Immuno-Stimulating Peptide Derived from HMGB1 is More Effective Than the N-Terminal Domain of Gp96 as an Endogenous Adjuvant for Improvement of Protein Vaccines.

Up to now, different protein vaccine modalities against human papillomavirus (HPV) have been designed to control cervical cancer. The important issue is to increase their immunogenicity using appropriate adjuvants. Among heat shock proteins (HSPs), glycoprotein 96 (Gp96) and its Nterminal region (NT-gp96) have attracted a specific interest in stimulation of antigen-specific immune responses in vivo. Furthermore, the potency of high mobility group box 1 (HMGB1) protein and its fragment (Hp91) was reported to enhance the desired immune responses against various disorders. In this study, the recombinant (r) HPV16 E7 and rNT-gp96 proteins were generated in bacterial expression system. Mice were vaccinated three times with E7 antigen mixed with Montanide, Hp91, and NT-gp96 as the adjuvant and their preventive and therapeutic efficiencies were evaluated in a murine tumor model. Mice vaccinated with E7 co-delivered by Hp91 peptide induced higher IgG2a and IFN-γ responses in comparison with E7 co-injected with Montanide and NT-gp96 protein suggesting a strong Th1 cellular immune response. The data showed that vaccination with noncovalent rE7 + rNT-gp96 complex delayed the tumor growth as compared to control groups. Mice immunized with rE7 + Montanide and rE7 + Hp91 protected 100% of mice versus 75% survival in groups vaccinated with rE7 + rNT-gp96 after TC-1 tumor challenge. The percentage of tumor free mice was decreased in group immunized with rE7 + rNT-gp96 in therapeutic experiments (~ 50%). These results demonstrated that Hp91 peptide is a safe and strong adjuvant against rNT-gp96 with the potent anti-tumor effects similar to Montanide adjuvant.