Obtaining a Recombinant Protein Based on the E7 Antigen of Human Papillomavirus Type 18

Background: Cervical cancer is the fourth most common cancer in women worldwide and was the leading cause of death among approximately 300 000 cases in 2018. The main risk factor for developing this disease is the persistent infection of high-risk types of Human Papillomavirus (HPV); specifically, HPV-18 is recognized as one of the major contributors for adenocarcinoma and squamous cancer. There are three prophylactic vaccines to prevent infection by HPV, but these vaccines are not effective in infected people. On the other hand, despite the success of various types of therapeutic vaccine candidates in clinical trials, none of them is commercially available to treat women with HPV-related malignancies. As the methods used for obtaining those therapeutic candidates are awfully expensive, they could be inaccessible for developing countries. In this scenario, E7 antigen of HPV is considered an ideal target for developing therapeutic vaccines. In accordance with this, the aim of this work is to obtain a recombinant fusion protein with high levels of purity through a profitable process, which could be used as therapeutic alternative for treating tumors expressing the E7 antigen of HPV-18. Results: We have obtained the novel recombinant protein CIGB550-E718 that comprises the fusion between an E7 mutein of HPV-18 and the cell-penetrating peptide with immunostimulatory properties CIGB550. The expression of the fusion protein evaluated using two strains of E. coli and 16 culture media with different composition enabled us to choose the best setting in which the interest protein accounted for approximately 16% of the total cellular protein. The best results were obtained using BL21(DE3) cells as host system grown in a culture medium containing M9 salt, casein hydrolysate and glycerol as a carbon source. The recombinant protein was purified by a single affinity chromatographic step up to 90% purity. Yields of 32 mg of the CIGB550-E718 per liter of culture were achieved from 2.5 L scale. Conclusions: These results are a promising and cost-effective approach for the future production and scale-up of the protein CIGB550-E718, which could be a therapeutic alternative for treating women with lesions associated to HPV-18 infection.