Supplement bij veertiende jaargang, april 2006 - NVMM

as GEM (Gram-positive Enhancer Matrix), by means
of a peptidoglycan binding domain. The vaccine was
evaluated for immunogenicity and protective efficacy in
an intranasal challenge murine model for pneumococcal
pneumonia. Adjuvant properties of the GEM particles were
studied in vitro by dendritic cell maturation and TNF-alpha
production.
Results: The immune-stimulating potential of the GEMbased
pneumococcal vaccine is very high. Nasal immunisation
results in an immune-protective response against
invasive pneumococcal disease, and antibody responses
were induced at systemic and local levels. The adjuvant
capacity of the GEM particles was demonstrated by
their ability to maturate dendritic cells and induce the
production of TNF-alpha.
Conclusion: We conclude that intranasal immunization
with the trivalent pneumococcal vaccine without additional
adjuvants showed significant protection against fatal
pneumococcal pneumonia in mice. The display technology,
in which Lactococcus-based particles act as both carrier and
mucosal adjuvant, has great potential to develop a broadly
applicable mucosal S. pneumoniae vaccine.
05.18
Improvement of lPS-containing vaccines by modification of
lipid A biosynthesis in Neisseria meningitidis and Bordetella
pertussis
P. van der Ley
Nederlands Vaccin Instituut (NVI), Bilthoven
Lipopolysaccharide (LPS), a major constituent of the
outer membrane, is present in several bacterial vaccines
in significant amounts. As such, it can have a potential
role as both immunogen and adjuvant. However, its
endotoxic activity also causes significant reactogenicity
which may limit widespread acceptance of these vaccines.
Both the endotoxic and adjuvant activity of LPS are largely
determined by the specific acylation pattern of the lipid A
moiety, the membrane-anchoring part of LPS. Therefore,
modification of the lipid A biosynthetic pathway might
provide a means to obtain improved LPS-containing
vaccines. In the case of Neisseria meningitidis, we have
identified and mutated the genes encoding the acyltransferases
involved in lipid A biosynthesis. The resulting
altered acylation pattern might offer the possibility to
create novel LPS species with altered biological activity,
more suitable for inclusion in meningococcal outer
membrane vesicle vaccines. This led to the unexpected
discovery that an N. meningitidis lpxA mutant is viable
without LPS. Despite the complete lack of LPS, hardly
any defects were observed in the assembly of the major
integral outer membrane proteins. Still, the immunogenicity
of outer membrane preparations of this LPS-
Ned Tijdschr Med Microbiol 2006; 4:Supplement
S29
deficient mutant turned out to be very poor, but could
be restored by adding either wildtype LPS or less toxic
LPS of specifically constructed meningococcal lipid
A mutants having five instead of six fatty acyl chains.
Especially the penta-acylated lpxL1 mutant displayed
reduced toxicity as measured by cytokine induction, but
normal adjuvant activity. In the case of Bordetella pertussis,
whole-cell vaccines contain a different penta-acylated LPS
which significantly contributes to reactogenicity. Mutants
in the lpxL homologues of B. pertussis could not be
isolated, presumably because they are not viable. However,
additional possibilities for lipid A modification in this
organism are provided by the pagL and pagP genes, which
encode outer membrane enzymes capable of deacylation
and acylation, respectively, of fully synthesized LPS. We
have investigated the effect of these modifications on the
biological activity and immunogenicity of both purified B.
pertussis LPS and whole cells.
05.19
A comparative study on the immunotherapeutic efficacy
of recombinant Semliki Forest virus and recombinant
adenovirus
A. Riezebos-Brilman 1 , M. Rots2 , J. Regts1 , J. Wilschut1 ,
H. Haisma2 , T. Daemen1 1University Medical Center Groningen, Medical Microbiology,
Molecular Virology Section, Groningen, 2University Medical
Center Groningen, Therapeutic Gene Modulation, Groningen
Introduction: Viral vectors are being developed for
immunotherapy of cancer and infectious diseases. We
are developing an immunization strategy against Human
Papillomavirus (HPV)-induced cervical cancer based on an
alphavirus vector, i.e. Semliki Forest virus. In the present
study we compare the efficacy of recombinant SFV (rSFV)
with recombinant adenovirus (rAd).
Methods: Mice were immunized and boosted with rSFV
expressing a fusion protein of the HPV proteins E6 and
E7 (SFV-enhE6,7) or rAd encoding the same fusion
product. Cytotoxic T cells precursors (pCTLs) induced upon
immunization were determined with E7-specific MHC
class I tetramers. CTL activity was measured by standard
51Cr-release assay. The therapeutic efficacy was determined
in tumour treatment experiments. To unravel the observed
differences between the vectors, T cell depletion, and gene
expression experiments were conducted.
Results: Immunization with SFV-enhE6,7 resulted not only
in 2-fold higher pCTL frequencies and significantly higher
levels of CTL activity, but also in a significantly superior
therapeutic effect requiring 100-1000-fold lower doses
compared to Ad-enhE6,7 immunization. The difference in
activity could not be ascribed to different effectors induced.
Yet, while a priming immunization with rAd completely