An anti-idiotype vaccine against experimental schistosomiasis

Abstract

Schistosomiasis is a parasitic infection of man which is widespread in tropical countries, and which so far has resisted attempts at control. We have been approaching the problem from an immunological angle. We have previously reported¹ the production of a rat monoclonal IgG2a antibody against Schistosoma mansoni which exhibits marked cytoxicity for schistosomula in the presence of eosinophils and a high degree of protection by passive transfer in naive rats. This antibody, IPLSm1, was shown to bind specifically to a schistosomulum membrane target antigen defined as a glycoprotein of relative molecular mass 38,000 (38K)², which is strongly immunogenic in schistosome infection of various animal species including man³. Although theoretically the 38K protein represents an excellent candidate for a potential vaccine against schistosomiasis, the glycanic nature of the epitope recognized by IPLSm1 limits its production by DNA recombinant technology. It was, moreover, shown that, together with protective antibodies, the 38K molecule was able to induce the production of blocking IgG2c antibodies that inhibit the functional properties of IPLSml both in vitro and in vivo⁴. Therefore, following Jerne's network theory⁵, we considered an alternative approach, the possibility of immunization using anti-idiotype antibodies. In the present study, rat monoclonal anti-idiotype antibodies were produced against IPLSm1 (AB₁). Anti-idiotype antibodies (AB₂) were selected by their capacity to inhibit the binding of radioiodinated AB₁, to its 38K target antigen. Sera from naive LOU rats immunized with a purified AB₂ preparation contained specific anti-schistosome antibodies (AB₃), which bound to 38K. AB₃ antibodies were strongly cytotoxic for schistosomula in the presence of rat eosinophils and conferred highly significant protection by passive transfer. Most importantly, rats immunized with AB₂ demonstrated marked protection (50–80%) to a challenge infection.