Evaluation of murine immune responses elicited by a plasmid encoding the Toxoplasma gondii SAG1 gene delivered by various routes

Abstract

The efficacy of four methods of delivering recombinant plasmid DNA into a Balb/C mouse model was evaluated. A recombinant plasmid vector, pCMV-wtp30 was developed which allowed for expression of p30 antigen in mammalian cells. Delivery of this plasmid by intramuscular injection of unconjugated DNA, topical application of unconjugated DNA. topical application of liposomal complexed DNA and intra-peritoneal injection of liposomal complexed DNA were evaluated for their ability to stimulate the cellular and humoral immune responses of their subjects. ELISA studies suggest that none of the methods successfully induced a strong, sustained antibody response against the p30 antigen. Lymphocyte proliferation assays were performed to measure the cellular response. The results indicate that topical application of unconjugated DNA produced the strongest and most consistent cellular response while delivery of liposomal complexed DNA by either route could not efficiently raise cellular responses. Challenge studies, in which the immunised mice were inoculated with I00 live Toxoplasma tachyzoites, demonstrated that immunisation with the unconjugated plasmid via the topical route could confer partial protection even in the absence of an antibody response.