AIRE deficiency, from preclinical models to human APECED disease

Abstract

Autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED) is a rare life-threatening autoimmune disease that attacks multiple organs and has its onset in childhood. It is an inherited condition caused by a variety of mutations in the autoimmune regulator (AIRE) gene that encodes a protein whose function has been uncovered by the generation and study of Aire-KO mice. These provided invaluable insights into the link between AIRE expression in medullary thymic epithelial cells (mTECs), and the broad spectrum of self-antigens that these cells express and present to the developing thymocytes. However, these murine models poorly recapitulate all phenotypic aspects of human APECED. Unlike Aire-KO mice, the recently generated Aire-KO rat model presents visual features, organ lymphocytic infiltrations and production of autoantibodies that resemble those observed in APECED patients, making the rat model a main research asset. In addition, ex vivo models of AIRE-dependent self-antigen expression in primary mTECs have been successfully set up. Thymus organoids based on pluripotent stem cell-derived TECs from APECED patients are also emerging, and constitute a promising tool to engineer AIRE-corrected mTECs and restore the generation of regulatory T cells. Eventually, these new models will undoubtedly lead to main advances in the identification and assessment of specific and efficient new therapeutic strategies aiming to restore immunological tolerance in APECED patients.

Keywords: AIRE; APECED; APS-1; Knockout model; Organoid; mTEC.

Fig. 1.

Common symptoms of APECED. Representation of different manifestations usually observed in APECED patients, including the historical Whitaker's triad (candidiasis, hypoparathyroidism and adrenocortical insufficiency; red) and the symptoms that have been linked to APECED syndrome only recently (blue).

Fig. 2.

Comparison of the AIRE/Aire locus in human, mouse and rat, and strategies to generate APECED rodent models. (A) Schematic representation of AIRE/Aire locus organization in human, mouse and rat, showing the different genetic contexts. (B) Summary of the strategies used to develop APECED mouse and rat models, providing the location of the genetic editing and its consequence for the Aire protein.

Fig. 3.

TEC 3D organotypic co-culture model. (1) The scaffold of this tissue culture setup is the association of soluble fibrinogen polymerizing into insoluble strands of fibrin through the action of thrombin. (2) Dermal fibroblasts are added to fibrin strands. (3) A few days of pre-culture are required to activate the fibroblasts and to allow them to produce a unique extracellular matrix that is suitable for epithelial cell culture. (4) Freshly extracted thymic epithelial cells (TECs) from different species can be added to the culture together with certain maturation factors, such as the Rank ligand (RankL), which is key for the maintenance of mature and functional TECs. (4*) An optional, additional next step is lentiviral-based gene therapy or gene editing to correct AIRE deficiency or to knock down the expression of specific genes relevant to the particular APECED research question. (5) This model can also be used to perform sequencing experiments (bulk or single-cell RNA-seq) to analyze AIRE-dependent gene expression or to characterize TEC heterogeneity.

Fig. 4.

Research strategies that employ in vivo and in vitro models of APECED to develop new therapies. This schematic highlights the advantages and limitations of each model.