Schistosome vaccines: current progress and future prospects.

Vaccination against human schistosomes in laboratory hosts is now a reality. A number of different parasite molecules have been shown to confer partial protective immunity against challenge infection with Schistosoma mansoni or Schistosoma japonicum in rodent or primate hosts. These antigens are unusually diverse in their structure and stage specificity. Interestingly, although all of the vaccine molecules characterized are situated in the tegument, their exposure on the parasite surface, in most instances, is transient and/or non-essential. The properties of four of these immunogens, glutathione-S-transferase (P26,28), paramyosin (Sm97), GP38, and GP18 are discussed. Despite the identification and recombinant synthesis of several promising protective antigens, vaccination of humans against schistosomiasis remains in the realm of fantasy. At the technical level, a major problem is the failure of any of the current vaccine immunogens and immunization protocols to induce levels of resistance sufficient for significant reduction of human infection or disease. Once this important hurdle is passed, human immunization trials should be attempted as the potential beneficial impact of a vaccine against schistosomiasis remains enormous.