Resistance to HIV Engineered Via CRISPR

(Stem Cells News image)

Mice transplanted with human hematopoietic stem cells that have an HIV receptor gene, CCR5, disrupted by gene editing allows the animals to ward off HIV infection.

A minor proportion of people harbor a homozygous mutation in CCR5—a gene that encodes a receptor found on immune cells—that thwarts HIV’s attempts to get inside the cells. In an attempt to mimic this natural resistance, researchers mutated CCR5 in human fetal liver hematopoietic stem/progenitor cells (HSPCs) and showed that the cells could block HIV infection after transplantation into mice.

“These are expected observations that support prior data that targeting CCR5 can impede HIV replication and spread,” says neuroscientist Kamel Khalili who studies HIV infection at Temple University’s Lewis Katz School of Medicine in Philadelphia and who was not involved in the study. “CRISPR may be more convenient for gene editing than the prior gene editing tools used.”

The study is not the first to use gene editing to interrupt the CCR5 gene in human hematopoietic stem/progenitor cells. In a study published in 2010, Paula Cannon and her colleagues used zinc-finger nucleases to disrupt the gene and showed that the edited cells, when engrafted into mice, could clonally expand and retain the CCR5 deletion. This previous work has led to an on-going clinical trial to test this gene editing approach in HIV-infected individuals.

With CRISPR, Khalili’s team previously cut out HIV from the human genome, yet there are also studies of how HIV could evade CRISPR-based anti-HIV therapy. There is yet no CRISPR-based gene editing system being tested in clinical trials in the United States.

In the new work, published August 2 in Molecular Therapy, Hu Chen of the 307 Hospital of the Peoples Liberation Army, Hongkui Deng of the Peking University Stem Cell Research Center, both in Beijing, China, and their colleagues used CRISPR/Cas9 to disrupt CCR5 in CD34+ HSPCs. They demonstrated a 21 percent to 28 percent CCR5 editing efficiency, higher than the 17 percent efficiency reported using the zinc finger approach (…)

Next, the researchers challenged either mice transplanted with CCR5-edited or non-edited human CD34+ HSPCs with an HIV strain that uses CCR5 to gain access to T-cells. In the mice harboring the mutated human stem cells, there was a decrease in HIV RNA in the first few weeks of infection and a smaller decline in CD4+ T-cells compared to animals transplanted with normal human HSPCs.

“This is convincing evidence that CRISPR mediated deletion of CCR5 results in the intended resistance to the CD4+ progeny of the CCR5,” writes David DiGiusto, who directs Stanford University’s Laboratory for Cell and Gene Medicine and has helped development of the zinc finger approach for disrupting CCR5, in an email to The Scientist.

Still, it is unlikely that fetal liver stem cells will be used in human clinical trials, DiGiusto and Khalili agree. “Caution should be taken interpreting [these results] as generalizable to HSPCs from adult HIV patients,” writes DiGiusto (…)

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