‘Prime editing’ is what researchers are calling the proof-of-concept research that promises improved diagnostics and more effective treatments for patients with genetic defects

What if it were possible to edit genetic code and literally remove a person’s risk for specific chronic diseases? Such a personalized approach to treating at-risk patients would alter all of healthcare and is at the core of precision medicine goals. Well, thanks to researchers at the Broad Institute of MIT and Harvard, clinical laboratory diagnostics based on precise gene-editing techniques may be closer than ever.

Known as Prime Editing, the scientists developed this technique as a more accurate way to edit Deoxyribonucleic acid (DNA). In a paper published in Nature, the authors claim prime editing has the potential to correct up to 89% of disease-causing genetic variations. They also claim prime editing is more powerful, precise, and flexible than CRISPR.

The research paper describes prime editing as a “versatile and precise genome editing method that directly writes new genetic information into a specified DNA site using a catalytically impaired Cas9 endonuclease fused to an engineered reverse transcriptase, programmed with a prime editing guide RNA (pegRNA) that both specifies the target site and encodes the desired edit.”

And a Harvard Gazette article states, “Prime editing differs from previous genome-editing systems in that it uses RNA to direct the insertion of new DNA sequences in human cells.”

Assuming further research and clinical studies confirm the viability of this technology, clinical laboratories would have a new diagnostic service line that could become a significant proportion of a lab’s specimen volume and test mix.

Multiple Breakthroughs in Gene Editing

In 2015, Dark Daily reported on a breakthrough in gene editing by David Liu, PhD, Director of the Merkin Institute of Transformative Technologies in Healthcare at the Broad Institute, and his team at Harvard.

In that e-briefing we wrote that Liu “has led a team of scientists in the development of a gene-editing protein delivery system that uses cationic lipids and works on animal and human cells. The new delivery method is as effective as protein delivery via DNA and has significantly higher specificity. If developed, this technology could open the door to routine use of genome analysis, worked up by the clinical laboratory, as one element in therapeutic decision-making.”

Now, Liu has taken that development even further.

“A major aspiration in the molecular life sciences is the ability to precisely make any change to the genome in any location. We think prime editing brings us closer to that goal,” David Liu, PhD (above), Director of the Merkin Institute of Transformative Technologies in Healthcare at the Broad Institute, told The Harvard Gazette. “We’re not aware of another editing technology in mammalian cells that offers this level of versatility and precision with so few byproducts.”  (Photo copyright: Broad Institute.)

Cell Division Not Necessary

CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats. It is considered the most advanced gene editing technology available. However, it has one drawback not found in Prime Editing—CRISPR relies on a cell’s ability to divide to generate desired alterations in DNA—prime editing does not.

This means prime editing could be used to repair genetic mutations in cells that do not always divide, such as cells in the human nervous system. Another advantage of prime editing is that it does not cut both strands of the DNA double helix. This lowers the risk of making unintended, potentially dangerous changes to a patient’s DNA.  

The researchers claim prime editing can eradicate long lengths of disease-causing DNA and insert curative DNA to repair dangerous mutations. These feats, they say, can be accomplished without triggering genome responses introduced by other forms of CRISPR that may be potentially harmful. 

“Prime editors are more like word processors capable of searching for targeted DNA sequences and precisely replacing them with edited DNA strands,” Liu told NPR.

The scientists involved in the study have used prime editing to perform over 175 edits in human cells. In the test lab, they have succeeded in repairing genetic mutations that cause both Sickle Cell Anemia (SCA) and Tay-Sachs disease, NPR reported.

“Prime editing is really a step—and potentially a significant step—towards this long-term aspiration of the field in which we are trying to be able to make just about any kind of DNA change that anyone wants at just about any site in the human genome,” Liu told News Medical.

Additional Research Required, but Results are Promising

Prime editing is very new and warrants further investigation. The researchers plan to continue their work on the technology by performing additional testing and exploring delivery mechanisms that could lead to human therapeutic applications. 

“Prime editing should be tested and optimized in as many cell types as researchers are interested in editing. Our initial study showed prime editing in four human cancer cell lines, as well as in post-mitotic primary mouse cortical neurons,” Liu told STAT. “The efficiency of prime editing varied quite a bit across these cell types, so illuminating the cell-type and cell-state determinants of prime editing outcomes is one focus of our current efforts.”

Although further research and clinical studies are needed to confirm the viability of prime editing, clinical laboratories could benefit from this technology. It’s worth watching.

—JP Schlingman

Related Information:

Scientists Create New, More Powerful Technique to Edit Genes

Search-and-replace Genome Editing without Double-strand Breaks or Donor DNA

New CRISPR Genome “Prime Editing” System

Genome Editing with Precision

You had Questions for David Liu about CRISPR, Prime Editing, and Advice to Young Scientists. He has Answers

A Prime Time for Genome Editing

Prime Editing with pegRNA: A Novel and Precise CRISPR Genome Editing System

Prime Editing: Adding Precision and Flexibility to CRISPR Editing

Gene-Editing Advance Puts More Gene-Based Cures Within Reach

Harvard, MIT Researchers Develop New Gene Editing Technology

Broad Institute’s New Prime Editing Tech Corrects Nearly 90 Percent of Human Pathogenic Variants

Researchers at Several Top Universities Unveil CRISPR-Based Diagnostics That Show Great Promise for Clinical Laboratories

New CRISPR Genetic Tests Offer Clinical Pathologists Powerful Tools to Diagnose Disease Even in Remote and Desolate Regions

Harvard Researchers Demonstrate a New Method to Deliver Gene-editing Proteins into Cells: Possibly Creating a New Diagnostic Opportunity for Pathologists