Plant-based vaccines for oral delivery of type 1 diabetes-related autoantigens: Evaluating oral tolerance mechanisms and disease prevention in NOD mice

Amanda L Posgai,Clive H Wasserfall,Henry Daniell,Mark A Atkinson,Desmond A Schatz,Kwang-Chul Kwon

doi:10.1038/srep42372

Amanda L Posgai, Clive H Wasserfall + Show 4 more

Open Access

https://doi.org/10.1038/srep42372

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Abstract

Autoantigen-specific immunological tolerance represents a central objective for prevention of type 1 diabetes (T1D). Previous studies demonstrated mucosal antigen administration results in expansion of Foxp3+ and LAP+ regulatory T cells (Tregs), suggesting oral delivery of self-antigens might represent an effective means for modulating autoimmune disease. Early preclinical experiments using the non-obese diabetic (NOD) mouse model reported mucosal administration of T1D-related autoantigens [proinsulin or glutamic acid decarboxylase 65 (GAD)] delayed T1D onset, but published data are conflicting regarding dose, treatment duration, requirement for combinatorial agents, and extent of efficacy. Recently, dogma was challenged in a report demonstrating oral insulin does not prevent T1D in NOD mice, possibly due to antigen digestion prior to mucosal immune exposure. We used transplastomic plants expressing proinsulin and GAD to protect the autoantigens from degradation in an oral vaccine and tested the optimal combination, dose, and treatment duration for the prevention of T1D in NOD mice. Our data suggest oral autoantigen therapy alone does not effectively influence disease incidence or result in antigen-specific tolerance assessed by IL-10 measurement and Treg frequency. A more aggressive approach involving tolerogenic cytokine administration and/or lymphocyte depletion prior to oral antigen-specific immunotherapy will likely be required to impart durable therapeutic efficacy.

Highlights

Autoantigen-specific immunological tolerance represents a central objective for prevention of type 1 diabetes (T1D)
In type 1 diabetes (T1D), immunosuppression offered in a variety of forms provides a temporary reprieve from autoimmunity, but is unable to induce lasting immunological tolerance allowing for a reversal of disease once established[1]
The constructed transformation vector was designed to allow for the specific integration of hGAD65 expression cassette into the intergenic space between isoleucyl-tRNA synthetase and alanyl-tRNA synthetase of the wild type chloroplast genome by double homologous recombination (Fig. 1A)

Summary

Introduction

Autoantigen-specific immunological tolerance represents a central objective for prevention of type 1 diabetes (T1D). A recent report by Pham et al argued that oral insulin treatment is unable to delay or prevent T1D onset in NOD mice, possibly due to autoantigen digestion prior to reaching the mucosal immune interface, a process that limits bioavailability and subsequent tolerance induction[15]. To address this in the setting of T1D, transgenic plant cells expressing disease-related autoantigens[16,17,18,19] Even at low doses (1.5 μg), oral administration of the plant-made CTB-acid alpha-glucosidase (GAA) fusion protein prior to GAA injection significantly suppressed GAA-specific immunoglobulin formation in a mouse model of Pompe disease[29]

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