Nanobubbles Containing sPD-1 and Ce6 Mediate Combination Immunotherapy and Suppress Hepatocellular Carcinoma in Mice

Immune checkpoint inhibitors (ICIs) and sonodynamic therapy (SDT) are types of immunotherapy. In order to combine soluble programmed cell death protein 1 (sPD-1)-mediated immune checkpoint therapy and chlorin e6 (Ce6)-assisted SDT, nanobubbles (NBs) were generated to simultaneously load sPD-1 and Ce6.

The sPD-1/Ce6-NBs, which were prepared by thin-film hydration and mechanical oscillation, had a stable physical condition, and delivered sPD-1 and Ce6 in a targeted manner. NBs could strengthen tumor suppression by increasing tumor-targeting accumulation of Ce6 and sPD-1, and by inducing ultrasound-targeted NB destruction. A mouse H22 cell hepatoma xenograft model was used to evaluate the synergetic immunotherapeutic effect and mechanism of sPD-1/Ce6-NBs.

By observing the tumor inhibition rate, tissue and cell apoptosis, apoptosis-related genes and protein expression, the best immunotherapeutic effect was exhibited by the sPD-1/Ce6-NBs group. The immunotherapeutic mechanism initially demonstrated that when tumor cells were transfected by sPD-1 delivered by NBs, which downregulated the expression of programmed death-ligand 1 (PD-L1) in tumor cells, and blocked the PD-1/PD-L1 signaling pathway, which improved T-cell-mediated tumor inhibition. Furthermore, ICIs combined with SDT induced immunogenic cell death by translocating calreticulin to the cell surface and then synergistically enhancing antitumor immune responses.

In conclusion, sPD-1/Ce6-NBs were successfully designed. Ultrasound-mediated sPD-1/Ce6-NBs are potentially effective delivery systems for combination immunotherapy of hepatocellular carcinoma.