Immunization with plasmid DNA encoding the integral membrane protein, Sm23, elicits a protective immune response against schistosome infection in mice

Schistosomes are helminth parasites infecting at least 200 million people w orldwide. In this study. we evaluated the feasibility of using a nucleic ac id vaccine to induce protective immune responses to the Schistosoma mansoni integral membrane protein Sm23. C57BL/6 mice were immunized by intramuscul ar injection in three separate vaccination trials. ELISA and Western Blot a nalyses indicated that mice immunized with a DNA plasmid construct encoding Sm23 (Sm23-pcDNA) generated specific IgG for Sm23. while sera from mice im munized with the control pcDNA plasmid did not. The vaccine elicited IgG(2a ), and IgG(1) antibody isotypes. We also tested the adjuvant activity of IL -12 and IL-4 on humoral responses to Sm23. Co-immunization with plasmid enc oding IL-12 did not affect the level of anti-Sm23 IgG(2a), but did reduce t he IgG(1) level. In contrast, co-injection with a plasmid encoding IL-4 sig nificantly reduced the level of anti-Sm23 IgG(2a), while the level of IgG(1 ) was largely unchanged. Importantly. the Sm23-pcDNA vaccine provided stati stically significant levels of protection against challenge infection (21-4 4%. P < 0.001-0.02). Co-administration of plasmids encoding either IL-12 or IL-4 did not significantly enhance this protective effect. (C) 2001 Elsevi er Science Ltd. All rights reserved.