Expression in plants and immunogenicity of a fusion protein containing an epitope from the swine transmissible gastroenteritis virus S protein

One interesting possibility offered by recent advances in plant biotechnology is the production of antigens in plants for use as orally administered vaccines. In this work, a subunit vaccine was designed for production in transgenic alfalfa. A genetic construct encoding a fusion protein containing a neutralizing epitope from the transmissible gastroenteritis virus (TGEV) was generated and introduced into tobacco and alfalfa. The fusion partner was a portion of the pollen-specific alfalfa protein PO2. This PO2-D protein was detected in plants using antibodies to PO2, and was found to be more extensively glycosylated in alfalfa leaves than in tobacco leaves. However, as both the alfalfa and tobacco plants matured, the expression of PO2-D diminished. To determine the immunogenicity of PO2-D, crude protein extracts from transgenic leaf tissue were injected intraperitoneally (i.p.) into mice and the serum antibodies examined for reactivity with TGEV. Both TGEV-specific and TGEV neutralizing antibodies were detected.