The Adjuvant Double Mutant Escherichia coli Heat Labile Toxin Enhances IL-17A Production in Human T Cells Specific for Bacterial Vaccine Antigens

Abstract

The strong adjuvant activity and low enterotoxicity of the novel mucosal adjuvant double mutant Escherichia coli heat labile toxin, LT(R192G/L211A) or dmLT, demonstrated in mice, makes this molecule a promising adjuvant candidate. However, little is known about the mechanisms responsible for the adjuvant effect of dmLT or whether dmLT also has an adjuvant function in humans.We investigated the effect of dmLT on human T cell responses to different bacterial vaccine antigens: the mycobacterial purified protein derivative (PPD) antigen, tested in individuals previously vaccinated with Bacillus Calmette-Guérin, the LT binding subunit (LTB), evaluated in subjects immunised with oral inactivated whole cell vaccines against enterotoxigenic Escherichia coli, and Streptococcus pneumoniae whole cell vaccine antigens, tested in subjects naturally exposed to pneumococci. We found that dmLT enhanced the production of IL-17A by peripheral blood mononuclear cells in response to all antigens tested. dmLT had comparable effects on IL-17A responses to PPD as the single mutant LT(R192G) adjuvant, which has demonstrated clinical adjuvant activity in humans. Neutralisation of IL-1β and IL-23, but not IL-6, suppressed the IL-17A-enhancing effect of dmLT. Furthermore, CD4+ T cells produced higher levels of IL-17A when stimulated with monocytes pulsed with PPD and dmLT compared to PPD alone, supporting an important role of antigen presenting cells in enhancing IL-17A responses. dmLT also potentiated mitogen-induced IL-17A and IL-13 production. However, dmLT had variable influences on IFN-γ responses to the different stimuli tested.Our demonstration of a potent ability of dmLT to enhance human Th17 type T cell responses to bacterial vaccine antigens encourages further evaluation of the adjuvant function of dmLT in humans.

Cholera Toxin, and the Related Nontoxic Adjuvants mmCT and dmLT, Promote Human Th17 Responses via Cyclic AMP–Protein Kinase A and Inflammasome-Dependent IL-1 Signaling

“…1B-D), and pretreatment of CT, mmCT, or dmLT with GM1 ganglioside completely blocked their adjuvant effects on IL-17A production (data not shown). Consistent with our previous findings (19), no enhancement or inhibition of cell proliferation was observed when PBMCs were stimulated with SEB, PPD, or WCA 6 CT or related adjuvants (data not shown).…”

“…1A, upper panel), consistent with our previous findings (19). Interestingly, the recently developed adjuvant mmCT also enhanced IL-17A production compared with treatment with SEB alone (3.5-fold increase compared with SEB alone).…”

“…However, less is known about the mode of action of nontoxic yet adjuvant active LT and CT derivatives. Earlier work in our laboratory has demonstrated the ability of not only CT and LT, but also dmLT to strongly promote Th17 responses in human PBMCs and monocyte-CD4 + T cell cocultures, with the enhancement of Th17 responses being at least partly dependent on IL-1 secretion (19). Accordingly, inducing or potentiating Th17 immune responses with the use of enterotoxinderived adjuvants may be a desirable strategy in the rational design of vaccines against mucosal pathogens.…”

Safety and Immunogenicity of a Single Oral Dose of Recombinant Double Mutant Heat-Labile Toxin Derived from Enterotoxigenic Escherichia coli

“…Furthermore, there is evidence that dmLT can elicit Th17-type T cell responses, providing further justification for continued product development (31). One potential disadvantage of oral administration of the current dmLT vaccine is the need to buffer gastric acidity by preadministering sodium bicarbonate, which may be unpalatable to some recipients.…”

Delivery strategies to enhance oral vaccination against enteric infections

“…This led to regulatory authorities cautioning against the intranasal use of GM1 binding adjuvants [127] although these molecules may still hold significant promise as oral adjuvants where they can exhibit unique potency. Recently a double mutant LT (dmLT) was developed [128], having greater stability in the presence of trypsin, strong oral adjuvant properties [129] and an acceptable enterotoxicity profile, even at high doses, and is currently being assessed as part of a prototype oral ETEC vaccine in clinical trials [130].…”