Study Shows HIV Can Develop Resistance to Promising HIV Therapy

A recent study has shown that although the CRISPR/Cas9 gene editing technology can stop human immunodeficiency virus (HIV) replication, it also results in unexpected viral resistance and thereby limits use of the technology in HIV therapy.

A recent study has shown that although the CRISPR/Cas9 gene editing technology can stop human immunodeficiency virus (HIV) replication, it also results in unexpected viral resistance and thereby limits use of the technology in HIV therapy.

Zhen Wang, from McGill University, Montreal, Canada, and colleagues published the results of their study in Cell Reports.

“Cas9 cleaves specific DNA sequences with the assistance of a programmable single guide RNA (sgRNA). Repairing this broken DNA by the cell’s error-prone non-homologous end joining (NHEJ) machinery leads to insertions and deletions (indels) that often impair DNA function,” the authors write. “Using HIV-1, we have now demonstrated that many of these indels are indeed lethal for the virus, but that others lead to the emergence of replication competent viruses that are resistant to Cas9/sgRNA.”

CRISPR (clustered regularly interspaced short palindromic repeats) is a relatively new tool that allows scientists to use engineered enzymes to edit genomes with extreme precision and efficiency. Originally discovered as a naturally occurring defense mechanism in bacteria, CRISPR uses a programmable single guide RNA (sgRNA) to target the Cas9 (CRISPR-associated proteins) endonuclease enzyme to locate an invading virus in order to cut and break down the viral DNA.

Previous studies have demonstrated the potential for this technology to cure HIV infection, by editing HIV DNA out of the genome of an infected immune cell, thereby preventing the virus from replicating and re-infecting the same cell.

However, until now, it was unknown whether HIV might be able to escape from Cas9/sgRNA inhibition. With this in mind, the researchers conducted a study using CD4+ T cells that express Cas9/sgRNA that targets the HIV-1 genome.

They found that the CRISPR/Cas9 system resulted in viral mutations that inhibited the replication of HIV-1. However, they subsequently performed DNA analysis which showed that the mutations had developed near a particular CRISPR/Cas9-targeted DNA sequence, thereby allowing HIV to become resistant to and escape CRISPR attack.

However, according to the researchers, this resistance does not necessarily rule out the possibility of CRISPR-based HIV therapy. “One potential solution might be to simultaneously target two or multiple sites in the viral genome with an array of sgRNAs in the way that multiple siRNAs [small interfering RNAs] have been used to durably suppress HIV-1 replication,” they write.

The authors concluded that indels that are compatible with viral viability should be considered if Cas9/sgRNA is used to treat virus infection. They expect that such indels would contribute to virus escape, not only when Cas9/sgRNA is used to control new infections, but also in the context of eliminating latent viral DNA of HIV and other viruses.

Dr. Parry graduated from the University of Liverpool, England in 1997 and is a board-certified veterinary pathologist. After 13 years working in academia, she founded Midwest Veterinary Pathology, LLC where she now works as a private consultant. She is passionate about veterinary education and serves on the Indiana Veterinary Medical Association’s Continuing Education Committee. She regularly writes continuing education articles for veterinary organizations and journals, and has also served on the American College of Veterinary Pathologists’ Examination Committee and Education Committee.