Edible vaccine protects mice against Escherichia coli heat-labile enterotoxin (LT):: potatoes expressing a synthetic LT-B gene

The authors have designed and constructed a plant-optimized synthetic gene encoding the Escherichia coli heat-labile enterotoxin B subunit (LT-B), for use in transgenic plants as an edible vaccine against enterotoxigenic E, coli Expression of the synthetic LT-B gene in potato plants under the control of a constitutive promoter yielded increased accumulation of LT-B in leaves and tubers, as compared to the bacterial LT-B gene. The plant-derived LT-B assembled into native pentameric structures as evidenced by its ability to bind ganglioside. The authors demonstrated immunogenicity by feeding mice the raw tubers and comparing the anti-LT-B serum IgG and faecal IgA to that produced in mice gavaged with bacterial LT-B. Mice were fed three weekly doses of 5g tuber tissue containing either 20 or 50 mu g LT-B, or gavaged weekly with 5 mu g of LT-B from recombinant E, coli One week after the third nose, mice immunized with potato LT-B had higher levels of serum and mucosal anti-LT-B than those gavaged with bacterial LT-B. Mice were challenged by oral administration of 25 mu g LT and protection assessed by comparing the gut/carcass mass ratios, Although none of the mice were completely protected, the higher dose potato vaccine compared flavourably with the bacterial vaccine. These findings show that an edible vaccine against E, coli LT-B is feasible. (C) 1998 Elsevier Science Ltd. All rights reserved.