Tetanus toroid loaded 'preformed microspheres' of cross-linked dextran

The conformation of an antigen and hence its biological activity may get co mpromised when encapsulated in controlled release microspheres during formu lation. In order to obviate the need for exposure of the antigen to the ina ctivating conditions, such as exposure to organic solvent and the high shea r stress of emulsification required for microencapsulation, an alternate st rategy was employed. 'Pre-formed' microspheres (20-340 mum in size) made of cross-linked dextran (Der) were employed as matrix for conjugation of teta nus toroid (TT) under aqueous conditions. The native immunoreactivity of TT was completely retained after conjugation, as checked by immunofluorescenc e and quantitative ELISA. Immunogenicity of Dex-TT conjugate was tested in rodents. No untoward mortality or adverse effects of immunization with the test material were observed on histopathology of the site of injection. A s ingle immunization with the long-acting depot formulation elicited anti-TT antibody response lasting for I year without any need of booster. The titre s were comparable after 12 weeks with those obtained using the conventional alum adsorbed toroid. (C) 2001 Elsevier Science Ltd. All rights reserved.