Transcutaneous Immunization Using Colonization Factor and Heat-Labile Enterotoxin Induces Correlates of Protective Immunity for EnterotoxigenicEscherichia coli

Abstract

Enterotoxigenic Escherichia coli (ETEC) diarrheal disease is a worldwide problem that may be addressed by transcutaneous delivery of a vaccine. In several human settings, protective immunity has been associated with immune responses to E. coli colonization factors and to the heat-labile toxin that induces the diarrhea. In this set of animal studies, transcutaneous immunization (TCI) using recombinant colonization factor CS6 and cholera toxin (CT) or heat-labile enterotoxin (LT) as the adjuvant induced immunoglobulin G (IgG) and IgA anti-CS6 responses in sera and stools and antibody responses that recognized CS6 antigen in its native configuration. The antitoxin immunity induced by TCI was also shown to protect against enteric toxin challenge. Although immunization with LT via the skin induced mucosal secretory IgA responses to LT, protection could also be achieved by intravenous injection of the immune sera. Finally, a malaria vaccine antigen, merzoite surface protein 1 42 administered with CT as the adjuvant, induced both merzoite surface protein antibodies and T-cell responses while conferring protective antitoxin immunity, suggesting that both antiparasitic activity and antidiarrheal activity can be obtained with a single vaccine formulation. Overall, our results demonstrate that relevant colonization factor and antitoxin immunity can be induced by TCI and suggest that an ETEC traveler's diarrhea vaccine could be delivered by using a patch.

Cholera toxin activates nonconventional adjuvant pathways that induce protective CD8 T-cell responses after epicutaneous vaccination

“…Whereas several previous studies demonstrate expansion of antigen-specific CD8 T cells after EPI, most focused on responses early after immunization and/or did not evaluate induction of protective responses against pathogens (4-7). Our finding that EPI using the ADP ribosylating exotoxin CT evokes optimal CD8 T-cell responses (in terms of magnitude, durability, and functional efficacy) parallel work in mice and humans that exploit CT and the related toxin LT (4,10,(13)(14)(15). In agreement with previous studies (6, 7), we found that CpG could also prime CD8 T cells via EPI, although the responses induced with this adjuvant did not persist to generate protective memory.…”

“…Our data extend previous reports on the potency of CT and the related exotoxin LT in epicutaneous priming of cellular and humoral responses in mice and humans (12)(13)(14)(15), but raised the question of how CT confers its adjuvant effects. Most adjuvants induce "danger" signals to activate the innate immune response through pattern recognition receptors (PRRs) (19).…”

“…These include toll-like receptor (TLR) agonists such as imiquimod and CpG (6)(7)(8)(9), but also the ADP ribosylating bacterial exotoxins such as cholera toxin (CT) and the closely related Escherichia coli heat-labile enterotoxin (LT) (10)(11)(12). Application of such toxins to the skin is safe and effective in priming humoral and cellular responses in both mice and humans (4,10,(13)(14)(15). However, previous studies failed to define which adjuvants afford optimal priming of CD8 T-cell responses and durable protective memory.…”

Transcutaneous immunization in mice: Induction of T-helper and cytotoxic T lymphocyte responses and protection against human papillomavirus-induced tumors

“…TCI in the presence of CT as adjuvant after hydration was reported to generate Th responses. [15][16][17] CT leads to activation of LCs after topical application, indicated by the increased expression of CD11c, ICAM-1 and MHC class II molecules and by morphologic changes such as rounding and loss of dendrites. 48 Moreover, CT induces LC migration to draining lymph nodes even after application to intact skin.…”

“…This kind of pretreatment of the skin leads to development of humoral 13,14 and Th responses after TCI with proteins or peptides. [15][16][17] Another way of antigen entry through the skin is uptake via noncornified epithelial cells of the HF. Wax depilation induces development of homogenous anagen phase, which is accompanied by a locally increased number of LCs.…”