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Scientists Eliminate HIV From Human Cells for First Time
The human immunodeficiency virus (HIV) has proved to be tenacious, inserting its genome permanently into its victims’ DNA, forcing patients to take a lifelong drug regimen to control the virus and to prevent a fresh attack.
According to an article published July 21 in the Proceedings of the National Academy of Sciences, researchers at Temple University School of Medicine in Philadelphia have designed a way to snip out the integrated HIV-1 genes for good.
“This is one important step on the path toward a permanent cure for AIDS,” said lead investigator Kamel Khalili, PhD. “It’s an exciting discovery, but it’s not yet ready to go into the clinic. It’s a proof-of-concept that we’re moving in the right direction.”
Khalili and his colleagues created molecular tools to delete the HIV-1 proviral DNA. When deployed, a combination of a DNA-snipping enzyme called a nuclease and a targeting strand of RNA called a guide RNA (gRNA) hunt down the viral genome and excise the HIV-1 DNA. From there, the cell’s gene-repair machinery takes over, “soldering” the loose ends of the genome back together, resulting in virus-free cells.
“Since HIV-1 is never cleared by the immune system, removal of the virus is required in order to cure the disease,” Khalili said. The same technique could theoretically be used against a variety of viruses, he added.
The new research demonstrated that these molecular tools also hold promise as a therapeutic vaccine; cells armed with the nuclease-RNA combination proved impervious to HIV infection.
The investigators based the two-part HIV-1 editor on a system that evolved as a bacterial defense mechanism to protect against infection, Khalili explained. His laboratory engineered a 20-nucleotide strand of gRNA to obtain the HIV-1 DNA and paired it with the Cas9 nuclease. The gRNA targets the control region of the gene called the long terminal repeat (LTR). LTRs are present on both ends of the HIV-1 genome. By targeting both LTRs, the Cas9 nuclease can snip out the 9,709 nucleotides that comprise the HIV-1 genome. To avoid any risk of the gRNA accidentally binding with any part of the patient’s genome, the researchers selected nucleotide sequences that do not appear in any coding sequences of human DNA, thereby avoiding off-target effects and subsequent cellular DNA damage.
The editing process was successful in several cell types that can harbor HIV-1, including microglia and macrophages, as well as in T-lymphocytes. “T-cells and monocytic cells are the main cell types infected by HIV-1, so they are the most important targets for this technology,” Khalili said.The HIV-1 eradication approach faces several significant challenges before the technique is ready for patients. Foremost, the researchers must devise a method to deliver the therapeutic agent to every single infected cell. Moreover, because HIV-1 is prone to mutations, treatment may need to be individualized for each patient’s unique viral sequences.
“We are working on a number of strategies so we can take the construct into preclinical studies,” Khalili said. “We want to eradicate every single copy of HIV-1 from the patient. That will cure AIDS. I think this technology is the way we can do it.”