Vaccine Strategies against Schistosomiasis: From Concepts to Clinical Trials

Abstract

Schistosomiasis, the second major parasitic disease in the world after malaria, affects 200 million people. Vaccine strategies represent an essential component of the control of this chronic debilitating disease where the deposition of millions of eggs in the tissues is the main cause of pathology. Research developed in our laboratory over the last 20 years has led to the identification of novel effector mechanisms, pointing for the first time to the protective role of Th2 responses and of IgE antibodies now supported by seven studies in human populations. The identification and molecular cloning of a target antigen, a glutathione S-transferase (GST), has made it possible to demonstrate its vaccine potential in several animal species (rodents, cattle, primates) and to establish consistently the capacity of vaccination to reduce female worm fecundity and egg viability through the production of neutralizing antibodies (IgA and IgG). Following promising preclinical studies, clinical trials (phase I and II) have been undertaken using Schistosoma haematobium GST, Sh28GST. High titers of neutralizing antibodies were produced (IgG3 and IgA) together with Th2 cytokines, consistently with the concepts developed from experimental models. With these results we are on the way towards a feasible approach of vaccine development against a major human parasitic disease.