Immunization with mutant HPV16 E7 protein inhibits the growth of TC-1 cells in tumor-bearing mice

Two human papillomavirus (HPV) 16 oncogenic proteins, E6 and E7, are co‑expressed in the majority of HPV16‑induced cervical cancer cells. Thus, the E6 and E7 proteins are good targets for developing therapeutic vaccines for cervical cancer. In the present study, immunization with the mutant non‑transforming HPV16 E7 (mE7) protein was demonstrated to inhibit the growth of TC‑1 cells in the TC‑1 mouse model. The HPV16 mE7 gene was amplified by splicing overlap extension polymerase chain reaction using pET‑28a(+)‑E7 as a template, and the gene was cloned into pET‑28a(+) to form pET‑28a(+)‑mE7. Compared with the E7 protein, mE7 lacks amino acid residues 94‑98, and at residue 24, there is a Cys to Gly substitution. pET‑28a(+)‑mE7 was then introduced into Escherichia coli Rosetta. The expression of mE7 was induced by isopropyl β‑D‑1‑thiogalactopyranoside. The mE7 protein was purified using Ni‑NTA agarose and detected by SDS‑PAGE and western blot analysis. In the tumor prevention model, no tumor was detected in the mice vaccinated with the mE7 protein. After 40 days, the tumor‑free mice and control mice were challenged with 2x105 TC‑1 cells. All control mice developed tumors six days later, but mE7 immunized mice were tumor free until 90 days. In the tumor therapy model, the TC‑1 cells were initially injected subcutaneously, and the mice were subsequently vaccinated. Vaccination against the mE7 protein may significantly inhibit TC‑1 cell growth compared to the control. These results demonstrated that immunization with the HPV16 mE7 protein elicited a long‑term protective immunity against TC‑1 tumor growth and generated a significant inhibition of TC‑1 growth in a TC‑1 mouse model.