After refining their methods, researchers at the University of Nebraska Medical Center and Temple University have doubled the percentage of infected, humanized mice from which they were able to eliminate the human immunodeficiency virus, or HIV.
In 2019, the researchers demonstrated that they could eliminate the virus from the genomes of about one-third of infected mice for a time using a combination of two different therapies.
At that time, they used slow-release, long-lasting formulations of HIV drugs developed at UNMC to suppress the virus in the mice, followed by a gene-editing therapy created by Temple scientists in Philadelphia to cut the virus’s DNA from its hiding spots in the mice’s genomes.
In the years since, the UNMC researchers have improved their drugs, and the Temple team has devised a second gene-editing system to also knock out CCR5, a receptor on the surface of some cells that helps HIV get inside.
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In a paper published online Monday in the journal Proceedings of the National Academy of Sciences or PNAS, the researchers reported that they had eliminated the virus from 58% of the infected mice, which have been given human immune systems.
“We’re super excited about that,” said Dr. Howard Gendelman, chairman of UNMC’s pharmacology and experimental neurosciences department and a senior investigator on the study.
Targeting the CCR5 receptor made sense, Gendelman said. Four cures of HIV have been documented in infected humans. All of those patients had undergone bone marrow transplants for blood cancer, which begins with wiping out their immune systems. Those patients then were given donor marrow from people with genetic mutations that disable the receptor, essentially locking out HIV.
Knocking out the CCR5 receptor helped address a problem the researchers faced after the first study: No matter how good their long-acting antiretroviral drugs — dubbed LASER ART — were at suppressing HIV, some residual virus would remain, Gendelman said. HIV integrates its DNA into the genome of host cells and can lie dormant in tissue reservoirs for long periods of time, despite the use of the drugs. Once treatment is stopped, that residual virus can cause new infections.
To prevent rebound infections, the Temple team began working on the dual gene-editing system that would target both available HIV and the receptor.
The CCR5 knockout, however, only worked for about a week before the mice’s human immune systems began pumping out new immune cells that contained the receptor.
The Nebraska researchers figured out a sequence for treating the animals, Gendelman said, first giving the drugs to get maximal suppression of the virus and then sending in the CRISPR-based, gene-editing tools to first inactivate the receptor, preventing new infections, then eliminate the virus that was left.
Kamel Khalili, chairman of the microbiology, immunology and inflammation department at Temple’s Lewis Katz School of Medicine, said the new dual CRISPR gene-editing strategy holds exceptional promise for treating HIV in humans.
“It is a simple and inexpensive approach,” Khalili, the other senior investigator on the study, said in a statement. “The type of bone marrow transplant that has brought about cures in humans is reserved for patients who also have blood cancers. It requires multiple rounds of radiation and is not applicable in resource-limited regions, where HIV infection tends to be most common.”
The Nebraska researchers, Gendelman said, also figured out that they needed to send in the two gene-editing tools using two different versions of a type of an adenovirus often used in research to deliver therapies inside cells. If they use the same one, the first triggers an immune response that can kill the second one. Using different versions of the virus allowed them to avoid triggering the immune response. Prasanta Dash, an expert in molecular virology and assistant professor at UNMC, led the mouse studies and served as the study’s lead author. Another key collaborator was UNMC’s Santhi Gorantla, an authority on mouse models.
Not only did the researchers eliminate the virus in the majority of the mice — 11 of 19 — they also did it safely, with no toxic effects, Gendelman said.
“We’re getting closer,” he said. “In 2019, people said this was a curiosity ... there are a lot of problems. But we went after those problems step by step, and we were able to show now we can do this in a majority of animals.”
Dr. Robert Gallo, who co-discovered HIV as the cause of AIDS in 1984, said the UNMC-Temple approach is one of several that researchers are discussing and, in some cases, devising, in efforts to reach a functional cure for HIV.
“They have made substantial advances as shown in this report and following their work will be of great interest to the field,” he said in a statement.
Both research teams already are proceeding with next steps. The Temple group already has conducted trials using the approach the researchers took in 2019. They anticipate testing the dual gene-editing strategy in primates. Khalili co-founded a company called Excision BioTherapeutics that has licensed the gene-editing technology from Temple.
Gendelman and his team also have begun testing using tiny lipid particles, instead of a virus, to deliver the gene-editing system to infected cells. Similar lipid particles are used to deliver the Pfizer and Moderna mRNA vaccines that have been successful in millions of people against COVID-19.
Gendelman said the team also is working to take the lipid particles to another level by adding targeting schemes that would allow them to seek and destroy the virus present in infected cells.
He and Benson Edagwa, an associate professor at UNMC, also continue to work to commercialize the long-lasting drugs, which Gendelman’s previous research shows can be taken less often than the current daily routines. They are co-founders of Exavir Therapeutics, which has licensed the drug technology from UNMC.
“There’s great promise in this collaboration, especially as we push to get to the finish line,” Gendelman said.