MYC and lentivirus infection: In the future, to avoid three-round lentivirus infections, other approaches, such as CRISPR/Cas9, could be employed to knockout of endogenous c-Myc at first and then re-express wild-type c-Myc or c-Myc(4K/R) mutant plus ELL or ELL(C595A) mutant as well as ELL-shRNA for establishing stable cell lines.