Evaluation of the genetically attenuated E. coli heat-labile enterotoxin (LTR192G) as adjuvant for mucosal and intradermal immunization (P4421)

Abstract

Abstract Among the challenges to developing a subunit vaccine against the diarrhea-causing pathogen enterotoxigenic E. coli (ETEC) is the selection of a proper administration route and adjuvant. We assessed the adjuvant LTR192G, an attenuated form of the heat-labile enterotoxin (LT), co-administered with dscCfaE protein, the prototype ETEC CFA/I fimbrial tip adhesin, by two different routes. BALB/c mice received dscCfaE+LTR192G by intranasal (IN) or intradermal (ID) immunization on days 0 and 21. Serum, spleen and bone marrow (BM) were collected on day 28. Both regimens elicited comparable serum IgG anti-dscCfaE and functional Ab levels, the latter measured by hemagglutination inhibition (HAI). IN immunization, however, resulted in higher serum and fecal IgA anti-dscCfaE Ab levels, and fecal HAI titers. IgG1 was the only adhesin-specific subclass detected in the ID group, while IN immunization also elicited low titers of IgG2a anti-dscCfaE Ab, suggesting a more balanced Th1/Th2 response. The number of IgG and IgA anti-dscCfaE antibody-secreting cells in spleens and BM were two-fold higher in the IN vs ID group. After in vitro stimulation with dscCfaE protein, similar numbers of IFN-γ spot-forming cells (SFC) were observed in both groups. The IN group showed lower numbers of IL-5 SFC compared to the ID group. The composite results suggest that ID immunization with dscCfaE+LTR192G elicits a mucosal immune response, but the magnitude and immune profile differ from the IN-immunized group.