sentence: Najm et al. developed a lentiviral vector and cloning strategy to generate high-complexity pooled dual-knockout libraries ( Big Papi – paired S. aureus and S. pyogenes Cas9 endonucleases for independent perturbations ) to identify synthetic lethal and buffering gene pairs across multiple cell types ( A375 , Meljuso , HT29 , A549 , 786O , and OVCAR8 ) .