Our objective is to contribute to the development of defined antigen vaccines for schistosomiasis by evaluating the protective efficacy of Schistosoma bovis and S. japonicum antigens in their natural bovine hosts. Antigens under evaluation include some already identified as vaccine candidates: glutathione S transferases (GSTs); KLH, which shares protective epitopes with the protective antigen GP38 of S. mansoni; and Sj23, the analogue of the vaccine candidate Sm23 antigen, In another approach, since crude freeze/thaw schistosomular antigen. plus BCG(F/T vaccine) has proved protective against S. japonicum in bovines, as it was against S. mansoni in mice, we are carrying out further evaluations both of this crude antigen and of recombinant derived paramyosins, In a third line of work, novel vaccine candidate antigens identified by screening our cDNA libraries with various passively protective animal sera are being evaluated in animal experiments. In the Sudan we have shown that vaccination of calves with either native S. bovis GSTs or KLH induces high levels of fecundity suppression without causing a significant reduction in adult worm recoveries. Therefore, recombinant-derived S. bovis 28kD GST is now being evaluated, as are the effects of combined GST/KLH vaccination, In China, sheep have been vaccinated with either S. japonicum GSTs, with KLH, or with the F/T vaccine, as a prelude to trials in bovines, As judged by adult worm recoveries, each type of vaccine induced significant protection, and there was also evidence, particularly with the GST and F/T vaccines, of fecundity-suppressive effects. As with the S. bovis/cattle system therefore, both GST and KLH showed protective effects against S. japonicum in sheep. With the latter model, however, both adult worm reductions and fecundity reductions were shown, whereas with S. bovis the vaccines induced strong anti fecundity effects but no worm reductions. Two irradiated vaccine-dominant antigens of S. japonicum have been cloned and sequenced, IVGS3, which shows approximately 80% identity with S. mansoni calreticulin and IVRB4, shown to be homologous to calcium activated neutral protease from S. mansoni. Several antigens have been produced by cloning and expression of S. japonicum cDNA: a fragment of S. japonicum paramyosin; various regions including the large hydrophilic domain of Sj23; both the 26kD & 28kD S. japonicum GST isoforms. These antigens are currently being tested in protection experiments in mice, Most of these recombinant antigens and also purified native paramyosin are also available for large animal experiments in China.
