Improved conditionally replicative adenovirus delivery system against hepatocellular carcinoma by armed with bispecific T-cell engager

Background Recently, many strategies have emerged to develop the conventional treatment of hepatocellular carcinoma (HCC). Previously, we have established an HCC targeting system of conditionally replicative adenovirus (CRAd) delivered by human umbilical cord-derived mesenchymal stem cells (HUMSCs). At present, the system needs to be developed for enhancing anti-tumor effect and overcoming limitation caused by alpha-fetoprotein (AFP) heterogeneity of HCC. Methods A bispecific T cell engager (BiTE) targeting programmed death ligand 1 (PD-L1) controlled by human telomerase reverse transcriptase (hTERT) promoter was armed on the CRAd of old system. A series of experiments in vitro such as ELISA, flow cytometry, electron microscope and so on were performed for identification of the novel system. Then the anti-tumor effect was explored on orthotopic transplantation model mice and AFP heterogeneous model mice by bioluminescent imaging and the side effects were assessed by levels of serum AST and ALT and HE staining for extrahepatic organs. The distributions of CRAd and BiTE in tumor tissue were detected using confocal microscope and the intratumoral T cell was analyzed by flow cytometry. Results Firstly, the characters of the new system including the selective killing activity of CRAd, the release of BiTE and the CRAd package and delivery by HUMSC were identified. And then the result on orthotopic transplantation model mice showed that the new system had better anti-tumor activity and less hepatotoxicity than the old. In the tumor tissue of model mice treated by the new system, the infiltration and activation of T cells were significantly enhanced. Lastly, the new system could eliminate the AFP negative cells in AFP heterogeneous tumor efficiently. Conclusions Comparing the old system, the new provides a more effective and safer strategy against HCC.