Using the innovative genome editing technique CRISPR/Cas9, scientists have identified five genes that are essential for HIV infection and could act as potential therapeutic targets. The findings confirm the power of CRISPR/Cas9, which is quickly becoming an indispensable tool in a number of scientific research fields.
Due to their small numbers of genes, viruses like HIV take advantage of their hosts' genomes for replication and transmission.
In the study published in the journal Nature Genetics, the researchers wanted to investigate whether some human genes that HIV needs to replicate in T cells (white blood cells), but that humans don't need to live, could be knocked out. These human genes are known as host dependency factors.
"A good example is CCR5, a receptor on the surface of T-cells. Alongside the receptor CD4, it allows HIV to enter the cell. However, a mutation to the CCR5 gene called CCr5-delta32 makes people resistant to HIV infections. We wanted to find other human genes that could be blocked, to stop the HIV infection without harming the cells", study author Bruce Walker, director of Ragon Institute at MGH, MIT and Harvard, Harvard Medical School, told IBTimes UK.
Five host dependency factors
Previous research had identified hundreds of host dependency factors, but there had been little overlap between the findings of these different studies and few of these factors had been validated.
Here, the scientists used the CRISPR/Cas9 technique to inactivate a great number of genes in human T cells in the lab. They then infected these cells with HIV and screened for the inactivated genes that made the cells resistant to HIV, without affecting their normal functions.
A total of five genes were identified as host dependency factors including HIV co-receptors CD4 and CCR5. The three others were ALCAM (which is responsible for the cell aggregation required for cell-to-cell- HIV transmission) and TPST2 and SCL35B2 (which facilitate CCR5 recognition by the HIV enveloppe). The scientists say these genes' pathways may be interesting therapeutic targets to investigate in the future.
The study is also important because it confirms the power of the CRISPR/Cas9 technique. It is likely that it will be used again in the field of HIV research, potentially in vivo, in animal models. In this case, scientists will have to make sure that inactivating genes in live organisms to stop HIV transmission doesn't have unintended effects.
"We have worked with tissue cultures, but we are not sure whether knocking out these genes in live organisms would have exactly the same effects. There is obvious concern about whether knocking them out would have other negative effects in vivo", Walker said.
How does CRISPR-Cas9 work?
CRISPR-Cas9 is a new genome editing tool with the potential to revolutionise the field of biology and medical research. 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 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. 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.