Genetic engineering and a schistosome vaccine.

Early attempts to develop a vaccine against schistosomiasis have been largely empirical, relying on use of live, attenuated larvae or homogenates and extracts of the various life-cycle stages of the parasite. Although some success has been reported using attenuated larvae, by and large the early attempts at vaccination have proved unsuccessful. Recently, we have begun to apply recombinant DNA technology to the problem of schistosome vaccine development. A majority of the evidence pertaining to immunity against schistosome infection suggests that the schistosomula is the primary target of the immune attack. Therefore, it follows that antigens found on the surface of the young larvae would be prime candidates for inclusion in an experimental vaccine. This lecture summarizes work aimed at the identification of schistosomula surface antigens and molecular cloning of their corresponding genes. cDNA clones have been prepared from both egg and adult mRNA. Relevant clones have been identified by "message" selection. This approach relies on identification of relevant antigen precursors among in vitro translation products. At least 5 schistosomula surface-antigen precursors have been recognised among in vitro translation products directed by adult mRNA. Some of these peptides are also encoded by mRNA isolated from eggs. One egg-specific peptide has been cloned and there is evidence that this is immunodiagnostic for Schistoma mansoni infections. A long-term aim is hoped that such molecules would contribute to a schistosome vaccine as well as providing immunodiagnostic reagents.