Long-term high immune response to diphtheria toxoid in rodents with diphtheria toxoid conjugated to dextran as a single contact point delivery system.

Cross-linked dextran beads were used as a carrier for development of a 'single-contact' vaccine delivery system. Diphtheria toxoid (DT) was covalently coupled to dextran beads (DEX-DT conjugate). The conjugate was immunoreactive with antibodies raised against native DT. Immunization of rats with DEX-DT conjugate generated on average 24 times higher antibody titres against diphtheria toxoid than immunization with the conventional DT absorbed on alum. The immune response was sustained for 9 months, with gradual decline of antibody titres thereafter. Significant antibody titres were measurable in rats after 1 year of immunization. DEX-DT had neither acute nor long-term adverse effects on the health of animals, as evidenced by local reactions, general behaviour, food intake, body weight gain and survival compared with controls.