Colorectal cancer-derived extracellular vesicles induce liver premetastatic immunosuppressive niche formation to promote tumor early liver metastasis

Dear Editor,To date,the effect of colorectal cancer(CRC)-derived extracellular vesicles(EVs)on liver pre-metastatic niche(PMN)remain incompletely understood.1 To investigate the role of CRC-derived EVs in the remodeling of the liver PMN,we isolated EVs from CT26 cell culture supernatant.The characteristics of EVs(the morphology,size,and markers)were identified by transmission electron microscopy(TEM),Nanoparticle Tracking Analysis(NTA),and western blotting(Supplementary Fig.S1a–e).Then,BALB/c mice with an intact liver immune status were pretreated with CRCderived EVs and phosphate-buffered saline(PBS)for one month,and a liver metastasis model was established via spleen injection of tumor cells to determine whether EVs influence liver metastasis(Fig.1a).Two hours after the operation,in vivo imaging indicated that the animal model was successfully established,and the tumor fluorescence intensity in the liver was consistent between the two groups(Supplementary Fig.S2a,b).Amazingly,the liver tumor fluorescence intensity in the EVs group was significantly stronger than that in the PBS group after 24 h(Fig.1b;Supplementary Fig.S2c,d).The number of liver tumor nodules in the EVs group was also significantly higher than that in the PBS group on day 4(Fig.1c;Supplementary Fig.S2e,f).