Vaccine potential of a recombinant glutathione S-transferase cloned from Schistosoma haematobium in primates experimentally infected with an homologous challenge

Patas monkeys were twice immunized with a Schistosoma haematobium-derived r ecombinant glutathione S-transferase (Sh28GST) then challenged with an homo logous calibrated challenge. BCG and Freund's Complete Adjuvant (FCA) were used as adjuvants in two distinct protocols. Specific IgG and IgA antibody responses were intense and homogeneous in the animals receiving Sh28GST in the presence of FCA, whereas BCG could only induce moderate and heterogeneo us antibody titres. No significant effect on worm burdens was evidenced 36 weeks post-infection in either group of Sh28GST-immunized animals compared to their matched controls receiving an irrelevant protein. Although not sig nificant, 50% reductions in the numbers of eggs located in all tissues (FCA group) and in the urogenital system (BCG group) were noted. Moreover, the total number of excreted eggs was dramatically diminished by 60% and 77% in the BCG and FCA groups, respectively. These reductions reached 75% and 80% in the urines of vaccinated monkeys. Bladder pathology was also reduced in the animals displaying the lowest urinary egg excretions. There was no cle ar positive or negative correlate between antibody responses and individual levels of protection. Taken as a whole, our results show that Sh28GST was capable of significantly reducing S. haematobium worm fecundity in experime ntally infected primates. Although FCA induced higher levels of protection, the efficacy of BCG as an adjuvant appeared sufficient to justify consider ation of the future application of this new formulation as a vaccine agains t human urogenital schistosomosis. (C) 1998 Elsevier Science Ltd. All right s reserved.