A Dual-Viral Delivery Platform Enables Efficient Site-Specific Integration of Therapeutic-Length Genes in Human Primary Stem Cells.

Site-specific integration of large genes in human primary stem cells remains a significant challenge in gene therapy, particularly for treating multiallelic diseases. Gene editing efficiency in primary stem cells is heavily influenced by the delivery strategy, which often faces issues with programmability, efficiency, and specificity. Here, we developed a dual-viral delivery system, targeted integration via virus-like particles and integrase-deficient lentivirus (TIVID). This system combines virus-like Cas9 edit particles for delivering Cas9/sgRNA ribonucleoprotein complexes and integrase-deficient lentiviral vectors for delivering HDR donor templates. The TIVID system achieves a knock-in efficiency of 65% ± 5% in human induced pluripotent stem cells (iPSCs). In erythroid progenitor HUDEP2 cells, TIVID mediates precise integration of a 7.1 kb HBB-GFP cassette (from cut site to cut site) at the AAVS1 locus with 20% efficiency and stable expression. Crucially, we demonstrate that TIVID overcomes stringent packaging constraints to deliver an approximately 6 kb full-length HBB therapeutic cassette into primary human CD34+ hematopoietic stem and progenitor cells. This platform achieved 5-10% targeted integration efficiency and preserved robust lineage-specific differentiation capacity, demonstrating its potential for treating β-thalassemia and other multiallelic disorders. In head-to-head comparisons, TIVID outperformed lentivirus-derived nanoparticles (∼50% vs. <10% at AAVS1 in K562 with M3814) and plasmid-based eePASSIGE in iPSCs (∼20% vs. ∼1.5%). Compared with traditional electroporation delivery, TIVID offers lower early cytotoxicity, promotes predominantly mono-allelic integration, and exhibits enhanced compatibility with primary stem cells. By decoupling nuclease and donor delivery, TIVID circumvents the payload constraints of single-vector systems and the toxicity of physical transfection, providing a robust ex vivo engineering platform for complex gene replacement therapies.