How do I enrich HDR edited cells without antibiotic selection or a fluorescent reporter?

We recommend optimizing transfection conditions of NHEJ-mediated editing prior to including the donor oligo (Cas9 nuclease + highest functional crRNA: tracrRNA). After efficient NHEJ-mediated editing is achieved we recommend optimizing the amount of the donor template. Using this method, we found 2. 5 nM to 10 nM concentrations of the donor oligo were optimal for U2OS cells.