The innovative genome editing tool known as CRISPR-Cas9 could accelerate the search for an effective HIV cure, scientists say. They have used the technology to investigate whether specific genetic tweaks to immune cells' DNA could increase resistance to an HIV infection.
In the past decades, there has been major progresses in the fight against HIV. The development of antiretroviral therapy (ART) has been one of the most important advances and is credited with having dramatically reduced the number of AIDS-related deaths – it is believed that with prevention, ART has saved 7.8 million lives over the last 15 years. Yet, there is still no definite cure for HIV.
This new research, published in the journal Cell Reports, tested the promising CRISPR-Cas9 method, which is described as having the potential to treat many genetic diseases.
HIV does not infect all individuals in the same manner – in some cases, the immune system resists in an effective way against the infection. In most cases, these are people who carry a specific genetic mutation in the CCR5 gene, known as CCR5-delta32 but many other genes may also be involved – some controlling the virus's ability to enter immune cells, others controlling how the virus tricks cells into expressing its genes.
The scientists' idea was to get inspiration from the immune system of all these different people in order to edit immune cells with CRISPR-Cas9, and see which of the edited versions could resist an HIV infection.
How does CRISPR-Cas9 work?
CRISPR-Cas9 is a new genome editing tool with the potential to revolutionise the field of biology. Indeed, it is at present the simplest, most effective and accurate way of conducting genetic manipulations – whether by editing parts of the genome, cutting them out or adding some to DNA sequences.
The technique is based on the use of two molecules which work together to change the DNA. The first is the Cas9 enzyme, a molecular scissors able to cut two strands of DNA at a specific location. The second is a piece of RNA, known as gRNA, whose task is to guide Cas9 to the desired location of the genome.
CRISPR-Cas9 has not been "invented" by scientists. Instead, the technique reproduces what happens in some bacteria that naturally benefit from a CRISPR-Cas9 built-in system which allows them to fight off virus by cutting off bits of their DNA. This system essentially acts like the immune system – the snippets of DNA which have been cut are memorised by the bacteria to come up with a quicker defence next time the virus strikes.
The researchers from UC San Francisco and the affiliated Gladstone Institutes created a cell-editing platform using a variant of the CRISPR/Cas9 technology. They used this platform to mutate different genes in hundreds of thousands of immune T cells from healthy volunteers. The researchers then exposed these cells to the virus to find out which one resisted.
Mutations to the CXCR4 and CCR5 genes — which encode receptor molecules used by the HIV virus to infect immune cells – appeared to block the infection. Indeed, when these genes were inactivated by the mutations, the virus was successfully prevented from integrating into T cells.
The researchers then developed 146 different CRISPR-based edits to confirm the potential of the method. Each edit was designed to deactivate one of 45 genes which have in the past been associated with the virus 's ability to integrate into immune cells. This allowed the scientists to identify several genes whose absence conferred HIV resistance.
More studies will soon take place to further confirm the validity of the method and see how it can concretely be applied to come up with HIV treatments.
Co-senior author Alexander Marson concluded: "This toolkit has been a huge missing piece in infectious disease research. Now we have the ability to make modifications in human immune cells and right away see the effects. The potential is immense – this is just the tip of the iceberg."