EXPRESSION OF NORWALK-VIRUS CAPSID PROTEIN IN TRANSGENIC TOBACCO AND POTATO AND ITS ORAL IMMUNOGENICITY IN MICE

Alternatives to cell culture systems for production of recombinant pro teins could make very safe vaccines at a lower cost. We have used gene tically engineered plants for expression of candidate vaccine antigens with the goal of using the edible plant organs for economical deliver y of oral vaccines. Transgenic tobacco and potato plants were created that express the capsid protein of Norwalk virus, a calicivirus that c auses epidemic acute gastroenteritis in humans. The capsid protein cou ld be extracted from tobacco leaves in the form of 38-nm Norwalk virus -like particles. Recombinant Norwalk virus-like particle (rNV) was pre viously recovered when the same gene was expressed in recombinant bacu lovirus-infected insect cells. The capsid protein expressed in tobacco leaves and potato tubers cosedimented in sucrose gradients with insec t cell-derived rNV and appeared identical to insect cell-derived rNV o n immunoblots of SDS/polyacrylamide gels. The plant-expressed rNV was orally immunogenic in mice. Extracts of tobacco leaf expressing rNV we re given to CD1 mice by gavage, and the treated mice developed both se rum IgG and secretory IgA specific for rNV. Furthermore, when potato t ubers expressing rNV were fed directly to mice, they developed serum I gG specific for rNV. These results indicate the potential usefulness o f plants for production and delivery of edible vaccines. This is an ap propriate technology for developing countries where vaccines are urgen tly needed.