Combining CRISPR gene editing and slow-release antiretroviral treatment to cure HIV
Two out of seven mice who received novel treatment and gene editing technology have had HIV eliminated from their bodies, reveals a ground-breaking study.
Scientists have successfully eliminated HIV in mice which carry human genes, cells and tissues, known as humanised mice. While still a long way off, the findings provide a proof-of-concept strategy for an HIV cure in humans using a combination of slow-release antiretroviral treatment (ART) to suppress viral replication, followed by gene editing.
Why can’t current antiretroviral treatments cure HIV?
HIV is currently incurable but it can be controlled through antiretroviral treatment. This is able to reduce the amount of virus in the body to such low levels that it cannot be detected in HIV tests, known as ‘undetectable’. However some HIV remains hidden in latently-infected t-cells, macrophages and dendritic cells in tissues, including those found in the gut, lymph nodes, brain and spleen.
Current approved antiretroviral treatment options are so far unable to target these sites, they also cannot remove HIV from cells which already have HIV DNA integrated inside of them. The search for an HIV cure requires a strategy to address these challenges, without any adverse effects on the immune system.
In this present study, researchers at the Lewis Katz School of Medicine at Temple University and the University of Nebraska Medical Center (UNMC) used a combination of two approaches that had previously shown promising but insufficient success on their own: long-acting slow-effective release (LASER) ART and CRISPR.
What are LASER ART and CRISPR?
LASER ART is a long-acting version of existing antiretroviral drugs which has been engineered to reach viral reservoirs. These treatments slowly release the drug over several weeks, halting the replication of HIV. This has been made possible through pharmacological changes to the drugs dolutegravir (DTG), lamivudine (3TC), abacavir (ABC) and rilpivirine, which are then packaged into nanocrystals that can enter tissues where HIV is hiding.
While LASER ART can reduce viral replication to undetectable levels, it cannot remove the HIV DNA, this is where CRISPR-CAS technology comes in. CRISPR-CAS9 is a gene editing tool that has gained considerable attention for its ability to target specific gene locations, meaning it can efficiently cut out fragments of integrated HIV DNA from the host genome.
Previously, CRISPR-CAS9 could not efficiently delete all HIV because it was replicating too fast. A combination of both approaches was therefore hypothesised to be more effective.
Were the mice really cured?
To test their hypothesis, mice were transplanted with human T cells susceptible to HIV infection. These mice were then infected with HIV. After confirmation of viral infection, 29 of these infected humanized mice were subdivided into four groups.
Six mice were left infected with HIV and formed the control group. In group two, CRISPR was given to six mice nine weeks after viral infection; in group three, LASER ART was delivered to ten mice two weeks after infection; and finally, group four comprised of seven mice who received LASER ART three weeks after infection followed by CRISPR nine weeks after infection.
After a couple of months, LASER ART treatment was stopped and after an additional five weeks, antiretroviral drug levels were assessed to be at or below detectable. Plasma viral load was then tested for HIV-1 RNA at 2, 7, 9, and 14 weeks of infection for the different treatment groups of humanised mice.
All animals who received CRISPR or LASER ART alone experienced viral rebounds within eight weeks of treatment interruption. In two mice that had received the dual therapy, viral DNA and RNA was not detected in plasma or in body tissues and organs.
CRISPR is a powerful tool that allows the targeting of specific areas of the genome, but ensuring this is done safely is one critical challenge to scale-up of this approach. Unwanted deletions and/or edits to DNA could affect bodily function or create cancerous cells, so deletion of only the HIV-infected DNA is critical.
In this study, CRISPR was found to be safe, with no detectable off-target effects. They investigated 100 different sites in the body, and no negative consequences could be attributed to CRISPR.
In their press conference last week, lead investigator Dr Howard Gendelman, M.D from UNMC said that the next steps would be to up-scale this approach to larger animal models, eventually leading to the first human trials.
Trials with primates will fill the knowledge gap and answer pending questions we have from the mice trials, specifically around toxicity, dosing, administration, and efficacy of this approach, he said. “We hope… that this can be done in a few years, and not in decades. We hope we can move this science forward quickly.”
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