Recombinant stable HEK293 cell line constitutively expressing RFP (Red Fluorescent Protein) and GFP (Green Fluorescent Protein), which have been stably integrated into the AAVS1 safe harbor locus on chromosome 19._x000D_Expression of RFP is driven by a CMV promoter, whereas GFP is driven by an EF1A promoter. The combined DNA fragment (CMV-RFP-bGH Poly A-EF1A-GFP-T2A-Puro-SV40 Poly A) (Figure 1) was integrated at the AAVS1 safe harbor locus using CRISPR/Cas9 technology. Cells were cloned by limiting dilution to obtain a monoclonal population. Without the adverse effects resulting from random integrations of RFP-GFP into the HEK293 genome, this cell line behaves like parental HEK293 cells.