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

Susannah Leach,Joanna Kaim,John D Clements,Anna Lundgren,Guillermo H Giambartolomei

doi:10.1371/journal.pone.0051718

Susannah Leach, Joanna Kaim + Show 3 more

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https://doi.org/10.1371/journal.pone.0051718

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Journal: PloS one	Publication Date: Dec 20, 2012
Citations: 62	License type: CC BY 4.0

Affiliation: University of Gothenburg, Tulane University

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.

Highlights

Mucosal infections remain a major global health problem and a considerable cause of child mortality and morbidity [1]
We show that dmLT can enhance human IL-17A responses in Peripheral blood mononuclear cells (PBMCs) to the model bacterial antigen purified protein derivative (PPD) in Bacillus Calmette-Guerin (BCG) immunised individuals, while having little effect on IFN-c production or proliferation in response to this antigen
Depletion experiments verified that the IL-17A produced by PBMCs in the presence of PPD in combination with dmLT primarily originated from CD4+ T cells

Summary

Introduction

Mucosal infections remain a major global health problem and a considerable cause of child mortality and morbidity [1]. To enable use in humans, several parallel attempts have been made to develop mutated LT toxins with lower enterotoxicity yet retain adjuvanticity, including LT(R192G), or single-mutant LT (mLT) [3] This molecule has a single mutation within the subtended disulphide region of the A subunit, which prevents trypsin-activation and cleavage of the Asubunit, with subsequent reduced toxicity but retained potent adjuvant activity in animal models [3]. To further detoxify mLT, an additional mutation was introduced in the A2-A1 activation loop site [6] This toxoid, LT(R192G/L211A), double-mutant LT or dmLT, has been demonstrated to enhance immune responses to whole cell vaccines against ETEC, Streptococcus pneumoniae and Helicobacter pylori in different mouse models [7,8]

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