One of the major causes of sickness, death, and economic loss in the cattle industry is Mannheimia haemolytica, which causes bovine pasteurellosis, or shipping fever. Noninvasive delivery of a vaccine using transgenic plants expressing immunogens would reduce labor costs and trauma to livestock. An early step toward developing an edible vaccine is to determine whether an injected version of an antigen (usually a derivative of the pathogen) is capable of stimulating the development of antibodies in a test organism. The following table assesses the ability of a transgenic portion of a toxin (Lkt) of M. haemolytica to stimulate development of specific antibodies in rabbits. Immunogen Injected Antibody Production in Serum Lkt50*—saline extract + Lkt50*—column extract + Mock injection - *Lkt50 is a smaller derivative of Lkt that lacks all hydrophobic regions. indicates at least 50 percent neutralization of toxicity of Lkt; indicates no neutralization activity. Source: Modified from Lee et al. (2001). Infect. and Immunity 69:5786–5793. With regards to development of a usable edible vaccine, what work remains to be done?