Swine Transmissible Gastroenteritis Virus (TGEV)
Envelope Corona viruses (cf. SARS virus). 
Replicates in small intestine enterocytes, leads to fatal purging.
Recently evolved swine respiratory coronavirus in which deletion in the spike protein on the virus surface leads to limited replication in GI tract but high replication in upper and lower respiratory tract of pigs, leading to pneumonia.

Plant Made Pharmaceuticals (Prodigene)
Envelope coronavirus; has several coat proteins that are important as antigens.
One of these, a large surface glycoprotein  (spike=S protein), has been engineered into corn.

Streatfield S. J., et al. 2001. Plant-based vaccines: unique advantages. Vaccine 19: 1742-2748.
Lamphear B.J,. et al. 2002. Delivery of subunit vaccines in maize seed. Journal of Controlled Release 85: 169-180
Lamphear B. J., et al. 2004. A corn-based delivery system for animal vaccines: an oral transmissible gastroentiritis virus vaccine boosts lactogenic immunity in swine. Vaccine22:2420-2424

Synthetic gene: Gene sequence altered to suit codon-usage in corn.  N-terminal cell surface targeting signal (barley alpha-amylase) added, which enables protein export and  accumulation in the cell wall. Constitutive promoter, therefore expression expected everywhere.
Synthetic gene sub-cloned into maize expression cassette within transformation vector Transformation vector includes right and left border sequences of an Agrobacterium tumefaciens Ti plasmid and gene conferring resistance to herbicide Basta.

Transformation of  corn using A. tumefaciens:
 Transgenic lines expressing high levels of S protein in the seed backcrossed to commercial lines [why?]
S protein expressed at high levels, at about 13 mg/kg. This provides a dose of 20-30 mg protein in a single feed (sufficient for immunization).
S protein-producing corn tested on piglets; the immune system of the pigs could 'see' the S protein and respond to it.  The immunity shown to be passed on by sows to piglets via milk.