Nature Papers Detail Two Prime Editing Routes For Large DNA Insertions Without Double-Strand Breaks

Two papers published in Nature Biotechnology this week tackle the same bottleneck from different angles: how to place larger pieces of DNA into genomes precisely without relying on double-strand breaks. That matters because existing approaches for larger insertions or replacements can introduce indels, larger deletions, chromosomal aberrations and cell death, limiting their therapeutic usefulness even when they work.

The studies present separate prime editing-based systems. One, called prime assembly, or PA, is framed as a gene replacement tool that adapts prime editors to create one or two pairs of 3′-flaps on both the genome and donor DNA so the flaps anneal precisely, similar to Gibson assembly in DNA oligonucleotides. The other, donor-complementary prime editing, or DoPE, combines a 3′-overhang double-stranded DNA donor with overhang-complementary prime editing guide RNAs and a PE2* prime editor to support large insertions in a one-step, DSB-free format.

The signal is less that one paper has solved genome engineering at therapeutic scale than that prime editing is starting to extend into a harder category of edits: kilobase-scale insertion and replacement workflows that aim to preserve precision while avoiding the repair liabilities of nuclease cutting.

The data

In the PA study, the authors say the method accepts DNA plasmids and linear double-stranded DNA donors ranging from 1.0 to 6.5 kb. In HEK293T cells, they report efficiency of up to 57.8% for replacing endogenous sequences with a 2.9-kb donor DNA fragment, with accuracy of more than 90% for integrated PA fragments. The study also reports site-specific chimeric antigen receptor integration in primary human T cells with up to 28.1% efficiency.

The in vivo result is more modest but important for translation: when PA containing a GFP donor was delivered to mice by hydrodynamic injection, the paper reports an average integration efficiency of 4.3% in GFP-positive hepatocytes. That does not by itself establish therapeutic readiness, but it moves the approach beyond a cell-culture-only proof of concept.

DoPE pushes in a somewhat different direction. The authors report precise insertion of DNA sequences up to 12.5 kb using short, approximately 30-nucleotide overhangs. They also show the system can work with donor pools constructed from synthesized single-stranded oligonucleotides, enabling in situ saturation mutagenesis across a targeted EGFP region at both amino acid and nucleotide resolutions.

That library-compatible feature gives DoPE a different practical profile from methods built mainly for single bespoke edits. The paper also describes replacement of mutant exons of PRKCSH, either individually or simultaneously, to create what the authors call a mutation-agnostic approach that corrects distinct alleles uniformly in vitro.

Why these papers matter

The shared commercial and scientific message is that large-fragment editing is becoming less synonymous with nuclease cutting. The PA paper explicitly positions its approach against double-strand break-dependent methods such as homology-directed repair, homology-independent targeted integration and PE-assisted approaches such as PAINT, arguing that the DSB step itself drives a substantial part of the risk profile.

DoPE makes a related case from an engineering perspective: one-step insertion of large fragments without recombinases or transposases could simplify workflows that otherwise require multistep installation of landing pads or additional enzymatic systems. For research tools, cell therapy engineering and mutation-agnostic correction strategies, that simplification could matter as much as absolute efficiency.

Neither paper makes the field’s delivery and manufacturability problems disappear. But together they suggest the next phase of prime editing competition may be defined not only by correction of small sequence errors, but by which systems can most cleanly handle larger insertions, exon replacement and programmable cell engineering while retaining enough fidelity to be useful outside tightly controlled lab settings.