Expression of a modified Mannheimia haemolytica GS60 outer membrane lipoprotein in transgenic alfalfa for the development of an edible vaccine against bovine pneumonic pasteurellosis

The GS60 antigen is one of the protective antigens of Mannheimia haemolytica A1. GS60 contains conserved domains belonging to the LppC family of bacterial outer membrane lipoproteins. A high antibody titer to GS60 has been shown to be significantly correlated with resistance to pneumonic pasteurellosis. Calves vaccinated with a commercial vaccine (Presponse™) and demonstrating protection against M. haemolytica A1 produced antibodies directed against GS60. Alfalfa was chosen as the platform for an edible vaccine. Agrobacterium tumefaciens was used to mediate the transformation of alfalfa with sequences encoding a slightly shortened derivative of the GS60 antigen (GS6054). Stable transgenic alfalfa lines were recovered and production of GS6054 was examined by Western immunoblot analysis. The antigen is stable in dried transgenic plant material stored at ambient temperature for more than a year. The plant-produced GS6054 protein was shown to be immunogenic when injected into rabbits. Feeding of the dried transgenic alfalfa expressing the GS6054 to rabbits is capable of inducing seroconversion, suggesting that GS6054 could be an effective oral antigen for stimulating mucosal immune responses.