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Crispr Edits Out HIV-Like Genes from Monkey DNA

Kamel Khalili and Tricia Burdo

Foreground: Kamel Khalili, left, and Tricia Burdo (Temple University Health)

1 Dec. 2020. Researchers show the gene-editing technique Crispr can remove genes gained from infections similar to HIV in lab monkeys, as well as viral signals from their bodies. A team from Temple University in Philadelphia describes the technique in Friday’s issue of the journal Nature Communications.

According to Centers for Disease Control and Prevention, some 1.2 million people in the U.S. are living with HIV infections that can lead to AIDS, with 14 percent of this population not yet diagnosed. While the number of new HIV cases is stable, nearly 38,000 new cases were reported in 2018. Globally, according to World Health Organization, some 38 million people were living with HIV in 2019, with 1.7 million new cases reported.

The standard of care for HIV infections is antiretorviral therapy, which suppresses and controls, but does not eliminate the virus. Antiretorviral medications must be taken daily to prevent viral loads from rebounding, since residual levels of HIV remain in infected individuals. Researchers led by Temple’s Kamel Khalili, professor of virology and neurology, and neuroscientist Tricia Burdo are seeking ways to eliminate HIV from those infected, which led to their study of gene editing with Crispr as a technique for removing HIV.

Crispr, short for clustered regularly interspaced short palindromic repeats, is a genome-editing process based on bacterial defense mechanisms that use RNA to identify, monitor, and edit targeted locations in DNA. In their study, Khalili, Burdo, and colleagues tested the feasibility of using Crispr to remove SIV, a virus much like HIV, from infected rhesus macaque monkeys. In May 2017, Temple researchers and others reported on research with lab mice where Crispr editing removed genes supporting latent HIV, reducing expression of RNA that maintains the virus, as well as overall infection levels in the animals.

In the new study, the team looked to not only determine the feasibility of using Crispr to remove SIV genes from the monkeys’ DNA, but also find out if the virus is reduced in their usual reservoirs in the body, such as lymph nodes. The researchers infected four monkeys with SIV, then infused three of the monkeys with Crispr and Cas9 editing enzymes, delivered with adeno-associated viruses and directed at genes expressing SIV infections. After three weeks, the researchers harvested blood and tissue from the monkeys for genetic and viral analysis.

The results show the edits successfully removed genes expressing SIV from the DNA in the monkeys receiving the Crispr-Cas9 infusions, while the fourth monkey not given Crispr-Cas9, continued to show SIV-related genes. In addition, the researchers found Cas9 enzymes in the lymph nodes, bone marrow, spleen, gut, liver, brain, spinal cord, and other organs in the Crispr-recipient monkeys, where the team also found little or no SIV signaling.

“We show for the first time,” says Kahlili in a university statement, “that a single inoculation of our Crispr gene-editing construct, carried by an adeno-associated virus, can edit out the SIV genome from infected cells in rhesus macaque monkeys.” Khalili adds, “We hope to soon move our work into clinical studies in humans as well.”

Khalili is a scientific founder and adviser to the company Excision Biotherapeutics in San Francisco and Philadelphia that licenses the viral gene editing technology from Temple University. Burdo and other co-authors are also advising the company. In September 2017, Science & Enterprise reported on Excision Biotherapeutics starting up and raising $10 million in seed funds.

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