GAD-alum immunotherapy in type 1 diabetes expands bifunctional Th1/Th2 autoreactive CD4 T cells

Diabetologia. 2020 Jun;63(6):1186-1198. doi: 10.1007/s00125-020-05130-7. Epub 2020 Apr 4.

Abstract

Aims/hypothesis: Antigen-specific therapy aims to modify inflammatory T cell responses in type 1 diabetes and restore immune tolerance. One strategy employs GAD65 conjugated to aluminium hydroxide (GAD-alum) to take advantage of the T helper (Th)2-biasing adjuvant properties of alum and thereby regulate pathological Th1 autoimmunity. We explored the cellular and molecular mechanism of GAD-alum action in the setting of a previously reported randomised placebo-controlled clinical trial conducted by Type 1 Diabetes TrialNet.

Methods: In the clinical trial conducted by Type 1 Diabetes TrialNet, participants were immunised with 20 μg GAD-alum (twice or three times) or alum alone and peripheral blood mononuclear cell samples were banked at baseline and post treatment. In the present study, GAD-specific T cell responses were measured in these samples and GAD-specific T cell lines and clones were generated, which were then further characterised.

Results: At day 91 post immunisation, we detected GAD-specific IL-13+ CD4 T cell responses significantly more frequently in participants immunised with GAD-alum (71% and 94% treated twice or three times, respectively) compared with those immunised with alum alone (38%; p = 0.003 and p = 0.0002, respectively) accompanied by high secreted levels of IL-13, IL-4 and IL-5, confirming a GAD-specific, GAD-alum-induced Th2 response. Of note, GAD-specific, IL-13+ CD4 T cells observed after immunisation co-secreted IFN-γ, displaying a bifunctional Th1/Th2 phenotype. Single-cell transcriptome analysis identified IL13 and IFNG expression in concert with the canonical Th2 and Th1 transcription factor genes GATA3 and TBX21, respectively. T cell receptor β-chain (TCRB) CDR3 regions of GAD-specific bifunctional T cells were identified in circulating naive and central memory CD4 T cell pools of non-immunised participants with new-onset type 1 diabetes and healthy individuals, suggesting the potential for bifunctional responses to be generated de novo by GAD-alum immunisation or via expansion from an existing public repertoire.

Conclusions/interpretation: GAD-alum immunisation activates and propagates GAD-specific CD4 T cells with a distinctive bifunctional phenotype, the functional analysis of which might be important in understanding therapeutic responses.

Keywords: Autoreactive; Epitopes; GAD; GAD-alum; Glutamic acid decarboxylase; IL-13; Immunotherapy; T cell receptor; T cells; TCR; Th2; TrialNet.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • CD4-Positive T-Lymphocytes / metabolism*
  • Cell Line
  • Cryopreservation
  • Diabetes Mellitus, Type 1 / immunology*
  • Diabetes Mellitus, Type 1 / therapy*
  • Humans
  • Immunotherapy / methods*
  • Randomized Controlled Trials as Topic
  • Receptors, Antigen, T-Cell / metabolism
  • Th1 Cells / immunology*
  • Th1 Cells / metabolism
  • Th2 Cells / immunology*
  • Th2 Cells / metabolism

Substances

  • Receptors, Antigen, T-Cell