 30 years, and take no medications whatsoever to combat HIV.

In some, called "elite controllers," the virus cannot be detected in traditional HIV tests. But the virus's signature is still present

The discovery about genetics suggests that the immune system can be manipulated to make infected individuals control HIV better, but "we are still a little bit far from being able to apply this to a vaccine or even a therapy," Pereyra said.

"It’s just a step forward and we’re definitely going in the right direction," Pereyra said.