Presenting a fine-tuned CRISPR-Cas9 gene editor

The novel approach adopted for the “molecular scissors” significantly reduces the chance of potentially harmful mutations

By Faisal Khan | 12 July 2022
Medium

Cell colony differentiated from gene repaired human hematopoietic stem cells. Only the repaired stem cells could form such a colony. (Image Credit: Van Trung Chu, MDC)

It has been ten years since microbiologist Emmanuelle Charpentier and biochemist Jennifer Doudna published the research that paved the way for CRISPR–Cas9 gene editing. While the technique has been undergoing rigorous testing trials in other countries like the U.S, “China’s Frankenstein” genetically modified the DNA of the twin baby girls using the CRISPR tool — as far back as 2018. Over the years, improved editing techniques like CRISPR 2.0 have been developed. Soon after the Chinese experiment, successful CRISPR human trials were announced by two American biotechs.

More recently, Stanford researchers developed a mini version of the gene-editing tool, dubbed ‘CasMINI’. Scientists have continued to improve the technique to make it more effective, safe, and less invasive for patients. CRISPR-Cas9 gene-editing tool has presented us with groundbreaking therapeutic potential — acting as “molecular scissors” can be used to very precisely cut out and repair gene mutations that are responsible for hereditary diseases.

Despite the improvements in this novel tech, ever since its inception, the tool is not completely error free. Incorrect cuts made at the wrong section of the DNA can lead to “off-target mutations.” This can lead to complications resulting in unrelated health issues. In addition to this, errors can still occur even with correct DNA cuts with something called “on-target mutations.” Addressing both these errors was the focus of the new study under discussion today.

“We use this spacer to ensure that the two nicks are made 200 to 350 base pairs apart and that double-strand breaks in the DNA are avoided.”

Dr. Van Trung Chu, Co-Last Author of the Paper

Researchers from Berlin Max Delbrück Center for Molecular Medicine in the Helmholtz Association (MDC) in collaboration with scientists from Humboldt-Universität zu Berlin have now proposed a refined approach, which addresses these challenges. Dubbed as “spacer-nick”, this method employs a modified pair of molecular scissors, known as nickases, that make nicks on opposite strands of the DNA at two different points.

Rather than the conventional approach, which slices right through the entire double strand of DNA, the novel tool makes two smaller nicks — each cutting one DNA strand. A built-in spacer keeps those nicks at a safe distance of 200 and 350 base pairs — an optimal distance found out by experiments done on hematopoietic stem cells and T cells by the team.

The team claims that their spacer-nick system brings down the on-target mutations to under 2%, compared to over 40% in the CRISPR-Cas9 method. Quantifying the off-target mutations has been a little challenging — however, the team does claim that even they were rare in their approach as compared to the frequent occurence in classic genetic scissors method.

When it comes to effectiveness of the tool, the results in the space nick tool were similar to the conventional tool — both methods repairing between 20 and 50 percent of the treated cells. Summarizing the method, spacer-nick repairs the faulty genes in the Blood-forming stem cells, taken from people with a monogenic inherited disorder, before being administered back into the patient to produce new healthy cells.

Looking ahead, the team intends to conduct animal and human trials to verify the results of their study. Complete Research was published in the Journal of Science Advances.

Reprinted with permission from the author.

Faisal Khan is a prolific Canada-based tech blogger and influencer. He is the founder and editor of the Technicity publication which focuses on technical, scientific and financial knowledge sharing. Follow him on Twitter @fklivestolearn.

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