Rhesus macaques in an enclosure. By Sandeep Handa on Pixabay.

Scientists at the Kunming Institute of Zoology in China have released a report outlining the results of their ongoing studies with CRISPR in rhesus macaques. CRISPR is the DNA-editing technology that has repeatedly made media headlines since 2012.

The study, led by senior author Professor Bing Su at the State Key Laboratory of Genetic Resources and Evolution, tested whether CRISPR-Cas9 used in rhesus macaques would lead to any off-target effects or unexpected mutations when used in non-human primates. Macaque monkeys are frequently used in biomedical research because they are among the list of primates that can be genetically modified without serious ethical regulations.

Scientists injected rhesus macaque zygotes (fertilized eggs) with the CRISPR-Cas9 system and guide RNAs targeting two different exons (exon 2 and exon 4) of the MCPH1 gene. MCPH is a microcephaly gene; its deletion can lead to abnormal smallness of the head and incomplete brain development.

Zygote under the microscope. Actin polymers are stained and appear in purple. Image from Wikimedia by Chaigne A, Campillo C, Voituriez R, Gov N, Sykes C, Verlhac M, Terret M, published in Nature Communications.

The researchers injected 15 rhesus embryos with the CRISPR-Cas9 system; of these, 13 tested positive for MCPH deletion. The scientists confirmed that these deletions were not associated with any other unexpected mutations in the rhesus macaque genomes using whole-genome sequencing on muscle, liver, brain and blood samples.

Despite the fact that the scientists did not observe unexpected mutations (based on computational predictions), they did still observe mutations elsewhere in the genome when using CRISPR — the sites at which these mutations occurred were just able to be predicted ahead of time.

The publishing of this report appears on the heels of the FDA’s pause of one of the first human clinical CRISPR trials in the United States. The US human CRISPR study, which aims to treat selected patients for sickle cell disease, was halted by the regulatory agency in the final days of May. A different clinical trial, spearheaded by Cambridge, Massachussetts-based company CRISPR Therapeutics, has recently received approval to begin a human CRISPR clinical trial in Europe later this year. At this time, it is unclear how these newly released reports with rhesus macaques will influence the future of CRISPR trials.

To learn more about the CRISPR DNA-editing technology, read our guide here.