Researchers from Temple University have used the CRISPR/Cas9 gene editing tool to clear out the entire HIV-1 genome from a patient's infected immune cells. It's a remarkable achievement that could have profound implications for the treatment of AIDS and other retroviruses. When we think about CRISPR/Cas9 we tend to think of it as a tool to eliminate heritable genetic diseases, or as a way to introduce new genes altogether. But as this new research shows, it also holds great promise as a means to eliminate viruses that have planted their nefarious genetic codes within host cells. This latest achievement now appears in Nature Scientific Reports.
Retroviruses, unlike regular run-of-the-mill viruses, insert copies of their genomes into host cells in order to replicate. Antiretroviral drugs have proven effective at controlling HIV after infection, but patients who stop taking these drugs suffer a quick relapse. Once treatment stops, the HIV reasserts itself, weakening the immune system, thus triggering the onset of acquired immune deficiency syndrome, or AIDS.
Over the years, scientists have struggled to remove HIV from infected CD4+ T-cells, a type of white blood cell that fights infection. Many of these "shock and kill" efforts have been unsuccessful. The recent introduction of CRISPR/Cas9 has now inspired a new approach.
Geneticist Kamel Khalili and colleagues from Temple University extracted infected T-cells from a patient. The team's modified version of CRISPR/Cas9 — which specifically targets HIV-1 DNA — did the rest. First, guide RNA methodically made its way across the entire T-cell genome searching for signs of the viral components. Once it recognised a match, a nuclease enzyme ripped out out the offending strands from the T-cell DNA. Then the cell's built-in DNA repair machinery patched up the loose ends.
Not only did this remove the viral DNA, it did so permanently. What's more, because this microscopic genetic system remained within the cell, it staved off further infections when particles of HIV-1 tried to sneak their way back in from unedited cells.
The study was performed on T-cells in a petri dish, but the technique successfully lowered the viral load in the patient's extracted cells. This strongly suggests it could be used as a treatment. However, it could be years before we see that happen. Still, the researchers ruled out off-target effects (that is, unanticipated side-effects of gene-editing) and potential toxicity. They also demonstrated that the HIV-1-eradicated cells were growing and functioning normally.
These findings "demonstrate the effectiveness of our gene editing system in eliminating HIV from the DNA of CD4 T-cells and, by introducing mutations into the viral genome, permanently inactivating its replication," Khalili said in a statement. "Further, they show that the system can protect cells from reinfection and that the technology is safe for the cells, with no toxic effects."
This technique for snipping out alien DNA could have implications for related research, including treatments for retroviruses that cause cancer and leukaemia, and the suite of retroviruses currently affecting companion and farm animals. As noted by Excision BioTherapeutics' CEO and President Thomas Malcolm, "These exciting results also reflect our ability to select viral gene targets for safe eradication of any viral genome in our current pipeline of gene editing therapeutics."
And Malcolm has good reason to be excited: his company holds exclusive rights to commercialise this technology.
An electron micrograph of HIV particles infecting a human T cell. Image: National Institute of Allergy and Infectious Diseases