Immunization of rabbits with enterotoxigenic E. coli colonization factor antigen (CFA/I) encapsulated in biodegradable microspheres of poly (lactide-co-glycolide).

We have searched for an effective oral delivery system for a purified enterotoxigenic Escherichia coli (ETEC) fimbrial adhesin, CFA/I, which elicits anti-colonization immunity. Purified CFA/I antigen encapsulated in biodegradable polymer microspheres of poly (DL-lactide-co-glycolide) (PLG) induced a vigorous, systemic CFA/I IgG antibody response in rabbits immunized once via intragastric tube; oral, unencapsulated CFA/I induced little or no circulating antibody. CFA/I-specific, S-IgA coproantibody was detected in one of three rabbits fed with the CFA/I-PLG microsphere vaccine. We conclude that PLG microspheres protected CFA/I from degradation in the stomach and effectively delivered the antigen for processing by the host's immune system.