Written by Charlotte Harrison, Science Writer.
HIV infection can be managed with antiretroviral therapy (ART) but cannot be cured because latent HIV-1 infection establishes in immune cells. A new study by researchers from Temple University and the University of Nebraska showed that it is possible to eliminate HIV infection in mice using a CRISPR gene editing approach aimed at two targets – HIV-1 and the HIV-1 co-entry receptor CCR5.
The researchers’ previous work showed that in HIV-1-infected humanized mice, CRISPR gene-editing targeting HIV-1 combined with long-acting ART cured some animals, but rebound infection eventually occurred.
With the aim of preventing rebound infection, the researchers’ strategy in the current study was based on case studies of HIV cures in humans:
“From success stories of HIV patients who have undergone bone marrow transplantation for leukemia and been cured of HIV, our hypothesis was that the loss of the virus’s receptor, CCR5, is important to permanently eliminate HIV infection,” said lead author Kamel Khalili in a press release.
A three-step approach
The researchers used a three-step treatment paradigm in HIV-1-infected humanised mice. Long-acting ART was used first to suppress viral replication, followed by administration of AAV6-delivered CRISPR-Cas9 to edit the CCR5 gene and mitigate viral spread. Then, removal of targeted proviral DNA fragments was achieved by AAV9-delivered CRISPR-Cas9 to cleave the LTR-Gag region of HIV-1.
This regimen suppressed virus replication, restored CD4+ T cell levels, then eliminated replication-competent virus in 58% of infected mice. At a molecular level, the treatment regimen enabled the excision of integrated pro-viral DNA in infected human cells within live infected mice.
Viral elimination was confirmed using highly sensitive nucleic acid nested and droplet digital PCR, RNAscope and viral outgrowth assays. Moreover, HIV-1 was not detected in potential reservoir sites, namely the blood, spleen, lung, kidney, liver, gut and bone marrow. And viral rebound did not occur when ART was stopped.
No evidence of off-target toxicities was seen in the treated mice.
As a next step, the researchers anticipate testing the HIV-1–CCR5 gene-editing strategy in non-human primates, noting that it has “potential for translation to the clinic.”