Programmable Enzymes for Large-Cargo Genome Engineering: From Targeted DNA Integration to Therapeutic Genome Writing

Abstract

Genome engineering is undergoing a conceptual transition from the correction of individual sequence variants toward the programmable installation of larger functional genetic elements. CRISPR-associated nucleases established RNA-guided genome targeting as a broadly accessible technology, while base and prime editing subsequently demonstrated that precise sequence modification can be achieved without relying exclusively on DNA double-strand breaks. Nevertheless, efficient and controlled insertion of kilobase-scale DNA remains a substantially more difficult problem. Large-cargo integration is particularly attractive for genetically heterogeneous disorders because insertion of a complete coding sequence, a multi-exon therapeutic cassette, or another functional genetic module could restore gene activity across multiple pathogenic variants rather than requiring a separate editor for each mutation. Nature provides several mechanistically distinct solutions to large-scale DNA movement, including DNA transposases, site-specific recombinases, non-long terminal repeat retrotransposons, RNA-guided bridge recombinases, and CRISPR-associated transposases. Each platform offers a different balance among cargo capacity, targeting flexibility, integration efficiency, product architecture, and genomic specificity. Recent developments have increasingly focused on combining the catalytic efficiency of mobile genetic elements with programmable nucleic-acid recognition. Prime-editing-assisted recombinase systems, bridge RNA-guided recombination, retargeted R2 retrotransposition, and CRISPR-associated transposases exemplify this convergence. Particularly important advances in CRISPR-associated transposase engineering demonstrate that bacterial integration systems can be adapted for substantial activity in human cells, although increased activity may expose previously limited off-target pathways. This chapter examines the biological principles underlying programmable large-cargo insertion, compares the major emerging technological platforms, and discusses the engineering, delivery, specificity, product quality, and safety requirements that will determine their therapeutic potential. Collectively, these developments suggest that the next stage of genome engineering may extend beyond editing existing sequence toward the controlled writing of complete genetic functions into selected genomic locations.