Immune evasive DNA donors and recombinases license kilobase-scale writing

Genome-editing technologies that use recombinases to insert kilobase-scale DNA sequences into mammalian genomes canonically require large double-stranded DNA (dsDNA) donors^1,2. However, dsDNA molecules evoke problematic and toxic innate immune responses, limiting integration efficiencies and generally constraining applicability to ex vivo or immune-deficient contexts. By harnessing mechanisms of integrative prokaryotic viruses and mobile genetic elements, here we demonstrate that recombinases are compatible with immune evasive circular single-stranded DNA molecules optimally bearing a partial-duplex region that reconstitutes the recombinase recognition sequence. This approach, which we term integration through nucleus-synthesized template addition of large lengths (INSTALL), is compatible with diverse protein and RNA-guided recombinases for high-fidelity kilobase-scale human genome writing. INSTALL minimizes innate immune responses in primary human cells and in mice, improving recombinase-mediated integration efficiencies and supporting systemic in vivo non-viral DNA delivery by substantially increasing tolerability and broadening the dosing range compared with lipid nanoparticle-delivered dsDNA molecules. Together, INSTALL overcomes fundamental challenges for DNA delivery and integration methods by synergizing immune-stealth nucleic acids with recombinases to enable kilobase-scale integration strategies without viral vectors.