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.
Franconi
R
R
ENEA, Italian National Agency for New Technologies, Energy and the Environment, BIOTEC-GEN, I-00100 Rome, Italy. franconi@casaccia.enea.it
Massa
S
S
Illiano
E
E
Mullar
A
A
Cirilli
A
A
Accardi
L
L
Di Bonito
P
P
Giorgi
C
C
Venuti
A
A
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