Vaccine properties of antigens entrapped in microparticles produced by spray-drying technique and using various polyester polymers

The present study investigated the suitability of various microparticles pr oduced by spray-drying technique to entrap and preserve the physiochemical and biological properties of an antigen. These microparticles were constitu ted either by poly(lactide) polymers characterized by various molecular wei ght or poly(lactide-co-glycolide) polymers. The recombinant 28 kDa glutathi one S-transferase of Schistosoma mansoni (rSm28GST) characterized by major epitopes involved in the active site of this enzyme was selected as model a ntigen, The microparticles were characterized by a mean size less than or e qual to 5 mu m and an antigen loading of approximately 2% (w/w), The analys is by SDS-PAGE electrophoresis of the rSm28GST released from microparticles confirmed the conservation of its physicochemical characteristics. The con servation of the native structure of the entrapped antigen was confirmed by detecting its enzymatic activity after release from microparticles, A sing le intraperitoneal immunization of mice with rSm28GST entrapped in micropar ticles resulted in a specific antibody response, which remained high for at least 7 months, The analysis of the isotype profile indicated that immuniz ed mice primarily produced anti-rSm28GST immunoglobulin (Ig) G1 with the co existence of lower IgG2a and IgG2b levels. Finally, the recognition of the major epitopic regions and the neutralization of the enzymatic activity of the rSm28GST by the antisera confirmed the specificity of the response agai nst the native structure of the antigen,These results confirmed the integri ty of the entrapped antigen. Moreover, our results supported the hypothesis that the duration of antigen release is the limiting factor for the durati on of antibody production. Indeed, the use of polymers characterized by dif ferent molecular weights allowed us to modify the duration of the immune re sponse. Together, these results demonstrated that microencapsulation of an antigen by spray-drying preserved its crucial characteristics required to g enerate an effective humoral immune response after a single-dose administra tion, (C) 2000 Elsevier Science Ltd, All rights reserved.