Vaccination of full-length HPV16 E6 or E7 protein inhibits the growth of HPV16 associated tumors

Abstract

Cervical cancer is the second most common cancer in women worldwide. Human papillomavirus (HPV) is the primary etiologic agent of cervical cancer. Two HPV16 proteins, E6 and E7, are consistently expressed in tumor cells. Most therapeutic vaccines target one or both of these proteins. Taking the advantages of safety and no human leukocyte antigen restriction, protein vaccine has become the most popular form of HPV therapeutic vaccines. Here we demonstrate that immunization with full-length HPV16 E6 or E7 protein elicited specific immunological effect and inhibition of TC-1 cell growth using TC-1 mouse model. HPV16 E6 and E7 genes were cloned into pET-28a(+) and introduced into E. coli Rosetta. Expression of the genes was induced by IPTG. Proteins were purified by Ni-NTA agarose and they were detected by SDS-PAGE and Western blotting. C57BL/6 mice were vaccinated with 1.5 nmol HPV16 E6 or E7 protein. Then they were implanted with 1x10(5) TC-1 cells. No tumor was detected in any mouse vaccinated with E7 protein. Forty days later, the tumor-free mice and control mice were challenged with 2x10(5) TC-1 cells. All control mice developed tumors 6 days later, but E7 immunized mice were tumor free until 90 days. Tumor growth was slow in the E6 immunized mice, but 83% of the mice developed tumors and the survival percentage was not significantly different from the control. An adoptive immune model was used to demonstrate the therapeutic effect. Results showed that the development of TC-1 cells was obviously reduced by transfusion of T-cells but not serum from mice immunized with E7 protein. T-cells from E7 immunized mice also induced the lysis of TC-1 cells in the cytotoxic T lymphocyte assay. These findings show that immunization with HPV16 E6 or E7 protein was able to elicit specific protective immunity against TC-1 tumor growth.