EVALUATION OF DEFINED ANTIGEN VACCINES AGAINST SCHISTOSOMA-BOVIS AND SCHISTOSOMA-JAPONICUM IN BOVINES

Our objective is to contribute to the development of defined antigen v accines for schistosomiasis by evaluating the protective efficacy of S chistosoma bovis and S. japonicum antigens in their natural bovine hos ts. Antigens under evaluation include some already identified as vacci ne candidates: glutathione S transferases (GSTs); KLH, which shares pr otective epitopes with the protective antigen GP38 of S. mansoni; and Sj23, the analogue of the vaccine candidate Sm23 antigen, In another a pproach, 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 evaluation s both of this crude antigen and of recombinant derived paramyosins, I n 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 K LH induces high levels of fecundity suppression without causing a sign ificant reduction in adult worm recoveries. Therefore, recombinant-der ived S. bovis 28kD GST is now being evaluated, as are the effects of c ombined GST/KLH vaccination, In China, sheep have been vaccinated with either S. japonicum GSTs, with KLH, or with the F/T vaccine, as a pre lude to trials in bovines, As judged by adult worm recoveries, each ty pe of vaccine induced significant protection, and there was also evide nce, particularly with the GST and F/T vaccines, of fecundity-suppress ive effects. As with the S. bovis/cattle system therefore, both GST an d KLH showed protective effects against S. japonicum in sheep. With th e latter model, however, both adult worm reductions and fecundity redu ctions were shown, whereas with S. bovis the vaccines induced strong a nti fecundity effects but no worm reductions. Two irradiated vaccine-d ominant 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 proteas e 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 current ly being tested in protection experiments in mice, Most of these recom binant antigens and also purified native paramyosin are also available for large animal experiments in China.