The Institute of Medical Science, The University of Tokyo

Mucosal vaccination is considered ideal for the global control of infectious diseases since it is capable of inducing antigen-specific immune responses in both systemic and mucosal compartments without the use of syringe and needle. We here developed a rice-based oral vaccine expressing cholera toxin B subunit (CTB) as a cholera vaccine. An average of 30 µg of CTB per seed was stored in the protein body, a storage organelle of rice seed. Orally fed rice seeds expressing CTB induced antigen-specific serum IgG and mucosal IgA responses with neutralizing activity through antigen-sampling M cells. When expressed in rice, CTB was protected from pepsin digestion in vitro. Rice-expressed CTB also remained stable and thus maintained immunogenicity at room temperature for more than 1.5 years. Because they would require neither needles nor refrigeration ("cold-chain management"), these rice-based mucosal vaccines offer a highly practical as well as cost-effective strategy against infectious diseases occurred naturally or stemmed from acts of bioterrorism.