A cutting edge over HIV? CRISPR-Cas 9 and the search for a cure

Thanks to cutting-edge DNA editing technology, we may be one step closer to finding a cure for HIV. 

In a mouse model of HIV, Dash et al. (2019) combined some of the traditional treatments for HIV with the DNA-editing capabilities of CRISPR-Cas 9.  Out of 23 infected mice subjected to the novel treatment, 8 showed evidence of complete HIV clearance. This is remarkable considering that although HIV is treatable, it remains incurable.  The Human Immunodeficiency Virus (HIV), if left untreated, will lead to the development of Autoimmune Immunodeficiency Syndrome (AIDS). People with AIDS have high levels of virus and low T cell counts, leaving them susceptible to infections and cancer.  In 2017, there were 36.9 million people living with HIV worldwide and an estimated 940,000 people dying due to AIDS-related illnesses.   

One of the things that makes HIV so challenging to treat is its high mutation rate.  Although many disease-causing viruses can be prevented by a vaccine, HIV’s high mutation rate makes this approach very challenging. Seasonal influenza, like HIV, is another highly mutating virus where it is difficult to isolate an antigen that is protective against its inevitable variants.  Without a robust, specific, and immune-provoking antigen, vaccines aren’t effective. HIV can also lay dormant in cells, meaning that the viral DNA may be incorporated into our own without causing any adverse immune response. To cure HIV, the dormant HIV DNA must also be eliminated. 

Current methods for treating HIV infection involve a technique known as anti-retroviral therapy (ART).  Patients infected with HIV typically take multiple anti-retroviral drugs simultaneously due to the high mutation rate of HIV.  Taken together, these drugs are potent enough to dramatically decrease viral replication to the point that the virus can become nearly undetectable.  The inhibition of viral replication is essential for preserving CD4+ T cells, which play a major role in the adaptive immune response. 

While ART can extend the life expectancy of HIV patients dramatically and greatly reduce the risk of transmission, the search for a definitive cure continues.  ART can only prevent viral reproduction in cells that are actively replicating- dormant HIV DNA an reactivate the infection at any time. The method proposed by Dash et al. presents a potential method for treatment and the possibility of an eventual cure by targeting the issue of dormant HIV DNA using CRISPR-Cas 9

CRISPR, which stands for Clustered Regularly Interspersed Short Palindromic Repeats, is an enzyme isolated from bacteria.  Originally it evolved as a way for bacteria to defend themselves against their own viral infections.  When given an RNA template, the CRISPR enzyme acts as a detective searching for the viral DNA that complements the template.  Once the suspect is found, the CRISPR enzyme cuts the molecular bonds surrounding the complementary DNA and inserts a new piece of DNA in its place.  This new DNA will serve as a mutation, effectively inactivating the viral DNA.

Prior to using the CRISPR-Cas 9 technology, Dash et al. first treated mice with a variant of ART known as LASER ART.  This treatment helped to greatly reduce the HIV levels in the mice.  Then mice were subjected to the CRISPR-Cas 9 treatment, designed to specifically target HIV DNA.  

The 23 mice who received both the LASER ART and CRISPR-Cas 9 treatment showed decreased viral DNA, viral RNA, and a rebound of CD4+ T cells. 

Eight mice in the experimental group showed undetectable levels of HIV, with ultrasensitive HIV DNA detection unable to detect the virus in blood, lymphoid tissue, bone marrow, or brain. 

Transferring cells from those mice with undetectable HIV levels to mice that had never been exposed to the virus also failed to transfer the virus.

Together, these results suggest that the combined LASER ART and CRISPR Cas-9 treatment can result in an HIV cure in some cases.

Even for those mice that did not show evidence of HIV elimination using the combined LASER ART/CRISPR Cas-9 treatment, this treatment performed better that either LASER ART or CRISPR Cas-9 alone.  The authors suggest that the reduction in viral load provided by LASER ART was crucial for the success of CRISPR Cas-9. With a third of mice showing evidence of HIV viral elimination, this study provides proof-of-concept and an important step forward in the fight against HIV.

Although it appears that 4 mice were cured of HIV in this study, future studies are needed to determine how to increase the effectiveness and cure rate even further.  While CRISPR Cas-9 is a powerful DNA-editing tool, more work is needed to understand how to increase its success and accuracy. Even though the authors of this study did not find evidence for off-target effects of CRISPR Cas-9, such effects have been known to occur in other instances.  Finding ways to improve the delivery, accuracy, and safety of CRISPR Cas-9 will go a long way to finding a cure for this seemingly incurable disease.

 

Author: Amber Stedman, MS

https://www.linkedin.com/in/amber-stedman-576262146/

Article: Dash, P. K., Kaminski, R., Bella, R., Su, H., Mathews, S., Ahooyi, T. M., … Gendelman, H. E. (2019). Sequential LASER ART and CRISPR Treatments Eliminate HIV-1 in a Subset of Infected Humanized Mice. Nature Communications, 10(1), 2753. https://doi.org/10.1038/s41467-019-10366-y

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