HIV's deliberate evolution uncovered

Laboratory scientist holding a blood sample with a upright compound microscope in the background

What doesn't kill HIV might be making it stronger.

Of course, that's how evolution is supposed to work; but scientists trying to find a way to stop HIV from replicating have found some of the time, their efforts actually make things worse.

According to new research published in journal Cell Press today, researchers can kill HIV by "cleaving" a particular DNA sequence -- but it doesn't always work.

"HIV is notoriously good at surviving and thriving with new mutations, so while many viruses are killed by the targeted approach, those that escape… become more difficult to target."

This is because they mutate and can no longer be recognised by Cas9, the enzyme used to kill the HIV -- that's evolution. But what has surprised researchers is the mutations saving the viruses aren't random.

"The majority of the mutations that the virus has are nicely aligned at the site where Cas9 cleaves the DNA, which immediately indicates that these mutations… are introduced by the cellular non-homologous end joining machinery when repairing the broken DNA," says senior study author Chen Liang.

That means the mutations are occurring at the exact spot where the cleaving occurred, as the DNA tried to repair itself -- so the very act of trying to kill them in this particular way has prompted the HIV to mutate, so it can't be.

"Some mutations are tiny -- only a single nucleotide -- but the mutation changes the sequence so Cas9 cannot recognise it anymore. Such mutations do no harm to the virus, so these resistant viruses can still replicate."

The researchers say this doesn't mean HIV can't be defeated using this process, called CRISPR/Cas9 -- they just might have to hit it in more than one place at the same time, or use a different enzyme.

"CRISPR/Cas9 gives a new hope toward finding a cure, not just for HIV-1, but for many other viruses," says Dr Liang.

"We have a long road toward the goal, and there may be many barriers and limitations that we need to overcome, but we're confident that we will find success."

HIV-1 is the most prevalent form of the HIV virus, which causes AIDS. Somewhere between 30 and 40 million people alive today are infected.