Mammalian cells comprising integrated CAS9 genes to produce stable integration sites, and mammalian cells comprising stable integration sites and other sites

A mammalian cell comprising a site for integration of a gene of interest, wherein the cell comprises a first Stable Integration Site located in a Genomic Safe Harbor and a second Stable Integration Site that is not located in the Genomic Safe Harbor,

• wherein the first Stable Integration Site comprises a first DNA polynucleotide encoding a first reporter protein, wherein the first DNA polynucleotide comprises in 5′ to 3′ order a first recombinase recognition site (RRS), a first reporter gene encoding the first reporter protein, a Cas9gene and a second RRS;
• and wherein the second Stable Integration Site comprises a second DNA polynucleotide encoding a second reporter protein, wherein the second DNA polynucleotide comprises in 5′ to 3′ order a first Genomic Safe Harbor homology arm containing a CRISPR single guide RNA (sgRNA) target site, a third RRS, a second reporter gene encoding the second reporter protein, a fourth RRS and a second Genomic Safe Harbor homology arm containing an CRISPR sgRNA target site, and wherein the first RRS, the second RRS, the third RRS and the fourth RRS are different.