On March 4th, a research team from Temple University successfully removed latent human immunodeficiency virus (HIV) from infected human cells using an emerging gene editing technology called CRISPR-Cas9 (2), a promising treatment that could improve the quality of life for millions (1). By April 19th, a competing team demonstrated that HIV could mutate to escape CRISPR-Cas9. Rather than discrediting Temple University’s findings, the competing research demonstrates process as a core tenet of science and underscores the importance of collaboration.
More than 35 million people in the world are infected with HIV and that number continues to grow (1). Once HIV enters the body, it targets key immune cells, such as T-cells, and incorporates HIV genetic information into the host genome. At this stage, HIV can remain latent- the viral DNA exists in the host genome but is not being used to produce more HIV (4). In its active form, HIV replicates using the host cell’s own mechanisms and destroys T-cells.
HIV targets a specific subset of T-cells, called T-helper cells (TH cells), that are responsible for fighting infection. Acquired Immunodeficiency Syndrome (AIDS), HIV’s deadly successor, occurs when HIV has drastically reduced the TH cell population to the point that the body’s immune system is ineffective (5).
Currently, HIV is managed through antiretroviral treatment that prevents viral replication within the body6. This prevents HIV from spreading to other cells and can aid in restoring the TH cell population. While antiretroviral therapy has been effective in prolonging and improving the quality of life, the drugs are expensive and must be taken vigilantly for the remainder of one’s life. Antiretroviral treatment does not eradicate HIV in its latent stage and some strains of HIV have developed resistance to the treatments6. At this point in time, HIV is impossible to cure.
CRISPR offers the unique opportunity to remove HIV in its latent stage from the genome of cells, effectively curing cells of infection and preventing reinfection by the virus.
The advent of CRISPR-Cas gene editing technology marked a huge advance in modern science. Clustered regularly interspaced short palindromic repeats (CRISPR) and the CRISPR associated proteins (Cas) provide immune protection to bacteria, but have recently been harnessed as a potent gene editing technology (3). CRISPR-Cas systems are capable of modifing DNA in cells, including human cells. CRISPR has the potential to edit out genes responsible for detrimental human diseases as well as making genetic modifications that prevent mushrooms from browning on the shelf of a grocery store. The applications of CRISPR are seemingly limitless.
Upon CRISPR’s release, researchers at Temple University were immediately interested in using CRISPR-Cas9 to treat and possibly cure HIV. The Cas9 protein can be “programmed” to target removal of specific segments of a genome using a genetic template created by researchers (3).
At Temple University, Rafal Kaminski and his team used CRISPR-Cas9 to effectively remove HIV from the genome of human TH cells in a petri dish, the first step to making modifications in a living organism. The CRISPR-Cas9 treatment prevented HIV infection of treated human THcells and inhibited viral replication in peripheral blood cells from HIV+ samples. Kaminski and his team had not only cured cells of latent HIV infection, they had prevented other cells from being infected by the virus.
The possibility of curing HIV using CRISPR-Cas9 was within reach. However, scientific breakthroughs rarely happen in one fell swoop and it was not long before a different research team found flaws in Rafal Kaminski’s model.
Six weeks later, Zhen Wang of McGill University published evidence that HIV develops evasion resistance to CRISPR-Cas9 technology. The introduction of Cas9, while fostering deletion of HIV in some THcells, caused mutations in others that promoted HIV resistance and increased viral infectivity. These mutations occurred exactly where Cas9 bound to the DNA targeted for removal, indicating that Cas9 is responsible for the mutations. The mutated HIV replicated more quickly than control HIV, increasing the potency of the virus and the potential for infection (2).
Collectively, this research suggests that CRISPR-Cas9 technology requires some fine tuning before it will be successful for treating HIV. Several labs have confirmed the findings of Kaminski, including Wang, but there is no doubt that the CRISPR treatment must undergo revision. Wang suggested that targeting multiple sites within the HIV genome with a variety of templates may prevent the dangerous mutations that currently occur.
A room full of scientists will earnestly declare that science is a process, not simply a collection of facts. Science is driven by the kind of discussion demonstrated by Rafal Kaminski and Zhen Wang; no one is expected to have the answer right on the first try. Wang’s findings do not invalidate CRISPR-Cas use in HIV treatment, but advise caution. As is true with most things in science, harnessing CRISPR-Cas technology to treat HIV will be a process.
1. Kaminski, R., Chen, Y., Fischer, T., Tedaldi, E., Napoli, A., Zhang, Y., Karn, J., Hu, W., and Kahili, K. (2016). Elimination of HIV-1 Genomes from Human T-lymphoid Cells by CRISPR/Cas9 Gene Editing. Scientific Reports. 6.
2. Wang, Z., Pan, Q., Gendron, P., Cen, S., Wainberg, M., and Liang, C. (2016). CRISPR/Cas9-Derived Mutations Both Inhibit HIV-1 Replication and Accelerate Viral Escape. Cell Reports. 15. 481-489.
3. Jink, M., Chylinski, K., Fonfara, I., Hauer, M., Doudna, J., and Charpentier, E. (2012). A Programmable Dual-RNA-Guided DNA Endonuclease in Adaptive Bacterial Immunity. Science. 333. 816-821.
4. Douek, D. C., Roederer, M., and Koup, R. (2009). Emerging Concepts in the Immunopathogenesis of AIDS. Annu Rev Med. 60. 471-484
5. Okoye, A.A., and Picker, L.J. (2013). CD4+ T cell Depletion in HIV Infection: Mechanisms of Immunological Failure. Immunolo Rev. 254. 54-64.
6. National Institute of Health AIDSinfo. (2016). HIV Treatment: The Basics.