HIV can resist promising 'molecular knife' therapy

The idea that HIV is notoriously good at surviving and thriving with new mutations proved to be true again.

A new study by Canadian and Chinese researchers said Thursday that the AIDS virus can quickly develop resistance to the promising CRISPR/Cas9 gene editing technology, also known as molecular Swiss army knife.

The findings, published in the US journal Cell Reports, showed that CRISPR/Cas9 may need a little bit more tweaking before it can be used as an effective antiviral tool.

Upon entry into a cell, HIV's RNA genome is converted into DNA and becomes entwined with the cellular DNA, where CRISPR/Cas9 can be programmed to target a DNA sequence and cleave viral DNA.

The new study used the "molecular knife" therapy to cut off HIV-1 within cellular DNA and found while the resulting mutations can inhibit viral replication, some also led to unexpected resistance, or virus escape.

"When we sequence the viral RNA of escaped HIV, the surprise is that the majority of the mutations ... instead of resulting from the errors of viral reverse transcriptase, are rather introduced by the cellular non-homologous end joining machinery when repairing the broken DNA," said senior author Chen Liang, senior investigator at the Jewish General Hospital, Canada.

"Some mutations are tiny -- only a single nucleotide -- but the mutation changes the sequence so Cas9 cannot recognize it anymore. Such mutations do no harm to the virus, so these resistant viruses can still replicate," said Liang, also associate professor of Medicine at the McGill University AIDS Center.

The study was a collaborative effort between researchers at McGill University and the University of Montreal in Canada and the Chinese Academy of Medical Sciences and Peking Union Medical College in China.

The researchers said it serves as a cautionary tale for those who hope to apply CRISPR/Cas9 as an antiviral tool.

They proposed some strategies that could overcome this limitation, including targeting multiple sites with CRISPR/Cas9 or using other enzymes aside from Cas9.

Once a solution is identified, the next barrier will be identifying ways to deliver the treatment to patients, Liang said.

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

"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."