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An investigation into the mechanism of adjuventicity of immuno-stimulating complexes (ISCOMS) of defined chemical composition using a primate model of Epstein-Barr virus induced lymphoma


Iscoms carrying protein antigens are supra-molecular structures which self-assemble by virtue of their amphipathic characteristics when detergent is removed from a solution of Quillaja saponin triterpenoids. Natural Quillaja saponin contains many different components and some of these have side-effects when administered to experimental animals. In order to overcome this, the composition of Iscoms has been precisely defined and the number of components greatly reduced. During this project one objective has been to further develop the technology for the construction of Epstein-Barr virus (EBV) gp340 Iscoms which may ultimately be used to vaccinate humans to prevent infectious mononucleosis and cancers associated with this virus. A second objective has been to develop the techniques for assessing immune responses in the tamarin in which EBV induces B-cell lymphomas.. Other objectives have been to analyse immune responses in mice to Iscoms of defined composition. Preparation of chemically defined Iscoms (Sweden) The manufacturing capacity of has been sufficiently large to supply partners in the project with ISCOPREP(TM) which has been used in different formulations of defined EBV Iscoms and Iscom-matrix for adjuvant evaluation. Data has been continuously produced and compiled in a Drug Master File (DMF). A new HPLC test was devised which quantitates purified Quillaja fractions QH-A and QH-C. Construction of gp340 Iscoms (Sweden) A new methodology has been devised for the lipidation of EBV gp340 by periodate prior to incorporation into Iscoms which retains immunogenicity. Iscom immunisation in mice (All partners) The safety and effectiveness of an Iscom vaccine in young and newborn animals has been examined. Previous studies demonstrated that juvenile (2 weeks) mice vaccinated with Iscoms containing influenza virus proteins were completely protected against live virus challenge. Analysis of the immune responses from juvenile and adult mice revealed that similar qualitative and quantitative humoral and cellular immune responses were elicited indicating that vaccines of this type are likely to be effective in very young children. Iscoms can be safely injected into new born mice whether they are born from vaccinated or unvaccinated mothers and similar immune response profiles are generated in comparison with vaccinated juvenile mice. The onset of Leishmania in mice was significantly delayed following the induction of Th1 biased responses to Iscoms incorporating gp63. Current studies on the activation of antigen-presenting cells by Iscom-borne antigens shows that the Iscom and the Iscom-matrix efficiently stimulate the secretion of IL-6 in vivo. As reported previously with IL-1 and IL-12, the Iscom is a more efficient inducer of IL-6 than the Iscom-matrix, and the Iscom-matrix is more efficient than the free adjuvant components in the same proportions. The uptake and localization of free antigens and similar antigens incorporated in Iscoms was compared. Iscom-associated antigens were retained for longer periods in lymph nodes than free antigens. Macrophages in lymph nodes appear to be responsible for antigen uptake and retention, especially when the antigen is given in a particulate form. Antigens injected with adjuvants generally induced higher antibody titres than antigens injected after incorporation in antigen-carrier systems and mainly IgG1 and some IgG2b were induced. The effect of macrophage-depletion depended on the adjuvant/carrier system applied and appeared to be different for different isotypes. IgG2a and IgG3 levels were enhanced if macrophage-depletion was carried out before administration of antigen incorporated in carriers. CTL responses were induced by all antigen-carrier systems and by monophosphoryl lipid A. CTL responses were abolished after macrophage depletion in all cases. Macrophages play an important role in the induction of immunity, however, their role depends on the form in which the antigen is administered. Immune system of tamarins (Great Britain) T-cell proliferative responses to gp340 can now be measured in the tamarin. Furthermore, a correlation has been established between protective immunity against EBV-induced lymphoma and the presence of EBV-specific MHC class II-restricted CD4+ CTLs. It has also been observed that EBV-infected B-cells can be regulated by CD4+ T-cells through antigen-independent Fas/Fas ligand-mediated apoptotic mechanisms. Fas/Fas ligand induced apoptosis of activated lymphocytes is an important regulatory mechanism of normal immune responses. Regulation of EBV infected B-cells via Fas has important implications for the understanding of the control of EBV infection and its associated B-cell lymphomas in humans.

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University Walk
BS8 1TD Bristol, Clifton
United Kingdom

Participants (4)

Hellenic Pasteur Institute
127,Vassilissis Sofias Avenue
11521 Athens
Iscotec AB
951 62 Luleä
The Swedish University of Agricultural Sciences
Dag Hammarskjölds V.
751 23 Uppsala
Vrije Universiteit Amsterdam
7,Van Der Boechorststraat
1081 BT Amsterdam