for better vaccines
Faculty of Veterinary Medicine,
University of Liège (BE)
has had a major impact on the design and development of new medicinal
products, especially vaccines. In some cases, use of biotechnology has
lead to results which would have been impossible to obtain through classical
or conventional routes, for example, defining the complete sequence of
human hepatitis C virus, which still cannot be grown in cell culture.
Biotechnology has also helped to develop products which are safer than
conventional ones; one notable example is the use in humans of growth
hormone produced in genetically engineered bacteria instead of natural
growth hormone, the use of the latter being responsible for the transmission
of Creutzfeldt-Jakob Disease. Another example is the use of a recombinant
vaccinia-rabies virus for vaccinating foxes against rabies, which is more
efficacious and safer than the conventional attenuated SAD B19 strain.
This strain, which is still used, is pathogenic for some non-target mammals
and since its safety for man is unknown, people in contact with it must
undergo post-exposure anti-rabies treatment.
products are among the most stringently regulated products in the market
place. They are evaluated for quality and efficacy but, above all, for
safety, and if they consist of a genetically modified organism they must
comply with specific regulations. If a medicinal product is developed
using a biotechnological procedure it must be evaluated at a European
level by the relevant scientific committee using the so-called Centralised
Procedure: the Committee for Proprietary Medicinal Products (CPMP) deals
with human products and the Committee for Veterinary Medicinal Products
(CVMP) with products intended for use in animals; both are part of the
European Agency for the Evaluation of Medicinal products (EMEA), based
pharmaceutical products including genetically modified organisms are often
developed primarily for veterinary use, taking advantage of the fact that
efficacy and safety can be studied experimentally directly in the target
species, and that the environmental impact for non-target species can
also be studied experimentally.
DNA vaccination is the new frontier in vaccinology and, thanks to the
existence of already available biosafety research results, the Immunological
Working Party (IWP) of the CVMP was able to produce guidance notes on
DNA vaccines for use by pharmaceutical companies and the relevant competent
The research projects on vaccine biosafety reported here include five
applications of a generic nature and two more focused on specific animal
Two serious concerns have been raised concerning the biosafety of conventional
or recombinant vaccines for human and animal uses. The first one is the
fact that vaccine strains may persist in the vaccinated recipients and,
if the target species is a food-producing animal, later on in the food
chain. The second one is that administration of a vaccine may trigger
long-term adverse effects in normal or immunodeficient recipients. Project
BIO4-CT98-0031 showed that those effects
could be discarded by using a recombinant alphavirus, namely Semliki Forest
Virus (SFV), in mice, chicken and sheep. The vaccine virus does not persist
more than seven days after vaccination.
Identification of genes involved in latency and reactivation of Pseudorabies
virus (PRV), a herpesvirus primarily infecting pigs, was the subject
of project BIOT-CT91-0297. A limited
region of the PRV genome (LAP) was identified which appears to be transcribed
mostly during the latent stage of the infection. A deletion mutant was
produced (from which the putative LAP had been totally deleted) and pigs
were infected either with wild type virus or the deleted mutant without
showing significant differences.
Another project (BIO4-CT96-0637) was
devoted to the immunological biosafety of DNA vaccines. Potential immunological
problems associated with this new vaccination technology include unexpected
immunopathological reactions or tolerance. The objectives of the project
were to investigate circumstances which may lead to an undesirable immune
response to a DNA vaccine and to establish an assay for assessing the
integration of a plasmid DNA vaccine. These studies have shown that the
purity of injected DNA vaccines can affect the inflammatory response and
also that the type of vaccination can influence the nature of the response.
This kind of work is of primary importance in establishing a scientific
basis for proper regulation of DNA vaccines, but also to limit ill-informed
opinions impeding clinical trials, which is detrimental both to the vaccine
industry and also for human and animal health.
Biosafety of mucosa-specific RNA-vectors expressing foreign antigens and
recombinant antibodies for disease prevention was the subject of project
BIO4-CT98-0239. This project led to the
engineering of the largest RNA-virus genome as an infectious bacterial
artificial chromosome, which was a major outcome. Two expression systems
for the introduction of genetically modified elements in animals were
developed among which was an efficient single genome coronavirus vector
expressing foreign genes. The two systems proved to be suitable models
to examine biosafety of introduced GMOs.
The last of the generic projects (BIOT-CT91-0286)
was related to the safety of genetically engineered retroviruses used
for gene transfer. The objective of this project was to accumulate basic
information regarding cellular and viral mechanisms involved in modulating
the behaviour of retroviral vector systems, in order to construct safe,
efficient and targeted retroviral vector systems.
Two projects concerned biosafety aspects of the use of a recombinant vaccinia-rabies
virus for wildlife vaccination against rabies (BAP-0368/0381/0382
and BIOT-CT91-0298). The
recombinant vaccinia-rabies virus appeared to be perfectly safe and even
safer than some attenuated rabies virus strains presently used in the
field in Western Europe. The use of this recombinant vaccine did lead
to the elimination of rabies in large areas and, as a consequence, to
a drastic decrease in the number of human post-exposure treatments.
To conclude, all these projects have contributed to the provision of a
sound scientific basis and a more rationale approach to the construction
and development of safe GMOs and also towards better regulations for the
benefit of both human and animal health.