Features of the antibody response attributable to plasmid backbone adjuvanticity after DNA immunization

DNA vaccination induces antigen-specific immune responses with characterist ics distinct from other vaccination modes. In the present study, the contri bution of the plasmid backbone adjuvant effect to the quality of the DNA-ra ised antibody response was investigated. For this purpose. three intraderma l primings were compared in mice using: (1) the recombinant Schistosoma hae matobium glutathione S-transferase antigen (rSh28GST): (2) rSh28GST supplem ented with a non-coding plasmid; and (3) a Sh28GST-encoding plasmid. In con trast to immunization with the protein, DNA immunization elicited a very st able antibody (Ab) response over a prolonged period of time. This feature w as attributed to the plasmid backbone, because co-administration of the non -coding plasmid with rSh28GST allowed the maintenance of the specific Ab re sponse. A strong anamnestic Ab response was induced after intradermal boost with rSh28GST only in the mice primed with pMSh. This indicated that the s elective ability of DNA vaccination to induce memory humoral response was i ndependent of the plasmid backbone. In contrast the plasmid backbone was fo und to strongly participate in the preferential IgG2a Ab production observe d. These results suggest that, following DNA immunization, the Th1-biased p rofile and the maintenance of the long-lived Ab response could be attribute d to an adjuvant effect of the plasmid backbone during priming, whereas the strength of B-cell memory was independent of this effect. (C) 2001 Elsevie r Science Ltd. All rights reserved.