Friend or Foe? Evidence Indicates Endogenous Exosomes Can Deliver Functional gRNA and Cas9 Protein.

The clustered regularly interspaced short palindromic repeats (CRISPR)/associated nuclease (Cas) system is an efficient gene editing tool. In this study, it is found that both single guide RNA (gRNA) and Cas9 protein could be exported from the CRISPR/Cas9-expressing cells by endogenous exosomes independently. Further experiments demonstrate that these naturally produced endogenous exosomes could be used as a vehicle to deliver the functional Cas9 and hepatitis B virus (HBV)-specific gRNA to cut HBV DNA transfected in HuH7 cells or human papilloma virus (HPV)-specific gRNA to cut the integrated HPV DNA in HeLa cells, respectively. In conclusion, this study indicates the potential of endogenous exosomes as a safe and effective delivery vehicle of the functional gRNA and Cas9 protein. Meanwhile, the endogenous exosomes-mediated delivery of gene editing activity to adjacent and distant cells or tissues may further complicate the off-target and safety concerns about the CRISPR/Cas9 system.