Exploiting the plant secretory pathway to improve the anticancer activity of a plant-derived HPV16 E7 vaccine.
The human papillomavirus 16 (HPV16) E7 oncoprotein can be considered a "tumor-specific antigen", and therefore it represents a promising target for a therapeutic vaccine against HPV-associated tumors. Efficient production of E7 protein with a plant-based transient expression system has been already described and it was demonstrated that E7-containing crude plant extracts confer partial protection against tumor challenge in a mouse model system. Before adopting the plant-based system as a cost-effective method for the production of an E7-based anti-cancer vaccine, some aspects, such as the oncoprotein yield, need further investigation. In the present study, we report the transient expression, mediated by a potato virus X (PVX)-derived vector, of the E7 protein targeted to the secretory system of Nicotiana benthamiana plants by using a plant-derived signal sequence. Targeting the antigen to the secretory pathway enhanced the E7 protein expression levels about five-fold. Mice immunized by s.c. administration with crude foliar extracts containing E7 showed strong stimulation of cell-mediated immune response after five boosters, as detected by ELISPOT. After challenging with the E7-expressing C3 tumor cells, tumor growth was completely inhibited in 80% of the vaccinated animals and a drastic reduction of tumor burden was observed in the remaining tumor-affected mice. These data demonstrate that, by enhancing E7 yield, it is possible to improve the anti-cancer activity of the plant-based experimental vaccine and open the way for a large-scale production of the E7 protein which could be purified or used as in planta formulation, also suitable for oral therapeutic vaccination.
ENEA, Italian National Agency for New Technologies, Energy and the Environment, BIOTEC-GEN, I-00100 Rome, Italy. franconi@casaccia.enea.it
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Franconi
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Massa
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Illiano
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Mullar
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Cirilli
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Accardi
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Di Bonito
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Giorgi
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Venuti
D000818:Animals; D000956:Antigens, Viral / Q000276:immunology; D015153:Blotting, Western; D019496:Cancer Vaccines / Q000276:immunology* / Q000494:pharmacology*; D018744:DNA, Plant / Q000235:genetics / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D007114:Immunization; D015151:Immunoblotting; D007371:Interferon-gamma / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000276:immunology*; D027383:Papillomaviridae / Q000235:genetics / Q000276:immunology*; D050725:Papillomavirus E7 Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013601:T-Lymphocytes / Q000276:immunology; D014026:Nicotiana / Q000737:chemistry / Q000276:immunology*; D014765:Viral Vaccines / Q000276:immunology* / Q000494:pharmacology*
D000956:Antigens, Viral; D019496:Cancer Vaccines; D018744:DNA, Plant; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D014765:Viral Vaccines; C059731:oncogene protein E7, Human papillomavirus type 16; D007371:Interferon-gamma