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Evaluation of the radiation-attenuated schistosome vaccine in primates as a model for human vaccine development


* To investigate the radiation-attenuated (RA) schistosome vaccine in chimpanzees and simultaneously examine the development of the granulomatous responses to schistosome egg disposition in the liver of control animals.
* To compare the immunological and pathological responses of human patients, exposed to schistosome infection in endemic areas of Brazil, with those of the chimpanzees.
* To explore in baboons aspects of the RA vaccine, crucial to its evaluation as a model for a human recombinant vaccine.
Expected Outcome

Immunological parameters will be monitored in primates from the start of experiments so that the effects of exposure to the RA vaccine should rapidly become apparent. In the case of chimpanzees, the most crucial sampling period will be after challenge with normal cercariae when the level of protection achieved will be determined by indirect methods. In the case of the baboon experiments, a definitive estimate of protection will be obtained by counting the portal worm burdens. In both situations, the level of protection will be related to the range of immunological parameters measured. Studies in human patients in Brazil will take place in parallel with the primate vaccination experiments and attempts will be made to relate these to the experimental findings in order to evaluate the utility of the primates as models for human schistosomiasis. These cross-comparisons will also be important in the studies on liver pathogenesis in the chimpanzee.
A core vaccination experiment will be performed involving three test and three control chimpanzees.

The immune responses to vaccination and challenge will be compared in two distinct physiological compartments, the peripheral blood and the airways of the lung. Serum will also be obtained for determination of specific antibody responses. Leucocytes will be recovered from blood for determination of antigen-driven proliferation and cytokine production after 72-96h of in vitro culture. Lymphocytes in whole blood will be phenotyped by flow cytometric analysis. Airway leucocytes will be recovered from test and control animals by bronchoalveolar lavage over the vaccination period to determine whether the lungs have been pre-armed with schistosome-reactive cells. The efficacy of vaccination after challenge with normal cercariae will be estimated from faecal egg counts. Mature worm burdens will also be estimated by the measurement of parasite gut-derived circulating antigens (CAA and CCA) in serum and urine. The pathogenic mechanisms operating after the start of egg deposition in challenged animals will also be intensively monitored. The liver will be sampled at regular intervals by needle biopsy. A wedge surgical biopsy will be taken late in the study. The recovered tissue will be subjected to a detailed histopathological and immunocytochemical analysis. Observations will be made on the gross pathology induced by a schistosome infection by estimating the extent of hepatic fibrosis using non-invasive ultrasound scanning of the liver.

Human responses to schistosome infection will be evaluated in a cross-sectional study of Brazilians patients during the acute and chronic phases of the disease. Characterization will use primarily peripheral blood leucocytes, but also cells from other compartments that may become available. Phenotypic analysis of lymphocytes will be performed for the same range of CD markers as in chimpanzees. The expanded T cell populations will also be phenotype to pinpoint the characteristics of schistosome-reactive T cell subsets. Cytokine levels in all PBL cultures will be evaluated by ELISA. Biopsy samples of livers and spleen, obtained from patients with chronic (hepatosplenic) disease, will be analysed by immunocytochemistry.

Two experiments will be undertaken in baboons to define further certain parameters of the RA vaccine. The question of whether protection is long-lasting will be addressed in an experiment requiring 15 test and 15 control baboons. The test animals will be given 3 vaccinations using the same pools of parasites. Protection will then be measured by portal perfusion to determine adult worm burden at one, three and six months by challenging five test and five control animals on each occasion.

A second experiment is designed to discover whether there is a celling to protection. Three groups of test animals will receive five, three of one vaccinations, respectively, before they and a single group of controls are all challenged with the same pool of normal cercariae; protection will be measured six weeks after challenge. Assays of immune reactivity, including antigen-driven proliferation, secretion of some cytokine proteins (IL-2, 4, 5 and IFN-gamma), and specific IgG titres, will be performed. Serum samples will be obtained at perfusion, to determine circulating antigen levels.

Call for proposal

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YO1 5YW York
United Kingdom

Participants (5)

151,Lange Kleiweg 151
2280 GH Rijswijk Zh
1715,Av. Augusto De Lima 1715
30190-002 Belo Horizonte
62,Wassenaarseweg 62
2300 RC Leiden
Ololua Forest ,Karen Road National Museum Of Keny
00403 Karen
15,Rue De L'ecole De Médecine 15 Ura 1458
75006 Paris