Proceedings of the XLVI Italian
Society of Agricultural Genetics - SIGA Annual Congress
Giardini
Naxos, Italy - 18/21 September, 2002
ISBN 88-900622-3-1
Oral
Communication Abstract - S2b
PLANT-DERIVED VACCINES AND RECOMBINANT
ANTIBODIES FOR IMMUNOTHERAPY OF PAPILLOMAVIRUS 16 (HPV16) - ASSOCIATED CANCER
FRANCONI R.*, ILLIANO E.*,
GOBBI C.*, MASSA S.*, DIBELLO F.*, BITTI O.*, GIORGI C.**, VENUTI A.***
*) ENEA, CR Casaccia,, BIOTEC GEN, Via
Anguillarese n. 301, 00060, Roma
**) Istituto Superiore di
Sanità, V.le R. Elena
n° 299, 00161, Roma
***) Istituti Fisioterapici Ospitalieri (IFO)
- Istituto Regina Elena per lo Studio e la Cura dei Tumori, Via delle Messi
d'Oro 156, 00158 Roma
PVX, plant-derived vaccine, HPV,
cancer therapy, scFv
The human papilloma virus (HPV) is the causative agent of cervical cancer (second
most common cause of cancer death in women worlwide),
with HPV16 being the type most frequently found in these tumors. Vaccine
strategies for treatment of HPV-induced cervical cancer are mainly based on the recombinant E7 oncoprotein (considered a
tumor-associated antigen) while prophylactic vaccination essentially
uses ‘virus-like particles’ (VLPs), self-assembled structures from
the L1 major capsid protein, only obtained by eukaryotic expression systems.
Clinical trials are currently being performed with both types of vaccines,
whose production is highly expensive.
In this study, we describe
the expression of the HPV16 E7 protein in Nicotiana benthamiana (Nb) plants using a PVX-derived
vector. On immunoblotting of
Nb-PVXE7 extracts, in
addition to the E7 signal, a smear constituted by high molecular mass products
was observed. These aggregates were resistant to SDS treatment and boiling. The
presence of stable macro aggregates, resembling those formed in vaccine
preparations with adjuvants, suggested that the foliar extract, containing E7,
could be per se an
antigen with adjuvant-like activity. In fact C57BL/6
mice immunized with crude foliar extracts developed both humoral and
cell-mediated immune responses and resulted protected from tumor development
after challenge with a C3 tumoral cell line. Our data support the possibility
of producing a cost-effective anti-cancer vaccine in plant with intrinsic
adjuvant-like properties.
In addition, transgenic microtomato
plants for the HPV16 L1 gene were obtained. Molecular characterization
performed on primary regenerants identified some transgenic lines positive for
L1 mRNA expression.
Due to the lack of good diagnostic tools,
E7 has been also considered to isolate recombinant antibodies. Selections
(‘biopanning’) are currently being performed to isolate
single-chain variable fragment (scFv) antibodies specific to E7 using a
synthetic proprietary phage display library composed of intrinsically stable scFvs
(see poster Desiderio et al.). At the same time we are constructing a natural scFv phage display
library from the mice immunized with E7-containing
crude foliar extracts. The isolation of anti-E7 recombinant antibodies
could find application also in the field of prophylaxis and/or passive
anticancer immunization.