CutIn: a ready-to-use construct for rapid generation of urgently needed transgenic cell lines in emerging infection...

Site-directed exogenous gene knock-in for stable cell line generation remains a multi-step procedure that heavily relies on expertise. Therefore, there is a need for a competent and easily manageable method, particularly when there is an urgent demand for cell lines, especially for emerging infection research. We present here a universal construct called CutIn that expresses the Cas9 protein and dual sgRNAs targeting a host cell genome locus and the ampicillin resistance (AmpR) gene of a cotransfected donor plasmid commercially available. This construct specifically induces double-strand breaks (DSBs) in cotransfected plasmids and host cell genomes, thereby facilitating whole plasmid integration through nonhomologous end joining (NHEJ) repair mechanisms. As pilot tests, adeno-associated virus integration site 1 (AAVS1) or hypoxanthine phosphoribosyl transferase (HPRT) locus was selected as host genome target, commonly used human cell lines 293T, HeLa and HCT116 were employed. CutIn was subjected for reporter plasmid knock-in in all three cell lines, either AAVS1 and AmpR or HPRT and AmpR loci were efficiently targeted. Fluorescent protein, human angiotensin-converting enzyme 2 (ACE2) and dengue virus (DENV) infection reporter transgenic cells were rapidly obtained via CutIn-mediated whole expression vector integration. This method is designed to be user-friendly and shows potential for supporting the investigation of emerging/re-emerging infectious diseases. Further validation in diverse research contexts will be necessary to fully assess its applicability and effectiveness.