According to the Centers for Disease Control and Prevention (CDC), more than 36 million people across the world are HIV positive, and approximately 1.2 million people in the United States live with the virus.
While there is currently no cure for the infection, scientists have just moved closer to finding one. Using a gene editing technology called "CRISPR/Cas9," the researchers successfully excised the HIV-1 provirus in three animal models.
A provirus is an inactive form of virus. It occurs when the virus has integrated into the genes of a cell. In the case of HIV, these host cells are the so-called CD4 cells - once the virus has been incorporated into the DNA of the CD4 cells, it replicates itself with each generation of CD4 cells.
The three mouse models used in the current research included a "humanized" model, in which the mice were genetically modified to have human immune cells, which were then infected with HIV-1.
The team was co-led by Dr. Wenhui Hu, Ph.D., associate professor in the Center for Metabolic Disease Research and the Department of Pathology at the Lewis Katz School of Medicine (LKSOM) at Temple University in Philadelphia, together with Kamel Khalili, Ph.D., Laura H. Carnell Professor and chair of the Department of Neuroscience at LKSOM, and Won-Bin Young, Ph.D, who just recently joined LKSOM.
The new study - published in the journal Molecular Therapy - builds on previous research by the same team, during which they used genetically modified rodents to demonstrate that their gene editing technology could eliminate the HIV-1-infected segments of DNA.
"Our new study is more comprehensive," Dr. Hu explains. "We confirmed the data from our previous work and have improved the efficiency of our gene editing strategy. We also show that the strategy is effective in two additional mouse models, one representing acute infection in mouse cells and the other representing chronic, or latent, infection in human cells."
Gene editing strategy 96 percent effective
Dr. Hu and team inactivated HIV-1, significantly reducing the RNA expression of viral genes in the organs and tissues of genetically modified mice.
Specifically, the RNA expression was reduced by approximately 60 to 95 percent.
The researchers then tested their findings by acutely infecting mice with EcoHIV - the equivalent of the HIV-1 in humans. Dr. Khalili explains the procedure:
"During acute infection, HIV actively replicates. With EcoHIV mice, we were able to investigate the ability of the CRISPR/Cas9 strategy to block viral replication and potentially prevent systemic infection."
The CRISPR/Cas9 method was up to 96 percent efficacious in eradicating EcoHIV in mice.
Finally, in the third model, mice received a transplant of human immune cells, including T cells, which were then infected with HIV-1.
One of the main reasons that a cure for HIV has yet to be discovered is the virus's ability to "hide" in the genomes of T cells, where it lives latently. This is why researchers applied the CRISPR/Cas9 technology to these mice with infected T cells.
After a single round of gene editing, the viral segments were excised from the human cells that had been integrated into the mouse tissues and organs. They removed the provirus from the mice's spleen, lungs, heart, colon, and brain after only one therapy injection.
The injection was with "quadruplex sgRNAs/saCas9 AAV-DJ/8" - an improved adeno-associated viral (AAV) vector.
AAV vectors are commonly used in gene therapy, but "the AAV-DJ/8 subtype combines multiple serotypes, giving us a broader range of cell targets for the delivery of our CRISPR/Cas9 system," Dr. Hu explains.
To assess the success of the genetic interventions, the team measured HIV-1 RNA levels using live bioluminescence imaging.
Findings bring scientists one step closer to an HIV cure
This is the first time that a team of researchers has managed to halt the replication of the HIV-1 virus and eliminate it completely from the infected cells in animals.
The team also provided the first evidence that HIV-1 can be successfully eradicated and full infection with the virus can be prevented using the CRISPR/Cas9 gene editing strategy.
The study was deemed "a significant step towards human clinical trials" by the authors, and the findings represent a breakthrough in the search for an HIV cure.
"The next stage would be to repeat the study in primates, a more suitable animal model where HIV infection induces disease, in order to further demonstrate elimination of HIV-1 DNA in latently infected T cells and other sanctuary sites for HIV-1, including brain cells. Our eventual goal is a clinical trial in human patients."
Kamel Khalili, Ph.D.