of vaccines based on self-replicating recombinant alphavirus
Two serious concerns have been raised about the biosafety of both conventional
and novel recombinant vaccines for medical and veterinary use. Firstly,
that vaccines may persist in the vaccinated individual, or in food, with
possible adverse effects. Secondly, that administration of a vaccine may
trigger adverse long-term effects in normal or immune-deficient individuals,
which may or may not be linked to persistence. While preclinical research
has demonstrated that vaccination with alphavirus-based vaccines can result
in protective immunity, concerns about their safety have been expressed
by assessment panels, both at national and European levels.
The broad aim of this project is to obtain experimental data which substantiates
or alleviates these concerns, and which can be used during the assessment
of these vaccines for commercial exploitation. The specific aim is to
test and assess the above-mentioned biosafety issues for new generation
vaccines based on the recombinant alphavirus, Semliki Forest virus
(SFV), using several model systems developed during the course of other
micrograph showing accumulations of viral protein and viral particles
in a Semliki Forest virus infected cell. In the vector, a foreign
gene coding for a protective antigen is substituted for the viral
structural protein genes, resulting in the synthesis of large amounts
of this protein in infected cells in place of the viral structural
proteins. This induces efficient protective immunity in an inoculated
Approach and methodology
The model systems used include influenza and louping ill flavivirus
(LI) infection in mice, birnavirus in chickens (infectious bursal
disease virus, IBDV) and LI in sheep. Avirulent SFV infection of mice
is used as a model for possible effects caused by a live attenuated vaccine.
In each case, constructs based on the SFV vector are compared to conventional
DNA vaccines expressing the same antigens from the cytomegalovirus (CMV)
The techniques developed for this project include reverse transcriptase
polymerase chain reaction (RT-PCR) to detect vaccine persistence, detection
of cytokine induction and persistence, immunohistochemistry to detect vaccine
and cytokine persistence, and immunopathology. Normal mice, immunodeficient
mice and the natural hosts of prototype vaccines will be used.
Main findings and outcome
In the first phase of the project, the techniques described above were
established and standardised. Results should allow us to draw firm conclusions
regarding the persistence of the vaccine constructs in mouse tissues and
the degree of tissue damage inflicted.
One unexpected and intriguing result was the rapid dispersal of vaccine
constructs from the inoculation site. This has been confirmed by two groups
in this project using immunocompetent mice, by a third group using chickens
and by a fourth group using immunodeficient mice. Preliminary results
indicate that SFV-based particle vaccines persist for less than seven
days in mice, chickens and sheep, but that the persistence of other DNA
vaccines is much longer.
Information about the persistence of introduced recombinant vaccine constructs
in animal tissues is extremely relevant when making assessments of the
biosafety risks involved in the use of new vaccines. SFV-based vaccines
appear to offer advantages over standard DNA vaccines, both in terms of
efficiency and biosafety.
Atkins G.J., Sheahan B.J. and Liljeström P., Semliki
Forest virus a model virus made useful?.
Journal of General Virology, 80,
1999, pp. 2287-2297.
Atkins G.J., Mc Quaid S., Morris-Downes M.M., Galbraith S.E., Amor
S., Cosby S.L. and Sheahan B.J., Transient virus infection
and multiple sclerosis.
Reviews in Medical Virology, 10,
2000, pp. 291-303.
Fleeton M.N., Liljeström P., Sheahan B.J. and Atkins G.J.,
Recombinant Semliki Forest virus particles expressing
louping ill virus antigens induce a better protective response than
plasmid-based DNA vaccines or an inactivated whole particle vaccine.
Journal of General Virology, 81,
2000, pp. 749-758.
Morris-Downes M.M., Phenix K.V., Sheahan B.J., Mooney D.A., Lindquist
S., Liljeström P., Todd D. and Atkins G.J., "Semliki
Forest virus-based vaccines: persistence, distribution and pathological
analysis in two animal systems".
Vaccine, 19, 2001, pp. 1978-1988.
Smith J-P., Morris-Downes M.M., Brennan F., Wallace G.J. and Amor
S., A role for alpha-4-integrin in Semliki Forest virus
infection of Biozzi ABH mice.
Journal of Neuroimmunology, 106, 2000, pp. 60-78.
September 1998 - August 2000
University College Dublin (IE)
Imperial College School of Medicine
National University of Ireland